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1. 213 1124 7165 0 24 wan 0 0 0 0 0 wan ANS WA GS 5 A Web Interface To see the configured routing table 1 Go to Routing gt Routing Tables 2 Select and right click the main routing table in the grid 3 Choose Edit in the menu The main window will list the configured routes To see the active routing table select the Routes item in the Status dropdown menu in the menu bar the main window will list the active routing table Core Routes NetDefendOS automatically populates the active routing table with Core Routes These routes are present for the system to understand where to route traffic that is destined for the system itself There is one route added for each interface in the system In other words two interfaces named lan and wan and with IP addresses 192 168 0 10 and 193 55 66 77 respectively will result in the following routes When the system receives an IP packet whose destination address is one of the interface IPs the packet will be routed to the core interface In other words it is processed by NetDefendOS itself There is also a core route added for all multicast addresses To include the core routes when you display the active routing table you have to specify an option to the routing command Example 4 2 Displaying the Core Routes This example illustrates how to display the core routes in the active routing table CLI gw world gt routes all Flags Network Gateway Tocai 1e Shared
2. e Smurf and Papasmurf floods will be seen as ICMP Echo Responses at the victim side Unless FwdFast rules are in use such packets are never allowed to initiate new connections regardless of whether or not there are rules that allow the traffic e Fraggle packets may arrive at any UDP destination port targeted by the attacker Tightening the inbound rule set may help 200 6 6 8 TCP SYN Flood Attacks Chapter 6 Security Mechanisms The Traffic Shaping feature built into NetDefendOS also help absorb some of the flood before it reaches protected servers 6 6 8 TCP SYN Flood Attacks The TCP SYN Flood attack works by sending large amounts of TCP SYN packets to a given port and then not responding to SYN ACKs sent in response This will tie up local TCP stack resources on the victim machine until it is unable to respond to more SYN packets until the existing half open connections have timed out NetDefendOS will protect against TCP SYN Flood attacks if it is enabled in a Service object associated with the rule in the IP rule set that allows the traffic By default this is the case for the pre defined services http in https in smtp in and ssh in If a new custom Service object is defined by the administrator then Syn Flood Protection can be enabled or disabled as desired The SynRelay protection works by completing the 3 way handshake with the client before doing a second handshake of its own with the target service Overload s
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4. Instead of specifying a total group limit the alternative is to enable the Dynamic Balancing option This ensures that the available bandwidth is divided equally between all addresses regardless of how many there are and this is done up to the limit of the pipe If a total group limit of 100 bps is also specified as before then no one user may take more than that amount of bandwidth Group Limits and Guarantees In addition to specifying a total limit for group users limits can be specified for each preference If we specify a group user limit of 30 bps for precedence 2 then this means that users assigned a precedence of 2 by a Pipe Rule will be guaranteed 30 bps no matter how many users use the pipe Just as with normal pipe precedences traffic in excess of 30 bps for users at precedence 2 is moved down to the Best Effort precedence Continuing with the previous example we could limit how much guaranteed bandwidth each inside user gets for inbound SSH traffic This prevents a single user from using up all available high priority bandwidth First we group the users of the ssh in pipe so limits will apply to each user on the internal network Since the packets are inbound we select the grouping for the ssh in pipe to be Per DestIP Now we specify per user limits by setting the precedence 2 limit to 16 kbps per user This means that each user will get no more than a 16 kbps guarantee for their SSH traffic If desired we could also limit t
5. Name GWToGK Action Allow 167 6 2 8 H 323 Chapter 6 Security Mechanisms Service H323 Gatekeeper Source Interface dmz Destination Interface vpn hq Source Network ip branchgw Destination Network hq net Comment Allow the Gateway to communicate with the Gatekeeper connected to the Head Office Click OK Note There is no need to specify a specific rule for outgoing calls NetDefendOS monitors the communication between external phones and the Gatekeeper to make sure that it is possible for internal phones to call the external phones that are registered with the gatekeeper 168 6 3 Web Content Filtering Chapter 6 Security Mechanisms 6 3 Web Content Filtering 6 3 1 Overview Web traffic is one of the biggest sources for security issues and misuse of the Internet Inappropriate surfing habits can expose a network to many security threats as well as legal and regulatory liabilities Productivity and Internet bandwidth can also be impaired NetDefendOS provides three mechanisms for filtering out web content that is deemed inappropriate for an organization or group of users e Active Content Handling can be used to scrub web pages of content that the administrator considers a potential threat such as ActiveX objects and Java Applets e Static Content Filtering provides a means for manually classifying web sites as good or bad This is also known as URL blacklisting and whitelisting
6. The advanced setting SNMPReqLimit restricts the number of SNMP requests allowed per second This can help prevent attacks through SNMP overload Example 2 13 Enabling SNMP Monitoring This example enables SNMP access through the internal lan interface from the network mgmt net using the community string Mg1RQqR Since the management client is on the internal network we don t need to implement a VPN tunnel for it CLI gw world gt add RemoteManagement RemoteMgmtSNMP my_snmp Interface lan Network mgmt net SNMPGetCommunit y Mg1RQqR Should it be necessary to enable SNMPBeforeRules which is enabled by default then the command is gw world gt set Settings RemoteMgmtSettings SNMPBeforeRules Yes Web Interface Goto System gt Remote Management gt Add gt SNMP management For Remote access type enter Name a suitable name Community MgiRQqR For Access Filter enter Interface lan Network mgmi net Click OK Should it be necessary to enable SNMPBeforeRules which is enabled by default then the setting can be found in System gt Remote Management gt Advanced Settings 44 2 5 Maintenance Chapter 2 Management and Maintenance 2 5 Maintenance 2 5 1 Auto Update Mechanism A number of the NetDefendOS security features rely on external servers for automatic updates and content filtering The Intrusion Prevention and Detection system and Anti Virus modules require access to updated signature d
7. e Ensure that another IPsec Tunnel definition isn t preventing the correct definition being reached The tunnel list is scanned from top to bottom and a tunnel in a higher position with the Remote Network set to all nets and the Remote Gateway set to none could prevent the correct tunnel being reached The symptom of this problem is often an Incorrect Pre shared Key message e Try and avoid duplication of IP addresses between the remote network being accessed by a client and the internal network to which a roaming client belongs If a roaming client becomes temporarily part of a network such as a Wi Fi network at an airport the client will get an IP address from the Wi Fi network s DHCP server If that IP also belongs to the network behind the D Link Firewall accessible through a tunnel then Windows will still continue to assume that the IP address is to be found on the client s local network Windows therefore won t correctly route packets bound for the remote network through the tunnel but instead route them to the local network The solution to this problem of local remote IP address duplication is to create a new route in the client s Windows routing table that explicitly routes the IP address to the tunnel e If roaming client user authentication is not asking the users for their username password then ensure that the following advanced settings are enabled I PsecBeforeRules for pure IPsec roaming clients e PPP_L2TPBeforeRules for
8. ec ce cece cc ee ce eece neces eeeeeaeeeeeeaeeeaesenes 296 12 Zone Defense toss ones gs c205 us rebce agese dan ase sy ote d aO EEE E EERE E RENSE REE P OTEP 298 12T OVERVICW esas Satteweshs des Sook dominant EA E S E teseet aay Sees dus 298 12 22 ZoneDefense Switches yc ki cee wees kde dessus E Sel ede eee 299 12 3 Zone Defense Operatlon persek ore sues sevens ss ybed enue eE E A deste SOE 300 User Manual 123 J SNMP e vane ndss teases Saeed ous ce EE E E cteas cuss viens EREEREER RER 300 123 2 Threshold RUES coese sha oaee Shas aE Lands Dean easrwilies eet aas 300 12 3 3 Manual Blocking and Exclude Lists 20 00 00 cece cece cece ence eneeeeeenee 300 1234 Term talons sarrin etenn te thaute oh uae spans EEDE EE DE 302 13 Advanced Settings e ia o ete E E E TE E E oped tab eaten N ENT 304 131 IP Level Settings anie E e E eee E E e NE 304 13 2 TCP Level Sethin gs 2 335 a ak rE AE S 307 13 3 ICMP evel Setting sosser reserse ra eo mn eri stands O TERRES PES TEPO TES 311 13 4 ARP Settings ei oii ea aa e EEE E OT S ieee 312 13 5 Stateful Inspection Settings rssicon esr nr eiie 314 13 6 Connection Timeouts 2 0 0 0 eee serino si E EEEIEE EEE G ENEE Ee 316 13 7 Size Limits by Protocol sisstin sacs doing ds arses vest aaesdenesscosaesesdotadaseeds 318 13 8 Fragmentation Settings 2 0 00 eee ec ee cence cece ence ee ceneeeeeeeeseeeeaeeeaeeeaes 320 13 9 Local Fragment Reassembly Settings 20 0 0 cece ceeeceeeee
9. 2 QO Client 3 Client 2 Client 1 Window Time Time When the Round Robin algorithm is used the first arriving requests R1 and R2 from Client 1 are both assigned to one sever say Server 1 according to stickiness The next request R3 from Client 2 is then routed to Server 2 When R4 from Client 3 arrives Server 1 gets back its turn again and will be assigned with R4 Figure 10 7 Stickiness and Round Robin 283 10 3 5 Server Health Monitoring Chapter 10 Traffic Management Servers Server 2 Server 1 Time If Connection Rate is applied instead R1 and R2 will be sent to the same server because of stickiness but the subsequent requests R3 and R4 will be routed to another server since the number of new connections on each server within the Window Time span is counted in for the distribution Figure 10 8 Stickiness and Connection Rate Servers Server 2 Server 1 Time Regardless which algorithm is chosen if a server goes down traffic will be sent to other servers And when the server comes back online it can automatically be placed back into the server farm and start getting requests again 10 3 5 Server Health Monitoring SLB uses Server Health Monitoring to continuously check the condition of the servers in an SLB configuration SLB monitors different OSI layers to check the connection rate for each server as well as its current state Regardless of the algorithm if a server fails SLB will not send a
10. Output Bytes The number of bytes sent by the user Input Packets The number of packets received by the user e Output Packets The number of packets sent by the user e Session Time The number of seconds this session lasted e Termination Cause The reason why the session was terminated e How Authenticated How the user was authenticated This is set to either RADIUS if the user was authenticated via RADIUS or LOCAL if the user was authenticated via a local user database e Delay Time See the above comment about this parameter e Timestamp The number of seconds since 1970 01 01 Used to set a timestamp when this packet was sent from the D Link Firewall In addition to this two more attributes are possibly sent e Input Gigawords Indicates how many times the Input Bytes counter has wrapped This is only sent if Input Bytes has wrapped and if the Input Bytes attribute is sent e Output Gigawords Indicates how many times the Output Bytes counter has wrapped This is only sent if Output Bytes has wrapped and if the Output Bytes attribute is sent Note The symbol in the above list indicates that the sending of the parameter is user configurable 40 2 3 4 Activating RADIUS Accounting Chapter 2 Management and Maintenance 2 3 3 Interim Accounting Messages In addition to START and STOP messages NetDefendOS can optionally periodically send Interim Accounting Messages to update the acc
11. Set Outer server IP to ip_ext For Microsoft Point to Point Encryption it is recommended to disable all options except 128 bit encryption Set IP Pool to pptp_pool Enable Proxy ARP on the int interface As in L2TP enable the insertion of new routes automatically into the main routing table Define a User Authentication Rule this is almost identical to L2TP 4 Now set up the IP rules in the IP rule set As described for L2TP the NAT rule lets the clients access the public Internet via the D Link Firewall 5 Set up the client For Windows XP the procedure is exactly as described for L2TP above but without entering the pre shared key 9 2 7 VPN Troubleshooting General Troubleshooting In all types of VPNs some basic troubleshooting checks can be made e Check that all IP addresses have been specified correctly e Check that all pre shared keys and usernames passwords are correctly entered 237 9 2 7 VPN Troubleshooting Chapter 9 VPN e If certificates have been used check that the correct certificates have been used and that they haven t expired e Use ICMP Ping to confirm that the tunnel is working With roaming clients this is best done by Pinging the internal IP address of the local network interface on the D Link Firewall from a client in LAN to LAN setups pinging could be done in any direction If NetDefendOS is to able to respond to a Ping then the following rule must exist in the IP rule set
12. The routing table consequently contains the following default route Now a secondary route is added over a backup DSL connection and Route Monitoring is enabled for this The updated routing table will look like this Notice that Route Monitoring is enabled for the first route but not the backup failover route As long as the preferred wan route is healthy everything will work as expected Route Monitoring will also be functioning so the secondary route will be enabled should the wan route fail There are however some problems with this setup if a route failover occurs the default route will then use the dsl interface When a new HTTP connection is then established from the intnet network a route lookup will be made resulting in a destination interface of dsl The IP rules will then be evaluated but the original NAT rule assumes the destination interface to be wan so the new connection will be dropped by the rule set In addition any existing connections matching the NAT rule will also be dropped as a result of the change in the destination interface Clearly this is undesirable To overcome this issue potential destination interfaces should be grouped together into an Interface Group and the Security Transport Equivalent flag should be enabled for the Group The Interface Group is then used as the Destination Interface when setting policies For more information on groups see Section 3 3 6 Interface Groups Gratuito
13. gt set ALG ALG_HTTP anti_virus Antivirus Protect Then create a Service object using the new HTTP ALG gw world gt add ServiceTCPUDP http_anti_virus Type TCP DestinationPorts 80 ALG anti_virus Finally modify the NAT rule to use the new service gw world gt set IPRule NATHttp Service http_anti_virus Web Interface A First create an HTTP Application Layer Gateway ALG Object 6 4 6 Anti Virus Options Chapter 6 Security Mechanisms Go to Objects gt ALG gt Add gt HTTP ALG Specify a suitable name for the ALG for instance anti_virus Click the Antivirus tab Select Protect in the Mode dropdown list Click OK B Then create a Service object using the new HTTP ALG Go to Local Objects gt Services gt Add gt TCP UDP service Specify a suitable name for the Service for instance http_anti_virus Select the TCP in the Type dropdown list Enter 80 in the Destination Port textbox Select the HTTP ALG you just created in the ALG dropdown list Click OK C Finally modify the NAT rule called NATHttp in this example to use the new service Go to Rules gt IP Rules In the grid control click the NAT rule handling the traffic between lannet and all nets Click the Service tab Select your new service http_anti_virus in the pre defined Service dropdown list Click OK Anti Virus scanning is now activated for all web traffic from lannet to all nets 187 6 5 Intrusion Detection and Chapter 6 Secu
14. Advanced Settings in the WebUI and changing the setting WebUI HTTP Port Port number 81 could instead be used for this setting Agent Options For HTTP and HTTPS authentication there is a set of options in Authentication Rules called Agent Options These are e Login Type This can be one of e FORM The user is presented with an HTML page for authentication which is filled in and the data sent back to NetDefendOS with a POST An HTML pre defined in NetDefendOS will be used but this can be customized as described below e BASICAUTH This sends a 401 Authentication Required message back to the browser which will cause it to use its own inbuilt dialog to ask the user for a username password combination A Realm String can optionally be specified which will appear in the browser s dialog FORM is recommended over BASICAUTH because the in some cases the browser might hold the login data in its cache e If the Agent is set to HTTPS then the Host Certificate and Root Certificate have to be chosen from a list of certificates already loaded into NetDefendOS Setting Up IP Rules HTTP authentication can t operate unless a rule is added to the IP rule set to explicitly allow authentication to take place If we consider the example of a number of clients on the local network lannet who would like access to the public Internet on the wan interface then the IP rule set would contain the following rules The first rule allows the authentica
15. CLI gw world gt add Interface PPPoETunnel PPPoEClient EthernetInterface wan Network all nets Username exampleuser Password examplepw Web Interface 1 Goto Interfaces gt PPPoE gt Add gt PPoE Tunnel 2 Then enter e Name PPPoEClient Physical Interface wan e Remote Network all nets as we will route all traffic into the tunnel 3 3 5 GRE Tunnels Chapter 3 Fundamentals Service Name Service name provided by the service provider Username Username provided by the service provider Password Password provided by the service provider Confirm Password Retype the password Under Authentication specify which authentication protocol to use the default settings will be used if not specified Disable the option Enable dial on demand Under Advanced if Add route for remote network is enabled then a new route will be added for the interface Click OK Note To provide a point to point connection over Ethernet each PPP session must learn the Ethernet address of the remote peer as well as establish a unique session identifier PPPoE includes a discovery protocol that provides this 3 3 5 GRE Tunnels Overview The Generic Router Encapsulation GRE protocol is a simple encapsulating protocol that can be used whenever there is a need to tunnel traffic across networks and or through network devices GRE does not provide any security features but this means that its use has extremely low overhead Us
16. How the user was authenticated This is set to either RADIUS if the user was authenticated via RADIUS or LOCAL if the user was authenticated via a local user 39 2 3 3 Interim Accounting Messages Chapter 2 Management and Maintenance database e Delay Time The time delay in seconds since the AccountingRequest packet was sent and the authentication acknowledgement was received This can be subtracted from the time of arrival on the server to find the approximate time of the event generating this AccountingRequest Note that this does not reflect network delays The first attempt will have this parameter set to 0 e Timestamp The number of seconds since 1970 01 01 Used to set a timestamp when this packet was sent from NetDefendOS STOP Message Parameters Parameters included in STOP messages sent by NetDefendOS are e Type Marks this accounting request as signaling the end of a session STOP e ID An identifier matching a previously sent AccountingRequest packet with Acct Status Type set to START e User Name The user name of the authenticated user e NAS IP Address The IP address of the D Link Firewall e NAS Port The port on the NAS on which the user was authenticated this is a physical port and not a TCP or UDP port e User IP Address The IP address of the authenticated user This is sent only if specified on the authentication server e Input Bytes The number of bytes received by the user
17. Maximum number of transactions at the same time Default 32 DHCPRelay_TransactionTimeout For how long a dhcp transaction can take place Default 70 seconds DHCPRelay_MaxPPMPerlface How many dhcp packets a client can send to through NetDefendOS to the dhcp server during one minute Default 500 packets DHCPRelay_MaxHops How many hops the dhcp request can take between the client and the dhcp server Default 5 DHCPRelay_MaxLeaseTime The maximum leastime allowed through NetDefendOS if the DHCP server have higher leases this value will be shorted down to this value Default 70000 seconds DHCPRelay_MaxAutoRoutes How many relays that can be active at the same time Default 256 DHCPServer_SaveRelayPolicy What policy should be used to save the relay list to the disk possible settings are Disabled ReconfShut or ReconfShutTimer Default ReconfShut DHCPRelay_AutoSaveRelayinterval How often should the relay list be saved to disk if DHCPServer_SaveRelayPolicy is set to ReconfShutTimer Default 56400 326 13 12 DHCPServer Settings Chapter 13 Advanced Settings 13 12 DHCPServer Settings DHCPServer_SaveLeasePolicy What policy should be used to save the lease database to the disk possible settings are Disabled ReconfShut or ReconfShutTimer Default ReconfShut DHCPServer_AutoSaveLeaselinterval How often should the leases database be saved to disk if DHCPServer_SaveLeasePolicy is se
18. Name A suitable name for the rule eg Queries_if1 Type Query Action Proxy Output if1 this is the relay interface Under Address Filter enter Source Interface wan Source Network UpstreamRouterlp Destination Interface core Destination Network auto Multicast Source 192 168 10 1 Multicast Group 239 192 10 0 24 Click OK Example 4 12 Configuration if2 Group Translation The following steps needs to be executed to create the report and query rule pair for if2 which translates the multicast group Note that the group translated therefore the IGMP reports include the translated IP addresses and the queries will contain the original IP addresses Web Interface A Create the first IGMP Rule 1 Go to Routing gt IGMP gt IGMP Rules gt Add gt IGMP Rule 2 Under General enter Name A suitable name for the rule eg Reports_if2 117 4 5 3 IGMP Configuration Chapter 4 Routing Type Report Action Proxy e Output wan this is the relay interface Under Address Filter enter Source Interface if2 Source Network if2net Destination Interface core Destination Network auto Multicast Source 192 168 10 1 Multicast Group 239 192 10 0 24 Click OK B Create the second IGMP Rule 1 Again go to Routing gt IGMP gt IGMP Rules gt Add gt IGMP Rule 2 Under General enter Name A suitable name for the rule eg Queries_if2 Type Query Action Proxy Output if2 this is the relay interface
19. Note A new date and time will be applied by NetDefendOS as soon as it is set Time Zones The world is divided up into a number of time zones with Greenwich Mean Time GMT in London at zero longitude being taken as the base time zone All other time zones going east and west from zero longitude are taken as being GMT plus or minus a given integer number of hours All locations counted as being inside a given time zone will then have the same local time and this will be one of the integer offsets from GMT The NetDefendOS time zone setting reflects the time zone where the D Link Firewall is physically located 82 3 8 2 Time Servers Chapter 3 Fundamentals Example 3 21 Setting the Time Zone To modify the NetDefendOS time zone to be GMT plus 1 hour follow the steps outlined below CLI gw world gt set DateTime Timezone GMTplus1 Web Interface 1 Goto System gt Date and Time 2 Select GMT 01 00 in the Timezone drop down list 3 Click OK Daylight Saving Time Many regions follow Daylight Saving Time DST or Summer time as it is called in some countries and this means clocks are advanced for the summer period Unfortunately the principles regulating DST vary from country to country and in some cases there can be variations within the same country For this reason NetDefendOS does not automatically know when to adjust for DST Instead this information has to be manually provided if daylight saving time is to
20. The central database residing on the dedicated server s contains all user credentials as well as details of connections significantly reducing administration complexity The Remote Authentication Dial in User Service RADIUS is an Authentication Authorization and Accounting AAA protocol widely used to implement this approach and is used by NetDefendOS to implement user accounting The RADIUS protocol is based on a client server architecture The D Link Firewall acts as the client of the RADIUS server creating and sending requests to a dedicated server s In RADIUS terminology the firewall acts as the Network Access Server NAS For user authentication the RADIUS server receives the requests verifies the user s information by consulting its database and returns either an ACCEPT or REJECT decision to the requested client In RFC2866 RADIUS was extended to handle the delivery of accounting information and this is the standard followed by NetDefendOS for user accounting The benefits of having centralized servers are thus extended to user connection accounting For details of the usage of RADIUS for NetDefendOS authentication see Section 8 2 Authentication Setup 2 3 2 RADIUS Accounting Messages Statistics such as number of bytes sent and received and number of packets sent and received are updated and stored throughout RADIUS sessions All statistics are updated for an authenticated user whenever a connection related to an au
21. Thus the firewall knows what port to be opened for the data channel Moreover the FTP ALG also provides functionality to filter out certain control commands and provide a basic buffer overrun protection The most important feature of the FTP ALG is its unique capability to perform on the fly conversion between active and passive mode The conversion can be described as follows e The FIP client can be configured to use passive mode which is the recommended mode for clients e The FTP server can be configured to use active mode which is the safer mode for servers e When an FTP session is established the D Link Firewall will automatically and transparently receive the passive data channel from the FTP client and the active data channel from the server and tie them together This implementation results in both the FTP client and the FTP server working in their most secure mode The conversion also works the other way around that is with the FTP client using active mode and the FTP server using passive mode Example 6 2 Protecting an FTP Server with an ALG As shown an FTP Server is connected to the D Link Firewall on a DMZ with private IP addresses shown below 141 6 2 3 FTP Chapter 6 Security Mechanisms To make it possible to connect to this server from the Internet using the FTP ALG the FTP ALG and rules should be configured as follows Web Interface A Define the ALG Go to Objects gt ALG gt Add gt F
22. Under Address Filter enter Source Interface wan Source Network UpstreamRouterlp Destination Interface core Destination Network auto Multicast Source 192 168 10 1 Multicast Group 239 192 10 0 24 Click OK Advanced IGMP Settings There are a number of advanced settings which are global and apply to all interfaces which do not have IGMP setttings explicitly specified for them These global settings can be found in Chapter 13 Advanced Settings Individual IGMP settings are found in the IGMP section of the administration interface 118 4 6 Transparent Mode Chapter 4 Routing 4 6 Transparent Mode 4 6 1 Overview of Transparent Mode Deploying D Link Firewalls operating in Transparent Mode into an existing network topology can significantly strengthen security It is simple to do and doesn t require reconfiguration of existing nodes Once deployed NetDefendOS can then allow or deny access to different types of services for example HTTP and in specified directions As long as users of the network are accessing permitted services through the D Link Firewall they are not aware of its presence Transparent Mode is enabled by specifying a Switch Route instead of a standard Route A typical example of Transparent Mode s ability to improve security is in a corporate environment where there might be a need to protect different departments from one another The finance department might require access to only a restricted set of s
23. become neighbors as soon as they see themselves listed in the neighbor s Hello packet This way a two way communication is guaranteed The following Neighbor States are defined Down This is the initial stat of the neighbor relationship Init When a HELLO packet is received from a neighbor but does NOT include the Router ID of the firewall in it the neighbor will be placed in Init state As soon as the neighbor in question receives a HELLO packet it will know the sending routers Router ID and will send a HELLO packet with that included The state of the neighbors will change to 2 way state 2 Way In this state the communication between the router and the neighbor is bi directional On Point to Point and Point to Multipoint interfaces the state will be changed to Full On Broadcast interfaces only the DR BDR will advance to Fullstate with their neighbors all the remaining neighbors will remain in the 2 Way state ExStart Preparing to build adjacency Exchange Routers are exchanging Data Descriptors Loading Routers are exchanging LSAs Full This is the normal state of an adjacency between a router and the DR BDR Aggregates OSPF Aggregation is used to combine groups of routes with common addresses into a single entry 105 4 4 2 OSPF Chapter 4 Routing in the routing table This is commonly used to minimize the routing table Virtual Links Virtual links are used for e Linking an area that does not have a direct co
24. e 5 modp 1536 bit Security increases as the PFS group bits grow larger as does the time taken for the exchanges This is a Diffie Hellman group much like the one for IKE However this one is used solely for PFS The encryption algorithm to use on the protected traffic This is not needed when AH is used or when ESP is used without encryption The algorithms supported by D Link Firewall VPNs are e AES e Blowfish e Twofish e Cast128 e 3DES e DES This specifies the authentication algorithm used on the protected traffic This is not used when ESP is used without authentication although it is not recommended to use ESP without authentication The algorithms supported by D Link Firewall VPNs are e SHAI e MD5 This is the lifetime of the VPN connection It is specified in both time seconds and data amount kilobytes Whenever either of these values is exceeded a re key will be initiated providing new IPsec encryption and authentication session keys If the VPN connection has not been used during the last re key period the connection will be terminated and re opened from scratch when the connection is needed again This value must be set lower than the IKE lifetime The simplest way of configuring a VPN is by using a method called manual keying This is a 245 9 3 3 IKE Authentication Chapter 9 VPN method where IKE is not used at all the encryption and authentication keys as well as some other
25. gt TCP gt TCPUrg WinNuke attacks will usually show up in NetDefendOS logs as normal drops with the name of the rule in your policy that disallowed the connection attempt For connections allowed through the system TCP or DROP category depending on the TCPUrg setting entries will appear with a rule name of TCPUrg The sender IP address is not likely to be spoofed a full three way handshake must be completed before out of band segments can be sent 6 6 7 Amplification attacks Smurf Papasmurf Fraggle This category of attacks all make use of amplifiers poorly configured networks who amplify a stream of packets and send it to the ultimate target The goal is excessive bandwidth consumption consuming all of the victim s Internet connection capacity An attacker with sufficient bandwidth can forgo the entire amplification stage and simply stream enough bandwidth at the victim However these attacks allows attackers with less bandwidth than the victim to amplify their data stream to overwhelm the victim e Smurf and Papasmurf send ICMP echo packets to the broadcast address of open networks with many machines faking the source IP address to be that of the victim All machines on the open network then respond to the victim e Fraggle uses the same general idea but instead using UDP echo port 7 to accomplish the task Fraggle generally gets lower amplification factors since there are fewer hosts on the Internet that hav
26. http Source Interface wan Destination Interface dmz Source Network all nets Destination Network wan_ip Click OK 125 4 6 6 Transparent Mode Scenarios Chapter 4 Routing 126 Chapter 5 DHCP Services This chapter describes DHCP services in NetDefendOS e Overview page 127 e DHCP Servers page 128 e Static DHCP Assignment page 130 e DHCP Relaying page 131 e IP Pools page 132 5 1 Overview DHCP Dynamic Host Configuration Protocol is a protocol that allows network administrators to automatically assign IP numbers to computers on a network IP Address Assignment A DHCP Server implements the task of assigning IP addresses to DHCP clients These addresses come from a pre defined IP address pool which DHCP manages When a DHCP server receives a request from a DHCP client it returns the configuration parameters such as an IP address a MAC address a domain name and a lease for the IP address to the client in a unicast message DHCP Leases Compared to static assignment where the client owns the address dynamic addressing by a DHCP server leases the address to each client for a pre defined period of time During the lifetime of a lease the client has permission to keep the assigned address and is guaranteed to have no address collision with other clients Before the expiration of the lease the client needs to renew the lease from the server so it can keep using the assigned IP address The
27. packets with lower priorities This approach is used since a precedence limit is also a guarantees for that precendence Figure 10 3 Minimum and Maximum Pipe Precedence Precedences have no effect until the total bandwidth allocated for a pipe is reached In other words when the pipe is full At that point traffic is prioritized by NetDefendOS with higher precedence packets being sent before lower precedence packets The lower precedence packets are buffered If buffer space becomes exhausted then they are dropped Applying Precedences Continuing from the previous example we add the requirement that SSH and Telnet traffic is to have a higher priority than all other traffic To do this we add a Pipe Rule specifically for SSH and Telnet and set the priority in the rule to be a higher priority say 2 We specify the same pipes in this new rule as are used for other traffic The effect of doing this is that the SSH and Telnet rule sets the higher priority on packets related to these services and these packets are sent through the same pipe as other traffic The pipe then makes sure that these higher priority packets are sent first when the total bandwidth limit specified in the pipe s configuration is exceeded Lower priority packets will be buffered and sent when higher priority traffic uses less than the maximum specified for the pipe The buffering process is sometimes referred to as throttling back since it reduces the flow rate The N
28. since many real time applications use large fragmented UDP packets If no such protocols are used the size limit imposed on UDP packets can probably be lowered to 1480 bytes Default 60000 bytes MaxiICMPLen Specifies the maximum size of an ICMP packet ICMP error messages should never exceed 600 bytes although Ping packets can be larger if so requested This value may be lowered to 1000 bytes if you do not wish to use large Ping packets Default 10000 bytes MaxGRELen Specifies the maximum size of a GRE packet GRE Generic Routing Encapsulation has various uses including the transportation of PPTP Point to Point Tunneling Protocol data This value should be set at the size of the largest packet allowed to pass through the VPN connections regardless of its original protocol plus approx 50 bytes Default 2000 bytes MaxESPLen Specifies the maximum size of an ESP packet ESP Encapsulation Security Payload is used by IPsec where encryption is applied This value should be set at the size of the largest packet allowed to pass through the VPN connections regardless of its original protocol plus approx 50 bytes Default 2000 bytes MaxAHLen Specifies the maximum size of an AH packet AH Authentication Header is used by IPsec where only authentication is applied This value should be set at the size of the largest packet allowed to pass through the VPN connections regardless of its original protocol plus approx 50
29. 107 E ethernet 58 default gateway 59 IP addresses 59 with DHCP 59 evasion attack prevention 191 events 35 distribution 35 messages 35 F FragmentedICMP setting 322 FragReassemblyFail setting 321 FTP ALG 140 FwdFast IP rule 75 G Generic Router Encapsulation see GRE gratuitous ARP generation 96 GRE 63 additional checksum 64 and IP rules 64 setup 63 groups in authentication 221 in pipes 275 H H 323 ALG 155 HA see high availability HA cluster see high availability high availability 289 cluster ID 296 issues 296 mechanisms 291 setup 293 with transparent mode 120 HighBuffers setting with high availability 295 HTTP ALG 139 authentication 223 HWM_PollInterval setting 334 HWMMem_AlertLevel setting 334 HWMMem _CriticalLevel setting 334 HWMMem Interval setting 334 HWMMem_LogRepetition setting 334 HWMMem_UsePercent setting 334 HWMMem_WarningLevel setting 334 ICMPSendPerSecLimit setting 311 icons 13 IDENT and IP rules 75 identification lists 251 IDP see intrusion detection and prevention IKE 240 lifetimes 240 IKECRLValidityTime setting 328 IKEMaxCAPuath setting 328 IKESendCRLs setting 328 IKESendInitialContact setting 328 ikesnoop troubleshooting with 238 IllegalFrags setting 320 insertion attack prevention 191 interfaces 57 groups 66 internet key exchange see IKE intrusion detection and prevention 188 signature groups
30. 2 6 POP3 POP3 is a mail transfer protocol that differs from SMTP in that the transfer of mail is directly from a server to a user s client software POP3 ALG Options Key features of the POP3 ALG are Block Clear Text Authentication Block connections between client and server that send the username password combination as clear text which can be easily read some servers may not support other methods than this 151 6 2 7 SIP Chapter 6 Security Mechanisms Hide User This option prevents the POP3 server from revealing that a username does not exist This prevents users from trying different usernames until they find a valid one Allow Unknown Commands Non standard POP3 commands not recognised by the ALG can be allowed or disallowed Fail Mode When content scanning find bad file integrity then the file can be allowed or disallowed Verify MIME type Mail attachment file content can be checked against its filetype A list of all filetypes checked can be found in Appendix C Checked MIME filetypes Anti Virus Scanning The NetDefendOS Anti Virus module can scan email attachments searching for malicious code This feature is described fully in Section 6 4 Anti Virus Scanning The available options are e Disable Turn off scanning e Protect Drop downloads that may contain a virus and log e Audit Log but do not drop downloads that may contain a virus Anti Virus Options If Anti Virus scanning
31. 24 server load balancing 281 service based routing services 52 custom 55 ICMP 55 max sessions 54 353 Alphabetical Index TCP and UDP 53 SilentlyDropStateICMPErrors setting 311 simple network management protocol see SNMP SIP ALG 152 SMTP ALG 146 header verification 149 SNMP community string 43 MIB 43 monitoring 43 traps 37 with IP rules 43 source based routing spam see content filtering SPAM filtering 147 caching 150 logging 149 tagging 148 spoofing 135 SSH 24 state engine 16 packet flow 19 stateful inspection see state engine stateful NAT pools 207 Static address translation see SAT StaticARPChanges setting 312 StripDFOnSmall setting 306 SYN flood protection 54 201 and ALGs 138 syslog logging 36 7 TCPECN setting 309 TCPFinUrg setting 309 TCPMSSAutoClamping setting 307 TCPMSSLogLevel setting 307 TCPMSSMax setting 307 TCPMSSMin setting 307 TCPMSSOnHigh setting 307 TCPMSSOnLow setting 307 TCPMSSVPNMax setting 307 TCPNULL setting 310 TCPOPT_ALTCHKDATA setting 308 TCPOPT_ALTCHKREQ setting 308 TCPOPT_CC setting 309 TCPOPT_OTHER setting 309 TCPOPT_SACK setting 308 TCPOPT_TSOPT setting 308 TCPOPT_WSOPT setting 308 TCPOptionSizes setting 307 TCPRE setting 310 TCPSequenceNumbers setting 310 TCPSynPsh setting 309 TCPSynUrg setting 309 TCPUrg setting 309 TCPZeroUnusedACK setting 308 TCPZeroUnusedURG setting 308 TFTP ALG 145
32. 3 3 3 WLAN e PPPoE PPP over Ethernet interfaces for connections to PPPoE servers For more information about PPPoE please see Section 3 3 4 PPPoE Tunnel interfaces are used when network traffic is being tunneled between the system and another tunnel end point in the network before it gets routed to its final destination To accomplish tunneling additional headers are added to the traffic that is to be tunneled Furthermore various transformations can be applied to the network traffic depending on the type of tunnel interface When routing traffic over an IPsec interface for instance the payload is usually encrypted to achieve confidentiality NetDefendOS supports the following tunnel interface types e IPsec interfaces are used as end points for IPsec VPN tunnels For more information about IPsec VPN please see Section 9 3 IPsec e PPTP L2TP interfaces are used as end points for PPTP or 57 3 3 2 Ethernet Chapter 3 Fundamentals L2TP tunnels For more information about PPTP L2TP please see Section 9 5 PPTP L2TP e GRE interfaces are used to establish GRE tunnels For more information about GRE please see Section 3 3 5 GRE Tunnels Even though the various types of interfaces are very different in the way they are implemented and how they work NetDefendOS treats all interfaces as logical IP interfaces This means that all types of interfaces can be used almost interchangeabl
33. 6 18 Activating Anti Virus Scanning sesesesererersererererereresrerersrerssrerererersrsresrere 186 6 19 Configuring an SMTP Log Receiver sesssesessserrsrrerrsrrrrrrrerrrrrsrrerrrrrerrereerre 194 6 20 Setting up IDP for a Mail Server 0 cece cece ce nece penin eeni e es 195 TAy Adding a NAT Tule sace severe a sesh sea geoss Suades pened eee AN AEREA EAE E E p vane st 205 7 2 U sing NAT ROOMS S pieno ra eaa E ious Er ee Mes eek a EES E week onc NEE 208 7 3 Enabling Traffic to a Protected Web Server in a DMZ ceeeeeeeeeeeeeeeeeeeeeneeeees 210 7 4 Enabling Traffic to a Web Server on an Internal Network 00 00 00 eeee eee 212 7 5 Translating Traffic to Multiple Protected Web Servers ccceeceeeeeeeeeeeeeeee teen es 214 8 1 Creating an authentication user group 2 1 00 00 cece cece cence cece eee n eee eeeeeeceeeeeeeeaeeeaes 226 8 2 User Authentication Setup for Web Access 1 0 0 0 ece cece cc ence ence eeeeeeeeeeeeeeeaeeenes 226 8 3 Configuring a RADIUS server 2 0 0 0 cece ceec nec c nee c eee ce een eeneeeeeeeeeeeeeaeeeaeeeaes 227 9 1 Using a Proposal List arrisera iranda Rae nS se PESEE EE DITES ES 249 9 2 Using a Pre Shared Key o cec scesvgccesados gesevouGeseste ys EEE E EE EESE E 250 9 3 Using an Identity List soriire tetce ess ncpengss o eenen a e EE E TE T 251 9 4 Setting up a PSK based VPN tunnel for roaming clients 00 eee cece eee eee eee 254 9 5 Setting up a Self s
34. ARP cache is empty at system startup and will be populated with entries as needed The contents of a typical minimal ARP Cache looks similar to the following table The first item in this ARP Cache is a dynamic ARP entry which tells us that IP address 192 168 0 10 is mapped to an Ethernet address of 08 00 10 0f bc a5 The second item dynamically maps the IP address 193 13 66 77 to Ethernet address 0a 46 42 4f ac 65 Finally the third item is a static ARP entry binding the IP address 10 5 16 3 to Ethernet address 4a 32 12 6c 89 a4 The third column in the table Expire is used to indicate for how much longer the ARP entry will be valid The first item for instance has an expiry value of 45 which means that this entry will be rendered invalid and removed from the ARP Cache in 45 seconds If traffic is going to be sent to the 192 168 0 10 IP address after the expiration NetDefendOS will issue a new ARP request 68 3 4 4 Static and Published ARP Chapter 3 Fundamentals Entries The default expiration time for dynamic ARP entries is 900 seconds 15 minutes This can be changed by modifying the Advanced Setting ARPExpire The setting ARPExpireUnknown specifies how long NetDefendOS is to remember addresses that cannot be reached This is done to ensure that NetDefendOS does not continously request such addresses The default value for this setting is 3 seconds Example 3 14 Displaying the ARP Cache The contents of the ARP Cache
35. Adding VLAN interfaces vlan1 and vlan2 that should relay to an interface group named as ipgrp dhcp Go to Interface gt Interface Groups gt Add gt InterfaceGroup Now enter Name ipgrp dhcp e Interfaces select viani and vian2 from the Available list and put them into the Selected list Click OK Adding a DHCP relay named as vlan to dhcpserver Go to System gt DHCP gt Add gt DHCP Relay Now enter Name vlan to dhcpserver Action Relay Source Interface ipgrp dhcp DHCP Server to relay to ip dhcp Allowed IP offers from server all nets Under the Add Route tab check Add dynamic routes for this relayed DHCP lease Click OK 131 5 5 IP Pools Chapter 5 DHCP Services 5 5 IP Pools Overview IP pools are used to offer other subsystems access to a cache of DHCP IP addresses These addresses are gathered into a pool by internally maintaining a series of DHCP clients one per IP The DHCP servers used by a pool can either be external or be DHCP servers defined in NetDefendOS itself External DHCP servers can be specified as the server on a specific interface or by a unique IP address Multiple IP Pools can be set up with different identifying names The primary usage of IP Pools is with IKE Config Mode which a feature used for allocating IP addresses to remote clients connecting through IPsec tunnels For more information on this see Section 9 4 3 4 Using Config Mode Basic IP Pool Options Th
36. Anti Virus databases and other product features require that the system clock is accurately set In addition log messages are tagged with time stamps in order to indicate when a specific event occured Not only does this assume a working clock but also that the clock is correctly synchronized with other devices in the network To maintain current date and time NetDefendOS makes use of a built in real time hardware clock This clock is also equipped with a battery backup to guard against a temporary loss of power In addition NetDefendOS supports Time Synchronization Protocols in order to automatically adjust the clock based on queries sent to special external servers 3 8 1 General Date and Time Settings Current Date and Time The administrator can set the date and time manually and this is recommended when a new NetDefendOS installation is started for the first time Example 3 20 Setting the Current Date and Time To adjust the current date and time follow the steps outlined below CLI gw world gt time set YYYY mm DD HH MM SS Where YYYY mm DD HH MM SS is the new date and time Note that the date order is year then month and then day For example to set the date and time to 9 25 in the morning on April 27th 2007 the command would be gw world gt time set 2007 04 27 09 25 00 Web Interface Go to System gt Date and Time Click Set Date and Time Set year month day and time via the dropdown controls Click OK
37. Exempted Connections 2 0 0 0 0 ceceeceecceece ence eeceeeceeeeeeeeeeeaeeeneeeaes 280 10 2 7 Threshold Rules and ZoneDefense eee eeeceee cee ce eeeeeeen es 280 10 2 8 Threshold Rule Blacklisting 2 0 0 0 eee cece ceeeceeeca seen seen eenee 280 10 3 Server Load Balancing i sscsssessscocssgseccetnes soccases se cse sah sevbangeerdeaessseveseapeess 281 103 1 OVERVIEW soisi ro eideann o seein Rebates cd E T tes ees toes 281 10 3 2 Identifying the Servers cece cece pnei ei e 282 10 3 3 The Load Distribution Mode 00 0 0 cece cence eee eeceeeeeeeeneeenes 282 10 3 4 The Distribution Algorithm 2 0 0 0 cece eeeceeeceeeceeeen seen eeneeenee 282 10 3 5 Server Health Monitoring 2 0 0 0 eee cece eee eeceeeeeeeeneeeaes 284 10 3 6 SLB SA F Rules 2 050 ac tess peed ee as ed ie a a eed ae 284 Fi Bagh Availability coc vsscsevves such sn ennce ronal aE spe tedeoes E E EESE ESSEE wate 289 TL Ve ON CEVICW Beds See a Heit we ch he ee geen teueva eck teehee eT ao eg sia E A aR 289 11 2 High Availability Mechanisms cee eeeceeec ee ce ee ceeeeeeeeeeeeeesaeseaeeeaes 291 11 3 High Availability Setup 2 cece cece E A A A Y 293 11 3 Hardware Setups iess tenisie reant Vor EA arp POSEE E PERES POE EEEE EPER TSS 293 11 3 2 NetDefendOS Setup 00 0 israse neinet ipes ase 294 11 3 3 Verifying Cluster Functioning ss eseesseersserrsrrerreresrrreerrerrerree 294 11 4 High Availability Issues 2 0 00
38. IP Rules gt Add gt IPRule Specify a suitable name for the rule eg NAT_HTTP Now enter Action NAT Service http Source Interface lan Source Network lannet Destination Interface any Destination Network all nets Under the NAT tab make sure that the Use Interface Address option is selected Click OK 205 7 1 Dynamic Network Address Chapter 7 Address Translation Translation Protocols Handled by NAT Dynamic address translation is able to deal with the TCP UDP and ICMP protocols with a good level of functionality since the algorithm knows which values can be adjusted to become unique in the three protocols For other IP level protocols unique connections are identified by their sender addresses destination addresses and protocol numbers This means that e An internal machine can communicate with several external servers using the same IP protocol e An internal machine can communicate with several external servers using different IP protocols e Several internal machines can communicate with different external server using the same IP protocol e Several internal machines can communicate with the same server using different IP protocols e Several internal machines can not communicate with the same external server using the same IP protocol Note gt These restrictions apply only to IP level protocols other than TCP UDP and ICMP such as OSPF L2TP etc They do not apply to protocols transported by
39. Objects gt VPN Objects gt ID List gt Add gt ID List Enter a suitable name eg sales Click OK Go to Objects gt VPN Objects gt ID List gt Sales gt Add gt ID Enter the name for the client Select Email as Type In the Email address field enter the email address selected when you created the certificate on the client Create a new ID for every client that you want to grant access rights according to the instructions above D Configure the IPsec tunnel Go to Interfaces gt IPsec gt Add gt IPsec Tunnel Now enter Name Roaming PsecTunnel Local Network 10 0 1 0 24 This is the local network that the roaming users will connect to Remote Network all nets Remote Endpoint None Encapsulation Mode Tunnel 255 9 4 3 Roaming Clients Chapter 9 VPN For Algorithms enter IKE Algorithms Medium or High IPsec Algorithms Medium or High For Authentication enter Choose X 509 Certificate as authentication method Root Certificate s Select all your client certificates and add them to the Selected list Gateway Certificate Choose your newly created firewall certificate Identification List Select your ID List that you want to associate with your VPN Tunnel In our case that will be sales Under the Routing tab Enable the option Dynamically add route to the remote network when a tunnel is established Click OK E Finally configure the IP rule set to allow traffic inside the tunnel 9
40. On the left hand side of the WebUI is a tree which allows navigation to the various NetDefendOS modules The central area of the WebUI displays information about those modules Current performance information is shown by default D Link Building Networks for People Menu Bar 3 Oore ian aian Pe MELAT 1527 aD EPU teot I Urine 0 tom 22170 wav rovo Consqeastnn verten 3 tosses one 435000 3 phr omits mw Pre ome 3 trate Drg irer ae P 1300 S tons Cornes Latt SARON 17 AEII AS AVIDA SABAD enamine a a Ditra Last woken 2008 003 aT tae arw Tree view List O System Veer and med aatem paianet aid a drie and bae semam oag p pnd ramte mprocema st Mesage Ba ws sess samot tare sien ser m bemat ae t ne IA the term a Rowing Cae DeE me mamae LATED AE TE MEN nenna dyahe ami polio bane d n smp ie User Authentication AAA AP vet DAA OOP pre ater AIAD ated 174 Bman 19 we AN entation Lp Zone Defense Sere Detance w VNC WY atom amiatiy bine NET awake o1 a Pap at mitas 7 DAT rented asho wi nla ane omua LJ Objects The sbbert sccm contains amt athe saes ts ot ere COMMON ET OTE DAR FINE OTTO SCORE LON mp Interfaces tate taser pre phvmcal cr le posi andipe at Dr ch mew teat LAN iate S920 ci UPR Bene N tai ratane mame ig 0S 10P OT TEE e i ny Pade AE o iem LE Traffic Shaping TAA TRIPE DP DRANG BECTON UF NOE te SENAD IRA EDADE Main Window For information about the default use
41. Scanned The NetDefendOS Anti Virus module is able to scan the following types of downloads e HTTP FTP TFTP SMTP and POP3 file downloads e Any uncompressed file type transferred through these protocols e If the download has been compressed ZIP and GZIP files can be scanned The administrator has the option to always drop specific files as well as the option to specify a size limit on scanned files If no size limit is specified then there is no default upper limit on file sizes Simultaneous Scans There is no fixed limit on how many Anti Virus scans can take place simultaneously in a single 183 6 4 3 Activating Anti Virus Scanning Chapter 6 Security Mechanisms D Link Firewall However the available free memory can place a limit on the number of concurrent scans that can be initiated The administrator can increase the default amount of free memory available to Anti Virus scanning through changing the AVSE_MAXMEMORY advanced setting This setting specifies what percentage of total memory is to be used for Anti Virus scanning Protocol Specific Behaviour Since Anti Virus scanning is implemented through an Application Level Gateway ALG specific protocol specific features are implemented in NetDefendOS With FTP for example scanning is aware of the dual control and data transfer channels that are opened and can send a request via the control connection to stop a download if a virus in the download is detected 6 4 3 Act
42. VPN gw world gt add Interface L2TPServer MyPPTPServer ServerIP lan_ip Interface any IP wan_ip IPPool pp2p_Pool TunnelProtocol PPTP AllowedRoutes all nets Web Interface Go to Interfaces gt L2TP Servers gt Add gt L2TPServer Enter a name for the PPTP Server eg MyPPTPServer Now enter Inner IP Address lan_ip Tunnel Protocol PPTP Outer Interface Filter any Outer Server IP wan_ip Under the PPP Parameters tab select pptp_Pool in the IP Pool control Under the Add Route tab select all_nets from Allowed Networks Click OK Use User Authentication Rules is enabled as default To be able to authenticate the users using the PPTP tunnel you also need to configure authentication rules which will not be covered in this example 9 5 2 L2ZTP Layer 2 Tunneling protocol L2TP is an IETF open standard that overcomes many of the problems of PPTP Its design is a combination of Layer 2 Forwarding L2F protocol and PPTP making use of the best features of both Since the L2TP standard does not implement encryption it is usually implemented with an IETF standard known as L2TP IPsec in which L2TP packets are encapsulated by IPsec The client communicates with a Local Access Concentrator LAC and the LAC communicates across the Internet with a L2TP Network Server LNS The D Link Firewall acts as the LNS The LAC is in effect tunneling data such as a PPP session using IPsec to the LNS across the Internet In most cases the c
43. VPNs e Adapting VPN access policies for different groups of users e Creating key distribution policies A common misconception is that VPN connections are equivalents to the internal network from a security standpoint and that they can be connected directly to it with no further precautions It is important to remember that although the VPN connection itself may be secure the total level of security is only as high as the security of the tunnel endpoints It is becoming increasingly common for users on the move to connect directly to their company s network via VPN from their laptops However the laptop itself is often not protected In other words an intruder can gain access to the protected network through an unprotected laptop and already opened VPN connections A VPN connection should never be regarded as an integral part of a protected network The VPN firewall should instead be located in a special DMZ or outside a firewall dedicated to this task By doing this you can restrict which services can be accessed via VPN and modem and ensure that these services are well protected against intruders In instances where the firewall features an integrated VPN feature it is usually possible to dictate the types of communication permitted The NetDefendOS VPN module features such a facility 9 1 4 Key Distribution Key distribution schemes are best planned in advance Issues that need to be addressed include e How will keys be distributed Ema
44. Web Interface Go to Routing gt Routing Tables gt TestPBRTable gt Add gt Route Now enter Interface The interface to be routed Network The network to route Gateway The gateway to send routed packets to Local IP Address The IP address specified here will be automatically published on the corresponding interface This address will also be used as the sender address in ARP queries If no address is specified the firewall s interface IP address will be used e Metric Specifies the metric for this route Mostly used in route fail over scenarios Click OK 100 4 3 5 The Ordering parameter Chapter 4 Routing Example 4 5 Policy Based Routing Configuration This example illustrates a multiple ISP scenario which is a common use of Policy based Routing The following is assumed Each ISP will give you an IP network from its network range We will assume a 2 ISP scenario with the network 10 10 10 0 24 belonging to ISP A and 20 20 20 0 24 belonging to ISP B The ISP gateways are 10 10 10 1 and 20 20 20 1 respectively All addresses in this scenario are public addresses for the sake of simplicity This is a drop in design where there are no explicit routing subnets between the ISP gateways and the D Link Firewall In a provider independent network clients will likely have a single IP address belonging to one of the ISPs Ina single organization scenario publicly accessible servers will be configured with two
45. a moderate probability of being SPAM The NetDefendOS Implementation SMTP functions as a protocol for sending emails between servers NetDefendOS applies SPAM filtering to emails as they pass through a D Link Firewall from a remote SMTP server to the local SMTP server from which local clients will later download the emails Typically the local SMTP server will be set up on a DMZ and there will usually be only one hop between the sending server and the local receiving server A number of trusted organisations maintain publicly available databases of the origin IP address of known spamming SMTP servers and these can be queried over the public Internet These lists are known as DNS Black List DNSBL databases and the information is accessible using a standardized query method supported by NetDefendOS The image below illustrates all the components involved Figure 6 1 DNSBL SPAM Filtering 147 6 2 5 SMTP Chapter 6 Security Mechanisms A When the NetDefendOS SPAM filtering function is configured the IP address of the email s sending server can be sent to one or more DNSBL servers to find out if any DNSBL servers think it is from a spammer or not NetDefendOS examines the IP packet headers to do this The reply sent back by a server is either a not listed response or a listed response In the latter case of being listed the DSNBL server is indicating the email might be SPAM and it will usually also provide a information known
46. a separate concept from Section 6 7 Blacklisting Hosts and Networks Example 6 14 Setting up a white and blacklist This example shows the use of static content filtering where NetDefendOS can block or permit certain web pages based on blacklists and whitelists As the usability of static content filtering will be illustrated dynamic content filtering and active content handling will not be enabled in this example In this small scenario a general surfing policy prevents users from downloading exe files However the D Link website provides secure and necessary program files which should be allowed to download CLI Start by adding an HTTP ALG in order to filter HTTP traffic gw world gt add ALG ALG_HTTP content_filtering Then create a HTTP ALG URL to set up a blacklist gw world gt cc ALG ALG_HTTP content_filtering gw world content_filtering gt add ALG_HTTP_URL URL exe Action Blacklist Finally make an exception from the blacklist by creating a specific whitelist gw world content_filtering gt add ALG_HTTP_URL URL www D Link com exe Action Whitelist Web Interface Start by adding an HTTP ALG in order to filter HTTP traffic 1 Goto Objects gt ALG gt Add gt HTTP ALG 2 Enter a suitable name for the ALG for instance content_filtering 3 Click OK Then create a HTTP ALG URL to setup a blacklist Go to Objects gt ALG In the grid click on the recently created HTTP ALG content_filtering and
47. add route to the remote network when a tunnel is established Click OK D Finally configure the IP rule set to allow traffic inside the tunnel 9 4 3 4 Using Config Mode IKE Configuration Mode Config Mode is an extension to IKE that allows NetDefendOS to provide LAN configuration information to remote VPN clients It is used to dynamically configure IPsec clients with IP addresses and corresponding netmasks and to exchange other types of information associated with DHCP The IP address provided to a client can be either be based on a range of predefined static IP addresses defined for Config Mode or it can come from DHCP servers associated with an ZP Pool object An IP pool is a cache of IP addresses collected from DHCP servers and leases on these addresses are automatically renewed when the lease time is about to expire IP Pools also manage additional information such as DNS and WINS NBNS just as an ordinary DHCP server would For detailed information on pools see Section 5 5 IP Pools Defining the Config Mode Object 257 9 4 3 Roaming Clients Chapter 9 VPN Currently only one Config Mode object can be defined in NetDefendOS and this is referred to as the Config Mode Pool object The key parameters associated with it are as follows Use Pre defined IP Pool Object The IP Pool object that provides the IP addresses Use a Static Pool As an alternative to using an IP Pool a static set of IP addresses can be d
48. addresses visible to machines in the DMZ When internal machines connect to wan_ip port 80 they will be allowed to proceed by rule 2 as it matches that communication From an internal perspective all machines in the DMZ should be regarded as any other Internet connected servers we do not trust them which is the reason for locating them in a DMZ in the first place There are two possible solutions 1 You can change rule 2 so that it only applies to external traffic 2 You can swap rules 2 and 3 so that the NAT rule is carried out for internal traffic before the Allow rule matches Which of these two options is the best For this configuration it makes no difference Both solutions work just as well However suppose that we use another interface ext2 in the D Link Firewall and connect it to another network perhaps to that of a neighboring company so that they can communicate much faster with our servers If option 1 was selected the rule set must be adjusted thus 211 7 3 1 Translation of a Single IP Chapter 7 Address Translation Address 1 1 This increases the number of rules for each interface allowed to communicate with the web server However the rule ordering is unimportant which may help avoid errors If option 2 was selected the rule set must be adjusted thus This means that the number of rules does not need to be increased This is good as long as all interfaces can be entrusted to communicate with t
49. all three DNSBL servers would have to respond in order for the calculated sum to cause the email to be dropped 3 2 2 7 Tagging SPAM Emails If an email is considered probably to be SPAM because the calculated sum is above the SPAM threshold but it is below the Drop threshold then the Subject field of the email is changed and pre fixed with a message and the email is forwarded on to the intended recipient The tag message text is specified by the administrator but can be left blank although that is not recommended An example of tagging might be if the original Subject field is 148 6 2 5 SMTP Chapter 6 Security Mechanisms Buy this stock today And if the tag text is defined to be SPAM then the modified email s Subject field will become wets SEAN Irs Buy IclnLS Sicoclk iwocleiy And this is what the email s recipient will see in the summary of their inbox contents The individual user could then decide to set up their own filters in the local client to deal with such tagged emails possibly sending it to a separate folder In addition the content of the email has X SPAM fields added to it These consist of e X Spam Flag This value will always be Yes e X Spam Checker Version The NetDefendOS version that tagged the email e X Spam Status This will always be DNSBL e X Spam Report A list of DNSBL servers that flagged the email as SPAM These fields can be referred to in mail server filtering rules se
50. an alternate route should the primary preferred one fail Figure 4 1 A Route Failover Scenario for ISP Access Setting Up Route Failover Route Monitoring should be enabled on a per route basis To enable the Route Failover feature in a scenario with a preferred and a backup route the preferred route will have Route Monitoring enabled however the backup route does not require it to be enabled since it will usually have no route to failover to For a route with Route Monitoring enabled one of two Route Monitoring 94 4 2 3 Route Failover Chapter 4 Routing methods must be chosen Interface Link Status NetDefendOS will monitor the link status of the interface specified in the route As long as the interface is up the route is diagnosed as healthy This method is appropriate for monitoring that the interface is physically attached and that the cabling is working as expected As any changes to the link status are instantly noticed this method provides the fastest response to failure Gateway Monitoring If a specific gateway has been specified as the next hop for a route accessibility to that gateway can be monitored by sending periodic ARP requests As long as the gateway responds to these requests the route is considered to be functioning correctly Setting the Route Metric When specifying routes the administrator should manually set a route s Metric The Metric is a positive integer that indicates how preferred the r
51. are e Source Interface e Source Network e Destination Interface e Destination Network e Service The Service in an IP rule is also important because if an Application Layer Gateway object is to be applied to traffic then it must be associated with a Service object see Section 6 2 Application Layer Gateways When an IP rule is triggered by a match then one of the following Actions can occur Allow The packet is allowed to pass As the rule is applied to only the opening of a connection an entry in the state table is made to record that a connection is open The remaining packets related to this connection will pass through the NetDefendOS s stateful engine FwdFast Let the packet pass through the D Link Firewall without setting up a state for it in the state table This means that the stateful inspection process is bypassed and is therefore less secure than Allow or NAT rules Packet processing time is also slower than Allow rules since every packet is checked against the entire rule set NAT This functions like an Allow rule but with dynamic address translation NAT enabled see Section 7 1 Dynamic Network Address Translation in Chapter 7 Address Translation for a detailed description SAT This tells NetDefendOS to perform static address translation A SAT rule always requires a matching Allow NAT or FwdFast rule further down the rule set see Section 7 3 Static Address Translation in Chapter 7 Addres
52. as a TXT record which is a textual explanation for the listing The administrator can configure the NetDefendOS SMTP ALG to consult multiple DNSBL servers in order to form a consensus opinion on an email s origin address As each new email arrives servers are queried to assess the likelihood that the email is SPAM based on its origin address The NetDefendOS administrator assigns a weight greater than zero to each configured server so that a weighted sum can then be calculated based on all responses The administrator can configure one of the following actions based on the sum calculated 1 Ifthe sum is greater than or equal to a pre defined Drop threshold then the email is considered to be definately SPAM and is discarded or alternatively sent to a single special mailbox 2 Ifthe sum is greater than or equal to a pre defined SPAM threshold then the email is considered as probably being SPAM but forwarded to the recipient with notifying text attached to it A Threshold Calculation Example As an example lets suppose that three DNSBL servers are configured dnsbl1 dnsbl2 and dnsbl3 Weights of 3 2 and 2 are assigned to these respectively The SPAM threshold is then set to be 5 If dnsbll and dnsbl2 say an email is SPAM but dnsbl3 does not then the total calculated will be 3 2 0 5 Since the total of 5 is equal to or greater than the threshold then the email will be treated as SPAM If the Drop threshold in this example is set at 7 then
53. be added to the rule listings and it should be make sure there are no rules disallowing or allowing the same kind of ports traffic before these rules Web Interface Go to Rules gt IP Rules gt Add gt IPRule Now enter Name H3230ut Action NAT Service H323 Gatekeeper Source Interface lan Destination Interface any Source Network lannet Destination Network 0 0 0 0 0 all nets Comment Allow outgoing communication with a gatekeeper Click OK Note There is no need to specify a specific rule for outgoing calls NetDefendOS monitors the communication between external phones and the Gatekeeper to make sure that it 164 6 2 8 H 323 Chapter 6 Security Mechanisms is possible for internal phones to call the external phones that are registered with the gatekeeper Example 6 10 Using the H 323 ALG in a Corporate Environment This scenario is an example of a more complex network that shows how the H 323 ALG can be deployed in a corporate environment At the head office DMZ a H 323 Gatekeeper is placed that can handle all H 323 clients in the head branch and remote offices This will allow the whole corporation to use the network for both voice communication and application sharing It is assumed that the VPN tunnels are correctly configured and that all offices use private IP ranges on their local networks All outside calls are done over the existing telephone network using the gateway ip gateway connected to the
54. be used There are two parameters governing daylight saving time the DST period and the DST offset The DST period specifies on what dates daylight saving time starts and ends The DST offset indicates the number of minutes to advance the clock during the daylight saving time period Example 3 22 Enabling DST To enable DST follow the steps outlined below CLI gw world gt set DateTime DSTEnabled Yes Web Interface 1 Goto System Date and Time 2 Check the Enable daylight saving time checkbox control 3 Click OK 3 8 2 Time Servers The hardware clock which NetDefendOS uses can sometimes become fast or slow after a period of operation This is normal behavior in most network and computer equipment and is solved by utilizing Time Servers NetDefendOS is able to adjust the clock automatically based on information received from one or more Time Servers which provide a highly accurate time usually using atomic clocks Using Time Servers is highly recommended as it ensures NetDefendOS will have its date and time aligned with other network devices Time Synchronization Protocols 83 3 8 2 Time Servers Chapter 3 Fundamentals Time Synchronization Protocols are standardised methods for retrieving time information from external Time Servers NetDefendOS supports the following time synchronization protocols e SNTP Defined by RFC 2030 The Simple Network Time Protocol SNTP is a lightweight implementation of N
55. behaviour is that NetDefendOS will allow changes to take place but all such changes will be logged Another similar situation is where information in ARP replies or ARP requests would collide with static entries in the ARP cache Naturally this is never allowed to happen However changing the Adavnced Setting StaticARPChanges allow the administrator to specify whether or not such 71 3 4 5 Advanced ARP Settings Chapter 3 Fundamentals situations are to be logged Sender IP 0 0 0 0 NetDefendOS can be configured on what to do with ARP queries that have a sender IP of 0 0 0 0 Such sender IPs are never valid in responses but network units that have not yet learned of their IP address sometimes ask ARP questions with an unspecified sender IP Normally these ARP replies are dropped and logged but the behavior can be changed by modifying the Advanced Setting ARPQueryNoSenderIP Matching Ethernet Addresses By default NetDefendOS will require that the sender address at Ethernet level should comply with the Ethernet address reported in the ARP data If this is not the case the reply will be dropped and logged Change the behavior by modifying the Advanced Setting ARPMatchEnetSender 72 3 5 The IP Rule Set Chapter 3 Fundamentals 3 5 The IP Rule Set 3 5 1 Security Policies Policy Characteristics NetDefendOS Security Policies designed by the administrator regulate the way in which traffic can flow through
56. by Protocol page 318 e Fragmentation Settings page 320 e Local Fragment Reassembly Settings page 324 e DHCP Settings page 325 e DHCPRelay Settings page 326 e DHCPServer Settings page 327 e IPsec Settings page 328 e Logging Settings page 330 e Time Synchronization Settings page 331 e PPP Settings page 333 e Hardware Monitor Settings page 334 e Packet Re assembly Settings page 335 e Miscellaneous Settings page 336 13 1 IP Level Settings LogChecksumErrors Logs occurrences of IP packets containing erroneous checksums Normally this is the result of the packet being damaged during network transport All network units both routers and workstations drop IP packets that contain checksum errors However it is highly unlikely for an attack to be based on illegal checksums Default Enabled 304 LogReceivedTTLO Chapter 13 Advanced Settings LogNonIP4 Logs occurrences of IP packets that are not version 4 NetDefendOS only accepts version 4 IP packets everything else is discarded Default 256 LogReceivedTTLO Logs occurrences of IP packets received with the Time To Live TTL value set to zero Under no circumstances should any network unit send packets with a TTL of 0 Default Enabled Block0000Src Block 0 0 0 0 as source address Default Drop BlockONet Block 0 as source addresses Default DropLog Block127Net Block 127 as source addresses Default DropLog BlockM
57. can be displayed from within the CLI CLI gw world gt arp show ARP cache of iface lan Dynamic 10 4 0 1 1000 0000 4009 Expire 196 Dynamic 10 4 0 65 TOO an ese Teo Expire 506 Flushing the ARP Cache If a host in your network has recently been replaced with a new hardware but keeping the same IP address it is most likely to have a new Ethernet address If NetDefendOS has an ARP entry for that host the Ethernet address of that entry will be invalid causing data sent to the host to never reach its destination Naturally after the ARP expiration time NetDefendOS will learn the new Ethernet address of the requested host but sometimes it might be necessary to manually force a re query This is easiest achieved by flushing the ARP cache an operation which will delete all dynamic ARP entries from the cache thereby forcing NetDefendOS to issue new ARP queries Example 3 15 Flushing the ARP Cache This example shows how to flush the ARP Cache from within the CLI CLI gw world gt arp flush ARP cache of all interfaces flushed Size of the ARP Cache By default the ARP Cache is able to hold 4096 ARP entries at the same time This is feasible for most deployments but in rare occasions such as when there are several very large LANs directly connected to the firewall it might be necessary to adjust this value This can be done by by modifying the Adavnced Setting ARPCacheSize So called hash tables are used to rapidly
58. can be specified 10 3 4 The Distribution Algorithm There are several ways to determine how a load is shared across a server farm NetDefendOS SLB supports the following algorithms Round Robin The algorithm distributes new incoming connections to a list of servers on a rotating basis For the first connection the algorithm picks a server randomly and assigns the connection to it For subsequent connections the 282 10 3 4 The Distribution Algorithm Chapter 10 Traffic Management algorithm cycles through the server list and redirects the load to servers in order Regardless of each server s capability and other aspects for instance the number of existing connections on a server or its response time all the available servers take turns in being assigned the next connection This algorithm ensures that all servers receive an equal number of requests therefore it is most suited to server farms where all servers have an equal capacity and the processing loads of all requests are likely to be similar Connection Rate This algorithm considers the number of requests that each server has received over a certain timeframe SLB sends the next request to the server that has received the lowest number of connections in that time The administrator is able to specify the timeframe to use with this algorithm If the Connection Rate algorithm is used without stickiness it will behave as a Round Robin algorithm that allocates new connect
59. capabilities of the clients No routes can be predefined so the option Dynamically add route to the remote network when tunnel established should be enabled for the tunnel object Enable the option Require IKE XAuth user authentication for inbound IPsec tunnels This will enable a search for the first matching XAUTH rule in the authentication rules 3 The IP rule set should contain the single rule Once an Allow rule permits the connection to be set up bidirectional traffic flow is allowed which is why only one rule is used here Instead of all nets being used in the above a more secure defined IP object could be used which specifies the exact range of the pre allocated IP addresses B IP addresses handed out by NetDefendOS If the client IP addresses are not known then they must be handed out by NetDefendOS To do this the above must be modified with the following 1 Ifa specific IP address range is to be used as a pool of available addresses then Create a Config Mode Pool object there can only be one associated with a NetDefendOS installation and in it specify the address range Enable the IKE Config Mode option in the IPsec Tunnel object ipsec_tunnel 2 If client IP addresses are to be retrieved through DHCP Create an IP Pool object and in it specify the DHCP server to use The DHCP server can be specified as a simple IP address or alternatively as being accessible on a specific interface If an internal DHCP server is
60. ce eeee ence eeeeeeeeeeenees 82 3 6 2 TIME SELVES s sds warsissnucee does RE ERNE gy ctieaes ov nes EERE ER EE E 83 39 DNS Lookup see suedte wierd E a deat thee tle EE OEE KE AEN 87 A ROUNE os sewers ods bane ey wl E een has dabedten treet Seda ove Macthoess ads euutens EE 89 Al ONGEVICW 223 0055 itunes hata aa ee eh 89 4 2 State ROUNE asic sas r Ein a E vutaest sud EE E ss deed unten Setaee EA E stan cee 90 4 2 1 Basic Principles of Routing cece eee ee cece ce cece eee eeeaeena sean eeae eens 90 4 22 Static ROUUNG 5 sos ok hostess to erae ap yet eE EE K e TE S 91 4 2 3 Route Failo yeT rsisi cse rssi p Ee nE S ie Earr EE EES 94 4 24 Prozy ARP erresen a Ep a REEE SETORES ots capes PESEE EUPIA TEN S 96 4 3 Policy based Routing 2 0 0 0 sosser oseese isene EE e a 98 AIST OVETVICW radai ona a a a aa T a E aT 98 4 3 2 Policy based Routing Tables sseessseeeeseeesrreesrrerrsrrerrsrerreerereees 98 4 3 3 Policy based Routing Rules cece cece ence ee ee ce ceneeeneeeneeeneees 98 4 3 4 Policy based Routing Table Selection 2 0 0 0 cece eeeeceeeceeeceeeee eens 99 4 3 5 The Ordering parameter cece cece cece eee ce eece tena EEO r S 99 4 4 Dynamic ROUNE 2 052 096 sueasisy ones ais oE R E son EEEE EEEE EIERENS 103 4 4 1 Dynamic Routing Overview ec eee cece cere cence eee ne een eeneeeeeeeeees 103 ALA DS OSPE ecg tasctossabenea sss EE somtia sade couasia satis sss EET 104 4 4 3 Dynamic Rou
61. cn dessa suse ab esaad es rRe RE PEE STINNE EEE Ra OPET ERRE S PES EEP SRT 144 6 4 Protecting Phones Behind D Link Firewalls 00 0 0 ccc cece cence teen eeea ceca eeeeeenee 157 6 5 H 323 with private IP addresses s ccs chesccgeeessies soetuedssesveassabeetasneesaaa ss eS 159 6 6 Two Phones Behind Different D Link Firewalls 2 0 0 0 ccc ceeecnee ee eeee teen eenes 160 6 7 Using Private IP Addresses vos 2c cesedesbetes oecasascs ssovaSesseSegauessyeab gases sadbas S PESES YSS 161 6 8 323 with Gatekeeper scissor hee ook Sete oes S O asda eegoustieen cess cesses 162 6 9 H 323 with Gatekeeper and two D Link Firewalls 0 0c eee ce eeee teen teen es 164 6 10 Using the H 323 ALG in a Corporate Environment c cece ceeeeneeee eee eeeeeenes 165 6 11 Configuring remote offices for H 323 cece eeeeeecccseeceeeeeeeeceeueeeeueeeeaeseeuneeeees 167 6 12 Allowing the H 323 Gateway to register with the Gatekeeper ceeeeeeeee eee 167 6 13 Stripping ActiveX and Java applets 2 0 0 0 eee cee cence eee ceeece eee eeeeeeaeeeaeeenes 170 6 14 Setting up a white and blacklist ec ee cee ce ee ce eeceeeea eee eeeeeeaeeeaeeeaes 171 6 15 Enabling Dynamic Web Content Filtering 2 0 0 0 ee ceeeceee ee eeea ceca seen eenee 173 6 16 Enabling Audit Mode sisseostmise erine op twos E RE EEEE TEE EE 174 6 17 Reclassifying a blocked Site ssneseesseerseerrsrrerrrerrrrrssrerrsrrersrrerrerrerrereereee 176
62. command provides a means to control and monitor the operation of the SPAM filtering module The dnsbl command on its own without options shows the overall status of all ALGs If the SMTP ALG name on which DNSBL SPAM filtering is enabled is my_smtp_alg then the output would be 150 6 2 6 POP3 Chapter 6 Security Mechanisms gw world gt dnsbl DNSBL Contexts Name Status Spam Drop Accept my_smtp_alg active 156 65 34299 alt_smtp_alg inactive 0 0 0 The show option provides a summary of the SPAM filtering operation of a specific ALG gw world gt dnsbl my_smtp_alg show DNSBL used by ALG my_ aa oe alg Drop Threshold Spam Threshold Append TXT records IP Cache maximum size IP Cache current size IP Cache timeout Configured BlackLists Disabled BlackLists Current Sessions Sica LS Esg 20 10 yes 10 5 600 4 0 3 Total number of mails checked 34520 Number of mails dropped 65 Number of mails spam tagged 156 Number of mails accepted 34299 BlackList Status Value Morani Matches server spamcenter org active 25 34520 221 nodel spamlister org active 20 34520 65 To clean out the dnsbl cache for the my_smtp_alg and to reset all statistical counters for it use the command option gw world gt dnsbl my_smtp_alg clean Note The above DNSBL server URLs are fictitious and are only for illustration A DNSBL listing can be found at http en wikipedia org wiki Comparison_of DNS_blacklists 6
63. complexity Certificate based authentication may be used as part of a larger public key infrastructure making all VPN clients and firewalls dependent on third parties In other words there are more things that have to be configured and there are more things that can go wrong 9 3 4 IPsec Protocols ESP AH The IPsec protocols are the protocols used to protect the actual traffic being passed through the VPN The actual protocols used and the keys used with those protocols are negotiated by IKE There are two protocols associated with IPsec AH and ESP These are covered in the sections below AH Authentication Header AH is a protocol used for authenticating a data stream Figure 9 1 The AH protocol Original IP packet IP header IP data AH in transport mode IP header AH header IP data SS ee Authenticated AH in tunnel mode Outer IP header AH header IP header IP data Authenticated AH uses a cryptographic hash function to produce a MAC from the data in the IP packet This MAC is then transmitted with the packet allowing the remote gateway to verify the integrity of the original IP packet making sure the data has not been tampered with on its way through the Internet Apart from the IP packet data AH also authenticates parts of the IP header The AH protocol inserts an AH header after the original IP header and in tunnel mode the AH header is inserted after the outer header but before the original inner IP
64. data Default DropLog ARPQueryNoSenderIP What to do with ARP queries that have a sender IP of 0 0 0 0 Such sender IPs are never valid in responses but network units that have not yet learned of their IP address sometimes ask ARP questions with an unspecified sender IP Default DropLog ARPSenderIP Determines if the IP sender address must comply with the rules in the Access section Default Validate UnsolicitedARPReplies Determines how NetDefendOS will handle ARP replies that it has not asked for According to the ARP specification the recipient should accept these However because this can facilitate hijacking of local connections it is not normally allowed Default DropLog ARPRequests Determines if NetDefendOS will automatically add the data in ARP requests to its ARP table The ARP specification states that this should be done but as this procedure can facilitate hijacking of local connections it is not normally allowed Even if ARPRequests is set to Drop meaning that the packet is discarded without being stored NetDefendOS will provided that other rules approve the request reply to it Default Drop ARPChanges Determines how NetDefendOS will deal with situations where a received ARP reply or ARP request would alter an existing item in the ARP table Allowing this to take place may facilitate hijacking of local connections However not allowing this may cause problems if for example a network adap
65. destination in order to check connectivity e Destination Unreachable the source is told that a problem has occurred when delivering a packet There are codes from 0 to 5 for this type e Code 0 Net Unreachable e Code 1 Host Unreachable e Code 2 Protocol Unreachable e Code 3 Port Unreachable e Code 4 Cannot Fragment e Code 5 Source Route Failed e Redirect the source is told that there is a better route for a particular packet Codes assigned are as follows e Code 0 Redirect datagrams for the network e Code 1 Redirect datagrams for the host e Code 2 Redirect datagrams for the Type of Service and the network e Code 3 Redirect datagrams for the Type of Service and the host e Parameter Problem identifies an incorrect parameter on the datagram e Echo Reply the reply from the destination which is sent as a result of the Echo Request e Source Quenching the source is sending data too fast for the receiver the buffer has filled up e Time Exceeded the packet has been discarded as it has taken too long to be delivered 3 2 4 Custom IP Protocol Services Services that run over IP and perform application transport layer functions can be uniquely identified by ZP protocol numbers IP can carry data for a number of different protocols These protocols are each identified by a unique IP protocol number specified in a field of the IP header for example ICMP IGMP and EGP have protocol numbers 1 2 and 8 respectively NetDef
66. feature which specifically targets Syn Flood attacks If this option is enabled for a Service object then any ALG associated with that Service will not be used 6 2 2 HTTP Hyper Text Transfer Protocol HTTP is the primary protocol used to access the World Wide Web WWW It is a connectionless stateless application layer protocol based on a request response architecture A client such as a Web browser sends a request by establishing a TCP IP connection to a known port usually port 80 on a remote server The server answers with a response string followed by a message of its own That message might be for example an HTML file to be shown in the Web browser or an ActiveX component to be executed on the client or perhaps an error message The HTTP protocol faces particular issues because of the wide variety of web sites that can be accessed and the range of file types that can be downloaded as a result of such access The HTTP ALG is an extensive subsystem in NetDefendOS consisting of a number of modules These consist of the following features which are described in the indicated dedicated sections of the manual e Static Content Filtering This deals with Blacklisting and Whitelisting of specific URLs e URL Blacklisting Specific URLs can be blacklisted so that they are not accessible Wildcarding can be used when specifying these URLs e URL Whitelisting The opposite to blacklisting this makes sure certain URLs are always all
67. from specified address pool NetDefendOS DHCP servers are not limited to serving a single range of IP addresses but can use any IP address range that can be specified by a NetDefendOS address object Example 5 1 Setting up a DHCP server This example shows how to set up a DHCP server called DHCPServer1 which assigns and manages IP addresses from an IP address pool called DHCPRange1 This example assumes you have created an IP range for the DHCP Server CLI gw world gt add DHCPServer DHCPServerl Interface lan IPAddressPool DHCPRangel Netmask 255 255 255 0 Web Interface Go to System gt DHCP gt DHCP Servers gt Add gt DHCPServer Now enter Name DHCPServer1 Interface Filter lan IP Address Pool DHCPRange1 Netmask 255 255 255 0 Click OK 128 5 2 DHCP Servers Chapter 5 DHCP Services Example 5 2 Checking the status of a DHCP server Web Interface Go to Status gt DHCP Server in the menu bar CLI To see the status of all servers gw world gt dhepserver To list all configured servers gw world gt show dhcpserver Tip DHCP leases are remembered by the system between system restarts 129 5 3 Static DHCP Assignment Chapter 5 DHCP Services 5 3 Static DHCP Assignment Where the administrator requires a fixed relationship between a client and the assigned IP address NetDefendOS allows the assignment of a given IP to a specific MAC address Example 5 3 Setting up Static DHC
68. gt add IPRule Action SAT Service http SourceInterface any SourceNetwork all nets DestinationInterface core DestinationNetwork wwwsrv_pub SATTranslateToIP wwwsrv_priv_base SATTranslate DestinationIP Finally create a corresponding Allow Rule gw world gt add IPRule Action Allow Service http SourceInterface any SourceNetwork all nets DestinationInterface core DestinationNetwork wwwsrv_pub Web Interface Create an address object for the public IP address Go to Objects gt Address Book gt Add gt IP address Specify a suitable name for the object eg wwwsrv_pub Enter 195 55 66 77 195 55 66 77 81 as the IP Address Click OK Now create another address object for the base of the web server IP addresses 1 Goto Objects gt Address Book gt Add gt IP address 2 Specify a suitable name for the object eg wwwsrv_priv_base 3 Enter 70 10 10 5 as the IP Address 214 7 3 3 All to One Mappings N 1 Chapter 7 Address Translation 4 Click OK Publish the public adresses in the wan interface using ARP publish One ARP item is needed for every IP address Go to Interfaces gt ARP gt Add gt ARP Now enter Mode Publish Interface wan IP Address 195 55 66 77 Click OK and repeat for all 5 public IP addresses Create a SAT rule for the translation Go to Rules gt IP Rules gt Add gt IPRule Specify a suitable name for the rule eg SAT_HTTP_To_DMZ Now enter Action SAT Servece http Sourc
69. if the memory monitor uses a percentage as the unit for monitoring False if it uses Megabyte Applies to HWMMem_AlertLevel HWMMem_CriticalLevel and HWMMem_WanrningLevel Default True HWMMem AlertLevel Generate an Alert log message if free memory is below this value Disable by setting to 0 Maximum value is 10 000 Default 0 HWMMem_CriticalLevel Generate a Critical log message if free memory is below this value Disable by setting to 0 Maximum value is 10 000 Default 0 HWMMem_WarningLevel Generate a Warning log message if free memory is below this value Disable by setting to 0 Maximum value 10 000 Default 0 334 13 18 Packet Re assembly Settings Chapter 13 Advanced Settings 13 18 Packet Re assembly Settings Packet re assembly collects IP fragments into complete IP datagrams and for TCP reorders segments so that they are processed in the correct order and also to keep track of potential segment overlaps and to inform other subsystems of such overlaps The associated settings limit memory used by the re assembly subsystem Reassembly_MaxConnections This setting specifies how many connections can use the re assembly system at the same time It is expressed as a percentage of the total number of allowed connections Minimum 1 Maximum 100 Default SO Reassembly_MaxProcessingMem This setting specifies how much memory that the re assembly system can allocate to process packets It is expressed
70. in an unlikely event the two firewalls have the same external IP address e IP An IP address can be manually entered e DNS A DNS address can be manually entered e Email An email address can be manually entered 9 3 6 Proposal Lists To agree on the VPN connection parameters a negotiation process is performed As the result of the negotiations the IKE and IPsec security associations SAs are established As the name implies a proposal is the starting point for the negotiation A proposal defines encryption parameters for instance encryption algorithm life times etc that the VPN firewall supports There are two types of proposals IKE proposals and IPsec proposals IKE proposals are used during IKE Phase 1 IKE Security Negotiation while IPsec proposals are using during IKE Phase 2 IPsec Security Negotiation A Proposal List is used to group several proposals During the negotiation process the proposals in the proposal list are offered to the remote VPN firewall one after another until a matching proposal is found Several proposal lists can be defined in NetDefendOS for different VPN scenarios Two IKE proposal lists and two IPsec proposal lists are defined by default in NetDefendOS The ike roamingclients and esp tn roamingclients proposal lists are suitable for VPN tunnels that are used for roaming VPN clients These proposal lists are compatible with the default proposal lists in the D Link VPN Client As the name imp
71. instance wwwwsrv1 Enter 192 168 10 16 for the IP Address Click OK Example 3 2 Adding an IP Network This example adds an IP network named wwwsrvnet with address 192 168 10 0 24 to the Address Book CLI gw world gt add Address IP4Address wwwsrvnet Address 192 168 10 0 24 Web Interface Go to Objects gt Address Book gt Add gt IP address Specify a suitable name for the IP network for instance wwwsrvnet Enter 792 168 10 0 24 as the IP Address Click OK Example 3 3 Adding an IP Range This example adds a range of IP addresses from 192 168 10 16 to 192 168 10 21 and names the range wwwservers CLI gw world gt add Address IP4Address wwwservers Address 192 168 10 16 192 168 10 21 49 3 1 3 Ethernet Addresses Chapter 3 Fundamentals Web Interface Go to Objects gt Address Book gt Add gt IP address Specify a suitable name for the IP Range for instance wwwservers Enter 792 168 10 16 192 168 10 21 as the IP Address Click OK Example 3 4 Deleting an Address Object To delete an object named wwwsrv7 in the Address Book do the following CLI gw world gt delete Address IP4Address wwwsrvl Web Interface Go to Objects gt Address Book Select and right click the address object wwwsrv1 in the grid Choose Delete in the menu Click OK 3 1 3 Ethernet Addresses Ethernet Address objects are used to define symbolic names for Ethernet addresses also known as MAC addresses This
72. is a well known DV algorithm and involves sending regular update messages and reflecting routing changes in the routing table Path determination is based on the length of the path which is the number of intermediate routers also known as hops After updating its own routing table the router immediately begins transmitting its entire routing table to neighboring routers to inform them of changes Link State Algorithms In contrast to DV algorithms Link State LS algorithms enable routers to keep routing tables that reflect the topology of the entire network Each router broadcasts its attached links and link costs to all other routers in the network When a router receives these broadcasts it runs the LS algorithm and calculates its own set of least cost paths Any change of the link state will be sent everywhere in the network so that all routers keep the same routing table information Open Shortest Path First Open Shortest Path First OSPF is a widely used LS algorithm An OSPF enabled router first identifies the routers and subnets that are directly connected to it and then broadcasts the information to all the other routers Each router uses the information it receives to build a table of what the whole network looks like With a complete routing table each router can identify the subnetworks and routers that lead to any destination Routers using OSPF only broadcast updates that inform of changes and not the entire routing table
73. is enabled then the following options can be used to control file scanning Anti Virus Compression Rate Compressed files with a compression ration higher than the specified value will trigger one of the following actions e Allow Continue without the Anti Virus scan e Scan Continue scanning e Drop Drop the file and end the transfer Include Exclude Filetypes A list of filetypes which are to be included excluded from scanning can be specified 6 2 7 SIP Session Initiation Protocol SIP is an ASCII UTF 8 text based signalling protocol used to establish sessions between peers in an IP network It is a request response protocol that resembles HTTP and SMTP A session might consist of a Voice Over IP VOIP telephone call or it could be a collaborative multi media conference Using SIP with VOIP means that telephony can become another IP application which can integrate into other services SIP does not know about the details of a session s content and is only responsible for initiating terminating and modifying sessions Sessions set up by SIP are typically used for the streaming of audio and video over the Internet using the UDP protocol but they might also involve traffic based on the TCP protocol Although UDP based VOIP sessions are a common use communication using other protocols such as TCP or TLS might be involved in a session SIP is defined by the IETF standard RFC 3261 and is becoming popular as the standard for VOIP It i
74. is still active This situation should be avoided In the case that the D Link Firewall administrator issues a shutdown command while authenticated users are still online the AccountingRequest STOP packet will potentially never be sent To avoid this NetDefendOS has the advanced setting LogOutAccUsersAtShutdown This setting allows the administrator to explicitly specify that NetDefendOS must first send a STOP message for any authenticated users to any configured RADIUS servers before commencing with the shutdown 2 3 9 Limitations with NAT The User Authentication module in NetDefendOS is based on the user s IP address Problems can therefore occur with users who have the same IP address This can happen for instance when several users are behind the same network using NAT to allow network access through a single external IP address This means that as soon as one user is authenticated traffic coming through that NAT gateway IP address could be assumed to be coming from that one authenticated user even though it may come from other users on the same network NetDefendOS RADIUS Accounting will therefore gather statistics for all the users on the network together as though they were one user instead of individuals 42 2 4 Monitoring Chapter 2 Management and Maintenance 2 4 Monitoring 2 4 1 SNMP Monitoring Overview Simple Network Management Protocol SNMP is a standardized protocol for management of network devices An SNM
75. is used as the transit area In the configuration only the Router ID have to be configured as in the example above show fw2 need to have a Virtual Link to fw1 with the Router ID 192 168 1 1 and vice versa These VLinks need to be configured in Area 1 OSPF High Availability Support There are some limitations in High Availability support for OSPF that should be noted Both the active and the inactive part of an HA cluster will run separate OSPF processes although the inactive part will make sure that it is not the preferred choice for routing The HA master and slave will not form adjacency with each other and are not allowed to become DR BDR on broadcast networks This is done by forcing the router priority to 0 For OSPF HA support to work correctly the D Link Firewall needs to have a broadcast interface with at least ONE neighbor for ALL areas that the firewall is attached to In essence the inactive part of the cluster needs a neighbor to get the link state database from It should also be noted that is not possible to put an HA cluster on the same broadcast network without any other neighbors they won t form adjacency with each other because of the router priority 0 However it may be possible depending on the scenario to setup a point to point link between them instead Special care must also be taken when setting up a virtual link to an HA firewall The endpoint setting up a link to the HA firewall must setup 3 separate links one to
76. is useful for instance when populating the ARP table with static ARP entries or for other parts of the configuration where symbolic names are preferred over numerical Ethernet addresses When specifying an Ethernet address the format aa bb cc dd ee ff should be used Ethernet addresses are also displayed using this format Example 3 5 Adding an Ethernet Address The following example adds an Ethernet Address object named wwwsrv1_mac with a numerical MAC address of 08 a3 67 bc 2e f2 CLI gw world gt add Address EthernetAddress wwwsrvl_mac Address 08 a3 67 bc 2e f2 Web Interface Go to Objects gt Address Book gt Add gt Ethernet Address Specify a suitable name for the Ethernet Address object eg wwwsrv1_mac Enter 08 a3 67 bc 2e f2 as the MAC Address Click OK 50 3 1 4 Address Groups Chapter 3 Fundamentals gt gt gt 3 1 4 Address Groups Address objects can be grouped in order to simplify configuration Consider a number of public servers that should be accessible from the Internet The servers have IP addresses that are not in a sequence and can therefore not be referenced to as a single IP range Consequently individual IP Address objects have to be created for each server Instead of having to cope with the burden of creating and maintaining separate filtering policies allowing traffic to each server an Address Group named for instance Webservers can be created with the web server hos
77. limit which is also a guarantee Traffic that exceeds this will be sent at the minimum precedence which is also called the Best Effort precedence e At the Best Effort precedence all packets are treated on a first come first forwarded basis e Within a pipe traffic can also be separated on a Group basis For example by source IP address Each user in a group for example each source IP address can be given a maximum limit and precedences within a group can be given a limit guarantee e A pipe limit need not be specified if group members have a maximum limit e Dynamic Balancing can be used to specify that all users in a group get a fair and equal amount of bandwidth 278 10 2 Threshold Rules Chapter 10 Traffic Management 10 2 Threshold Rules 10 2 1 Overview The objective of a Threshold Rule is to have a means of detecting abnormal connection activity as well as reacting to it An example of a cause for such abnormal activity might be an internal host becoming infected with a virus that is making repeated connections to external IP addresses It might alternatively be some external source trying to open excessive numbers of connections A connection in this context refers to all types of connections such as TCP UDP or ICMP tracked by the NetDefendOS state engine The Threshold Rule feature is available on the D Link DFL 800 1600 2500 only A Threshold Rule is like a normal policy based rule A combination of sou
78. logins are handled where more than one user from different source IP addresses try to login with the same username The possible options are e Allow multiple logins so that more than one client can use the same username password 222 8 2 5 Authentication Processing Chapter 8 User Authentication combination e Allow only one login per username e Allow one login per username and logout an existing user with the same name if they have been idle for a specific length of time when the new login occurs 8 2 5 Authentication Processing The list below describes the processing flow through NetDefendOS for username password authentication 1 A user creates a new connection to the D Link Firewall 2 NetDefendOS sees the new user connection on an interface and checks the Authentication rule set to see if their is a matching rule for traffic on this interface coming from this network and data which is one of the following types e HTTP traffic e HTTPS traffic e IPsec tunnel traffic e L2TP tunnel traffic e PPTP tunnel traffic 3 If no Authentication Rule matches the connection is allowed if the IP rule set permits it and nothing further happens in the authentication process 4 Based on the settings of the matching authentication rule NetDefendOS prompts the user with an authentication request 5 The user replies by entering their identification information which is usually a username password pair 6 NetDefendOS vali
79. look up entries in the ARP Cache For maximum efficiency a hash should be twice as large as the table it is indexing so if the largest directly connected LAN contains 500 IP addresses the size of the ARP entry hash should be at least 1000 entries The administrator can modify the Advanced Setting ARPHashSize to reflect specific network requirements The default value of this setting is 512 The ARPHashSizeVLAN setting is similar to the ARPHashSize setting but affects the hash size for VLAN interfaces only The default value is 64 3 4 4 Static and Published ARP Entries 69 3 4 4 Static and Published ARP Chapter 3 Fundamentals Entries NetDefendOS supports defining static ARP entries static binding of IP addresses to Ethernet addresses as well as publishing IP addresses with a specific Ethernet address Static ARP Entries Static ARP items may help in situations where a device is reporting incorrect Ethernet address in response to ARP requests Some workstation bridges such as radio modems can have such problems It may also be used to lock an IP address to a specific Ethernet address for increasing security or to avoid denial of service if there are rogue users in a network Note however that such protection only applies to packets being sent to that IP address it does not apply to packets being sent from that IP address Example 3 16 Defining a Static ARP Entry This example will create a static mapping between IP addre
80. minimum firmware R3 01 B23 e D Link DES 3550 minimum firmware R3 01 B23 e D Link DGS 3324SR minimum firmware R4 10 B15 Note Make sure that the switches have the minimum required firmware versions before activating ZoneDefense 299 12 3 ZoneDefense Operation Chapter 12 ZoneDefense 12 3 ZoneDefense Operation 12 3 1 SNMP Simple Network Management Protocol SNMP is an application layer protocol for complex network management SNMP allows the managers and managed devices in a network to communicate with each other SNMP Managers A typical managing device such as a D Link Firewall uses the SNMP protocol to monitor and control network devices in the managed environment The manager can query stored statistics from the controlled devices by using the SVMP Community String This is similar to a userid or password which allows access to the device s state information If the community string type is write the manager will be allowed to modify the device s state Managed devices The managed devices must be SNMP compliant as are D Link switches They store state data in databases known as the Management Information Base MIB and provide the information to the manager upon receiving an SNMP query 12 3 2 Threshold Rules A threshold rule will trigger ZoneDefense to block out a specific host or a network if the connection limit specified in the rule is exceeded The limit can be one of two types e Connection R
81. no data was transmitted in the last incarnation of the IKE connection no new connection will be made until someone wants to use the VPN connection again This value must be set greater than the IPsec SA lifetime With PFS disabled initial keying material is created during the key exchange in phase 1 of the IKE negotiation In phase 2 of the IKE negotiation encryption and authentication session keys will be extracted from this initial keying material By using PFS Perfect Forwarding Secrecy completely new keying material will always be created upon re key Should one key be compromised no other key can be derived using that information PFS can be used in two modes the first is PFS on keys where a new key exchange will be performed in every phase 2 negotiation The other type is PFS on identities where the identities are also protected by deleting the phase 1 SA every time a phase 2 negotiation has been finished making sure no more than one phase 2 negotiation is encrypted using the same key PFS is generally not needed since it is very unlikely that any encryption or authentication keys will be compromised 244 9 3 3 IKE Authentication Chapter 9 VPN PFS Group IPsec DH Group IPsec Encryption IPsec Authentication IPsec Lifetime 9 3 3 IKE Authentication Manual Keying This specifies the PFS group to use with PFS The PFS groups supported by NetDefendOS are e 1 modp 768 bit e 2modp 1024 bit
82. or network IP addresses which can be utilized to protect against traffic coming from specific Internet sources Certain NetDefendOS modules specifically the Intrusion Detection and Prevention IDP module as well as Threshold Rules can make use of the Blacklist when certain conditions are encountered such as traffic triggering a Threshold Limit rule Adding a host or network to the Blacklist can be enabled in IDP and in Threshold Rules by specifying the Protect action for when a rule is triggered Once enabled there are three Blacklisting options Time to Block Host Network in The host or network which is the source of the traffic will seconds stay on the blacklist for the specified time and then be removed If the same source triggers another entry to the blacklist then the blocking time is renewed to its original full value in other words it is not cumulative Block only this Service By default Blacklisting blocks all Services for the triggering host Exempt already established If there are established connections that have the same source connections from Blacklisting as this new Blacklist entry then they won t be dropped if this option is set IP addresses or networks are added to the list and the traffic from these sources is then blocked for a period of time The Blacklist is maintained even if the D Link Firewall shuts down or reboots Whitelisting To ensure that good Internet traffic sources are not blacklisted under
83. ordinary telephone network The head office has placed a H 323 Gatekeeper in the DMZ of the corporate D Link Firewall This firewall should be configured as follows Web Interface Go to Rules gt IP Rules gt Add gt IPRule Now enter Name LanToGK Action Allow Service Gatekeeper Source Interface lan Destination Interface dmz Source Network lannet Destination Network ip gatekeeper 165 6 2 8 H 323 Chapter 6 Security Mechanisms e Comment Allow H 323 entities on lannet to connect to the Gatekeeper Click OK Go to Rules gt IP Rules gt Add gt IPRule Now enter Name LanToGK Action Allow Service H323 Source Interface lan Destination Interface dmz Source Network lannet Destination Network ip gateway Comment Allow H 323 entities on lannet to call phones connected to the H 323 Gateway on the DMZ Click OK Go to Rules gt IP Rules gt Add gt IPRule Now enter Name GWToLan Action Allow Service H323 Source Interface dmz Destination Interface lan Source Network ip gateway Destination Network lannet Comment Allow communication from the Gateway to H 323 phones on lannet Click OK Go to Rules gt IP Rules gt Add gt IPRule Now enter Name BranchToGW Action Allow Service H323 Gatekeeper Source Interface vpn branch Destination Interface dmz Source Network branch net Destination Network ip gatekeeper ip gateway Comment Allow communication with the Ga
84. over and above that which is stipulated in the rule set e LogSuspect Logs individual dropped fragments of reassembly attempts affected by suspect fragments e LogAll Always logs individual dropped fragments Default LogSuspect DuplicateFrags If the same fragment arrives more than once this can mean either that it has been duplicated at some point on its journey to the recipient or that an attacker is trying to disrupt the reassembly of the packet DuplicateFrags determines whether such a fragment should be logged Note that DuplicateFragData can also cause such fragments to be logged if the data contained in them does 321 FragmentedICMP Chapter 13 Advanced Settings not match up Possible settings are as follows e NoLog No logging is carried out under normal circumstances e LogSuspect Logs duplicated fragments if the reassembly procedure has been affected by suspect fragments e LogAll Always logs duplicated fragments Default LogSuspect FragmentedICMP Other than ICMP ECHO Ping ICMP messages should not normally be fragmented as they contain so little data that fragmentation should never be necessary FragmentedICMP determines the action taken when NetDefendOS receives fragmented ICMP messages that are not either ICMP ECHO or ECHOREPLY Default DropLog Minimum FragLength MinimumFragLength determines how small all fragments with the exception of the final fragment of a packet can be Al
85. place resulting in a IPsec VPN tunnel being established Note that an established IPsec tunnel does not automatically mean that all traffic from that IPsec tunnel is trusted On the contrary network traffic that has been decrypted will be transferred to the tule set for further evaluation The source interface of the decrypted network traffic will be the name of the associated IPsec Tunnel Furthermore a Route or an Access rule in the case of a roaming client has to be defined to have the NetDefendOS accept certain source IP addresses from the IPsec tunnel For network traffic going in the opposite direction that is going into a IPsec tunnel a reverse process takes place First the unencrypted traffic is evaluated by the rule set If a rule and route matches NetDefendOS tries to find an established IPsec tunnel that matches the criteria If not found NetDefendOS will try to establish a tunnel to the remote firewall specified by the matching IPsec Tunnel definition Note IKE and ESP AH traffic are sent to the IPsec engine before the rule set is consulted Encrypted traffic to the firewall therefore does not need to be allowed in the rule set This behaviour can be changed in the IPsec Advanced Settings section 9 4 2 LAN to LAN Tunnels with Pre shared Keys A VPN can allow geographically distributed Local Area Networks LANs to communicate securely over the public Internet In a corporate context this means LANs at geographically sepa
86. server will accept connections on this will be the earlier created I2tp_ipsec Also a ProxyARP needs to be configured for the IP s used by the L2TP Clients C Setup the L2TP Tunnel CLI gw world gt add Interface L2TPServer 12tp_tunnel IP lan_ip Interface 12tp_ipsec ServerIP wan_ip IPPool 12tp_pool TunnelProtocol L2TP AllowedRoutes all nets ProxyARPInterfaces lan Web Interface Go to Interfaces gt L2TP Servers gt Add gt L2TPServer Enter a name for the L2TP tunnel eg 2tp_tunnel Now enter Inner IP Address lan_ip Tunnel Protocol L2TP Outer Interface Filter 2tp_ipsec Server IP wan_ip Under the PPP Parameters tab check the Use User Authentication Rules control Select I2tp_pool in the IP Pool control Under the Add Route tab select all nets in the Allowed Networks control 263 9 5 2 L2TP Chapter 9 VPN 7 Inthe ProxyARP control select the lan interface 8 Click OK In order to authenticate the users using the L2TP tunnel a user authentication rule needs to be configured D Next will be setting up the authentication rules CLI gw world gt add UserAuthRule AuthSource Local Interface 12tp_tunnel OriginatorIP all nets LocalUserDB UserDB agent PPP TerminatorIP wan_ip name L2TP_Auth Web Interface 1 Goto User Authentication gt User Authentication Rules gt Add gt UserAuthRule 2 Enter a suitable name for the rule eg L2TP_Auth 3 Now enter Agent PPP Authentication Source Local I
87. sizes below this limit are handled according to the next setting Default 100 bytes TCPMSSOnLow Determines the action taken on packets whose TCP MSS option falls below the stipulated TCPMSSMin value Values that are too low could cause problems in poorly written TCP stacks Default DropLog TCPMSSMax Determines the maximum permissible TCP MSS size Packets containing maximum segment sizes exceeding this limit are handled according to the next setting Default 1460 bytes TCPMSSVPNMax As is the case with TCPMSSMax this is the highest Maximum Segment Size allowed However this setting only controls MSS in VPN connections This way NetDefendOS can reduce the effective segment size used by TCP in all VPN connections This reduces TCP fragmentation in the VPN connection even if hosts do not know how to perform MTU discovery Default 1400 bytes TCPMSSOnHigh Determines the action taken on packets whose TCP MSS option exceeds the stipulated TCPMSSMax value Values that are too high could cause problems in poorly written TCP stacks or give rise to large quantities of fragmented packets which will adversely affect performance Default Adjust TCPMSSAutoClamping Automatically clamp TCP MSS according to MTU of involved intafaces in addition to TCPMSSMax Default Enabled TCPMSSLogLevel Determines when to log regarding too high TCP MSS if not logged by TCPMSSOnHigh 307 TCPZeroUnusedACK Chapter 13 Advanced Se
88. so the evaluation will end there and the packet will be routed according to that entry 90 4 2 2 Static Routing Chapter 4 Routing 4 2 2 Static Routing This section describes how routing is implemented in NetDefendOS and how to configure static routing NetDefendOS supports multiple routing tables A default table called main is pre defined and is always present in NetDefendOS However additional and completely separate routing tables can be defined by the administrator to provide alternate routing These user defined extra routing toubles can be used to implement Policy Based Routing which means the administrator can set up rules in the IP rule set which decide which of the routing tables will handle certain types of traffic see Section 4 3 Policy based Routing The Route Lookup Mechanism The NetDefendOS route lookup mechanism has some slight differences to how some other router products work In many routers where the IP packets are forwarded without context in other words the forwarding is stateless the routing table is scanned for each and every IP packet received by the router In NetDefendOS packets are forwarded with state awareness so the route lookup process is tightly integrated into NetDefendOS s stateful inspection mechanism When an IP packet is received on any of the interfaces the connection table is consulted to see if there is an already open connection for which the received packet belongs I
89. soon as possible after connecting with the D Link Firewall Creating New Accounts Extra user accounts can be created if required Accounts can either can belong to the Administrators group of users in which case they have complete read write administrative access or they can belong to the Auditors user group in which case they have read only access 2 1 3 The CLI NetDefendOS provides a Command Line Interface CLD for administrators that prefer or require a command line approach or who need more granular control of system configuration The CLI is available either locally through the serial console port or remotely using the Secure Shell SSH protocol The CLI provides a comprehensive set of commands that allow the display and modification of configuration data as well as allowing runtime data to be displayed and allowing system maintenance tasks to be performed This section only provides a summary only of using the CLI For a complete reference for all CLI commands see the separate D Link CLI Reference Guide Serial Console CLI Access The serial console port is a RS 232 port on the D Link Firewall that allows access to the CLI through a serial connection to a PC or terminal To locate the serial console port on your D Link system see the D Link Quickstart Guide To use the console port you need the following equipment e A terminal or a computer with a serial port and the ability to emulate a terminal such as using the Hype
90. sportstoday com e www soccerball com 179 6 3 4 Dynamic Web Content Filtering Chapter 6 Security Mechanisms Category 17 www Email Sites A web site may be classified under the www Email Sites category if its content includes online web based email facilities Examples might be e www coldmail com e mail yazoo com Category 18 Violence Undesirable A web site may be classified under the Violence Undesirable category if its contents are extremely violent or horrific in nature This includes the promotion description or depiction of violent acts as well as web sites that have undesirable content and may not be classified elsewhere Examples might be e www itstinks com e Wwww ratemywaste com Category 19 Malicious A web site may be classified under the Malicious category if its content is capable of causing damage to a computer or computer environment including malicious consumption of network bandwidth This category also includes Phishing URLs which designed to capture secret user authentication details by pretending to be a legitimate organisation Examples might be e hastalavista baby nu Category 20 Search Sites A web site may be classified under the Search Sites category if its main focus is providing online Internet search facilities Refer to the section on unique categories at the start of this document Examples might be e www zoogle com e Wwww yazoo com Category 21 Health Sites A web s
91. teen seca seen scans 324 13 10 DHCP Settings oc secs vensdecsesned ceo stamespyess geo epshiedes pene shes sean ssnawen weep SSE 325 13 01 DHCPRelay Settings e ss vegibecivec tad sec itet salts ES TNE 326 13 12 DHCPServer S ctu oS 205 faccoraeehes do Syaken e e ata vents eesti gee sat 327 13 13 IPSec Settings 2 205 cee ees Ecce ee see teen a eae 328 13 14 LOGeING Setting S cosegsccsnss se vvat a se ted ede pe S E eateph E tee E somes 330 13 15 Time Synchronization Settings 2 0 0 0 eee eee cee cee ce neces eeeeeeeeeeeeeaeeeaes 331 13 16 PPP Setuin 88s tsces555 caste vs cass cg ssabetacestecsae ssa stteeassesbaeaas boned aaa eaate seh E 333 13 17 Hardware Monitor Settings 2 0 0 0 cece cee ce eeceeeceeeeeeeeeeeeeeeaeeeaeeeaes 334 13 18 Packet Re assembly Settings sisine seii eee cee ceeeceeeceeeca essa esau sean eeaes 335 13 19 Miscellaneous Settings 2 0 0 0 cece cece ce ee ce eece neces ceeesaeeeaeeeeeeaeeeaeeeaes 336 A Subscribing to Security Updates 20 0 0 tiesios redea ienna ee 338 IB LDP Signature Groups siose oien n eR geod susnes pated ose peswae AEREA EENE EIN aren Uae ss 340 C Checked MIME filetypes i eos ci seven EEE eed orcas ion websted E eee con kee 344 BD The OST Framework eene ine a agouti on dane E A E E eacheesaes 348 E D Link wordwideofticesiin ores Ss ednieh ods Sh Gay eds Ga dae acne eet aaa ees 349 Alphabetical Index Smyersin lover se mecenpntd ste E eT AEE E E EE ETES EEEN 351 List of Figures
92. that is going into a GRE tunnel Furthermore a Route has to be defined so NetDefendOS knows what IP addresses should be accepted and sent through the tunnel An Example GRE Scenario The diagram below illustrates a typical GRE scenario where two D Link Firewalls A and B must communicate with each other through the intervening internal network 172 16 0 0 16 Any traffic passing between A and B is tunneled through the intervening network using a GRE tunnel and since the network is internal and not public there is no need for encryption Figure 3 1 An Example GRE Scenario 64 3 3 5 GRE Tunnels Chapter 3 Fundamentals Setup for D Link Firewall A Assuming that the network 92 1 68 10 0 24 is lannet on the lan interface the steps for setting up NetDefendOS on A are 1 Inthe address book set up the following IP objects e remote_net_B 192 168 11 0 24 e remote_gw 172 16 1 1 e ip_GRE 192 168 0 1 2 Create a GRE Tunnel object called GRE_to_B with the following parameters e IP Address ip_GRE e Remote Network remote_net_B e Remote Endpoint remote_gw e Use Session Key 1 e Additional Encapulation Checksum Enabled 3 Define a route in the main routing table which routes all traffic to remote_net_B on the GRE_to_B GRE interface This is not necessary if the option Add route for remote network is enabled in the Advanced tab since this will add the route automatically 4 Create the following rules in the IP rule se
93. the number of new connections made per second or on the total number of connections being made The connections may be made by either a single host or all hosts within a specified CIDR network range an IP address range specified by a combination of an IP address and its associated network mask When NetDefendOS detects that a host or a network has reached the specified limit it uploads Access Control List ACL rules to the relevant switches and this blocks all traffic for the host or network displaying the unusual behaviour Blocked hosts and networks remain blocked until the system administrator manually unblocks them using the Web or Command Line interface Note gt ZoneDefense is available on the D Link DFL 800 860 1600 2500 models 298 12 2 ZoneDefense Switches Chapter 12 ZoneDefense 12 2 ZoneDefense Switches Switch information regarding every switch that is to be controlled by the firewall has to be manually specified in the firewall configuration The information needed in order to control a switch includes e The IP address of the management interface of the switch e The switch model type e The SNMP community string write access The ZoneDefense feature currently supports the following switches e D Link DES 3226S minimum firmware R4 02 B14 e D Link DES 3250TG minimum firmware R3 00 B09 e D Link DES 3326S minimum firmware R4 01 B39 D Link DES 3350SR minimum firmware R1 02 035 e D Link DES 3526
94. the shared one the master and one to the slave router id of the firewall 4 4 3 Dynamic Routing Policy Overview 107 4 4 3 Dynamic Routing Policy Chapter 4 Routing In a dynamic routing environment it is important for routers to be able to regulate to what extent they will participate in the routing exchange It is not feasible to accept or trust all received routing information and it might be crucial to avoid that parts of the routing database gets published to other routers For this reason NetDefendOS provides a Dynamic Routing Policy which is used to regulate the flow of dynamic routing information A Dynamic Routing Policy rule filters either statically configured or OSPF learned routes according to parameters like the origin of the routes destination metric and so on The matched routes can be controlled by actions to be either exported to OSPF processes or to be added to one or more routing tables The most common usages of Dynamic Routing Policy are e Importing OSPF routes from an OSPF process into a routing table e Exporting routes from a routing table to an OSPF process e Exporting routes from one OSPF process to another Note By default NetDefendOS will not import or export any routes In other words for dynamic routing to be meaningful it is mandatory to define at least one Dynamic Routing Policy rule Example 4 6 Importing Routes from an OSPF AS into the Main Routing Table In this example
95. the first fragment If the attacker chooses a fragment offset higher than the limits imposed by the Advanced Settings gt LengthLim in NetDefendOS the packets will not even get that far they will be dropped immediately Jolt2 attacks may or may not show up in NetDefendOS logs If the attacker chooses a too high fragment offset for the attack they will show up as drops from the rule set to LogOversizedPackets If the fragment offset is low enough no logging will occur The sender IP address may be spoofed 6 6 10 Distributed DoS Attacks A more sophisticated form of DoS is the Distributed Denial of Service DDoS attack DDoS attacks involve breaking into hundreds or thousands of machines all over the Internet to installs DDoS software on them allowing the hacker to control all these burgled machines to launch coordinated attacks on victim sites These attacks typically exhaust bandwidth router processing capacity or network stack resources breaking network connectivity to the victims Although recent DDoS attacks have been launched from both private corporate and public institutional systems hackers tend to favor university networks because of their open distributed nature Tools used to launch DDoS attacks include Trin00 TribeFlood Network TFN TFN2K and Stacheldraht 201 6 7 Blacklisting Hosts and Networks Chapter 6 Security Mechanisms 6 7 Blacklisting Hosts and Networks NetDefendOS implements a Blacklist of host
96. the receiving Ethernet interface becomes the source interface for the packet 3 The IP datagram within the packet is passed on to the NetDefendOS Consistency Checker The consistency checker performs a number of sanity checks on the packet including validation of checksums protocol flags packet length and so on If the consistency checks fail the packet gets dropped and the event is logged 4 NetDefendOS now tries to lookup an existing connection by matching parameters from the incoming packet A number of parameters are used in the match attempt including the source interface source and destination IP addresses and IP protocol If a match cannot be found a connection establishment process starts which includes steps from here to 9 below If a match is found the forwarding process continues at step 10 below 5 The Access Rules are evaluated to find out if the source IP address of the new connection is allowed on the received interface If no Access Rule matches then a reverse route lookup will be done In other words by default an interface will only accept source IP addresses that belong to networks routed over that interface If the Access Rules or the reverse route lookup determine that the source IP is invalid then the packet is dropped and the event is logged 6 A route lookup is being made using the appropriate routing table The destination interface for the connection has now been determined 7 The IP rules are now searche
97. the routes received using OSPF will be added into the main routing table First of all a Dynamic Routing Policy filter needs to be created The filter needs to have a name in this example mportOSPFRoutes is used as it explains what the filter does The filter must also specify from what OSPF AS the routes should be imported In this example a pre configured OSPF AS named as0 is used Depending on how your routing topology looks like you might want to just import certain routes using the Destination Interface Destination Network filters but in this scenario all routes that are within the all nets network which is the same as specifiying the IP address 0 0 0 0 0 are allowed CLI gw world gt add DynamicRoutingRule OSPFProcess as0 Name ImportOSPFRoutes DestinationNetworkExactly all nets Web Interface Go to Routing gt Dynamic Routing Rules gt Add gt Dynamic routing policy rule Specify a suitable name for the filter in this case ImportOSPFRoutes In the Select OSPF Process select as0 Choose all nets in the Exactly Matches dropdown control Click OK The next step is to create a Dynamic Routing Action that will do the actual importing of the routes into a routing table Specify the destination routing table that the routes should be added to in this case main CLI gw world gt cc DynamicRoutingRule ImportOSPFRoutes 108 4 4 3 Dynamic Routing Policy Chapter 4 Routing gw world ImportOSPFRoutes gt add Dy
98. threshold rules 279 300 in Zone Defense 300 TimeSync_DSTEnabled setting 331 TimeSync_DSTEndDate setting 332 TimeSync_DSTOffs setting 331 TimeSync_DSTStartDate setting 332 TimeSync_GroupIntervalSize setting 331 TimeSync_MaxAdjust setting 331 TimeSync_ServerType setting 331 TimeSync_SynclInterval setting 331 TimeSync_TimeServerIP1 setting 331 TimeSync_TimeServerIP2 setting 331 TimeSync_TimeServerIP3 setting 331 TimeSync_TimeZoneOffs setting 331 time synchronization 83 traffic shaping 267 bandwidth guarantees 274 bandwidth limiting 269 groups 275 precedences 272 recommendations 276 summary 277 transparent mode 119 implementation 119 with high availability 120 vs routing mode 119 TTLMin setting 305 TTLOnLow setting 305 tunnels 57 U UnsolicitedARPReplies setting 312 user authentication see authentication user based routing W webauth 223 WebUI 26 web user interface see WebUI whitelisting hosts and networks 202 URL 170 wildcarding 170 wildcarding in blacklists and whitelists 170 in IDP rules 192 V virtual LAN see VLAN virtual links 106 virtual private networks see VPN VLAN 60 license limitations 60 voice over IP with H 323 155 with SIP 152 VOIP see voice over IP VPN 229 planning 229 quickstart guide 231 troubleshooting 237 X 354 Alphabetical Index X 509 certificates 79 identification lists 251 with IPsec 234 Z zonedef
99. to this is if the multicast source is located on a network directly connected to the router In this case no query rule is needed A second exception is if a neighbouring router is statically configured to deliver a multicast stream to the D Link Firewall In this case also an IGMP query would not have to be specified NetDefendOS supports two IGMP modes of operation Snoop and Proxy Figure 4 6 Multicast Snoop SS 114 4 5 3 IGMP Configuration Chapter 4 Routing Figure 4 7 Multicast Proxy In Snoop mode the router will act transparently between the hosts and another IGMP router It will not send any IGMP Queries It will only forward queries and reports between the other router and the hosts In Proxy mode the router will act as an IGMP router towards the clients and actively send queries Towards the upstream router it will be acting as a normal host subscribing to multicast groups on behalf of its clients 4 5 3 1 IGMP Rules Configuration No Address Translation This example describes the IGMP rules needed for configuring IGMP according to the No Address Translation scenario described above We want our router to act as a host towards the upstream router and therefore we configure IGMP to run in proxy mode Example 4 10 IGMP No Address Translation The following example requires a configured interface group IfGrpClients including interfaces if1 if2 and if3 The ip address of the upstream IGMP router
100. user credentials later used by the various user authentication subsystems For more information on this see Chapter 8 User Authentication The following list presents the various types of addresses an IP Address object can hold along with what format that is used to represent that specific type Host A single host is represented simply by its IP address For example 192 168 0 14 IP Network An IP Network is represented using CIDR Classless Inter Domain Routing form CIDR uses a forward slash and a digit 0 32 to denote the size of the network netmask 24 corresponds to a class C net with 256 addresses netmask 255 255 255 0 27 corresponds to a 32 address net netmask 255 255 255 224 and so on The numbers 0 32 correspond to the number of binary ones in the netmask 48 3 1 2 IP Addresses Chapter 3 Fundamentals For example 192 168 0 0 24 IP Range A range of IP addresses is represented on the form a b c d e f g h Please note that ranges are not limited to netmask boundaries they may include any span of IP addresses For example 192 168 0 10 192 168 0 15 represents six hosts in consecutive order Example 3 1 Adding an IP Host This example adds the IP host wwwsrv1 with IP address 192 168 10 16 to the Address Book CLI gw world gt add Address IP4Address wwwsrvl Address 192 168 10 16 Web Interface Go to Objects gt Address Book gt Add gt IP address Specify a suitable name for the IP host for
101. which traffic is to be subject to the rule They differ from other policies in that the destination network interface is not of interest but only the source network interface An Authentication Rule has the following parameters e Interface The source interface on which the connections to be authenticated will arrive e Source IP The source network from which these connections will arrive e Authentication Source This specifies that authentication is to be done against a Local database defined within NetDefendOS or by using a RADIUS server discussed in detail below e Agent The type of traffic being authenticated This can one of e HTTP or HTTPS Web connections to be authenticated via a pre defined or custom web page see the detailed HTTP explanation below e PPP L2TP or PPP tunnel authentication e XAUTH IKE authentication which is part of IPsec tunnel establishment Connection Timeouts An Authentication Rule can specify the following timeouts related to a user session e Idle Timeout How long a connection is idle before being automatically terminated 1800 seconds by default e Session Timeout The maximum time that a connection can exist no value is specified by default If an authentication server is being used then the option to Use timeouts received from the authentication server can be enabled to have these values set from the server Multiple Logins An Authentication Rule can specify how multiple
102. writes all log data to a single line of text All data following the initial text is presented in the format name value This enables automatic filters to easily find the values they are looking for without assuming that a specific piece of data is in a specific location in the log entry Note The Prio field in SysLog messages contains the same information as the Severity field for D Link Logger messages however the ordering of the numbering is reversed Example 2 11 Enable Logging to a Syslog Host To enable logging of all events with a severity greater than or equal to Notice to a Syslog server with IP address 195 11 22 55 follow the steps outlined below CLI gw world gt add LogReceiverSyslog my_syslog IPAddress 195 11 22 55 Web Interface Go to System gt Log and Event Receivers gt Add gt Syslog Receiver Specify a suitable name for the event receiver eg my_syslog Enter 195 11 22 55 as the IP Address Select an appropriate facility from the Facility list The facility name is commonly used as a filter parameter in most syslog daemons Click OK The system will now be logging all events with a severity greater than or equal to Notice to the syslog server at 195 11 22 55 2 2 3 Event Message Distribution Chapter 2 Management and Maintenance Note The syslog server may have to be configured to receive log messages from NetDefendOS Please see the documentation for your specific Syslog server software in o
103. 0 HEOPIOR ORL 25950 0 0 10 4 2 143 NOR AR 2A 1 LOA 2 14s 255 255 255 255 IZ7 60 0 127 50 04 50 10 255 255 255 255 255 255 255 10 4 2 143 10 4 2 143 50 SS LIGA 3S 255725552597255 192 168 0 192 168 0 10 20 IZ7 0 0 6 255 605040 IZ7 0 0 1 127 0 0 1 il 192 168 040 255 25522550 IZ 168 0 10 192 168 0 10 20 192 1680 10 255 255 255 255 AT sO sO sul 2760 01 20 LOZ 168 0 255 255 255 255 255 1925168 0 10 i192 168 0 10 20 PAORO 240 0 0 0 LO 64 Anas 10 4 2 143 50 27 ARCO PO RAO ZAD 0 0 0 192 16S O10 192 16 0 0 20 DJA 3 5 OOI ADS 2555259552595 255 10 4 2 143 10 4 2 143 ill 255 255 295 295 255 255 255 255 1925168 0 10 192 168 0 10 1 Default Gateway 192 UGS lt 0 4 A 91 4 2 2 Static Routing Chapter 4 Routing Persistent Routes None The corresponding routing table in NetDefendOS is similar to this Flags Network Iface Gateway bocal Ie Merrie OPES TONOZ lan 20 LOPE O et ORLOV ES wan 1 0 00 00 wan 192 168 ROR 20 The NetDefendOS way of describing the routes is easier to read and understand Another advantage with this form of notation is that you can specify a gateway for a particular route without having a route that covers the gateways s IP address or despite the fact that the route covers the gateway s IP address is normally routed via another interface It is also worth mentioning that NetDefendOS allows you to specify routes for destinations that are not aligned with traditional subnet masks In ot
104. 192 intrusion detection rule 190 invalid checksum in cluster heartbeats 296 IP address objects 51 IPOPT_OTHER setting 306 IPOPT_SR setting 306 IPOPT_TS setting 306 IPOptionSizes setting 306 ip pools 132 with config mode 257 IPRF setting 306 IP rules evaluation order 74 IP rule set 73 IPsec 240 quickstart guide 231 troubleshooting 237 tunnels 253 IPsecBeforeRules setting 328 IPsecCertCacheMaxCerts setting 328 IPsecDeleteSAOnIPValidationFailure setting 328 ip validation with config mode 257 352 Alphabetical Index L L2TP 261 quickstart guide 234 Lan to Lan tunnels 253 LayerSizeConsistency setting 305 LDAP servers 259 link state algorithm 103 LocalReass_MaxConcurrent setting 324 LocalReass_MaxSize setting 324 LocalReass_NumLarge setting 324 LogChecksumErrors setting 304 LogConnections setting 314 LogConnectionUsage setting 314 logging 35 login authentication 222 log messages 35 LogNonIP4 setting 304 LogOpenFails setting 314 log out from CLI 26 LogOversizedPackets setting 319 LogReceivedTTLO setting 305 LogReverseOpens setting 314 LogSendPerSecLimit setting 330 LogStateViolations setting 314 M MAC addresses 68 management interfaces 23 MaxAHLen setting 318 MaxConnections setting 314 MaxESPLen setting 318 MaxGRELen setting 318 MaxICMPLen setting 318 MaxIPCompLen setting 319 MaxIPIPLen setting 319 MaxL2TPLen setting 319 MaxOSPFLen setting 319 MaxOt
105. 4 3 3 CA Server issued Certificates based client tunnels Setting up client tunnels using a Certification Authority issued X 509 certificate is largely the same as using Self Signed certificates with the exception of a couple of steps Most importantly it is the responsibility of the administrator to aquire the appropriate certificate from an issuing authority With some systems such as Windows 2000 Server there is built in access to a CA server in Windows 2000 Server this is found in Certificate Services For more information on CA server issued certificates see Section 3 7 X 509 Certificates It is the responsibility of the administrator to aquire the appropriate certificate from an issuing authority for client tunnels With some systems such as Windows 2000 Server there is built in access to a CA server in Windows 2000 Server this is found in Certificate Services For more information on CA server issued certificates see Section 3 7 X 509 Certificates Example 9 6 Setting up a CA Server issued Certificate based VPN tunnel for roaming clients This example describes how to configure an IPsec tunnel at the head office D Link Firewall for roaming clients that connect to the office to gain remote access The head office network uses the 10 0 1 0 24 network span with external firewall IP wan_ip Web Interface A Upload all the client certificates Go to Objects gt Authentication Objects gt Add gt Certificate Enter a s
106. 532 i vende Set oad Rub eds eee Aa ath O Ea 43 24 L SNMP Monitoring lt 5 cs ncence yy otaes E pune ss oh E EE E A sees 43 Qed Maintenance vs es eestcaks Sisus Sec E tafe pewen Gates deen E EENE 45 2 5 1 Auto Update Mechanism cee ccee eee ceeeceeeee seca eeeeeea seca sean eeaeeees 45 2 5 2 Configuration Backup and Restore cece cece cece eeeeceeeee eee eene eens 45 2 5 3 Resetting to Factory Defaults ce s sosisini ee cee cece cece ne eeneeeneeeneees 45 3 Fundamental S oeiee ee eo E E EEE E cite eed ay ens E S RESTE 48 3 1 TFheAddress BOOK tarmer anta e e a ea T A E 48 SLL OVERVIEW oepa corns er NE A ENE ORNE TIE E ES AN 48 IA 2 IP Addresses ei oiae E eR TAE R E ET R owas 48 3 13 Ethemet Addresses nirera a e e tee ate aa E a Ee 50 3 14 Address Groups ie n aa begin ee edd Geet R a EEN 51 3 1 5 Auto Generated Address Objects sseesesseesierrssrresrreresrrerrrrerreee 51 32 Sery CES ys ree E E ET E ed saved Gee AT rec O E rong EE Th 52 32 TA OVET VIEW orphna Sarn r E a AE EAE 52 3 2 2 TCP and UDP Based Services seeessseesireeesrerrsrrrerererereresrrersreee 53 3 2 3 ICMP SErVi CES omire anaa end sands AA E TE E E TAL SEE ia 55 3 2 4 Custom IP Protocol Services eceeeeeceeeeeceeeeceeeeeeeceresenereeanenes 55 33a Interfaces maic u a rata sate E E vet E E RA Danneel setae Pande aa 57 3 3 1 OVERVIEW eisoes EEE E E E EEEE EEEn EIEEE 57 33 2 Ethemet ae ran ys NEER E A ESE TEE be eee ep E
107. 58 SE e PATA EANN EE E EE EE E A E ES OEE ESEE EE 60 e PPPOE EE E E E TS 61 339 GRE TUNNELS oirr ans i E Ea E e E T E AATE O ee 63 3 3 6 Interface GTOUPS oeei iei a E E EE EE E A E EE EE aT 66 IA ARP oer n oui e a e contd sie E a a r ea e E 68 SATS OVERVICW 4 8 en E e E EE Se A le ee 68 3 4 2 ARP in NetDefendOS 3 sc onde ee seoser EE AEREE ERSTES 68 User Manual 3 4 3 ARP Cache i vs apse eta oaae EE sot ag E teas das Stas SShetiaa E RAPS 68 3 4 4 Static and Published ARP Entries ccc ce eee eece eee eeeeeeeee es 69 3 4 5 Advanced ARP Settings 2 0 0 0 cee a E scene E RIN A ENS 71 3 3 The IP Rule Setai a nae ee S VEE E EAE EEE AE E AS 73 3 3L Sec rity POMCIES ien bes hota e r r EE E EE Oa 73 3 3 2 IP Rule Evaluation iz cc teeSesen seedsnudect od Goths iene dae ee tence ssueta aa dayeeeeet 74 3 5 3 IP RUE Acon sick cetie ahs Set iece ede sed UE seo cede 75 3 54 Editing IP rule set Entries ss sssrini sccsgesssvscsaessedseadseoseeos seve ageeeasce 76 3 6 SCHECUIES sis ccsdesceth otese ec bessakesdoes a E EE eh sea EE ESEE ADT EE EEES 77 357 R509 Conti cates ii oien r aa a E a T seae yas EEES 79 3 TA OVELVIEW es tes roos ree oea chs coke EE Eo ESSEE E E EEE EESE EEES 79 3 7 2 X 509 Certificates in NetDefendOS eseeeeseeerrseeserreerreresrrererresere 80 3 8 Setting D teand Time w2 e0 c 5s sich esseuhs ienai En E EEEE EESE coven EES 82 3 8 1 General Date and Time Settings 20 00 00 eee
108. 9 Certificates with IPsec Tunnels 0 0 0 0 cece cece eee coerce eee 81 3 20 Setting the Current Date and Time 0 00 cc cece eee eee econ cen eeneeeeneeeees 82 3 21 Setting the Time Zone oi 5055s sep sccte coe cns eE EE EE oveecobsnsedovthoucevevagecssss 83 3 22 Enabling DSP oesi ouls cy pies eetere r eei veted adh sebtang Sect neseusb eta ds SEERE OSa TEE 83 3 23 Enabling Time Synchronization using SNTP 0 cece ee cece reece ce eee eeeeeeeee ees 84 3 24 Manually Triggering a Time Synchronization 2 0 00 0 eee eee cence ee ceece eee eeeee ees 84 3 25 Modifying the Maximum Adjustment Value 20 0 0 eee ce ee ce eeceeeeeeeeeeeee ees 85 3 26 Forcing Time Synchronization 2 0 0 0 cece cee cece eee cee ca eece cece cena eeu eenceeeeeneeeees 85 3 27 Enabling the D Link NTP Server 20 0 0 0 ccc ees cece cena aer ee 86 3 28 Configuring DNS Servers cs seie e E E EE E E e ai 87 4 1 Displaying the Routing Table s roren oieee se eo puen oro r EA NENE EENE 92 4 2 Displaying the Core Routes ss sseessesrssrerrsrrerrrresrrrrerrrrrsrrerrsrrrrerrerrsrrerreeeerrre 93 4 3 Creating a Policy Based Routing table 0 eee cee cc ence eece ener eeeeeeeeeeeaees 100 4 4 Creating the ROUTE soniers neren ioner nenie ee eE EE SENEE EE EEE ESE EEE E Eosi 100 4 5 Policy Based Routing Configuration sssessseeersseesrrsrssrerrsrrerrrrrrrsrrerrsrrerreresrt 101 4 6 Importing Routes from an OSPF AS into the Main Routin
109. Access Rules are a first filter of traffic before any other NetDefendOS modules can see it Sometimes problems can appear such as setting up VPN tunnels precisely because of this It is always advisable to check Access Rules when troubleshooting puzzling problems in case a rule is preventing some other function such as VPN tunnel astablishment from working properly 136 6 1 3 Access Rule Settings Chapter 6 Security Mechanisms Example 6 1 Setting up an Access Rule A rule is to be defined that ensures no traffic with a source address not within the lannet network is received on the lan interface CLI gw world gt add Access Name lan_Access Interface lan Network lannet Action Except Web Interface Go to Rules gt Access Select Access Rule in the Add menu Now enter Name lan_Access Action Except Interface lan e Network lannet Click OK 137 6 2 Application Layer Gateways Chapter 6 Security Mechanisms 6 2 Application Layer Gateways 6 2 1 Overview To complement low level packet filtering which only inspects packet headers in protocols such IP TCP UDP and ICMP D Link Firewalls provide Application Layer Gateways ALGs which provide filtering at the higher application OSI level An ALG object acts as a mediator in accessing commonly used Internet applications outside the protected network for example web access file transfer and multimedia transfer ALGs provide higher securit
110. Actions Chapter 6 Security Mechanisms group name Caution against using too many IDP signatures J Do not use the entire signature database and avoid using signatures and signature groups unecessarily Instead use only those signatures or groups applicable to the type of traffic you are trying to protect For instance using IDS_WEB IPS_WEB IDS_HTTP and IPS_HTTP IDP groups would be appropriate for protecting an HTTP server IDP traffic scanning creates an additional load on the hardware that in most cases shouldn t noticebly degrade performance Using too many signatures during scanning can make the load on the firewall hardware unecessarily high adversely effecting throughput 6 5 7 IDP Actions Action Options After pattern matching recognises an intrusion in traffic subject to an IDP Rule the Action associated with that Rule is taken The administrator can associate one of three Action options with an IDP Rule e Ignore Do nothing if an intrusion is detected and allow the connection to stay open e Audit Allow the connection to stay open but log the event e Protect This option drops the connection and logs the event with the additional option to blacklist the source of the connection or switching on ZoneDefense as described below IDP Blacklisting The Protect option includes the option that the particular host or network that triggers the IDP Rule can be added to a Blacklist of offending traffic sources This
111. BMS DB_SYBASE Sybase server DCOM_GENERAL MS DCOM DHCP_CLIENT DHCP Client related activities DHCP_GENERAL DHCP protocol DHCP_SERVER DHCP Server related activities DNS_EXPLOIT DNS attacks DNS_GENERAL Domain Name Systems DNS_OVERFLOW DNS overflow attack DNS_QUERY Query related attacks ECHO_GENERAL Echo protocol and implementations ECHO_OVERFLOW FINGER_BACKDOOR Echo buffer overflow Finger backdoor FINGER_GENERAL Finger protocol and implementation FINGER_OVERFLOW Overflow for Finger protocol implementation FS_AFS Andrew File System FTP_DIRNAME Directory name attack 340 Appendix B IDP Signature Groups Group Name Intrusion Type FTP_FORMATSTRING Format string attack FTP_GENERAL FTP_LOGIN FTP protocol and implementation Login attacks FTP_OVERFLOW FTP buffer overflow GAME_BOMBERCLONE Bomberclone game GAME_GENERAL Generic game servers clients GAME_UNREAL UnReal Game server HTTP_APACHE Apache httpd HTTP_BADBLUE Badblue web server HTTP_CGI HTTP CGI HTTP_CISCO Cisco Embedded Web Server HTTP_GENERAL General HTTP activities HTTP_MICROSOFTIIS HTTP Attacks specific to MS IIS web server HTTP_OVERFLOWS Buffer overflow for HTTP servers HTTP_TOMCAT Tomcat JSP ICMP_GENERAL ICMP protocol and implementatio
112. Create the required route s for the VLAN in the appropriate routing table 7 Create rules in the IP rule set to allow traffic through on the VLAN interface Example 3 11 Defining a VLAN This simple example defines a virtual LAN called VLAN70 with a VLAN ID of 70 Note that this Virtual LAN interface will use the IP address of the corresponding Ethernet interface as no IP address is specified CLI gw world gt add Interface VLAN VLAN10 Ethernet lan Network all nets VLANID 10 Web Interface Go to Interfaces gt VLAN gt Add gt VLAN Enter a suitable name for the VLAN in this case VLAN10 Now enter Interface lan e VLAN ID 10 Click OK 3 3 4 PPPoE Point to Point Protocol over Ethernet PPPoE is a tunneling protocol used for connecting multiple users on an Ethernet network to the Internet through a common serial interface such as a single DSL line wireless device or cable modem All the users on the Ethernet share a common connection while access control can be done on a per user basis Internet server providers ISPs often require customers to connect through PPPoE to their broadband service Using PPPoE the provider can e Implement security and access control using username password authentication e Trace IP addresses to a specific user e Allocate IP address automatically for PC users similar to DHCP IP address provisioning can be per user group 3 3 4 1 Overview of PPP Point to Point Protocol PP
113. DOPE SES 189 T The AE protocol a sv Ractdeot E cpu aseote ues cote gu E Seve hot anven dees tea ten uae lees 247 0 2 The ESP protocol 2205 33 63 eee Nae Rad Bee seed Aa eed ae dee ee 247 10 1 Pipe rule set to Pipe Packet FIOW seprene etines cece cece ne s e e E AS 269 10 2 The Eight Pipe Precedentes isien er ee cece scence a E EE E TE RSS 272 10 3 Minimum and Maximum Pipe Precedence 2 0 0 0 cee cece cece ceee cece eeceeeeeeeeaeeenes 273 10 4 Traffic grouped per IP address 2 0 0 0 c eee cc ence nece eee eeeeeeeeeeeeeeeeeeaeeeaeeeaes 275 10 5 A Server Load Balancing configuration 2 0 0 0 cece eee cee ce eeceeeca teen eeee eens eeaes 281 10 6 Connections from Three Clients 2 0 0 0 eee ceec eee ce neces ceeeceeeeeeeeeeeaeeeaeeeaes 283 10 7 Stickiness and Round Robin ec eece cece eee ce ence ence neces ceeeeaeceeseeseeeseaeeeaes 283 10 8 Stickiness and Connection Rate 20 0 0 cece cece cc ee ce eeceeeeeeeeeeesaeeeeeseeeeeeeeaeeeaes 284 LL High Availability Setup voces cssegs sven eects dass Ri sods saunas PES Eense ea PEE ERNES 293 D 1 The 7 layers of the OSI model 2 0 0 cece cece cc nece nce E E EN 348 List of Examples 1 Example Notat Ons aea vie ade EE aP lds cote aks castes A ENERO ELEA SINA 12 2 1 Enabling SSH Remote Access ssessseeersseesreeresreressrerrsrrsrreresreresrrerrsrreersreereeees 25 2 2 Enabling remote management via HTTPS ccc cee cece cence eeceeeca seca sean ee
114. Default Precedence is the precedence taken by a packet if it is not explicitly assigned by a Pipe Rule as described in the preceeding paragraph The minimum and maximum precedences define the precedence range that the pipe will handle If a packet arrives with an already allocated precedence below the minimum then its precedence is changed to the minimum Similarly if a packet arrives with an already allocated precedence above the maximum its precedence is changed to the maximum For each pipe separate bandwidth limits may be optionally specified for each precedence level 272 10 1 6 Precedences Chapter 10 Traffic Management These limits can be specified in kilobits per second and or packets per second if both are specified then the first limit reached will be the limit used In precedences are used then the total limit for the pipe as a whole must be specified so the pipe knows when what its capacity is and therefore when precedences are used The Best Effort Precedence The precedence defined as the minimum pipe precedence has a special meaning it acts as the Best Effort Precedence All packets arriving at this precedence will always be processed on a first come first forwarded basis and cannot be sent to another precendence Packets with a higher precedence and that exceed the limits of that precedence will automatically be transferred down into this Best Effort precedence and they will no longer be treated differently from
115. GES OR LOSSES RESULTING FROM THE APPLICATION OR IMPROPER USE OF THE D LINK PRODUCT OR FAILURE OF THE PRODUCT EVEN IF D LINK IS INFORMED OF THE POSSIBILITY OF SUCH DAMAGES FURTHERMORE D LINK WILL NOT BE LIABLE FOR THIRD PARTY CLAIMS AGAINST CUSTOMER FOR LOSSES OR DAMAGES D LINK WILL IN NO EVENT BE LIABLE FOR ANY DAMAGES IN EXCESS OF THE AMOUNT D LINK RECEIVED FROM THE END USER FOR THE PRODUCT Table of Contents Preface iaei Sevean Voie cow is gage ty R E EE unas cov bas EEE EE e RR TAE ER 12 1 Product OVeErvieW iinn a iseeerie oireet cat EE r E E E y sh ced ape E NE rE seeebest 14 1 1 About D Link NetDefendOS ccc cceece cece eeceeecceeceeeceeeseeeea seca eeaeeaeeees 14 1 2 NetDefendOS Architecture sorrencs eriin e E i E E 16 1 2 1 State based Architecture secerni es renie orri VEE ien E ES ETE EES 16 1 2 2 NetDefendOS Building Blocks 2 0 0 0 cece cece eee ceeeceeeeeeeen ees 16 1273 Basic Packet FIOM u senna N cade deinen ieee hes dan vetentve t hovatendaeees 17 1 3 NetDefendOS State Engine Packet FloW 0 0 cce cece eee enece teen eece een eene eens 19 2 Management and Maintenance lt 3 os0 ss ossesssseiaadesessecsassotsaasesdesepeassasaseseteassesdses 23 2 1 Managing NetDefendOS 00 00 00 cee cece cc ee ce eeceeeceeeseeeea seen eeaaeeaeeeae eens 23 QTV ON GIVICW stan sasuetais santas 55 ctl dea E aE a a E ares as E 23 2 1 2 Default Administrator Accounts 2 00 0 cece cece eeceeeeeceeeee
116. IP 6 GSE 0 5 al Iface IP 5 MBA GS LS Iface IP eWie Sigal Iface IP Oa Iface IP 168 0 0 24 Dis U2AR G5 10 24 224 0 0 0 4 Iface IP 0000 0 213 104 IES oooonoooceo 4 2 3 Route Failover Chapter 4 Routing Web Interface 1 Select the Routes item in the Status dropdown menu in the menu bar 2 Check the Show all routes checkbox and click the Apply button 3 The main window will list the active routing table including the core routes Tip For detailed information about the output of the CLI routes command Please see the CLI Reference Guide 4 2 3 Route Failover Overview D Link Firewalls are often deployed in mission critical locations where availability and connectivity is crucial A corporation relying heavily on access to the Internet for instance could have their operations severely disrupted if an Internet connection fails As a consequence it is quite common to have backup Internet connectivity using a secondary Internet Service Provider ISP The connections to the two service providers often use different access methods to avoid a single point of failure To facilitate a scenario such as multiple ISPs NetDefendOS provides a Route Failover capability so that should one route fail traffic can automatically failover to another alternate route NetDefendOS implements Route Failover through the use of Route Monitoring in which NetDefendOS monitors the availability of routes and switches traffic to
117. ISP Service based Routing A different routing table might need to be chosen based on the service Policy based Routing can route a given protocol such as HTTP through proxies such as Web caches Specific services might also be routed to a specific ISP so that one ISP handles all HTTP traffic User based Routing A different routing table might need to be chosen based on the user identity or the group to which the user belongs This is particularly useful in provider independent metropolitan area networks where all users share a common active backbone but each can use different ISPs subscribing to different providers Policy based Routing implementation in NetDefendOS is based on two building blocks e One or more user defined alternate Policy based Routing Tables in addition to the standard default main routing table e One or more Policy based routing rules which determines which routing table to use for which traffic 4 3 2 Policy based Routing Tables NetDefendOS as standard has one default routing table called main In addition to the main table it is possible to define one or more additional alternate routing tables this section will sometimes refer to these Policy based Routing Tables as alternate routing tables Alternate routing tables contain the same information for describing routes as main except that there is an extra parameter ordering defined for each of them This parameter decides how route lookup is done usin
118. Imago Orpheus module sound data Inf Sidplay info file it Impulse Tracker Music Module java Java source code jar Java JAR archive jng JNG Video Format JPEG file jpg jpeg jpe jff jfif jif jre Jrchive compressed archive jsw Just System Word Processor Ichitaro kdelnk KDE link file lha LHA compressed archive file lim Limit compressed archive lisp LIM archive data Izh LZH compressed archive file md MDCD compressed archive file mdb Microsoft Access Database mid midi Musical Instrument Digital Interface MIDI sequention Sound mmf Yamaha SMAF Synthetic Music Mobile Application Format mng Multi image Network Graphic Animation mod Ultratracker module sound data mp3 MPEG Audio Stream Layer III mp4 MPEG 4 Video file mpg mpeg MPEG 1 System Stream Video file mpv MPEG 1 Video file Microsoft files Microsoft office files and other microsoft files msa Atari MSA archive data niff nif Navy Interchange file Format Bitmap noa Nancy Video CODEC nsf NES Sound file obj o Windows object file linux object file OCX Object Linking and Embedding OLE Control Extension ogg Ogg Vorbis Codec compressed WAV file out Linux executable 345 Appendix C Checked MIME filetypes Filetype extension Application pac CrossePAC archive data pbf Portable Bitmap Format Image pbm Portable Bitmap Graphic paf Acrobat Portabl
119. L2TP roaming clients e PPP_PPTPBeforeRules for PPTP roaming clients These settings should be enabled by default and they ensure that user authentication traffic between NetDefendOS and the client can bypass the IP rule set If the appropriate setting is not enabled then an explicit rule needs to be added to the IP rule set to allow the authentication traffic to pass between roaming clients and NetDefendOS This rule will have a destination interface of core Troubleshooting IPsec Tunnels A number of commands can be used to diagnose IPsec tunnels The ipsecstat console command ipsecstat can be used to show that IPsec tunnels have correctly established A representative example of output is gt ipsecstat TRESEC OAS Displaying one line per SA bundl 238 9 2 7 VPN Troubleshooting Chapter 9 VPN IPsec Tunnel Local Net Remote Net Remote GW L2TP_IPSec DNA BS 5 BAS 5 AS S4 so GS 5 Lys 341 13 193 179 IPsec_Tunl LO 163 0 0 24 172 1651 0 24 82 242 Oil 203 To examine the first IKE negotiation phase of tunnel setup use gt ipsecstat ike To get complete details of tunnel setup use gt Hosecstat U y The ikesnoop console command A common problem with setting up IPsec is a proposal list that is unacceptable to the device at the other end of the tunnel The ikesnoop command can show up problems with the proposal list by showing the details of the negotiations that take place ikesnoop verbose O
120. N connections from the clients cannot be differentiated This means that the firewall is unable to control the access to various parts of the internal networks The concept of Identification Lists presents a solution to this problem An identification list contains one or more identities IDs where each identity corresponds to the subject field in an X 509 certificate Identification lists can thus be used to regulate what X 509 certificates that are given access to what IPsec tunnels Example 9 3 Using an Identity List This example shows how to create and use an Identification List for use in the VPN tunnel This Identification List will contain one ID with the type DN distinguished name as the primary identifier Note that this example does not illustrate how to add the specific IPsec tunnel object CLI First create an Identification List gw world gt add IDList MyIDList Then create an ID gw world gt cc IDList MyIDList gw world MyIDList gt add ID JohnDoe Type DistinguishedName CommonName John Doe OrganizationName D Link OrganizationalUnit Support Country Sweden EmailAddress john doe D Link com 251 9 3 8 Identification Lists Chapter 9 VPN gw world MyIDList gt ce Finally apply the Identification List to the IPsec tunnel gw world gt set Interface IPsecTunnel MyIPsecTunnel AuthMethod Certificate IDList MyIDList RootCertificates AdminCert GatewayCertificate AdminCert Web Interface First creat
121. NETWORK SECURITY FIREWALL USER MANUAL DFL 210 800 1 600 z500 D os 4 1 us X stfiparion ink NETWORK SECURITY SOLUTION NETDEFEND User Manual DFL 210 260 800 860 1600 2500 NetDefendOS version 2 20 D Link NetDefend Security http security dlink com tw Published 2008 08 05 Copyright 2008 User Manual DFL 210 260 800 860 1600 2500 NetDefendOS version 2 20 Published 2008 08 05 Copyright 2008 Copyright Notice This publication including all photographs illustrations and software is protected under international copyright laws with all rights reserved Neither this manual nor any of the material contained herein may be reproduced without written consent of the author Disclaimer The information in this document is subject to change without notice The manufacturer makes no representations or warranties with respect to the contents hereof and specifically disclaim any implied warranties of merchantability or fitness for any particular purpose The manufacturer reserves the right to revise this publication and to make changes from time to time in the content hereof without obligation of the manufacturer to notify any person of such revision or changes Limitations of Liability UNDER NO CIRCUMSTANCES SHALL D LINK OR ITS SUPPLIERS BE LIABLE FOR DAMAGES OF ANY CHARACTER E G DAMAGES FOR LOSS OF PROFIT SOFTWARE RESTORATION WORK STOPPAGE LOSS OF SAVED DATA OR ANY OTHER COMMERCIAL DAMA
122. OSPF depends on various metrics for path determination including hops bandwidth load and delay OSPF can provide a great deal of control over the routing process since its parameters can finely tuned Comparing Dynamic Routing Algorithms Due to the fact that the global link state information is maintained everywhere in a network LS algorithms offer a high degree of configuration control and scalability Changes result in broadcasts of just the updated information to other routers which means faster convergence and less possibility of routing loops OSPF can also operate within a hierarchy whereas RIP has no knowledge of sub network addressing NetDefendOS uses OSPF as its dynamic routing algorithm because of the many advantages it offers Routing metrics 103 4 4 2 OSPF Chapter 4 Routing Routing metrics are the criteria a routing algorithm uses to compute the best route to a destination A routing protocol relies on one or several metrics to evaluate links across a network and to determine the optimal path The principal metrics used include Path length The sum of the costs associated with each link A commonly used value for this metric is called hop count which is the number of routing devices a packet must pass through when it travels from source to destination Item Bandwidth The traffic capacity of a path rated by Mbps Load The usage of a router The usage can be evaluated by CPU utilization and throughput De
123. P This example shows how to assign the IP address 192 168 1 1 to the MAC address 00 90 12 13 14 15 The examples assumes that the DHCP server DHCPServer1 has already been defined CLI First change to the DHCPServer1 context gw world gt cc DHCPServer DHCPServerl Now add the static DHCP assignment gw world gt add DHCPServerPoolStaticHost Host 192 168 1 1 MACAddress 00 90 12 13 14 15 All static assignments can be listed and each is listed with an index number gw world gt show Comments An individual static assignment can be shown using its index number gw world gt show DHCPServerPoolStaticHost 1 Property Value Takes SAS ait ak Sak MACAddress 00 90 12 13 14 15 Comments none The assignment could be changed later to IP address 192 168 1 12 with the following command gw world gt set DHCPServerPoolStaticHost 1 Host 192 168 1 12 MACAddress 00 90 12 13 14 15 Web Interface Go to System gt DHCP gt DHCP Servers gt DHCPServer1 gt Static Hosts gt Add gt Static Host Entry Now enter e Host 19 168 1 1 MAC 00 90 12 13 14 15 Click OK 130 5 4 DHCP Relaying Chapter 5 DHCP Services 5 4 DHCP Relaying With DHCP clients send requests to locate the DHCP server s using broadcast messages However broadcasts are normally only propagated across the local network This means that the DHCP server and client would always need to be in the same physical network area to be ab
124. P is a protocol for communication between two computers using a serial interface such as the case of a personal computer connected through a switched telephone line to an ISP In terms of the OSI model PPP provides a layer 2 encapsulation mechanism to allow packets of any protocol to travel through IP networks PPP uses Link Control Protocol LCP for link establishment configuration and testing Once the LCP is initialized one or several Network 61 3 3 4 PPPoE Chapter 3 Fundamentals Control Protocols NCPs can be used to transport traffic for a particular protocol suite so that multiple protocols can interoperate on the same link for example both IP and IPX traffic can share a PPP link Authentication is an option with PPP Authentication protocols supported are Password Authentication Protocol PAP Challenge Handshake Authentication Protocol CHAP Microsoft CHAP version and 2 If authentication is used at least one of the peers has to authenticate itself before the network layer protocol parameters can be negotiated using NCP During the LCP and NCP negotiation optional parameters such as encryption can be negotiated 3 3 4 2 PPPoE Client Configuration The PPPoE interface Since the PPPoE protocol runs PPP over Ethernet the firewall needs to use one of the normal Ethernet interfaces to run PPPoE over Each PPPoE Tunnel is interpreted as a logical interface by the NetDefendOS with the same routing and configurat
125. P compliant client can connect to a network device which supports the SNMP protocol to query and control it NetDefendOS supports SNMP version and version 2 Connection can be made by any SNMP compliant clients to devices running NetDefendOS however only query operations are permitted for security reasons Specifically NetDefendOS supports the following SNMP request operations by a client e The GET REQUEST operation e The GET NEXT REQUEST operation e The GET BULK REQUEST operation SNMP Version 2c only The NetDefendOS MIB The Management Information Base MIB is a database usually in the form of a file which defines the parameters on a network device that an SNMP client can query or change The MIB file for a device running NetDefendOS is distributed with the standard NetDefendOS distribution pack as a file with the name DFLNNN TRAP MIB where NNN indicates the model number of the firewall and this should be transferred to the hard disk of the workstation that will run the SNMP client so it can be imported by the client software When the client runs the MIB file is accessed to inform the client of the values that can be queried on a NetDefendOS device Defining SNMP Access SNMP access is defined through the definition of a NetDefendOS Remote object with a Mode of SNMP The Remote object requires the entry of Interface The NetDefendOS interface on which SNMP requests will arrive e Network The IP address or network from wh
126. P rule set for the tunnel e An Allow rule for outbound traffic that has the previously defined ipsec_tunnel object as 231 9 2 2 IPsec Roaming Clients with Chapter 9 VPN Pre shared Keys the Destination Interface The rule s Destination Network is the remote network remote_net e An Allow rule for inbound traffic that has the previously defined ipsec_tunnel object as the Source Interface The Source Network is remote_net The Service used in these rules is A but it could be a predefined service 6 Define a new NetDefendOS Route which specifies that the VPN Tunnel ipsec_tunnel is the Interface to use for routing packets bound for the remote network at the other end of the tunnel 9 2 2 IPsec Roaming Clients with Pre shared Keys This section details the setup with roaming clients connecting through an IPsec tunnel with pre shared keys There are two types of roaming clients e A The IP addresses of the clients is known beforehand e B The IP address of clients is not known beforehand and must be handed out by NetDefendOS as they connect A IP addresses already allocated The IP addresses may be known beforehand and pre allocated to the roaming clients before they connect The client s IP address will be will be manually input into the VPN client software 1 Set up user authentication XAuth user authentication is not required with IPsec roaming clients but is recommended this step could initially be left out to s
127. P3_DOS Denial of Service for POP POP3_GENERAL POP3_LOGIN ATTACKS Post Office Protocol v3 Password guessing and related login attack POP3_OVERFLOW POPS server overflow POP3_REQUEST ERRORS Request Error PORTMAPPER_GENERAL PortMapper PRINT_GENERAL LP printing server LPR LPD PRINT_OVERFLOW Overflow of LPR LPD protocol implementation REMOTEACCESS_GOTOMYPC Goto MY PC REMOTEACCESS_PCANYWHERE PcAnywhere REMOTEACCESS_RADMIN Remote Administrator radmin REMOTEACCESS_VNC CLIENT Attacks targeting at VNC Clients REMOTEACCESS_VNC SERVER Attack targeting at VNC servers REMOTEACCESS_WIN TERMINAL Windows terminal Remote Desktop RLOGIN_GENERAL RLogin protocol and implementation RLOGIN_LOGIN ATTACK Login attacks ROUTER_CISCO Cisco router attack ROUTER_GENERAL General router attack ROUTING_BGP BGP router protocol RPC_GENERAL RFC protocol and implementation RPC_JAVA RMI Java RMI RSYNC_GENERAL Rsync SCANNER_GENERAL Generic scanners SCANNER_NESSUS Nessus Scanner SECURITY_GENERAL Anti virus solutions SECURITY_ISS Internet Security Systems software SECURITY_MCAFEE McAfee SECURITY_NAV Symantec AV solution SMB_ERROR SMB Error SMB_EXPLOIT SMB Exploit SMB_GENERAL SMB attacks SMB_NETBIOS NetBIOS attacks SMB_WORMS SMB worms SMTP_COMMAND ATTACK SMTP command attack SMTP_DO
128. Route tab select all_nets in the Allowed Networks control Click OK Use User Authentication Rules is enabled as default To be able to authenticate the users using the PPTP tunnel you also need to configure authentication rules which is not covered in this example Example 9 12 Setting up an L2TP Tunnel This example shows how to setup a fully working L2TP Tunnel and will cover many parts of basic VPN configuration Before starting you need to configure some address objects for example the network that is going to be assigned to the L2TP clients Proposal lists and PSK are needed as well Here we will use the objects created in previous examples To be able to authenticate the users using the L2TP tunnel a local user database will be used A Start by preparing a new Local User Database CLI gw world gt add LocalUserDatabase UserDB gw world gt cc LocalUserDatabase UserDB gw world UserDB gt add User testuser Password mypassword Web Interface Go to User Authentication gt Local User Databases gt Add gt Local User Database Enter a suitable for the user database for instance UserDB Go to User Authentication gt Local User Databases gt UserDB gt Add gt User Now enter e Username testuser Password mypassword e Confirm Password mypassword Click OK Now we will setup the IPsec Tunnel which will later be used in the L2TP section As we are going to use L2TP the Local Network is the same IP the L2TP tunne
129. S Denial of Service for SMTP SMTP_GENERAL SMTP protocol and implementation SMTP_OVERFLOW SMTP Overflow SMTP_SPAM SPAM SNMP_ENCODING SNMP encoding SNMP_GENERAL SNMP protocol implementation SOCKS_GENERAL SOCKS protocol and implementation SSH_GENERAL SSH protocol and implementation SSH_LOGIN ATTACK Password guess and related login attacks SSH_OPENSSH OpenSSH Server SSL_GENERAL TCP_GENERAL SSL protocol and implementation TCP protocol and implementation TCP_PPTP Point to Point Tunneling Protocol TELNET_GENERAL Telnet protocol and implementation TELNET_OVERFLOW Telnet buffer overflow attack TFTP_DIR_NAME TFTP_GENERAL Directory Name attack TFTP protocol and implementation 342 Appendix B IDP Signature Groups Group Name Intrusion Type TFTP_OPERATION Operation Attack TFTP_OVERFLOW TFTP_REPLY TFTP buffer overflow attack TFTP Reply attack TFTP_REQUEST TFTP request attack TROJAN_GENERAL Trojan UDP_GENERAL General UDP UDP_POPUP Pop up window for MS Windows UPNP_GENERAL UPNP VERSION_CVS CVS VERSION_SVN Subversion VIRUS_GENERAL Virus VOIP_GENERAL VoIP protocol and implementation VOIP_SIP SIP protocol and implementation WEB_CF FILE INCLUSION Coldfusion file inclusion WEB_FILE INCLUSION File inclusion WEB_GENERAL Web app
130. SIP sessions The default value is 43200 seconds Data Channel Timeout The maximum time allowed for periods with no traffic in a SIP session A timeout condition occurs if this value is exceeded The default value is 120 seconds SIP Setup Summary For setup we will assume a scenario where there is an office with VOIP users on a private internal network and the network s topology will be hidden using NAT This scenario is illustrated below The SIP proxy in the above diagram could alternatively be located remotely across the Internet The SIP proxy server should be configured with the feature Record Route Enabled to insure all SIP traffic to and from the office peers will be sent through the SIP Proxy This is recommended since the attack surface is minimimized by allowing only SIP signalling from the SIP Proxy to enter the local network The steps to follow are Note SIP User Agents and SIP Proxies should not be configured to employ NAT Traversal in a setup For instance the Simple Traversal of UDP through NATs STUN technique should not be used The NetDefendOS SIP ALG will take care of all traversal issues with NAT in a SIP setup 1 Define a SIP ALG object using the options described above 2 A Service object is used for the ALG which has the above SIP ALG associated with it The Service should have Destination Port set to 5060 e Type set to UDP 3 Define two rules in the IP rule set 154 6 2 8 H 323 Chapter 6 S
131. Service Advanced IDP is purchased as an additional component to the base NetDefendOS license It is a subscription service and the subscription means that the IDP signature database can be downloaded to a NetDefendOS installation and also that the database is regularly updated with the latest intrusion threats For full details about obtaining the IDP service please refer to Appendix A Subscribing to Security Updates Figure 6 3 IDP Database Updating A new updated signature database is downloaded automatically by NetDefendOS system at a configurable interval This is done via an HTTP connection to the D Link server network which delivers the latest signature database updates If the server s signature database has a newer version than the current local database the new database will be downloaded replacing the older version IDP IPS and IDS The terms Intrusion Detection and Prevention Intrusion Prevention System and Intrusion Detection System are used interchangeably in D Link literature Setting the Correct System Time It is important that a NetDefendOS has the correct system time set if the auto update feature in the IDP module can function correctly An incorrect time can mean the auto updating is disabled 189 6 5 3 IDP Rules Chapter 6 Security Mechanisms The console command gt updatecenter status will show the current status of the auto update feature This can also be done through the WebUI Updating in Hi
132. Shaping page 267 e Threshold Rules page 279 e Server Load Balancing page 281 10 1 Traffic Shaping 10 1 1 Introduction QoS with TCP IP A weakness of TCP IP is the lack of true Quality of Service QoS functionality QoS is the ability to guarantee and limit network bandwidth for certain services and users Solutions such as the Differentiated Services Diffserv architecture have been designed to try and deal with the QoS issue in large networks by using information in packet headers to provide network devices with QoS information NetDefendOS Diffserv Support NetDefendOS supports the Diffserv architecture in two ways firstly NetDefendOS forwarding the 6 bits which make up the Diffserv Differentiated Services Code Point DSCP as well as copying these bits from the data traffic inside VPN tunnels to the encapsulating packets Secondly and as described later in this chapter DSCP bits can be used by the NetDefendOS traffic shaping subsystem as a basis for prioritizing traffic passing through a D Link Firewall The Traffic Shaping Solution Architectures like Diffserv however fall short if applications themselves supply the network with QoS information In most networks it is rarely appropriate to let the applications the users of the network decide the priority of their own traffic If the users cannot be relied upon then the network equipment must make the decisions concerning priorities and bandwidth allocation NetDefendOS pro
133. Spreadsheet file asf Advanced Streaming Format file avr Audio Visual Research Sound aw Applix Word file bh Blackhole archive format file bmp Windows Bitmap Graphics box VBOX voice message file bsa BSARC Compressed archive bz bz2 Bzip UNIX compressed file cab Microsoft Cabinet file cdr Corel Vector Graphic Drawing file cgm Computer Graphics Metafile chz ChArc compressed file archive class Java byte code cmf Creative Music file core coredump Unix core dump cpl Windows Control Panel Extension file dbm Database file dcx Graphics Multipage PCX Bitmap file deb Debian Linux Package file djvu DjVu file dll Windows dynamic link library file dpa DPA archive data dvi TeX Device Independent Document eet EET archive egg Allegro datafile 344 Appendix C Checked MIME filetypes Filetype extension Application elc eMacs Lisp Byte compiled Source Code emd ABT EMD Module Song Format file esp ESP archive data exe Windows Executable fof Free Graphics Format file flac Free Lossless Audio Codec file flc FLIC Animated Picture fli FLIC Animation flv Macromedia Flash Video gdbm Database file gif Graphic Interchange Format file gzip gz tgz Gzip compressed archive hap HAP archive data hpk HPack compressed file archive hqx Macintosh BinHex 4 compressed archive icc Kodak Color Management System ICC Profile icm Microsoft ICM Color Profile file ico Windows Icon file imf
134. TCP UDP and ICMP such as telnet FTP HTTP SMTP etc NetDefendOS can alter port number information in the TCP and UDP headers to make each connection unique even though such connections have had their sender addresses translated to the same IP Some protocols regardless of the method of transportation used can cause problems during address translation 206 7 2 NAT Pools Chapter 7 Address Translation 7 2 NAT Pools Overview As discussed in Section 7 1 Dynamic Network Address Translation NAT provides a way to have multiple internal clients and hosts with unique private internal IP addresses communicate to remote hosts through a single external public IP address When multiple public external IP addresses are available then a NAT Pool object can be used to allocate new connections across these public IP addresses NAT Pools are usually employed when there is a requirement for huge numbers of unique port connections The NetDefendOS Port Manager has a limit of approximately 65 000 connections for a unique combination of source and destination IP addresses Where large number of internal clients are using applications such as file sharing software very large numbers of ports can be required for each client The situation can be similarly demanding if a large number of clients are accessing the Internet through a proxy server The port number limitation is overcome by allocating extra external IP addresses for Internet acces
135. TCPUDP TCP UDP SourcePorts 0 65535 PassICMPReturn No ALG none MaxSessions 1000 Comments Echo service Web Interface 1 Go to Objects gt Services 2 Select the specific service object in the grid control 3 A grid listing all services will be presented 3 2 2 TCP and UDP Based Services Most applications are using TCP and or UDP as transport protocol for transferring application data over IP networks TCP Transmission Control Protocol is a connection oriented protocol that among other things includes mechanisms for reliable transmission of data TCP is used by many common applications such as HTTP FTP and SMTP where error free transfers are mandatory For other types of applications where for instance performance is of great importance such as streaming audio and video services UDP User Datagram Protocol is the preferred protocol UDP is connection less provides very few error recovery services and give thereby much lower overhead traffic than when using TCP For this reason UDP is used for non streaming services as well and it is common in those cases that the applications themselves provide the error recovery mechanisms To define a TCP or UDP service in the D Link Firewall a TCP UDP Service object is used This type of object contains apart from a unique name describing the service also information on what protocol TCP UDP or both and what source and destination ports are applicable for the servi
136. TP RFC 1305 This is used by NetDefendOS to query NTP servers e UDP TIME The Time Protocol UDP TIME is an older method of providing time synchronization service over the Internet The protocol provides a site independent machine readable date and time The server sends back the time in seconds since midnight on January first 1900 Most public Time Servers run the NTP protocol and are accesible using SNTP Configuring Time Servers Up to three Time Servers can be configured to query for time information By using more than a single server situations where an unreachable server causes the time synchronization process to fail can be prevented NetDefendOS always queries all configured Time Servers and then computes an average time based on all responses Internet search engines can be used to list publicly available Time Servers Important q Make sure an external DNS server is configured so that Time Server URLs can be resolved see Section 3 9 DNS Lookup This is not needed if using server IP addresses Example 3 23 Enabling Time Synchronization using SNTP In this example time synchronization is set up to use the SNTP protocol to communicate with the NTP servers at the Swedish National Laboratory for Time and Frequency The NTP server URLs are ntp1 sp se and ntp2 sp se CLI gw world gt set DateTime TimeSynchronization custom TimeSyncServerl dns ntpl sp se TimeSyncServer2 dns ntp2 sp se TimeSyncInterval 86400 Web Int
137. TP ALG Enter Name ftp inbound Check Allow client to use active mode Uncheck Allow server to use passive mode Click OK B Define the Service Go to Objects gt Services gt Add gt TCP UDP Service Enter the following Name ftp inbound Type select TCP from the list Destination 21 the port the FTP server resides on ALG select the ftp inbound that has been created Click OK C Define a rule to allow connections to the public IP on port 21 and forward that to the internal FTP server 1 Goto Rules gt IP Rules gt Add gt IPRule 142 6 2 3 FTP Chapter 6 Security Mechanisms Now enter e Name SAT ftp inbound Action SAT e Service ftp inbound For Address Filter enter Source Interface any Destination Interface core Source Network all nets Destination Network wan_ip assuming the external interface has been defined as this For SAT check Translate the Destination IP Address Enter To New IP Address ftp internal assume this internal IP address for FTP server has been defined in the Address Book object New Port 21 Click OK D Traffic from the internal interface needs to be NATed Go to Rules gt IP Rules gt Add gt IPRule Now enter Name NAT ftp Action NAT e Service ftp inbound For Address Filter enter Source Interface dmz Destination Interface core Source Network dmznet Destination Network wan_ip For NAT check Use Interface Address Click OK E Allow incoming co
138. Windows XP L2TP client the appropriate certificates need to be imported into Windows before setting up the connection with the New Connection Wizard The step to set up user authentication is optional since this is additional security to certificates 9 2 6 PPTP Roaming Clients PPTP is simpler to set up than L2TP since IPsec is not used and instead relies on its own less strong encryption A major secondary disadvantage is not being able to NAT PPTP connections through a tunnel so multiple clients can use a single connection to the D Link Firewall If NATing is tried then only the first client that tries to connect will succeed The steps for PPTP setup are as follows 1 In Hosts amp Networks define the following IP objects e A pptp_pool IP object which is the range of internal IP addresses that will be handed out from an internal network 236 9 2 7 VPN Troubleshooting Chapter 9 VPN N W An int_net object which is the internal network from which the addresses come An ip_int object which is the internal IP address of the interface connected to the internal network let s assume this interface is int An ip_ext object which is the external public address which clients will connect to let s assume this is on the ext interface Define a PPTP L2TP object let s call it pptp_tunnel with the following parameters Set Inner IP Address to ip_net Set Tunnel Protocol to PPTP Set Outer Interface Filter to ext
139. _DSTStartDate Chapter 13 Advanced Settings DST offset in minutes Default 0 TimeSync_DSTStartDate What month and day DST starts in the format MM DD Default none TimeSync_DSTEndDate What month and day DST ends in the format MM DD Default none 332 13 16 PPP Settings Chapter 13 Advanced Settings 13 16 PPP Settings PPP_L2TPBeforeRules Pass L2TP traffic sent to the D Link Firewall directly to the L2TP Server without consulting the tule set Default Enabled PPP_PPTPBeforeRules Pass PPTP traffic sent to the D Link Firewall directly to the PPTP Server without consulting the tule set Default Enabled 333 13 17 Hardware Monitor Settings Chapter 13 Advanced Settings 13 17 Hardware Monitor Settings HWM_Polllnterval Polling intervall for Hardware Monitor which is the delay in milliseconds between reading of hardware monitor values Minimum 100 Maximum 10000 Default 500 ms HWMMem _Interval Memory polling interval which is the delay in minutes between reading of memory values Minimum 1 Maximum 200 Default 715 mins HWMMem_LogRepetition Should we send a log message for each poll result that is in the Alert Critical or Warning level or should we only send when a new level is reached If True a message is sent each time HWMMem Interval is triggered If False a message is sent when a value goes from one level to another Default False HWMMem_UsePercent True
140. a D Link Firewall Policies in NetDefendOS are defined by different NetDefendOS rule sets These rule sets share a common means of specifying filtering criteria which determine the type of traffic to which they will apply This set of criteria consists of Source Interface Source Network Destination Interface Destination Network Service An Interface or Interface Group where the packet is received at the D Link Firewall This can also be a VPN tunnel The network that contains the source IP address of the packet This might be a NetDefendOS IP object which could define a single IP address or range of addresses An Interface or an Interface Group from which the packet would leave the D Link Firewall This can also be a VPN tunnel The network to which the destination IP address of the packet belongs This might be a NetDefendOS IP object which could define a single IP address or range of addresses The protocol type to which the packet belongs Service objects define a protocol port type Examples might be HTTP or ICMP Custom services can also be defined see Section 3 2 Services for more information The NetDefendOS rule sets all of which use the same five filtering parameters include e I Prules e Pipe rules see Section 10 1 Traffic Shaping e Policy based Routing rules see Section 4 3 Policy based Routing e IDP rules see Section 6 5 Intrusion Detection and Prevention e Authent
141. a reasonable margin above the anticipated email size when setting this limit Email address blacklisting A blacklist of email addresses can be specified so that mail from those addresses is blocked Email address whitelisting A whitelist of email addresses can be specified so that mail from those addresses is allowed to pass by the ALG Verify MIME type Mail attachment file content can be checked against its filetype A list of all filetypes checked can be found in Appendix C Checked MIME filetypes Anti Virus Scanning The NetDefendOS Anti Virus module can scan email attachments searching for malicious code This feature is described fully in Section 6 4 Anti Virus Scanning 6 2 5 1 DNSBL SPAM Filtering Unsolicited email often referred to as SPAM has become both a major annoyance as well as a security issue on the public Internet Unsolicited email sent out in massive quantities by groups known as spammers can waste resources transport malware as well as try to direct the reader to webpages which might exploit browser vulnerabilities Integral to the NetDefendOS SMTP ALG is a SPAM module that provides the ability to apply spam filtering to incoming email based on its origin This can significantly reduce the burden of such email in the mailboxes of users behind a D Link Firewall NetDefendOS offers the options of e Dropping email which has a very high probability of being SPAM e Letting through but flagging email that has
142. a unique activation code to identify you as a user of the service e Go to Maintenance gt License in the web interface of your D Link Firewall system and enter this activation code NetDefendOS will indicate the code is accepted and the update service will be activated Make sure access to the public Internet is possible when doing this Note A step by step Registration manual which explains registration and update service procedures in more detail is available for download from the D Link website Subscription renewal In the Web interface go to Maintenance gt License to check which update services are activated and when your subscription is ends Caution s 2 Renew your subscription in good time before your current subscription ends Monitoring database updates In the Web interface go to Maintenance gt Update to configure the automatic database updating You can also check when the last update was attempted and what the status was for that attempt In the same area of the Web interface it is also possible to manually initiate updating by selecting Update now to download the latest signatures to the database Database Console Commands IDP and Anti Virus AV databases can be controlled directly through a number of console commands Pre empting Database Updates An IDP database update can be forced at any time by using the command gw world gt updatecenter update IDP An Anti Virus update can similarly be i
143. ack interface MAC Range A range of MAC addresses that will be use to create fake DHCP clients Used when the DHCP server s map clients by the MAC address An indication of the need for MAC ranges is when the DHCP server keeps giving out the same IP for each client Prefetched leases Specifies the number of leases to keep prefetched Prefetching will improve performance since there won t be any wait time when a system requests an IP while there exists prefetched IPs Maximum free The maximum number of free IPs to be kept Must be equal to or 132 5 5 IP Pools Chapter 5 DHCP Services greater than the prefetch parameter The pool will start releasing giving back IPs to the DHCP server when the number of free clients exceeds this value Maximum clients Optional setting used to specify the maximum number of clients IPs allowed in the pool Using Prefetched Leases As mentioned in the previous section the Prefetched Leases option specifies the size of the cache of leases which is maintained by NetDefendOS This cache provides fast lease allocation and can improve overall system performance It should be noted however that the entire prefetched number of leases is requested at system startup and if this number is too large then this can degrade initial performance As leases in the prefetch cache are allocated requests are made to DHCP servers so that the cache is always full The administrator therefore has to make a
144. acket correctly However many IP stacks are unable to handle incorrectly fragmented packets a fact that can be exploited by intruders to crash such systems NetDefendOS provides protection against fragmentation attacks in a number of ways PseudoReass_MaxConcurrent Maximum number of concurrent fragment reassemblies To drop all fragmented packets set PseudoReass_MaxConcurrent to 0 Default 1024 IllegalFrags Determines how NetDefendOS will handle incorrectly constructed fragments The term incorrectly constructed refers to overlapping fragments duplicate fragments with different data incorrect fragment sizes etc Possible settings include e Drop Discards the illegal fragment without logging it Also remembers that the packet that is being reassembled is suspect which can be used for logging further down the track e DropLog Discards and logs the illegal fragment Also remembers that the packet that is being reassembled is suspect which can be used for logging further down the track e DropPacket Discards the illegal fragment and all previously stored fragments Will not allow further fragments of this packet to pass through during ReassIllegalLinger seconds e DropLogPacket As DropPacket but also logs the event e DropLogAll As DropLogPacket but also logs further fragments belonging to this packet that arrive during ReassIllegalLinger seconds The choice of whether to discard individual fragment
145. affic Management Click OK Repeat the above to create an object called server2 for the 192 168 1 11 IP address B Create a Group which contains the 2 webserver objects Go to Objects gt Address Book gt Add gt IP4 Group Enter a suitable name eg server_group Add server and server2 to the group Click OK C Specify the SLB_SAT IP rule Go to Rules gt IP Rule Sets gt main gt Add gt IP Rule Enter Name Web_SLB Action SLB_SAT Service HTTP Source Interface any Source Network all nets Destination Interface core Destination Network ip_ext Select tab SAT SLB Under Server Addresses add server_group to Selected Click OK D Specify a matching NAT IP rule for internal clients Go to Rules gt IP Rule Sets gt main gt Add gt IP Rule Enter Name Web_SLB_NAT Action NAT Service HTTP Source Interface lan Source Network lannet Destination Interface core Destination Network ip_ext Click OK E Specify an ALLOW IP rule for the external clients Go to Rules gt IP Rule Sets gt main gt Add gt IP Rule Enter e Name Web_SLB_ALW Action ALLOW 286 10 3 6 SLB_SAT Rules Chapter 10 Traffic Management Service HTTP Source Interface any Source Network all nets Destination Interface core Destination Network ip_ext Click OK 287 10 3 6 SLB_SAT Rules Chapter 10 Traffic Management 288 Chapter 11 High Availability This chapter des
146. affic should be analyzed 2 What should we searched for in that traffic 3 What action should be carried out when an intrusion is detected NetDefendOS IDP Components NetDefendOS IDP addresses the above IDP issues with the following mechanisms 1 IDP Rules are defined up by the administrator to determine what traffic should be scanned 2 Pattern Matching is applied by NetDefendOS IDP to the traffic that matches an IDP Rule as it streams through the firewall 3 If NetDefendOS IDP detects an intrusion then the Action specified for the triggering IDP Rule is taken IDP Rules Pattern Matching and IDP Rule Actions are described in the sections which follow 6 5 2 IDP Availability in D Link Models Maintenance and Advanced IDP D Link offers two types of IDP e Maintenance IDP is a basic IDP system included as standard with the D Link 188 6 5 2 IDP Availability in D Link Chapter 6 Security Mechanisms Models DFL 210 800 1600 2500 firewalls This is a simplfied IDP that gives basic protection against attacks It is upgradeable to the professional level Advanced IDP e Advanced IDP is a subscription based IDP system with a much broader range of database signatures for professional installations It is available on all D Link firewalls Maintenance IDP can be viewed as a restricted subset of Advanced IDP and the following sections describe how the Advanced IDP Service functions Subscribing to the D Link Advanced IDP
147. al resources which means that the DoS attack floods the network and ties up critical resources used to run business critical applications In some cases vulnerabilities in the Unix and Windows operating systems are exploited to intentionally crash the system while in other cases large amounts of apparently valid traffic are directed at sites until they become overloaded and crash Some of the most commonly used DoS attacks have been e The Ping of Death Jolt attacks e Fragmentation overlap attacks Teardrop Bonk Boink Nestea e The Land and LaTierra attacks e The WinNuke attack e Amplification attacks Smurf Papasmurf Fraggle e TCP SYN Flood attack e The Jolt2 attack 6 6 3 Ping of Death and Jolt Attacks The ping of death is one of the earliest layer 3 4 attacks One of the simplest ways to execute it is 198 6 6 4 Fragmentation overlap attacks Chapter 6 Security Mechanisms Teardrop Bonk Boink and Nestea to run ping l1 65510 1 2 3 4 on a Windows 95 system where 1 2 3 4 is the IP address of the intended victim Jolt is simply a purpose written program for generating such packets on operating systems whose ping commands refuse to generate oversized packets The triggering factor is that the last fragment makes the total packet size exceed 65535 bytes which is the highest number that a 16 bit integer can store When the value overflows it jumps back to a very small number What happens then is a functio
148. alculation of a weighted sum e Specify the threshold for designating an email as SPAM If the weighted sum is equal or greater than this then an email will be considered to be SPAM e Specify a textual tag to prefix to the Subject field of email designated as SPAM e Specify the Drop threshold If the weighted sum is equal or greater than this then an email will be dropped entirely This threshold should be greater or equal to the SPAM threshold If they are equal then the Drop threshold will have precedence so that all email will be dropped when that threshold is reached e Optionally specify an email address to which dropped email will be sent as an alternative to simply discarding it Optionally specify that the TXT messages sent by the DNSBL servers that failed it be appended to these emails Caching Addresses for Performance To speed processing NetDefendOS maintains a cache of the most recently looked up sender addresses in local memory If the cache becomes full then the oldest entry is written over first The Address Timeout value for the cache can be changed by the administrator This determines how long any address will be valid for once it is saved in the cache After this period of time has expired anew query for a cached sender address must be sent to the DNSBL servers The cache is emptied at startup or reconfiguration and its size of this cache can be controlled by the administrator The dnsb CLI Command The dnsbl CLI
149. ame source IP address and port within a fixed period of time The reason for this is that some TFTP clients might issue requests from the same source port without allowing an appropriate timeout period 6 2 5 SMTP Simple Mail Transfer Protocol SMTP is a text based protocol used for transferring email between mail servers over the Internet Typically the local SMTP server will be located on a DMZ so that mail sent by remote SMTP servers will traverse the D Link Firewall to reach the local server this setup is illustrated later in Section 6 2 5 1 DNSBL SPAM Filtering Local users will then use email client software to retrieve their email from the local SMTP server SMTP ALG Options Key features of the SMTP ALG are 146 6 2 5 SMTP Chapter 6 Security Mechanisms Email Rate Limiting A maximum allowable rate of email messages can be specified Email Size Limiting A maximum allowable size of email messages can be specified This feature counts the total amount of bytes sent for a single email which is the header size plus body size plus the size of any email attachments after they are encoded It should be kept in mind that an email with for example an attachment of 100 KBytes will be larger than 100 KBytes The transferred size might be 120 KBytes or more since the encoding which takes place automatically for attachments may substantially increase the transferred attachment size The administrator should therefore add
150. ample 6 15 Enabling Dynamic Web Content Filtering This example shows how to setup a dynamic content filtering policy for HTTP traffic from intnet to all nets The policy will be configured to block all search sites and this example assumes that the system is using a single NAT rule for HTTP traffic from intnet to all nets CLI The NAT rule is called NATHttp for the CLI example First create an HTTP Application Layer Gateway ALG Object gw world gt add ALG ALG_HTTP content_filtering WebContentFilteringMode Enabled FilteringCategories SEARCH_SITES Then create a Service object using the new HTTP ALG gw world gt add ServiceTCPUDP http_content_filtering Type TCP DestinationPorts 80 ALG content_filtering Finally modify the NAT rule to use the new service gw world gt set IPRule NATHttp Service http_content_filtering Web Interface First create an HTTP Application Layer Gateway ALG Object Go to Objects gt ALG gt Add gt HTTP ALG Specify a suitable name for the ALG eg content_filtering Click the Web Content Filtering tab Select Enabled in the Mode list 173 6 3 4 Dynamic Web Content Filtering Chapter 6 Security Mechanisms 5 Inthe Blocked Categories list select Search Sites and click the gt gt button 6 Click OK Then create a Service object using the new HTTP ALG Go to Local Objects gt Services gt Add gt TCP UDP service Specify a suitable name for the Service eg http_co
151. and dynamically in accordance with rule 2 10 0 0 1 32789 gt 10 0 0 2 80 wwwsrv processes the packet and replies 10 0 0 2 80 gt 10 0 0 1 32789 The reply arrives and both address translations are restored 195 55 66 77 80 gt 10 0 0 3 1038 This way the reply arrives at PC1 from the expected address Another possible solution to this problem is to allow internal clients to speak directly to 10 0 0 2 which would completely avoid all the problems associated with address translation However this is not always practical 7 3 2 Translation of Multiple IP Addresses M N A single SAT rule can be used to translate an entire range of IP addresses In this case the result is a transposition where the first original IP address will be translated to the first IP address in the translation list and so on For instance a SAT policy specifying that connections to the 194 1 2 16 29 network should be translated to 192 168 0 50 will result in transpositions as per the table below In other words e Attempts to communicate with 194 1 2 16 will result in a connection to 192 168 0 50 e Attempts to communicate with 194 1 2 22 will result in a connection to 192 168 0 56 213 7 3 2 Translation of Multiple IP Chapter 7 Address Translation Addresses M N An example of when this is useful is when having several protected servers in a DMZ and where each server should be accessible using a unique public IP address Exampl
152. any circumstances a Whitelist is also maintained by NetDefendOS Tip It is advisable to add the D Link Firewall itself to the Whitelist as well as the IP addresses of the management workstation It is important to understand that although whitelisting prevents a source of network traffic being blacklisted it still doesn t mechanisms such as Threshold Rules from dropping or denying connections from that source All whitelisting does is prevent a source being added to a blacklist if that is the action a rule has specified For further details on usage see Section 6 5 7 IDP Actions Section 10 2 8 Threshold Rule Blacklisting and Section 10 2 Threshold Rules Note Content filtering blacklisting is a separate subject and uses a separate logical list see Section 6 3 Web Content Filtering 202 6 7 Blacklisting Hosts and Networks Chapter 6 Security Mechanisms 203 Chapter 7 Address Translation This chapter describes NetDefendOS address translation capabilities e Dynamic Network Address Translation page 204 e NAT Pools page 207 e Static Address Translation page 210 The ability of NetDefendOS to change the IP address of packets as they pass through a D Link Firewall is known as address translation NetDefendOS supports two types of translation Dynamic Network Address Translation NAT and Static Address Translation SAT Both translations are policy based meaning that they can be applied
153. arameters needed such as algorithms used to encrypt and authenticate the data and other parameters as described in section IKE Parameters IKE Phase 1 IKE Security Negotiation An IKE negotiation is performed in two phases The first phase phase 1 is used to authenticate the two VPN firewalls or VPN Clients to each other by confirming that the remote device has a matching Pre Shared Key However since we do not want to publish to much of the negotiation in plaintext we first agree upon a way of protecting the rest of the IKE negotiation This is done as described in the previous section by the initiator sending a proposal list to the responder When this has been done and the responder accepted one of the proposals we try to authenticate the other end of the VPN to make sure it is who we think it is as well as proving to the remote device that we are who we claim to be A technique known as a Diffie Hellman Key Exchange is used to intially agree a shared secret between the two parties in the negotiation and to derive keys for encryption 241 9 3 2 Internet Key Exchange IKE Chapter 9 VPN Authentication can be accomplished through Pre Shared Keys certificates or public key encryption Pre Shared Keys is the most common authentication method today PSK and certificates are supported by the NetDefendOS VPN module IKE Phase 2 IPsec Security Negotiation In phase two another negotiation is performed detailing the param
154. are used to authenticate VPN tunnels The keys are secrets that are shared by the communicating parties before communication takes place To communicate both parties prove that they know the secret The security of a shared secret depends on how good a passphrase is Passphrases that are common words are for instance extremely vulnerable to dictionary attacks Pre shared Keys can be generated automatically through the WebUI but they can also be generated through the CLI using the command pskgen this command is fully documented in the CLI Reference Guide Example 9 2 Using a Pre Shared key This example shows how to create a Pre shared Key and apply it to a VPN tunnel Since regular words and phrases are vulnerable to dictionary attacks they should not be used as secrets Here the pre shared key is a randomly generated hexadecimal key Note that this example does not illustrate how to add the specific IPsec tunnel object CLI First create a Pre shared Key To generate the key automatically with a 64 bit the default key use gw world gt pskgen MyPSK To have a longer more secure 512 bit key the command would be gw world gt pskgen MyPSK size 512 Or alternatively to add the Pre shared Key manually use gw world gt add PSK MyPSK Type HEX PSKHex lt enter the key here gt Now apply the Pre shared Key to the IPsec tunnel gw world gt set Interface IPsecTunnel MyIPsecTunnel PSK MyPSK Web Interface First crea
155. arently to the correct interface without modifying any of the source or destination information on the IP or Ethernet levels Two benefits of Transparent Mode are e When a client moves from one interface to another without changing IP address it can still obtain the same services as before for example HTTP FTP without routing reconfiguration e The same network address range can exist on several interfaces Note gt D Link Firewalls need not operate exclusively in Transparent Mode but can combine Transparent Mode with Routing Mode to operate in a hybrid mode That is to say the firewall can have both Switch Routes as well as standard routes defined It is also possible to create a hybrid case by applying address translation on otherwise transparent traffic 4 6 3 Transparent Mode Implementation In transparent mode NetDefendOS allows ARP transactions to pass through the D Link Firewall and determines from this ARP traffic the relationship between IP addresses physical addresses and interfaces NetDefendOS remembers this address information in order to relay IP packets to the correct receiver During the ARP transactions neither of the endpoints will be aware of the firewall s presence 119 4 6 4 Enabling Transparent Mode Chapter 4 Routing When beginning communication a host will locate the target host s physical address by broadcasting an ARP request This request is intercepted by NetDefendOS and it sets up an interna
156. as a percentage of the total memory available Minimum 1 Maximum 100 Default 3 335 13 19 Miscellaneous Settings Chapter 13 Advanced Settings 13 19 Miscellaneous Settings BufFloodRebootTime As a final way out NetDefendOS automatically reboots if its buffers have been flooded for a long time This setting specifies this amount of time Default 3600 MaxPipeUsers The maximum number of pipe users to allocate As pipe users are only tracked for a 20th of a second this number usually does not need to be anywhere near the number of actual users or the number of statefully tracked connections If there are no configured pipes no pipe users will be allocated regardless of this setting For more information about pipes and pipe users see chapter 10 Traffic Shaping Default 5 2 336 MaxPipeUsers Chapter 13 Advanced Settings 337 Appendix A Subscribing to Security Updates Introduction The NetDefendOS Anti Virus AV module the Intrusion Detection and Prevention IDP module and the Dynamic Web Content Filtering module all function using external D Link databases which contain details of the latest viruses security threats and URL categorization These databases are constantly being updated and to get access to the latest updates a D Link Security Update Subscription should be taken out This is done by e Purchasing a subscription from your local D Link reseller e On purchase you will receive
157. as the remote gateway This is particularly useful in cases of roaming access where the IP addresses of the remote VPN clients are not known beforehand Setting this to none will allow anyone coming from an IP address conforming to the remote network address discussed above to open a VPN connection provided they can authenticate properly The remote gateway is not used in transport mode The IKE negotiation has two modes of operation main mode and aggressive mode The difference between these two is that aggressive mode will pass more information in fewer packets with the benefit of slightly faster connection establishment at the cost of transmitting the identities of the security firewalls in the clear When using aggressive mode some configuration parameters such as Diffie Hellman groups and PFS can not be negotiated resulting in a greater importance of having compatible configurations on both ends The IPsec protocols describe how the data will be processed The two protocols to choose from are AH Authentication Header and ESP Encapsulating Security Payload ESP provides encryption authentication or both However we do not recommend using encryption only since it will dramatically decrease security More on ESP in ESP Encapsulating Security Payload AH only provides authentication The difference from ESP with authentication only is that AH also authenticates parts of the outer IP header for instance sour
158. ast_service 1 Goto Objects gt Services gt Add gt TCP UDP 2 Now enter Name multicast_service Type UDP Destination 1234 B Create an IP rule Go to Rules gt IP Rules gt Add gt IP Rule Under General enter Name a name for the rule eg Multicast_Multiplex e Action Multiplex SAT e Service multicast_service Under Address Filter enter e Source Interface wan e Source Network 192 168 10 1 113 4 5 3 IGMP Configuration Chapter 4 Routing Destination Interface core Destination Network 239 192 10 0 24 Click the Address Translation tab Add interface if1 but leave the IPAddress empty Add interface if2 but this time enter 237 192 10 0 as the IPAddress Make sure the forwarded using IGMP checkbox is set Click OK Note If address translation of the source address is required the Allow rule following the SAT Multiplex rule should be replaced with a NAT rule 4 5 3 IGMP Configuration IGMP signaling between hosts and routers can be divided into two categories IGMP Reports Reports are sent from hosts towards the router when a host wants to subscribe to new multicast groups or change current multicast subscriptions IGMP Queries Queries are IGMP messages sent from the router towards the hosts in order to make sure that it will not close any stream that some host still wants to receive Normally both these types of rules has to be specified for IGMP to work One exception
159. atabases in order to provide protection against the latest threats To facilitate the Auto Update feature D Link maintains a global infrastructure of servers providing update services for D Link Firewalls To ensure availability and low response times NetDefendOS employs a mechanism for automatically selecting the most appropriate server to supply updates For more details on these features see the following sections e Section 6 5 Intrusion Detection and Prevention e Section 6 4 Anti Virus Scanning e Section 6 3 Web Content Filtering e Appendix A Subscribing to Security Updates 2 5 2 Configuration Backup and Restore The NetDefendOS configuration of a D Link Firewall can be backed up or restored on demand This could for instance be used to recall the last known good configuration when experimenting with different configuration setups Example 2 14 Configuration Backup and Restore Web Interface To create a backup of the currently running configuration 1 Goto Tools gt Backup 2 Download configuration select a name and begin backup To restore a configuration backup 1 Goto Tools gt Backup 2 In Restore unit s configuration browse and locate the desired backup 3 Click Upload configuration and then choose to activate that configuration Note gt Backups include only static information in the firewall configuration Dynamic information such as the DHCP server lease database will not be bac
160. ate Limit This can be triggered if the rate of new connections per second to the firewall exceeds a specified threshold e Total Connections Limit This can be triggered if the total number of connections to the firewall exceeds a specified threshold Threshold rules have parameters which are similar to those for IP Rules These parameters specify what type of traffic a threshold rule applies to A single threshold rule has the parameters e Source interface and source network e Destination interface and destination network e Service e Type of threshold Host and or network based Traffic that matches the above criteria and causes the host network threshold to be exceeded will trigger the ZoneDefense feature This will prevent the host networks from accessing the switch es All blocking in response to threshold violations will be based on the IP address of the host or network on the switch es When a network based threshold has been exceeded the source network will be blocked out instead of just the offending host For a general description of how Threshold Rules are specified and function please see Section 10 2 Threshold Rules 12 3 3 Manual Blocking and Exclude Lists 300 12 3 3 Manual Blocking and Exclude Chapter 12 ZoneDefense Lists As a complement to threshold rules it is also possible to manually define hosts and networks that are to be statically blocked or excluded Manually blocked hosts and networ
161. ating to travel activities including travelling for recreation and travel reservation facilities Examples might be e www flythere nu e www reallycheaptix com au Category 6 Shopping A web site may be classified under the Shopping category if its content includes any form of advertisement of goods or services to be exchanged for money and may also include the facilities to perform that transaction online Included in this category are market promotions catalogue selling and merchandising services Examples might be e www megamall com 177 6 3 4 Dynamic Web Content Filtering Chapter 6 Security Mechanisms e www buy alcohol se Category 7 Entertainment A web site may be classified under the Entertainment category if its content includes any general form of entertainment that is not specifically covered by another category Some examples of this are music sites movies hobbies special interest and fan clubs This category also includes personal web pages such as those provided by ISPs The following categories more specifically cover various entertainment content types Pornography Sex 1 Gambling 4 Chatrooms 8 Game Sites 10 Sports 16 Clubs and Societies 22 and Music Downloads 23 Examples might be www celebnews com e www hollywoodlatest com Category 8 Chatrooms A web site may be classified under the Chatrooms category if its content focuses on or includes real time on line interactive discuss
162. ault 4096 ARPHashSize So called hash tables are used to rapidly look up entries in a table For maximum efficiency a hash should be twice as large as the table it is indexing so if the largest directly connected LAN contains 500 IP addresses the size of the ARP entry hash should be at least 1000 entries Default 5 2 ARPHashSizeVLAN So called hash tables are used to rapidly look up entries in a table For maximum efficiency a hash should be twice as large as the table it is indexing so if the largest directly connected LAN contains 500 IP addresses the size of the ARP entry hash should be at least 1000 entries Default 64 ARPIPCollision Determines the behaviour when receiving an ARP request with a sender IP address that collides with one already used on the receive interface Possible actions Drop or Notify Default Drop 313 13 5 Stateful Inspection Settings Chapter 13 Advanced Settings 13 5 Stateful Inspection Settings LogConnectionUsage This generates a log message for every packet that passes through a connection that is set up in the NetDefendOS state engine Traffic whose destination is the D Link Firewall itself for example NetDefendOS management traffic is not subject to this setting The log message includes port service source destination IP address and interface This setting should only be enabled for diagnostic and testing purposes since it generates unwieldy volumes of log messages a
163. ay be intrusions They have lower accuracy than IPS and may give some false positives so that s recommended that the Audit action is initially used before deciding to use Protect e Policy Signatures detect different types of application traffic They can be used to block certain applications such as filesharing applications and instant messaging 6 5 6 IDP Signature Groups 192 6 5 6 IDP Signature Groups Chapter 6 Security Mechanisms Using Groups Usually several lines of attacks exist for a specific protocol and it is best to search for all of them at the same time when analyzing network traffic To do this signatures related to a particular protocol are grouped together For example all signatures that refer to the FTP protocol form a group It is best to specify a group that relates to the traffic being searched than be concerned about individual signatures For performance purposes the aim should be to have NetDefendOS search data using the least possible number of signatures Specifying Signature Groups IDP Signature Groups fall into a three level hierarchical structure The top level of this hierarchy is the signature Type the second level the Category and the third level the Sub Category The signature group called POLICY_DB_MSSQL illustrates this principle where Policy is the Type DB is the Category and MSSQL is the Sub Category These 3 signature components are explained below 1 Signature Group Type The gr
164. between external IP addresses with no requirement for memory allocated to a state table and there is less processing time involved in setting up each new connection The disadvantage is that it is not suitable for communication that requires a constant external IP address Fixed NAT Pools The Fixed option means that each internal client or host is allocated one of the external IP addresses through a hashing algorithm Although the administrator has no control over which of the external connections will be used this scheme ensures that the a particular internal client or host will always communicate through the same external IP address The Fixed option has the advantage of not requiring memory for a state table and providing very fast processing for new connection establishment Although explicit load balancing is not part of this option there should be spreading of the load across the external connections due to the random nature of the allocating algorithm IP Pool Usage When allocating external IP addresses to a NAT Pool it is not necessary to explicitly state these Instead a NetDefendOS IP Pool object can be selected IP Pools gather collections of IP addresses automatically through DHCP and can therefore supply external IP addresses automatically to a NAT Pool See Section 5 5 IP Pools for more details on this topic Proxy ARP Usage Where an external router sends ARP queries to the D Link Firewall to resolve external IP address
165. ble bandwidth with other traffic 10 1 9 Groups NetDefendOS provides further granularity of control within pipes through the ability to split pipe bandwidth according to either the packet s source destination network IP port or interface This is referred to as creating Groups where the members of a group sometimes called the users can have limits and guarantees applied to them The most common usage of this division of traffic is to group by IP or interface If grouping by port is used then this implicitly also includes the IP address so that port 1024 of computer A is not the same as port 1024 of computer B and individual connections are indentifiable If grouping by network is chosen the network size should be also be specified this has the same meaning as the netmask A Simple Groups Scenario If the total bandwidth limit for a pipe is 400 bps and we want to allocate this bandwidth amongst many destination IP adddresses so no one IP address can take more then 100 bps of bandwidth we select Per DestIP grouping and enter the total limit for the grouping as 100 bps Bandwidth is then allocated on a first come first forwarded basis but no one destination IP address can ever take more than 100 bps No matter how many connections are involved the combined total bandwidth can still not excede the pipe limit of 400 bps Figure 10 4 Traffic grouped per IP address 275 10 1 10 Recommendations Chapter 10 Traffic Management
166. by a TCP segment will be compared to the receive window announced by the receiving peer before the segment is forwarded If the setting is set to ValidateLogBad or ValidateSilent segments that do not match the receive window announced by the receiving peer will be dropped If the setting is set to ValidateLogBad such drops will also be logged TCP sequence number validation is only possible on connections tracked by the state engine not on packets forwarded using a FwdFast rule Default ValidateLogBad 310 13 3 ICMP Level Settings Chapter 13 Advanced Settings 13 3 ICMP Level Settings ICMPSendPerSecLimit Specifies the maximum number of ICMP messages NetDefendOS may generate per second This includes ping replies destination unreachable messages and also TCP RST packets In other words this setting limits how many Rejects per second may be generated by the Reject rules in the Rules section Default 20 per second SilentlyDropStatelCMPErrors Specifies if NetDefendOS should silently drop ICMP errors pertaining to statefully tracked open connections If these errors are not dropped by this setting they are passed to the rule set for evaulation just like any other packet Default Enabled 311 13 4 ARP Settings Chapter 13 Advanced Settings 13 4 ARP Settings ARPMatchEnetSender Determines if NetDefendOS will require the sender address at Ethernet level to comply with the hardware address reported in the ARP
167. bytes Default 2000 bytes 318 MaxOSPFLen Chapter 13 Advanced Settings MaxSKIPLen Specifies the maximum size of a SKIP packet Default 2000 bytes MaxOSPFLen Specifies the maximum size of an OSPF packet OSPF is a routing protocol mainly used in larger LANs Default 71480 MaxIPIPLen Specifies the maximum size of an IP in IP packet IP in IP is used by Checkpoint Firewall 1 VPN connections when IPsec is not used This value should be set at the size of the largest packet allowed to pass through the VPN connections regardless of its original protocol plus approx 50 bytes Default 2000 bytes Max lPCompLen Specifies the maximum size of an IPComp packet Default 2000 bytes MaxL2TPLen Specifies the maximum size of a Layer 2 Tunneling Protocol packet Default 2000 bytes MaxOtherSubIPLen Specifies the maximum size of packets belonging to protocols that are not specified above Default 1480 bytes LogOversizedPackets Specifies if NetDefendOS will log oversized packets Default Enabled 319 13 8 Fragmentation Settings Chapter 13 Advanced Settings 13 8 Fragmentation Settings IP is able to transport up to 65536 bytes of data However most media such as Ethernet cannot carry such huge packets To compensate the IP stack fragments the data to be sent into separate packets each one given their own IP header and information that will help the recipient reassemble the original p
168. c routing is most appropriate to use in smaller network deployments where addresses are fairly fixed and where the amount of connected networks are limited to a few For larger networks however or whenever the network topology is complex the work of manually maintaining static routing tables will be time consuming and problematic As a consequence dynamic routing should be used in those cases For more information about the dynamic routing capabilities of NetDefendOS please see Section 4 4 Dynamic Routing Note however that even if you choose to implement dynamic routing for your network you will still need to understand the principles of static routing and how it is implemented in NetDefendOS 4 2 1 Basic Principles of Routing IP routing is the mechanism used in TCP IP based networks for delivering IP packets from their source to their ultimate destination through a number of intermediary nodes most often referred to as routers or firewalls In each router a routing table is consulted to find out where to send the packet next A routing table usually consists of several routes where each route in principle contains a destination network an interface to forward the packet on and optionally the IP address of the next gateway in the path to the destination The images below illustrates a typical D Link Firewall deployment and how the associated routing table would look like The above routing table provides the following informa
169. cannot be used with an HTTP ALG since HTTPS traffic is encrypted 6 2 3 FTP File Transfer Protocol FTP is a TCP IP based protocol for exchanging files between a client and a server The client initiates the connection by connecting to the FTP server Normally the client needs to authenticate itself by providing a predefined login and password After granting access the server will provide the client with a file directory listing from which it can download upload files depending on access rights The FTP ALG is used to manage FTP connections through the D Link Firewall FTP Connections FTP uses two communication channels one for control commands and one for the actual files being transferred When an FTP session is opened the FTP client establishes a TCP connection the control channel to port 21 by default on the FTP server What happens after this point depends on the mode of FTP being used Connection Modes FTP operates in two modes active and passive These determine the role of the server when opening data channels between client and server In active mode the FTP client sends a command to the FTP server indicating what IP address and port the server should connect to The FTP server establishes the data channel back to the FTP client using the received address information In passive mode the data channel is opened by the FTP client to the FTP server just like the command channel This is the often recommended default
170. cate was signed by The CA certificate may in turn be signed by another CA which may be signed by another CA and so on Each certificate will be verified until one that has been marked trusted is found or until it is determined that none of the certificates were trusted If there are more certificates in this path than what this setting specifies the user certificate will be considered invalid Default 75 iPsecCertCacheMaxCerts Maximum number of certificates CRLs that can be held in the internal certificate cache When the certificate cache is full entries will be removed according to an LRU Least Recently Used algorithm Default 1024 IPsecBeforeRules Pass IKE amp IPsec ESP AH traffic sent to NetDefendOS directly to the IPsec engine without consulting the rule set Default Enabled 328 IPsecDeleteSAOnIPValidationFailure Chapter 13 Advanced Settings IPsecDeleteSAOnIPValidationFailure Controls what happens to the SAs if IP validation in Config Mode fails If Enabled the security associations SAs are deleted on failure Default Disabled 329 13 14 Logging Settings Chapter 13 Advanced Settings 13 14 Logging Settings LogSendPerSecLimit This setting limits how many log packets NetDefendOS may send out per second This value should never be set too low as this may result in important events not being logged nor should it be set too high One situation where setting too high a value may ca
171. cation was not designed to handle NAT as IP addresses and ports are sent in the payload of H 323 messages The H 323 ALG modifies and translates H 323 messages to make sure that H 323 messages will be routed to the correct destination and allowed through the D Link Firewall The H 323 ALG has the following features 156 6 2 8 H 323 Chapter 6 Security Mechanisms e The H 323 ALG supports version 5 of the H 323 specification This specification is built upon H 225 0 v5 and H 245 v10 e In addition to support voice and video calls the H 323 ALG supports application sharing over the T 120 protocol T 120 uses TCP to transport data while voice and video is transported over UDP e To support gatekeepers the ALG monitors RAS traffic between H 323 endpoints and the gatekeeper in order to correctly configure the D Link Firewall to let calls through e NAT and SAT rules are supported allowing clients and gatekeepers to use private IP addresses on a network behind the D Link Firewall H 323 ALG Configuration The configuration of the standard H 323 ALG can be changed to suit different usage scenarios The configurable options are e Allow TCP Data Channels This option allows TCP based data channels to be negotiated Data channels are used for instance by the T 120 protocol e Number of TCP Data Channels The number of TCP data channels allowed can be specified e Address Translation For NATed traffic the Network can be sp
172. ce Port numbers can be specified in several ways Single Port For many services a single destination port is sufficient HTTP for instance uses destination port 80 in most cases SMTP uses port 25 and so on For these types of Service the single port number is simply specified in the TCP UDP Service object Port Ranges Some services use a range of destination ports As an example the NetBIOS protocol used by Microsoft Windows uses destination ports 137 to 139 To define a range of ports in a TCP UDP Service object the format mmm nnn is used A port range is inclusive meaning that a range specified as 137 139 covers ports 137 138 and 139 Multiple Ports and Port Ranges Multiple ranges or individual ports may also be entered separated by commas This provides the possibility to cover a wide range of ports using only a single TCP UDP Service object For instance all Microsoft Windows networking can be covered using a port definition specified as 135 139 445 HTTP and Secure HTTP HTTPS can be covered by stating destination ports 80 443 53 3 2 2 TCP and UDP Based Services Chapter 3 Fundamentals Tip The above methods of specifying port numbers are used not just for destination ports Source port definitions can follow the same conventions although it is most usual that the source ports are left as the default value which is 0 65535 and this corresponds to all possible source ports Example 3 8 Adding a TCP UDP S
173. ce and destination addresses making certain that the packet really came from who the IP header claims it is from More on AH in AH Authentication Header Note D Link Firewalls do not support AH This specifies the encryption algorithm used in the IKE negotiation and depending on the algorithm the size of the encryption key used The algorithms supported by NetDefendOS IPsec are e AES e Blowfish e Twofish 243 9 3 2 Internet Key Exchange IKE Chapter 9 VPN IKE Authentication IKE DH Diffie Hellman Group IKE Lifetime PFS e Cast128 e 3DES e DES DES is only included to be interoperable with other older VPN implementations Use of DES should be avoided whenever possible since it is an old algorithm that is no longer considered secure This specifies the authentication algorithms used in the IKE negotiation phase The algorithms supported by NetDefendOS IPsec are e SHAI e MD5 This specifies the Diffie Hellman group to use when doing key exchanges in IKE The Diffie Hellman groups supported by NetDefendOS are e DH group 768 bit e DH group 2 1024 bit e DH group 5 1536 bit Security of the key exchanges increases as the DH group bit become larger as does the time taken for the exchanges This is the lifetime of the IKE connection It is specified in time seconds as well as data amount kilobytes Whenever one of these expires a new phase 1 exchange will be performed If
174. ceived by the D Link Firewall The following example illustrates how NAT is applied in practice on a new connection 1 The sender for example 192 168 1 5 sends a packet from a dynamically assigned port for instance port 1038 to a server for example 195 55 66 77 port 80 192 168 1 5 1038 gt 195 55 66 77 80 2 In this example the Use Interface Address option is used and we will use 195 11 22 33 as the interface address In addition the source port is changed to a free port on the D Link Firewall usually one above 32768 In this example we will use port 32789 The packet is then sent to its destination 195 11 22 33 32789 gt 195 55 66 77 80 3 The recipient server then processes the packet and sends its response 195 55 66 77 80 gt 195 11 22 33 32789 4 NetDefendOS receives the packet and compares it to its list of open connections Once it finds the connection in question it restores the original address and forwards the packet 195 55 66 77 80 gt 192 168 1 5 1038 5 The original sender receives the response Example 7 1 Adding a NAT rule To add a NAT rule that will perform address translation for all HTTP traffic originating from the internal network follow the steps outlined below CLI gw world gt add IPRule Action NAT Service http SourceInterface lan SourceNetwork lannet DestinationInterface any DestinationNetwork all nets Name NAT_HTTP NATAction UselInterfaceAddress Web Interface Go to Rules gt
175. cess choose as0 Click OK 109 4 5 Multicast Routing Chapter 4 Routing 4 5 Multicast Routing 4 5 1 Overview Certain types of Internet interactions such as conferencing and video broadcasts require a single client or host to send the same packet to multiple receivers This could be achieved through the sender duplicating the packet with different receiving IP addresses or by a broadcast of the packet across the Internet These solutions waste large amounts of sender resources or network bandwidth and are therefore not satisfactory An appropriate solution should also be able to scale to large numbers of receivers Multicast Routing solves the problem by the network routers themselves replicating and forwarding packets via the optimum route to all members of a group The IETF standards that enable Multicast Routing are 1 Class D of the IP address space which is reserved for multicast traffic Each multicast IP address represent an arbitrary group of recipients 2 The Internet Group Membership Protocol IGMP allows a receiver to tell the network that it is a member of a particular multicast group 3 Protocol Independent Multicast PIM is a group of routing protocols for deciding the optimal path for multicast packets Multicast routing operates on the principle that an interested receiver joins a group for a multicast by using the IGMP protocol PIM routers can then duplicate and forward packets to all members of suc
176. cest 49 3 2 Adding an IP Networks iiss ctu eo iy eas Hie Ea hss ped ot RES ate 49 3 3 Adding an IP Ran 6st ss cote a Suedunde pe setacs ATER stance AT E ESAE eae SER 49 3 4 Deleting an Address Object eeror sosete ienn T teen T r E TES RER 50 3 5 Adding n Ethernet Address aieiaa e a E E a t 50 3 6 Listing the Available Services 0 0 0 0 cece cece cee ceeece seen teen ceca eeee cena eens een eeeeeeeneeenea 52 3 7 Viewing a Specific SeryiC isseire nier rms tri Seis NEI SENER Es odes cs t SIERE SPRAT ESEE 52 3 8 Adding a TCP UDP Service prrs ros sonir a E E SEEE ES E 54 3 9 Adding an IP Protocol Service circos tenp noian a oea EE oS 56 3 10 Enabling DHCP oi 2 25cie ten nei re Aane EEE TEEN EES EE EK EEES EENS EEES 59 3 11 Defining a VLAN s drepes rsr saaesd repie ap EE whens s Sas ieeaee syste ads sees seu suetangessosar 61 3 12 Configuring a PPPoE client on the wan interface with traffic routed over PPPoE 62 3 13 Creating an Interface Group vsi inre ee cece nec aE ceca cena EEE eA E aE 66 3 14 Displaying the ARP Cache sype openee ee RE EPER obey SEREEN EE REEE 69 3 15 Flushing the ARP Gachessse ire eee onea E E T ENO NE ET RS 69 3 16 Defining a Stati ARP ENY sperii na an E E E NE a DE E 70 3 17 Setting up a Time Scheduled Policy eseeeseeeesseesrreessrrrrsrrerrererrsrrerrereerreresee 77 3 18 Uploading an X 509 Certificate oseere orne rore esi pE tone Teos Ei PERES TAES ES EPE Ee Sii 80 3 19 Associating X 50
177. ch a matching rule does NetDefendOS execute the SAT rule 7 3 1 Translation of a Single IP Address 1 1 The simplest form of SAT usage is translation of a single IP address A very common scenario for this is to enable external users to access a protected server having a private address This scenario is also sometimes referred to as a Virtual IP or Virtual Server in some other manufacturer s products Example 7 3 Enabling Traffic to a Protected Web Server in a DMZ In this example we will create a SAT policy that will translate and allow connections from the Internet to a web server located in a DMZ The D Link Firewall is connected to the Internet using the wan interface with address object wan_ip defined as 195 55 66 77 as IP address The web server has the IP address 10 10 10 5 and is reachable through the dmz interface CLI First create a SAT rule gw world gt add IPRule Action SAT Service http SourceInterface any SourceNetwork all nets DestinationInterface core DestinationNetwork wan_ip SATTranslate DestinationIP SATTranslateToIP 10 10 10 5 Name SAT_HTTP_To_DMZ Then create a corresponding Allow rule gw world gt add IPRule action Allow Service http SourceInterface any SourceNetwork all nets DestinationInterface core DestinationNetwork wan_ip Name Allow_HTTP_To_DMZ Web Interface First create a SAT rule Go to Rules gt IP Rules gt Add gt IPRule Specify a suitable name for the rule eg SAT_HTTP_To_DMZ Now ent
178. ch is typically signed by itself A certification path refers to the path of certificates from one certificate to another When verifying the validity of a user certificate the entire path from the user certificate up to the trusted root certificate has to be examined before establishing the validity of the user certificate The CA certificate is just like any other certificates except that it allows the corresponding private key to sign other certificates Should the private key of the CA be compromised the whole CA including every certificate it has signed is also compromised Validity Time A certificate is not valid forever Each certificate contains the dates between which the certificate is valid When this validity period expires the certificate can no longer be used and a new certificate 79 3 7 2 X 509 Certificates in Chapter 3 Fundamentals NetDefendOS has to be issued Certificate Revocation Lists A Certificate Revocation List CRL contains a list of all certificates that have been cancelled before their expiration date This can happen for several reasons One reason could be that the keys of the certificate have been compromised in some way or perhaps that the owner of the certificate has lost the rights to authenticate using that certificate This could happen for instance if an employee has left the company from whom the certificate was issued A CRL is regularly published on a server that all certificat
179. ch traffic will pass A chain can be made up of at most 8 pipes If no pipe is specified in a list then traffic that matches the rule will not flow through any pipe but it will also mean that the traffic will not be subject to any other pipe rules found later in the rule set 10 1 3 Simple Bandwidth Limiting The simplest use of pipes is for bandwidth limiting This is also a scenario that doesn t require much planning The example that follows applies a bandwidth limit to inbound traffic only This is the direction most likely to cause problems for Internet connections Example 10 1 Applying a Simple Bandwidth Limit Begin with creating a simple pipe that limits all traffic that gets passed through it to 2 megabits per second regardless of what traffic it is CLI gw world gt add Pipe std in LimitKbpsTotal 2000 Web Interface Go to Traffic Management gt Traffic Shaping gt Pipes gt Add gt Pipe Specify a suitable name for the pipe for instance std in Enter 2000 in Total textbox Click OK Traffic needs to be passed through the pipe and this is done by using the pipe in a Pipe Rule We will use the above pipe to limit inbound traffic This limit will apply to the the actual data packets and not the connections In traffic shaping we re interested in the direction that data is being shuffled not which computer initiated the connection Create a simple rule that allows everything from the inside going out We add the pipe
180. client may also decide at any time that it no longer wishes to use the IP address it was assigned and may terminate the lease and release the IP address The lease time can be configured in a DHCP server by the administrator 127 5 2 DHCP Servers Chapter 5 DHCP Services 5 2 DHCP Servers NetDefendOS has the ability to act as one or more logical DHCP servers Filtering of DHCP client requests is based on interface so each NetDefendOS interface can have at most one single logical DHCP server associated with it In other words NetDefendOS can provision DHCP clients using different address ranges depending on what interface they are located on A number of standard options can be configured for each DHCP server instance e IP Address e Netmask netmask sent to the DHCP Client Subnet e Gateway Address what IP should be sent to the client for use as the default gateway If 0 0 0 0 is specified the IP given to the client will be sent as the gateway e Domain Name e Lease Time the time in seconds that a DHCP lease should be provided to a host after which the client must renew the lease e DNS Servers e WINS Servers e Next Server the IP address of the next server in the boot process this is usually a TFTP server In addition Custom Options can be specified in order to have the DHCP servers hand out all types of options supported by the DHCP standard DHCP servers assign and manage the IP addresses taken the
181. com au e www putsandcalls com Category 12 E Banking A web site may be classified under the E Banking category if its content includes electronic banking information or services This category does not include Investment related content refer to the Investment Sites category 11 Examples might be e www nateast co uk e www borganfanley com Category 13 Crime Terrorism A web site may be classified under the Crime Terrorism category if its content includes the description promotion or instruction in criminal or terrorist activities cultures or opinions Examples might be e www beatthecrook com Category 14 Personal Beliefs Cults A web site may be classified under the Personal Beliefs Cults category if its content includes the description or depiction of or instruction in systems of religious beliefs and practice Examples might be e www paganfed demon co uk e www cultdeadcrow com Category 15 Politics A web site may be classified under the Politics category if its content includes information or opinions of a political nature electoral information and including political discussion groups Examples might be e www democrats org au e www political com Category 16 Sports A web site may be classified under the Sports category if its content includes information or instructions relating to recreational or professional sports or reviews on sporting events and sports scores Examples might be e www
182. cribes the high availability fault tolerance feature in D Link Firewalls e Overview page 289 e High Availability Mechanisms page 291 e High Availability Setup page 293 e High Availability Issues page 296 11 1 Overview High Availability is a fault tolerant capability that is available on certain models of D Link Firewalls Currently the firewalls that offer this feature are the DFL 1600 and DFL 2500 models The pre installed licenses for these models include HA support HA Clusters D Link High Availability HA works by adding a back up slave D Link Firewall to an existing master firewall The master and slave are connected together and make up a logical HA Cluster One of the units in a cluster will be active when the other unit is inactive and on standby Initially the slave will be inactive and will monitor the master If the slave detects that the master is not responding a failover takes place and the slave becomes active If the master later regains full functionality the slave will continue to be active with the master now monitoring the slave and failover only taking place if the slave fails This is sometimes known as an active passive HA implementation The Master and Active Units It should be kept in mind that the master unit in a cluster is not always the same as the active unit The active unit is the D Link Firewall that is processing all traffic at a given point in time This could be the slave if a failover has occu
183. curred This results in an email being sent containing a summary of the IDP events Several more IDP events may occur after this but to prevent flooding the mail server NetDefendOS will wait 600 seconds equivalent to 10 minutes before sending a new email An SMTP server is assumed to have been configured in the address book with the name smtp server CLI Adding an SMTP log receiver gw world gt add LogReceiver LogReceiverSMTP smt4IDP IPAddress smtp server Receiverl youremail yourcompany com IDP Rules gw world gt cc IDPRule examplerule gw world examplerule gt set IDPRuleAction 1 LogEnabled Yes Web Interface Adding an SMTP log receiver Go to System gt Log and Event Receivers gt Add gt SMTP Event Receiver Now enter Name smtp4IDP SMTP Server smtp server Server Port 25 Specify alternative email addresses up to 3 Sender hostmaster Subject Log event from NetDefendOS Minimum Repeat Delay 600 Hold Time 120 Log Threshold 2 Click OK IDP Rules Go to IDP gt IDP Rules Select a rule in the grid right click and choose Edit Select the action you wish to log and choose Edit Check the Enable logging checkbox in the Log Settings tab Click OK Example 6 20 Setting up IDP for a Mail Server The following example details the steps needed to set up IDP for a simple scenario where a mail server is exposed to the Internet on the DMZ network with a public IP address The public Internet can be reached through th
184. d for a rule that matches the packet The following parameters are part of the matching process e Source and destination interfaces e Source and destination network e IP protocol for example TCP UDP ICMP e TCP UDP ports e ICMP types e Point in time in reference to a pre defined schedule If a match cannot be found the packet is dropped If a rule is found that matches the new connection the Action parameter of the rule decides what NetDefendOS should do with the connection If the action is Drop the packet is dropped 17 1 2 3 Basic Packet Flow Chapter 1 Product Overview 10 11 and the event is logged according to the log settings for the rule If the action is Allow the packet is allowed through the system A corresponding state will be added to the connection table for matching subsequent packets belonging to the same connection In addition the Service object which matched the IP protocol and ports might have contained a reference to an Application Layer Gateway ALG object This information is recorded in the state so that NetDefendOS will know that application layer processing will have to be performed on the connection Finally the opening of the new connection will be logged according to the log settings of the tule Note There are actually a number of additional actions available such as address translation and server load balancing The basic concept of dropping and allowing traffic is still the
185. d procedures for providing such multimedia communication including Internet phone and voice over IP VoIP For VOIP see also Section 6 2 7 SIP H 323 Components H 323 consists of four main components Terminals Devices used for audio and optionally video or data communication such as phones conferencing units or software phones such as the product NetMeeting 155 6 2 8 H 323 Chapter 6 Security Mechanisms Gateways Gatekeepers Multipoint Control Units H 323 Protocols An H 323 gateway connects two dissimilar networks and translates traffic between them It provides connectivity between H 323 networks and non H 323 networks such as public switched telephone networks PSTN translating protocols and converting media them A gateway is not required for communication between two H 323 terminals The Gatekeeper is a component in the H 323 system which is used for addressing authorization and authentication of terminals and gateways It can also take care of bandwidth management accounting billing and charging The gatekeeper may allow calls to be placed directly between endpoints or it may route the call signaling through itself to perform functions such as follow me find me forward on busy etc It is needed when there is more then one H 323 terminal behind a NATing device with only one public IP MCUs provide support for conferences of three or more H 323 terminals All H 323 terminals participat
186. dates the information against the Authentication Source specified in the authentication rule This will be either a local NetDefendOS database or an external RADIUS database server 7 NetDefendOS then allows further traffic through this connection as long as authentication was successful and the service requested is allowed by a rule in the IP rule set That rule s Source Network object has either the No Defined Credentials option enabled or alternatively it is associated with a group and the user is also a member of that group 8 If a timeout restriction is specified in the authentication rule then the authenticated user will be automatically logged out after that length of time without activity Any packets from an IP address that fails authentication are discarded unless they are caught be another rule 8 2 6 HTTP Authentication Where users are communicating through a web browser using the HTTP protocol then authentication can be done by presenting the user with HTML pages to retrieve required user information This is sometimes referred to as WebAuth and the setup requires further considerations 223 8 2 6 HTTP Authentication Chapter 8 User Authentication Changing the Management WebUI Port HTTP authentication will collide with the WebUI s remote management service which also uses TCP port 80 To avoid this the WebUI port number should be changed before configuring authentication Do this by going to Remote Management gt
187. ddress Objects Example 3 10 Enabling DHCP CLI 59 3 3 3 VLAN Chapter 3 Fundamentals gw world gt set Interface Ethernet wan DHCPEnabled Yes Web Interface Go to Interfaces gt Ethernet In the grid click on the ethernet object of interest Enable the Enable DHCP client option Click OK 3 3 3 VLAN Overview Virtual LANs VLANs are useful in several different scenarios for instance when filtering of traffic is needed between different VLANs in an organization or for any other reason where the administrator would like to expand the number of interfaces Virtual LAN support in NetDefendOS allows the definition of one or more Virtual LAN interfaces to be associated with a particular physical interface These are then considered to be logical interfaces by NetDefendOS and can be treated like physical interfaces in rule sets and routing tables VLAN Operation NetDefendOS follows the IEEE 802 1Q specification for VLAN On a protocol level VLAN works by adding a Virtual LAN Identifier VLAN ID to Ethernet frame headers The VLAN ID is a number from 0 up to 4095 which is used to identify the specific Virtual LAN to which the frame belongs In this way Ethernet frames can belong to different Virtual LANs but can still share the same physical interface With NetDefendOS the VLAN ID must be unique for the physical interface and the same VLAN ID can be used on different physical interfaces Packets recei
188. de a dropdown list containing all available categories If the user believes the requested web site is wrongly classified he can select a more appropriate category from the dropdown list and submit that as a proposal The URL to the requested web site as well as the proposed category will then be sent to D Link s central data warehouse for manual inspection That inspection may result in the web site being reclassified either according to the category proposed or to a category which is felt to be correct 175 6 3 4 Dynamic Web Content Filtering Chapter 6 Security Mechanisms Example 6 17 Reclassifying a blocked site This example shows how a user may propose a reclassification of a web site if he believes it is wrongly classified This mechanism is enabled on a per HTTP ALG level basis CLI First create an HTTP Application Layer Gateway ALG Object gw world gt add ALG ALG_HTTP content_filtering WebContentFilteringMode Enable FilteringCategories SEARCH_SITES AllowReclassification Yes Then continue setting up the service object and modifing the NAT rule as we have done in the previous examples Web Interface First create an HTTP Application Layer Gateway ALG Object Go to Objects gt ALG gt Add gt HTTP ALG Specify a suitable name for the ALG eg content_filtering Click the Web Content Filtering tab Select Enabled in the Mode list In the Blocked Categories list select Search Sites and click the gt gt b
189. dio 346 Appendix C Checked MIME filetypes 347 Appendix D The OSI Framework The Open Systems Interconnection Model defines a framework for intercomputer communications It categorizes different protocols for a great variety of network applications into seven smaller more manageable layers The model describes how data from an application in one computer can be transferred through a network medium to an application on another computer Control of data traffic is passed from one layer to the next starting at the application layer in one computer proceeding to the bottom layer traversing over the medium to another computer and then delivering up to the top of the hierarchy Each layer handles a certain set of protocols so that the tasks for achieving an application can be distributed to different layers and be implemented independently Figure D 1 The 7 layers of the OSI model The different layers perform the following functions Application Layer Defines the user interface that supports applications directly Protocols HTTP FTP DNS SMTP Telnet SNMP etc Presentation Layer Translates the various applications to uniform network formats that the rest of the layers canunderstand Session Layer Establishes maintains and terminates sessions across the network Protocols NetBIOS RPC etc Transport Layer Controls data flow and provides error handling Protocols TCP UDP etc Network Layer Perform
190. e 47 Chapter 3 Fundamentals This chapter describes the fundamental logical objects upon which NetDefendOS is built These objects include such things as addresses services and schedules In addition the chapter explains how the various supported interfaces work it outlines how secuirty policies are constructed and how basic system settings are configured e The Address Book page 48 e Services page 52 e Interfaces page 57 e ARP page 68 e The IP Rule Set page 73 e Schedules page 77 e X 509 Certificates page 79 e Setting Date and Time page 82 e DNS Lookup page 87 3 1 The Address Book 3 1 1 Overview The Address Book contains named objects representing various types of addresses including IP addresses networks and Ethernet MAC addresses Using Address Book objects has three distinct benefits it increases readability reduces the danger of entering incorrect network addresses and makes it easier to change addresses By using objects instead of numerical addresses you only need to make changes in a single location rather than in each configuration section where the address appears 3 1 2 IP Addresses IP Address objects are used to define symbolic names for various types of IP addresses Depending on how the address is specified an IP Address object can represent either a host a single IP address a network or a range of IP addresses In addition IP Address objects can be used for specifying
191. e Figure 1 3 Packet Flow Schematic Part III 20 1 3 NetDefendOS State Engine Packet Chapter 1 Product Overview Flow false Apply Rules ry SAT il Br FwdFast SAT ApplyR ulePack Route lookup DestIP FW a No ey f 1 3 NetDefendOS State Engine Packet Chapter 1 Product Overview Flow 22 Chapter 2 Management and Maintenance This chapter describes the management operations and maintenance related aspects of NetDefendOS e Managing NetDefendOS page 23 e Events and Logging page 35 e RADIUS Accounting page 39 e Monitoring page 43 e Maintenance page 45 2 1 Managing NetDefendOS 2 1 1 Overview NetDefendOS is designed to give both high performance and high reliability Not only does it provide an extensive feature set it also enables the administrator to be in full control of almost every detail of the system This means the product can be deployed in the most challenging environments A good understanding on how NetDefendOS configuration is performed is crucial for proper usage of the system For this reason this section provides an in depth presentation of the configuration subsystem as well as a description of how to work with the various management interfaces Management Interfaces NetDefendOS provides the following management interfaces The WebUI The Web User Interface WebUD provides a user friendly and intuitive graphical management interface accessibl
192. e 1 2 1 State based Architecture The NetDefendOS architecture is centered around the concept of state based connections Traditional IP routers or switches commonly inspect all packets and then perform forwarding decisions based on information found in the packet headers With this approach packets are forwarded without any sense of context which eliminates any possibility to detect and analyze complex protocols and enforce corresponding security policies Stateful Inspection NetDefendOS employs a technique called stateful inspection which means that it inspects and forwards traffic on a per connection basis NetDefendOS detects when a new connection is being established and keeps a small piece of information or state in it s state table for the lifetime of that connection By doing this NetDefendOS is able to understand the context of the network traffic which enables it to perform in depth traffic scanning apply bandwidth management and much more The stateful inspection approach additionally provides high throughput performance with the added advantage of a design that is highly scalable The NetDefendOS subsystem that implements stateful inspection will sometimes be referred to in documentation as the NetDefendOS state engine 1 2 2 NetDefendOS Building Blocks The basic building blocks in NetDefendOS are interfaces logical objects and various types of rules or rule sets Interfaces Interfaces are the doorways for network traf
193. e attacker now deliberately sends two packets p2 and p3 which will be rejected by the application but accepted by the IDP system The IDP system is now able to complete reassembly of the packets and believes it has the full data stream The attacker now sends two futher packets p2 and p3 which will be accepted by the application which can now complete reassembly but resulting in a different data stream to that seen by the IDP subsystem Evasion Attacks An evasion attack has a similar end result to the Insertion Attack in that it also generates two different data streams one that the IDP subsystem sees and one that the target application sees but it is achieved in the reverse way It consists of sending data packets that are rejected by the IDP subsystem but are acceptable to the target application Detection Action If an Insertion Evasion Attack is detected with the Insertion Evasion Protect option enabled NetDefendOS automatically corrects the data stream by removing the extraneous data associated with the attack Insertion Evasion Log Events The Insertion Evasion Attack subsystem in NetDefendOS can generate two types of log message e An Attack Detected log message indicating an attack has been indentified and prevented e An Unable to Detect log message when NetDefendOS has been unable to identify potential attacks when reassembling a TCP IP stream although such an attack may have been present This condition is caused by infreq
194. e local LAN as they will keep the old hardware address in their ARP caches until it times out Such units would have to have their ARP caches flushed Secondly this breaks the connection between the firewalls in the cluster for as long as they are using different configurations This will cause both firewalls to go active at the same time Invalid Checksums in Heartbeat Packets Cluster Heartbeats packets are deliberately created with invalid checksums This is done so that they won t be routed Some routers may flag this invalid checksum in their log messages 296 11 4 High Availability Issues Chapter 11 High Availability 297 Chapter 12 ZoneDefense This chapter describes the D Link ZoneDefense feature e Overview page 298 e ZoneDefense Switches page 299 e ZoneDefense Operation page 300 12 1 Overview ZoneDefense allows a D Link Firewall to control locally attached switches It can be used as a counter measure to stop a virus infected computer in a local network from infecting other computers When hosts or clients on a network become infected with viruses or another form of malicious code this can often show its presence through anomalous behaviour often by large numbers of new connections being opened to outside hosts By setting up Threshold Rules hosts or networks that are exceeding a defined connection threshold can be dynamically blocked using the ZoneDefense feature Thresholds are based on either
195. e 7 5 Translating Traffic to Multiple Protected Web Servers In this example we will create a SAT policy that will translate and allow connections from the Internet to five web servers located in a DMZ The D Link Firewall is connected to the Internet using the wan interface and the public IP addresses to use are in the range of 195 55 66 77 to 195 55 66 81 The web servers have IP addresses in the range 10 10 10 5 to 10 10 10 9 and they are reachable through the dmz interface To accomplish the task the following steps need to be performed Define an address object containing the public IP addresses Define another address object for the base of the web server IP addresses Publish the public IP addresses on the wan interface using the ARP publish mechanism Create a SAT rule that will perform the translation Create an Allow rule that will permit the incoming HTTP connections CLI Create an address object for the public IP addresses gw world gt add Address IP4Address wwwsrv_pub Address 195 55 66 77 195 55 66 81 Now create another object for the base of the web server IP addresses gw world gt add Address IP4Address wwwsrv_priv_base Address 10 10 10 5 Publish the public IP addresses on the wan interface using ARP publish One ARP item is needed for every IP address gw world gt add ARP Interface wan IP 195 55 66 77 mode Publish Repeat for all the five public IP addresses Create a SAT rule for the translation gw world
196. e Document Format pe Portable Executable file pfb PostScript Type 1 Font pgm Portable Graymap Graphic pkg SysV R4 PKG Datastreams pll PAKLeo archive data pma PMarc archive data png Portable Public Network Graphic ppm PBM Portable Pixelmap Graphic ps PostScript file psa PSA archive data psd Photoshop Format file qt mov moov QuickTime Movie file qxd QuarkXpress Document ra ram RealMedia Streaming Media rar WinRAR compressed archive rbs ReBirth Song file riff rif Microsoft Audio file rm RealMedia Streaming Media rpm RedHat Package Manager rtf wri Rich Text Format file sar Streamline compressed archive sbi SoundBlaster instrument data sc SC spreadsheet sgi Silicon Graphics IRIS Graphic file sid Commodore64 C64 Music file SID file sit Stufflt archives sky SKY compressed archive snd au Sun NeXT audio file so UNIX Shared Library file sof ReSOF archive sqw SQWEZ archive data sqz Squeeze It archive data stm Scream Tracker v2 Module svg Scalable Vector Graphics file svr4 SysV R4 PKG Datastreams swf Macromedia Flash Format file tar Tape archive file tfm TeX font metric data tiff tif Tagged Image Format file tnef Transport Neutral Encapsulation Format torrent BitTorrent Metainfo file ttf TrueType Font txw Yamaha TX Wave audio files ufa UFA archive data vcf Vcard file viv VivoActive Player Streaming Video file wav Waveform Au
197. e Dynamic Content Filtering is a powerful feature that enables the administrator to allow or block access to web sites depending on the category they have been classified into by an automatic classification service Dynamic content filtering requires a minimum of administration effort and has very high accuracy All Web Content Filtering is enabled via the HTTP Application Layer Gateway see Section 6 2 2 HTTP 6 3 2 Active Content Handling Some web content can contain malicious code designed to harm the workstation or the network from where the user is surfing Typically such code is embedded into various types of objects or files which are embedded into web pages NetDefendOS includes support for removing the following types of objects from web page content e ActiveX objects including Flash e Java applets e Javascript VBScript code e Cookies e Invalidly formatted UTF 8 Characters invalid URL formatting can be used to attack webservers The object types to be removed can be selected individually by configuring the corresponding HTTP Application Layer Gateway accordingly Caution tu Care should be taken before enabling removal of objects from web content Many web sites use Javascript and other types of client side code and in most cases the code is non malicous Common examples of this is the scripting used to implement drop down menus as well as hiding and showing elements on web pages Removing such legitimate cod
198. e IP rule set meaning that everything is denied In order to permit any traffic including NetDefendOS responding to ICMP Ping requests IP rules must be defined by the administrator that allow traffic to traverse the D Link Firewall Although dropping packets is achieved without an explicit IP rule for logging purposes it is recommended that a Drop IP rule with logging enabled is placed as the last rule in the IP rule set 3 5 2 IP Rule Evaluation When a new TCP IP connection is being established through the D Link Firewall the list of IP rules are evaluated from top to bottom until a rule that matches the parameters of the new connection is found The rule s Action is then performed If the action allows it then the establishment of the new connection will go ahead A new entry or State representing the new connection will then be added to NetDefendOS s internal state table which allows monitoring of opened and active connections passing through the D Link Firewall If the action is Drop or Reject then the new connection is refused Stateful Inspection After initial rule evaluation of the opening connection subsequent packets belonging to that connection will not need to be evaluated individually against the rule set Instead a highly efficient algorithm searches the state table for each packet to determine if it belongs to an established connection This approach is known as stateful inspection and is applied not only to stateful protoc
199. e Interface any Source Network all nets Destination Interface core Destination Network wwwsrv_pub Switch to the SAT tab Make sure that the Destination IP Address option is selected In the New IP Address dropdown list select wwwsrv_priv Click OK Finally create a corresponding Allow Rule Go to Rules gt IP Rules gt Add gt IPRule Specify a suitable name for the rule eg Allow_HTTP_To_DMZ Now enter Action Allow Service http Source Interface any Source Network all nets Destination Interface core Destination Network wwwsrv_pub Click OK 7 3 3 All to One Mappings N 1 215 7 3 4 Port Translation Chapter 7 Address Translation NetDefendOS can be used to translate ranges and or groups into just one IP address This rule produces a N 1 translation of all addresses in the group the range 194 1 2 16 194 1 2 20 and 194 1 2 30 to the IP 192 168 0 50 e Attempts to communicate with 194 1 2 16 port 80 will result in a connection to 192 168 0 50 e Attempts to communicate with 194 1 2 30 port 80 will result in a connection to 192 168 0 50 Note When all nets is the destination All to One mapping is always done 7 3 4 Port Translation Port Translation also known as Port Address Translation PAT can be used to modify the source or destination port This rule produces a 1 1 translation of all ports in the range 80 85 to the range 1080 1085 e Attempts to communicate with the web se
200. e added to the list Header The header row displays the titles of the columns in the list The tiny arrow images next to each title can be used for sorting the list according to that column Rows Each row in the list corresponds to one configuration item Most commonly each row starts with the name of the object if the item has a name followed by values for the columns in the list A single row in the list can be selected by clicking on the row on a spot where there is no hyperlink The background color of the row will turn dark blue Right clicking the row will bring up a menu where you can choose to edit or delete the object as well as modify the order of the objects Example 2 4 Displaying a Configuration Object The most simple operation on a configuration object is just to show its contents in other words the values of the object properties This example shows how to display the contents of a configuration object representing the telnet service CLI gw world gt show Service ServiceTCPUDP telnet Property telnet DestinationPorts 23 hype TCE SOurcePorts U0 65505 SYNRelay No PassICMPReturn No ALG none MaxSessions 1000 Comments Telnet The Property column lists the names of all properties in the ServiceTCPUDP class and the Value column lists the corresponding property values Web Interface 1 Goto Objects gt Services 2 Click on the telnet hyperlink in the list 3 A web page displaying the telnet ser
201. e an Identification List 1 Goto Objects gt VPN Objects gt ID List gt Add gt ID List 2 Enter a name for the identification list eg My DList 3 Click OK Then create an ID Go to Objects gt VPN Objects gt ID List In the grid control click on MyIDList Enter a name for the ID eg JohnDoe Select Distinguished name in the Type control Now enter Common Name John Doe Organization Name D Link Organizational Unit Support Country Sweden Email Address john doe D Link com 6 Click OK Finally apply the Identification List to the IPsec tunnel Go to Interfaces gt IPsec In the grid control click on the IPsec tunnel object of interest Under the Authentication tab choose X 509 Certificate Select the appropriate certificate in the Root Certificate s and Gateway Certificate controls Select MyIDList in the Identification List Click OK 252 9 4 IPsec Tunnels Chapter 9 VPN 9 4 IPsec Tunnels 9 4 1 Overview An IPsec Tunnel defines an endpoint of an encrypted tunnel Each IPsec Tunnel is interpreted as a logical interface by NetDefendOS with the same filtering traffic shaping and configuration capabilities as regular interfaces When another D Link Firewall or D Link VPN Client or any IPsec compliant product tries to establish a IPsec VPN tunnel to the D Link Firewall the configured IPsec Tunnels are evaluated If a matching IPsec Tunnel definition is found the IKE and IPsec negotiations then take
202. e basic options available for an IP Pool are DHCP Server behind interface Indicates that the IP pool should use the DHCP server s residing on the specified interface Server filter Optional setting used to specify which servers to use If unspecified any DHCP server on the interface will be used The order of the provided adddress or ranges if multiple will be used to indicate the preferred servers Specify DHCP Server Address Specify DHCP server IP s in preferred ascending order to be used Using the IP loopback address 127 0 0 1 indicates that the DHCP server is NetDefendOS itself Client IP filter Optional setting used to specify which offered IPs are valid to use In most cases this will be set to the default of all nets Alternatively a set of IP ranges might be specified The filter ensures that only certain IP addresses from DHCP servers are acceptable and is used in the situation where there might be a DHCP server response with an unacceptable IP address Advanced IP Pool Options Advanced options available for IP Pool configuration are Routing table Policy routing table to be used for lookups when resolving the destination interfaces for the configured DHCP servers Receive interface Simulated receive interface This can be used in policy based routing rules and or used to trigger a specific DHCP server rule if the pool is using a DHCP server in NetDefendOS and the IP address of that server has been specified as the loopb
203. e could at best cause the web site to look distorted at worst cause it to not work in a browser at all Active Content Handling should therefore only be used when the consequences are well understood 169 6 3 3 Static Content Filtering Chapter 6 Security Mechanisms Example 6 13 Stripping ActiveX and Java applets This example shows how to configure a HTTP Application Layer Gateway to strip ActiveX and Java applets The example will use the content_filtering ALG object and presumes you have done one of the previous examples CLI gw world gt set ALG ALG_HTTP content_filtering RemoveActiveX Yes RemoveApplets Yes Web Interface Go to Objects gt ALG In the grid click on our HTTP ALG obejct content_filtering Check the Strip ActiveX objects including flash control Check the Strip Java applets control Click OK 6 3 3 Static Content Filtering NetDefendOS can block or permit certain web pages based on configured lists of URLs which are called blacklists and whitelists This type of filtering is also known as Static Content Filtering The main benefit with Static Content Filtering is that it is a excellent tool to target specific web sites and make the decision as to whether they should be blocked or allowed Static and Dynamic Filter Ordering Additionally Static Content Filtering takes place before Dynamic Content Filtering described below which allows the possibility of manually making exceptions from the a
204. e firewall on the WAN interface as illustrated below 195 6 5 8 SMTP Log Receiver for IDP Chapter 6 Security Mechanisms Events CLI Create IDP Rule gw world gt add IDPRule Service smtp SourceInterface wan SourceNetwork wannet DestinationInterface dmz DestinationNetwork ip_mailserver Name IDPMailSrvRule Create IDP Action gw world gt cc IDPRule IDPMailSrvRule gw world IDPMailSrvRule gt add IDPRuleAction Action Protect IDPServity All Signatures IPS MATL SMTP Web Interface Create IDP Rule This IDP rule will be called IDPMailSrvRule and applies to the SMTP service Source Interface and Source Network define where traffic is coming from in this example the external network The Destination Interface and Destination Network define where traffic is directed to in this case the mail server Destination Network should therefore be set to the object defining the mail server Go to IDP gt IDP Rules gt Add gt IDP Rule Now enter Name IDPMailSrvRule Service smtp Also inspect dropped packets In case all traffic matching this rule should be scanned this also means traffic that the main rule set would drop the Also inspect dropped packets checkbox should be checked which is the case in this example Source Interface wan Source Network wannet Destination Interface dmz Destination Network ip_mailserver Click OK If logging of intrusion attempts is desired this can be configured in the Log Setti
205. e from a standard web browser The CLI The Command Line Interface CLI accessible locally via serial console port or remotely using the Secure Shell SSH protocol provides the most fine grain control over all parameters in NetDefendOS Note Microsoft Internet Explorer version 6 and later Firefox and Netscape version 8 and later are the recommended web browsers to use with the WebUI Other browsers may also provide full support Access to remote management interfaces can be regulated by a remote management policy so the administrator can restrict management access based on source network source interface and credentials Access to the web interface can be permitted for administrative users on a certain network while at the same time allowing CLI access for a remote administrator connecting through a specific IPsec tunnel By default Web User Interface access is enabled for users on the network connected via the LAN interface of the firewall on products where more than one LAN interface is available LAN1 is the default 2 1 2 Default Administrator Accounts 23 2 1 3 The CLI Chapter 2 Management and Maintenance By default NetDefendOS has a local user database AdminUsers with one user account pre defined e Username admin with password admin This account has full administrative read write privileges Important Q For security reasons it is recommended to change the default password of the default account as
206. e is then forwarded on a first come first forwarded basis Note Setting a maximum limit for the lowest Best Effort precedence or any lower precedences has no meaning and will be ignored by NetDefendOS 10 1 8 Differentiated Guarantees A problem arrises if you want to give a specific 32 kbps guarantee to Telnet traffic and a specific 64 kbps guarantee to SSH traffic You could set a 32 kbps limit for precedence 2 a 64 kbps limit for precedence 4 and pass the different types of traffic through each respective precedence However there are two obvious problems with this approach e Which traffic is more important This question does not pose much of a problem here but it becomes more pronounced as your traffic shaping scenario becomes more complex e The number of precedences is limited This may not be sufficient in all cases even barring the which traffic is more important problem The solution here is to create two new pipes one for telnet traffic and one for SSH traffic much like the surf pipe that we created earlier on First remove the 96 kbps limit from the std in pipe then create two new pipes ssh in and telnet in Set the default precedence for both pipes to 2 and the precedence 2 limits to 32 and 64 kbps respectively Then split the previously defined rule covering ports 22 through 23 into two rules covering 22 and 23 respectively Keep the forward chain of both rules as std out only Again to simplify t
207. e needs to be routed to the core interface By default the multicast IP range 224 0 0 0 4 is always routed to core and does not have to be manually added to the routing tables Each specified output interface can individually be configured with static address translation of the destination address The Interface field in the Interface Net Tuple dialog may be left empty if the IPAddress field is set In this case the output interface will be determined by a route lookup on the specified IP address 110 4 5 2 Multicast Forwarding using the Chapter 4 Routing SAT Multiplex Rule The multiplex rule can operate in one of two modes Use IGMP The traffic flow specififed by the multiplex rule must have been requested by hosts using IGMP before any multicast packets are forwarded through the specified interfaces This is the default behaviour of NetDefendOS Not using IGMP The traffic flow will be forwarded according to the specified interfaces directly without any inference from IGMP Note Since the Multiplex rule is a SAT rule an Allow or NAT rule has to be specified together with the Multiplex rule 4 5 2 1 Multicast Forwarding No Address Translation This scenario describes how to configure multicast forwarding together with IGMP The multicast sender is 192 168 10 1 and generates the multicast streams 239 192 10 0 24 1234 These multicast streams should be forwarded from interface wan through the interfaces if1 if2 and if3 The
208. e of an authentication address object in the Address Book a user group users is used to enable user authentication on lannet This example shows how to configure the user group in the NetDefendOS database Web Interface Step A Go to User Authentication gt Local User Databases gt Add gt LocalUserDatabase Now enter Name lannet_auth_users e Comments folder for lannet authentication user group users Click OK Step B Go to lannet_auth_users gt Add gt User Now enter Username Enter the user s account name eg user Password Enter the user s password Confirm Password Repeat the password Groups One user can be specified into more than one group Enter the group names here separated by comma eg users for this example Click OK Repeat Step B to add all the annet users having the membership of users group into the Jannet_auth_users folder Example 8 2 User Authentication Setup for Web Access The configurations below shows how to enable HTTP user authentication for the user group users on annet Only users that belong to the group users can get Web browsing service after authentication as it is defined in the IP rule We assume that annet users lan_ip local user database folder lannet_auth_users and an authentication address object Jannet_users have been specified Web Interface A Set up an IP rule to allow authentication 1 Goto Rules gt IP Rules gt Add gt IP rule 2 Now en
209. e phone incoming traffic need to be SATed as in the example below The object ip phone below should be the internal IP of the H 323 phone Web Interface Outgoing Rule Go to Rules gt IP Rules gt Add gt IPRule Now enter Name H3230ut Action NAT Service H323 Source Interface lan Destination Interface any Source Network lannet Destination Network 0 0 0 0 0 all nets Comment Allow outgoing calls 3 Click OK Incoming Rules Go to Rules gt IP Rules gt Add gt IPRule Now enter Name H323 In Action SAT Service H323 Source Interface any Destination Interface core Source Network 0 0 0 0 0 all nets Destination Network wan_ip external IP of the firewall Comment Allow incoming calls to H 323 phone at ip phone For SAT enter Translate Destination IP Address To New IP Address ip phone IP address of phone Click OK Go to Rules gt IP Rules gt Add gt IPRule Now enter Name H323 In Action Allow Service H323 Source Interface any 159 6 2 8 H 323 Chapter 6 Security Mechanisms Destination Interface core Source Network 0 0 0 0 0 all nets Destination Network wan_ip external IP of the firewall Comment Allow incoming calls to H 323 phone at ip phone Click OK To place a call to the phone behind the D Link Firewall place a call to the external IP address on the firewall If multiple H 323 phones are placed behind the firewall one SAT rule has to be configured
210. e the UDP echo service enabled Smurf attacks will show up in NetDefendOS logs as masses of dropped ICMP Echo Reply packets The source IP addresses will be those of the amplifier networks used Fraggle attacks will show up in NetDefendOS logs as masses of dropped or allowed depending on policy packets The source IP addresses will be those of the amplifier networks used Avoiding Becoming an Amplifier Even though the brunt of the bandwidth stream is at the ultimate victim s side being selected as an amplifier network can also consume great resources In its default configuration NetDefendOS explicitly drops packets sent to broadcast address of directly connected networks configurable via Advanced Settings gt IP gt DirectedBroadcasts However with a reasonable inbound policy no protected network should ever have to worry about becoming a smurf amplifier Protection on the Victim s Side Smurf and its followers are resource exhaustion attacks in that they use up Internet connection capacity In the general case the firewall is situated at the wrong side of the Internet connection bottleneck to provide much protection against this class of attacks The damage has already been done by the time the packets reach the firewall However NetDefendOS may be of some help in keeping the load off of internal servers making them available for internal service or perhaps service via a secondary Internet connection not targeted by the attack
211. e users can access using either the LDAP or HTTP protocols Certificates often contain a CRL Distribution Point CDP field which specifies the location from where the CRL can be downloaded In some cases certificates do not contain this field In those cases the location of the CRL has to be configured manually The CA updates its CRL at a given interval The length of this interval depends on how the CA is configured Typically this is somewhere between an hour to several days Trusting Certificates When using certificates NetDefendOS trusts anyone whose certificate is signed by a given CA Before a certificate is accepted the following steps are taken to verify the validity of the certificate e Construct a certification path up to the trusted root CA e Verify the signatures of all certificates in the certification path e Fetch the CRL for each certificate to verify that none of the certificates have been revoked Identification Lists In addition to verifying the signatures of certificates NetDefendOS also employs identification lists An identification list is a list naming all the remote identities that are allowed access through a specific VPN tunnel provided the certificate validation procedure described above succeeded Reusing Root Certificates In NetDefendOS root certificates should be seen as global entities that can be reused between VPN tunnels Even though a root certificate is associated with one VPN tunnel in Ne
212. eating a pipe for outbound bandwidth control add it to the forward pipe chain of the rule created in the previous example CLI gw world gt set PipeRule Outbound ForwardChain std out Web Interface 1 Go to Traffic Management gt Traffic Shaping gt Pipe Rules Right click on the piperule you created in the previous example and choose Edit 2 3 Under the Traffic Shaping tab select std out in the Forward Chain list 4 Click OK This results in all outbound connections being limited to 2 Mbps in each direction 10 1 5 Creating Differentiated Limits with Chains In the previous examples a static traffic limit for all outbound connections was applied What if we want to limit web surfing more than other traffic We could set up two surfing pipes for inbound and outbound traffic However we most likely won t need to limit outbound traffic because surfing usually consists of short outbound requests followed by long inbound answers Let s assume the total bandwidth limit is 250 kbps and 125 kbps of that is to be allocated to web surfing inbound traffic A surf in pipe is therefore setup for inbound traffic with a 125 kbps limit Next a new Pipe Rule is set up for surfing that uses the surf in pipe and it is placed before the rule that directs everything else through the std in pipe That way surfing traffic goes through the surf in pipe and everything else is handled by the rule and pipe created earlier Unfortunately this wi
213. ecified which is what is allowed to be translated The External IP for the Network is specified which is the IP address to NAT with If the External IP is set as Auto then the external IP is found automatically through route lookup e Translate Logical Channel Addresses This would normally always be set If not enabled then no address translation will be done on logical channel addresses and the administrator needs to be sure about IP addresses and routes used in a particular scenario e Gatekeeper Registration Lifetime The gatekeeper registration lifetime can be controlled in order to force re registration by clients within a certain time A shorter time forces more frequent registration by clients with the gatekeeper and less probability of a problem if the network becomes unavailable and the client thinks it is still registered Presented below are some network scenarios where H 323 ALG use is applicable For each scenario a configuration example of both the ALG and the rules are presented The three service definitions used in these scenarios are e Gatekeeper UDP ALL gt 1719 e H323 H 323 ALG TCP ALL gt 1720 e H323 Gatekeeper H 323 ALG UDP gt 1719 Example 6 4 Protecting Phones Behind D Link Firewalls In the first scenario a H 323 phone is connected to the D Link Firewall on a network lannet with public IP addresses To make it possible to place a call from this phone to another H 323 phone on the Internet and to a
214. econd which means that clients may experience a failover as a slight burst of packet loss In the case of TCP the failover time is well within the range of normal retransmit timeouts so TCP will retransmit the lost packets within a very short space of time and continue communication UDP does not allow retransmission since it is inherently an unreliable protocol Both master and slave know about the shared IP address ARP queries for the shared IP address or any other IP address published via the ARP configuration section or through Proxy ARP are answered by the active system The hardware address of the shared IP address and other published addresses are not related to the actual hardware addresses of the interfaces Instead the MAC address is constructed by NetDefendOS from the Cluster ID in the following form 10 00 00 C1 4A nn where nn comes from combining the Cluster ID configured in the Advanced Settings section with the hardware bus slot port of the interface The Cluster ID must be unique for each cluster in a network As the shared IP address always has the same hardware address there will be no latency time in updating ARP caches of units attached to the same LAN as the cluster when failover occurs When a cluster member discovers that its peer is not operational it broadcasts gratuitous ARP queries on all interfaces using the shared hardware address as the sender address This allows switches to re learn within milliseconds where to se
215. ecurity Mechanisms e A NAT rule for outbound traffic from user agents on the internal network to the SIP Proxy Server located externally The SIP ALG will take care of all address translation needed by the NAT rule This translation will occur both on the IP level and the application level Neither the user agents or the proxies need to be aware that the local users are being NATed e An Allow rule for inbound SIP traffic from the SIP proxy to the IP of the D Link Firewall This rule will use core in other words NetDefendOS itself as the destination interface The reason for this is due to the NAT rule above When an incoming call is received NetDefendOS will automatically locate the local receiver perform address translation and forward SIP messages to the receiver This will be executed based on the ALGs internal state A SAT rule is not needed since the ALG takes care of the mapping of the individual user IP address behind the gateway to the public Internet address When a user behind a D Link Firewall registers with a SIP proxy it sends its SIP URI to uniquely identify it to the firewall s public IP address When an exernal user then initiates a call the SIP traffic arrives at the public IP address and the ALG performs the necessary translation to the user s internal IP address 4 Ensure the peers are correctly configured The SIP Proxy Server plays a key role in locating the current location of the other peer for the session The prox
216. edule objects or simply schedules that can be selected and used with various types of security policies to accomplish time based control This functionality is in no way limited to IP Rules but is valid for most types of policies including Traffic Shaping rules and Intrusion Detection and Prevention IDP rules A Schedule object is in other words a very powerful component that can allow detailed regulation of when functions in NetDefendOS are enabled or disabled A Schedule object gives the possibility to enter multiple time ranges for each day of the week Furthermore a start and a stop date can be specified that will impose additional constraints on the schedule For instance a schedule can be defined as Mondays and Tuesdays 08 30 10 40 and 11 30 14 00 Fridays 14 30 17 00 Important q As schedules depend on an accurate date and time it is very important that the system date and time are set correctly Preferably time synchronization has also been enabled to ensure that scheduled policies will be enabled and disabled at the right time For more information please see Section 3 8 Setting Date and Time Example 3 17 Setting up a Time Scheduled Policy This example creates a schedule object for office hours on weekdays and attaches the object to an IP Rule that allows HTTP traffic CLI gw world gt add ScheduleProfile OfficeHours Mon 8 17 Tue 8 17 Wed 8 17 Thu 8 17 Fri 8 17 gw world gt add IPRule Action NAT Se
217. eed for Guarantees A problem can occur however if the prioritized traffic is a continous stream such as real time audio resulting in continuous use all available bandwidth and resulting in unacceptably long queuing times 273 10 1 7 Guarantees Chapter 10 Traffic Management for other services such as surfing DNS or FTP A means is therefore required to ensure that lower priority traffic gets some portion of bandwidth and this is done with Bandwidth Guarantees 10 1 7 Guarantees Bandwidth guarantees ensure that there is a minimum amount of bandwidth available for a given precedence This is done by specifying a maximum limit for the precedence in a pipe This will be the maximum amount of bandwidth that the precedence will accept and will send ahead of lower precedences Excess traffic above this limit will be sent at the Best Effort precedence behind traffic at precedences higher than Best Effort To change the prioritized SSH and Telnet traffic from the previous example to a 96 kbps guarantee you set the precedence 2 limit for the std inpipe to be 96 kbps This does not mean that inbound SSH and Telnet traffic is limited to 96 kbps Limits in precedences above the Best Effort precedence will only limit how much of the traffic gets to pass in that specific precedence If more than 96 kbps of precedence 2 traffic arrives any excess traffic will be moved down to the Best Effort precedence All traffic at the Best Effort precedenc
218. eeee 234 9 2 4 L2TP Roaming Clients with Pre Shared Keys cceeeeeeeeee eee eee 234 9 2 5 L2TP Roaming Clients with Certificates 1 0 0 0 cece eeee ee ee ee eenee 236 92 6 PPTP Roaming CHENtS proren ean E s wear E E E ness 236 9 2 7 VPN Troubleshooting si ssir reien e Er E E EEE EES 237 93 IPSEC emae r eaa e E dons e E aN ac ues E EE a E EE a aes 240 93 js OVERVIEW r e e E a E R EE TETE S ES 240 9 3 2 Internet Key Exchange IKE 0 00 0 0 eee eee cece cence eeceeeeeeeeeeeeaeeenes 240 9 3 3 IKE Authentication sessirnar ietin a eia does 245 9 3 4 IPsec Protocols ESP AH eeensnessessesesesessrsesereresesserereressrserereree 247 9 3 5 NAT Traversal soirs poranenie si ens ove oo in secesis EE KSSE EEEIEE 248 9 36 Proposal LAStssocss sss casagsasheas ipes k as eSssaghesviaa de EVES EE EPEAREN 249 9 3 7 Pre shated Keys rrn pinnes reed oys n e EE V E E iS 250 93 8 Identification Lists saeir a a EE EE ek EAS SENS 251 9 4 PSEC FPUnNElS siepe she a EE E a ee a e geehswudss 253 OAc Oye EW a eee Te rede esa de E es O ETT EEO E RSS 253 9 4 2 LAN to LAN Tunnels with Pre shared Keys ceeecsseeeneeeerrerrereeee 253 9 4 3 Roaming Chents aes n n r a E E eek re eee eae 253 9 4 4 Fetching CRLs from an alternate LDAP server sscsseeecceeereerereeees 259 9 5 PPTP E2 TP eireto e one A E E ee E E tes aE E E 260 9S PPEP eree e es E aE EE E EEE EEEE 260 952 L2 TP ir ene E EEEE E SE EEE it E EEE E 261 10 Traffic Managemen
219. eeeneeaeeneeaeenes 23 21 3 The CL iiss ss soa sass dens salva vets bi EnS ISEE E EERE S E o oeer Pdea TaS 24 Pa Ea A ETEA EDU EE EEEE ETES EEE AN TEA ET 26 2 1 5 Working with Configurations sseesssseesseeserrresreersrrerrrresrrererreeesse 29 22 Events and LOg Sing cece ioed Posent E suneostasse aes sh umes ones eats ERE E ean sens 35 22l ONCLVICW aerei veces ety eed E TAE secat nek AE E AE wath seek gh 35 2 22 Event Messa leS edena a ee a done caee a tasanu eshte souetaee des aaa 35 2 2 3 Event Message Distribution ssseessssersseesrrrresrrersrrerrererrrererreresre 35 2 3 RADIUS Accounting roires e oeno SPREE sss beessast ota adpsedbawas teeteag iE res 39 231s OVerVieW elen ra ra eaa aar e n a Teraa a on A N AE cw 39 2 3 2 RADIUS Accounting Messages cece cece cece eeeceeeece een eeneceneeeneees 39 2 3 3 Interim Accounting Messages e cece ceeeeeeeeeeceeece cena eeneeneeennees 41 2 3 4 Activating RADIUS Accounting 2 0 0 0 cece cece eeec cn eee teen eeea tena een eees 41 2 3 5 RADIUS Accounting Security 2 0 0 0 cee cece cece cece tena eeneeeneeeenees 41 2 3 6 RADIUS Accounting and High Availability 2 0 0 0 41 2 3 7 Handling Unresponsive Servers cee cece ceeeeneec eee eeea seca sean eene eens 42 2 3 8 Accounting and System Shutdowns 0c eee eee eee eneeee eee een eens 42 2 3 9 Limitations with NAT eiie nai creat a y canete bade aventate E ES 42 2A MONTONE 3 200
220. efault routes both having all nets as the destination but using two different gateways The first primary route has the lowest Metric and also has Route Monitoring enabled Route Monitoring for the second alternate route isn t meaningful since it has no failover route When a new connection is about to be established to a host on the Internet a route lookup will result in the route that has the lowest Metric being chosen If the primary WAN router should then fail this will be detected by NetDefendOS and the first route will be disabled As a consequence a new route lookup will be performed and the second route will be selected with the first one being marked as disabled Re enabling Routes Even if a route has been disabled NetDefendOS will continue to check the status of that route Should the route become available again it will be re enabled and existing connections will 95 4 2 4 Proxy ARP Chapter 4 Routing automatically be transferred back to it Route Interface Grouping When using route monitoring it is important to check if a failover to another route will cause the routing interface to be changed If this could happen it is necessary to take some precautionary steps to ensure that policies and existing connections will be maintained To illustrate the problem consider the following configuration First there is one IP rule that will NAT all HTTP traffic destined for the Internet through the wan interface
221. efendOS is able to retain this in its memory in order to prevent further fragments of that packet from arriving Default 60 seconds 323 13 9 Local Fragment Reassembly Chapter 13 Advanced Settings Settings 13 9 Local Fragment Reassembly Settings LocalReass_ MaxConcurrent Maximum number of concurrent local reassemblies Default 256 LocalReass_MaxSize Maximum size of a locally reassembled packet Default 70000 LocalReass_NumLarge Number of large over 2K local reassembly buffers of the above size Default 32 324 13 10 DHCP Settings Chapter 13 Advanced Settings 13 10 DHCP Settings DHCP_MinimumLeaseTime Minimum lease time seconds accepted from the DHCP server Default 60 DHCP_ValidateBcast Require that the assigned broadcast address is the highest address in the assigned network Default Enabled DHCP_AllowGlobalBcast Allow DHCP server to assign 255 255 255 255 as broadcast Non standard Default Disabled DHCP_UseLinkLocallP If this is enabled NetDefendOS will use a Link Local IP 169 254 instead of 0 0 0 0 while waiting for a lease Default Disabled DHCP_DisableArpOnOffer Disable the ARP check done by NetDefendOS on the offered IP The check issues an ARP request to see if the IP address is already in use Default Disabled 325 13 11 DHCPRelay Settings Chapter 13 Advanced Settings 13 11 DHCPRelay Settings DHCPRelay_MaxTransactions
222. efined DNS The IP address of the DNS used for URL resolution already provided by an IP Pool NBNS WINS The IP address for NBNS WINS resolution already provided by an IP Pool DHCP Instructs the host to send any internal DHCP requests to this address Subnets A list of the subnets that the client can access Example 9 7 Setting Up Config Mode In this example the Config Mode Pool object is enabled by associating with it an already configured IP Pool object called jp_pool1 Web Interface Go to Objects gt VPN Objects gt IKE Config Mode Pool The Config Mode Pool object properties web page now appears Select Use a pre defined IPPool object Choose the ip_pool1 object from the IP Pool drop down list Click OK After defining the Config Mode object the only remaining action is to enable Config Mode to be used with the IPsec Tunnel Example 9 8 Using Config Mode with IPsec Tunnels Assuming a predefined tunnel called von_tunnel1 this example shows how to enable Config Mode for that tunnel Web Interface Go to Interfaces gt IPsec Select the tunnel von_tunnel1 for editing Select IKE Config Mode drop down list Click OK IP Validation NetDefendOS always checks if the source IP address of each packet inside an IPsec tunnel is the same as the IP address assigned to the IPsec client with IKE Config Mode If a mismatch is detected the packet is always dropped and a log message generated with a severity level of Warn
223. en deploy The changes are automatically made to both units 11 3 3 Verifying Cluster Functioning To verify that the cluster is performing correctly first use an ha command on each unit The output will look similar to this for the master gt Inet 294 11 3 3 Verifying Cluster Functioning Chapter 11 High Availability This device is an HA MASTER This device is currently ACTIVE will forward traffic ay HA cluster peer is ALIVE r Then use the stat command to verify that both master and slave have about the same number of connections The output should contain a line similar to this Connect ionsko AG Oulie Onsale 000 where the lower number is the current number of connections and the higher number is the connections limit of the license The following points are also relevant to cluster setup e If this is not the first cluster in a network then the advanced setting ClusterID must be changed to have a unique value the default is 0 This makes sure the MAC address for the cluster is unique e Enabling the advanced setting HAUseUniqueSharedMacAddressPerInterface is also recommended so that each interface has its own MAC address If this is not enabled interfaces share a MAC address and this can confuse some switches Make sure that the advanced setting HighBuffers is set to automatic on all units in a cluster This setting allocates memory for handling connections Where a cluster has tens of tho
224. endOS supports these types of IP protocols by using the concept of Custom IP Protocol Services A Custom IP Protocol service is a service definition giving a name to an IP protocol 55 3 2 4 Custom IP Protocol Services Chapter 3 Fundamentals number Some of the common IP protocols such as IGMP are already pre defined in the NetDefendOS system configuration Similar to the TCP UDP port ranges described previously a range of IP protocol numbers can be used to specify multiple applications for one service Note The currently assigned IP protocol numbers and references are published by the Internet Assigned Numbers Authority IANA and can be found at http www iana org assignments protocol numbers Example 3 9 Adding an IP Protocol Service This example shows how to add an IP Protocol Service with the Virtual Router Redundancy Protocol CLI gw world gt add Service ServiceIPProto VRRP IPProto 112 Web Interface Go to Objects gt Services gt Add gt IP protocol service Specify a suitable name for the service eg VRRP Enter 112 in the IP Protocol control Optionally enter Virtual Router Redundancy Protocol in the Comments control Click OK 56 3 3 Interfaces Chapter 3 Fundamentals 3 3 Interfaces 3 3 1 Overview An Interface is one of the most important logical building blocks in NetDefendOS All network traffic that passes through or gets terminated in the system is done so through one or sev
225. ense IDP 194 zone defense 298 switches 299 355
226. entually the packet will be forwarded out on the destination interface according to the state If the destination interface is a tunnel interface or a physical sub interface additional processing such as encryption or encapsulation might occur The following section provides a set of diagrams which illustrate the flow of packets through NetDefendOS 1 3 NetDefendOS State Engine Packet Chapter 1 Product Overview Flow 1 3 NetDefendOS State Engine Packet Flow The diagrams in this section provide a summary of the flow of packets through the NetDefendOS state engine There are three diagrams each flowing into the next Figure 1 1 Packet Flow Schematic Part I Inbound packet VLAN packet Yes o gt Decapsulate p Dest MAC gt Yes lt m gt No DROP ae No Ethernet no a Yes ARP _ aa Pe is T Bad ARPforiP gt No gt DROP er 3 7 L IP e Yes Handle ARP lt 4 The packet flow is continued on the following page 1 3 NetDefendOS State Engine Packet Chapter 1 Product Overview Flow Figure 1 2 Packet Flow Schematic Part II Basic sanity checks including verification of IP header Drop CONN if it exists drop packet Check IDS Rawip signatures Drop No Yes Process fragment failed DROP Verify TCP UDP header etc Found matching true Forward packet connection false The packet flow is continued on the following pag
227. equired time This is done only once at the beginning of a consecutive sequence of response failures from a single server to avoid unecessarily repeating the message Verifying the Sender Email As part of the Anti SPAM module the option to verify the email sender denies emails with a mismatch of the SMTP From address and the header From address In other words the source address in the SMTP protocol header and the SMTP data load header must be the same Spamming can cause these to be different so this feature provides an extra check on email integrity 149 6 2 5 SMTP Chapter 6 Security Mechanisms Logging There are three types of logging done by the SPAM filtering module e Logging of dropped or SPAM tagged emails These log messages include the source email address and IP as well as its weighted points score and which DNSBLs caused the event e DNSBLs not responding DNSBL query timeouts are logged e All defined DNBSLs stop responding This is a high severity event since all email will be allowed through if this happens Network Setup Setup Summary To set up DNSBL SPAM filtering in the SMTP ALG the following list summarizes the steps e Specify which DNSBL servers are to be used There can be multiple and they can act both as backups to each other as well as confirmation of a sender s status e Specify a weight for each server which will determine how important it is in deciding if email is SPAM or not in the c
228. er Action SAT Service http Source Interface any Source Network all nets Destination Interface core Destination Network wan_ip Under the SAT tab make sure that the Destination IP Address option is selected In the New IP Address textbox enter 10 10 10 5 Click OK 210 7 3 1 Translation of a Single IP Chapter 7 Address Translation Address 1 1 Then create a corresponding Allow rule Go to Rules gt IP Rules gt Add gt IPRule Specify a suitable name for the rule eg Allow_HTTP_To_DMZ Now enter Action Allow Service http Source Interface any Source Network all nets Destination Interface core Destination Network wan_ip Under the Service tab select http in the Pre defined list Click OK The example results in the following two rules in the rule set These two rules allow us to access the web server via the D Link Firewall s external IP address Rule 1 states that address translation can take place if the connection has been permitted and rule 2 permits the connection Of course we also need a rule that allows internal machines to be dynamically address translated to the Internet In this example we use a rule that permits everything from the internal network to access the Internet via NAT hide Now what is wrong with this rule set If we assume that we want to implement address translation for reasons of security as well as functionality we discover that this rule set makes our internal
229. er this is called an area The topology of an area is hidden from the rest of the AS This information hiding reduces the amount of routing traffic exchanged Also routing within the area is determined only by the area s own topology lending the area protection from bad routing data An area is a generalization of an IP subnetted network All OSPF protocol exchanges can be authenticated This means that only routers with the correct authentication can join the Autonomous System Different authentication schemes can be used like none passphrase or MD5 digest It is possible to configure separate authentication methods for each Autonomous System Note The OSPF feature is available on the D Link DFL 800 1600 2500 only OSPF Areas The Autonomous System is divided into smaller parts called OSPF Areas This section describes what an area is and its associated terms Areas An area consists of networks and hosts within an AS that have been grouped together Routers that are only within an area are called internal routers all interfaces on internal routers are directly connected to networks within the area The topology of an area is hidden from the rest of the AS ABRs Routers that have interfaces in more than one area are called Area Border Routers ABRs these maintain a separate topological database for each area 104 4 4 2 OSPF Chapter 4 Routing to which they have an interface ASBRs Routers that exchange routing informati
230. er the News category if its content includes information articles on recent events pertaining to topics surrounding a locality for example town city or nation or culture including weather forecasting information Typically this would include most real time online news publications and technology or trade journals This does not include financial quotes refer to the Investment Sites category 11 or sports refer to the Sports category 16 Examples might be e www newsunlimited com e www dailyscoop com Category 3 Job Search A web site may be classified under the Job Search category if its content includes facilities to search for or submit online employment applications This also includes resume writing and posting and interviews as well as staff recruitment and training services Examples might be e www allthejobs com e Wwww yourcareer com Category 4 Gambling A web site may be classified under the Gambling category if its content includes advertisement or encouragement of or facilities allowing for the partaking of any form of gambling For money or otherwise This includes online gaming bookmaker odds and lottery web sites This does not include traditional or computer based games refer to the Games Sites category 10 Examples might be e www blackjackspot com e www pickapony net Category 5 Travel Tourism A web site may be classified under the Travel Tourism category if its content includes information rel
231. er to place calls on these phones over the Internet the following rules need to be added to the rule set in the firewall make sure there are no rules disallowing or allowing the same kind of ports traffic before these rules As we are using private IPs on the phones incoming traffic need to be SATed as in the example below The object ip phone below should be the internal IP of the H 323 phone behind each firewall Web Interface Outgoing Rule Go to Rules gt IP Rules gt Add gt IPRule Now enter Name H3230ut Action NAT Service H323 Source Interface lan Destination Interface any Source Network lannet Destination Network 0 0 0 0 0 all nets Comment Allow outgoing calls Click OK Incoming Rules 1 Goto Rules gt IP Rules gt Add gt IPRule 2 Now enter Name H323 In Action SAT Service H323 Source Interface any 161 6 2 8 H 323 Chapter 6 Security Mechanisms Destination Interface core Source Network 0 0 0 0 0 all nets Destination Network wan_ip external IP of the firewall Comment Allow incoming calls to H 323 phone at ip phone For SAT enter Translate Destination IP Address To New IP Address ip phone IP address of phone Click OK Go to Rules gt IP Rules gt Add gt IPRule Now enter Name H323 In Action Allow Service H323 Source Interface any Destination Interface core Source Network 0 0 0 0 0 all nets Destination Network wan_ip external IP of the f
232. eral interfaces An interface can be seen as a doorway for network traffic to or from the system Thus when traffic enters the system through an interface that interface would be referred to as the receiving interface or sometimes ingress or incoming interface Consequently when traffic is leaving the system the interface used to send the traffic is referred to as the sending interface or sometimes egress interface NetDefendOS supports a number of interface types which can be divided into the following four major groups Physical Interfaces Physical Sub Interfaces Tunnel Interfaces Each physical interface represents a physical port in a NetDefendOS based product Thus all network traffic that originates from or is terminated in the system will eventually pass through any of the physical interfaces NetDefendOS currently supports Ethernet as the only physical interface type For more information about Ethernet interfaces see Section 3 3 2 Ethernet Some interfaces require a binding to an underlying physical interface in order to transfer data This group of interfaces is called Physical Sub Interfaces NetDefendOS has support for two types of physical sub interfaces e Virtual LAN VLAN interfaces as specified by IEEE 802 1Q When routing IP packets over a Virtual LAN interface they will be encapsulated in VLAN tagged Ethernet frames For more information about Virtual LAN interfaces please see Section
233. eral public by way of their very extreme nature Examples might be e www verynastystuff com e www unpleasantvids com Category 26 Educational A web site classified under the Educational category may belong to other categories but has content that relates to educational services or has been deemed of educational value or to be an educational resource by educational organisations This category is populated by request or submission from various educational organisations Examples might be e highschoolessays org e www learn at home com Category 27 Advertising A web site may be classified under the Advertising category if its main focus includes providing advertising related information or services Examples might be www admessages com e www tripleclick com Category 28 Drugs Alcohol 181 6 3 4 Dynamic Web Content Filtering Chapter 6 Security Mechanisms A web site may be classified under the Drugs Alcohol category if its content includes drug and alcohol related information or services Some URLs categorised under this category may also be categorised under the Health category Examples might be e www the cocktail guide com e www stiffdrinks com Category 29 Computing IT A web site may be classified under the Computing IT category if its content includes computing related information or services Examples might be e www purplehat com e www gnu org Category 30 Swimsuit Lingerie Models A web
234. erface Go to System gt Date and Time Check the Enable time synchronization Now enter e Time Server Type SNTP Primary Time Server ntp1 sp se Seconadry Time Server ntp2 sp se Click OK Note If the TimeSyncInterval parameter is not specified when using the CLI to set the synchronization interval the default of 86400 seconds I day is used Example 3 24 Manually Triggering a Time Synchronization Time synchronization can be triggered from the CLI The output below shows a typical response 3 8 2 Time Servers Chapter 3 Fundamentals CLI gw world gt time sync Attempting to synchronize system time Server timer 2007 0227 1222152 OTCTFO0 00 Local tine 2007 02 27 T223 OUTO FOO 00I cliszeies T583 Local time successfully changed to server time Maximum Time Adjustment To avoid situations where a faulty Time Server causes the clock to be updated with a extremely inaccurate time a Maximum Adjustment value in seconds can be set If the difference between the current NetDefendOS time and the time received from a Time Server is greater than this Maximum Adjustment value then the Time Server response will be discarded For example assume that the maximum adjustment value is set to 60 seconds and the current NetDefendOS time is 16 42 35 If a Time Server responds with a time of 16 43 38 then the difference is 63 seconds This is greater than the Maximum Adjustment value so no update occurs for
235. erfaces the inactive unit gets an overall view of the active unit s health Even if syne is deliberately disconnected failover may not result if the inactive unit receives enough heartbeats from other interfaces via a shared switch however the sync interface sends twice as many heartbeats as any of the normal interfaces The administrator can disable heartbeat sending on any of the interfaces Heartbeats are not sent at smaller intervals because such delays may occur during normal operation An operation such as opening a file could result in delays long enough to cause the inactive system to go active even though the other is still active Cluster heartbeats have the following characteristics e The source IP is the interface address of the sending firewall e The destination IP is the shared IP address e The IP TTL is always 255 If NetDefendOS receives a cluster heartbeat with any other TTL it is assumed that the packet has traversed a router and hence cannot be trusted e Itis a UDP packet sent from port 999 to port 999 e The destination MAC address is the ethernet multicast address corresponding to the shared hardware address In other words 00 00 C1 4A nn Link level multicasts are used over normal unicast packets for security using unicast packets would mean that a local attacker could fool switches to route heartbeats somewhere else so the inactive system nevers receives them The time for failover is typically about one s
236. ernet MAC address of a host by using its IP address When a host needs to resolve an IP address to the corresponding Ethernet address it broadcasts an ARP request packet The ARP request packet contains the source MAC address and the source IP address and the destination IP address Each host in the local network receives this packet The host with the specified destination IP address sends an ARP reply packet to the originating host with its MAC address 3 4 2 ARP in NetDefendOS NetDefendOS provides not only standard support for ARP but also adds a number of security checks on top of the protocol implementation As an example NetDefendOS will by default not accept ARP replies for which the system has not sent out a corresponding ARP query for Without this type of protection the system would be vulnerable to connection hijacking NetDefendOS supports both dynamic ARP as well as static ARP and the latter is available in two modes Publish and XPublish Dynamic ARP is the main mode of operation for ARP where NetDefendOS sends out ARP requests whenever it needs to resolve an IP address to an Ethernet address The ARP replies are stored in the ARP cache of the system Static ARP is used for manually lock an IP address to a specific Ethernet address This is explained in more detail in the sections below 3 4 3 ARP Cache The ARP Cache is the temporary table in NetDefendOS for storing the mapping between IP and Ethernet addresses The
237. ervice This example shows how to add a TCP UDP Service using destination port 3306 which is used by MySQL CLI gw world gt add Service ServiceTCPUDP MySQL DestinationPorts 3306 Type TCP Web Interface Go to Objects gt Services gt Add gt TCP UDP service Specify a suitable name for the service eg MySQL Now enter e Type TCP Source 0 65535 Destination 3306 Click OK Apart from protocol and port information TCP UDP Service objects also contain several other parameters that are being described in more detail in other sections of this users guide SYN Flood Protection A TCP based service can be configured to enable protection against SYN Flood attacks For more details on how this feature works see Section 6 6 8 TCP SYN Flood Attacks Passing ICMP Errors If an attempt to open a TCP connection is made by a user application behind the D Link Firewall and the remote server is not in operation an ICMP error message is returned as the response These ICMP errors can either be ignored or allowed to pass through back to the requesting application Application Layer Gateway A TCP UDP Service can be linked to an Application Layer Gateway to enable deeper inspection of certain protocols For more information see Section 6 2 Application Layer Gateways Max Sessions An important parameter associated with a Service is Max Sessions This parameter is allocated a default value when the Service is associated wi
238. ervices HTTP for example on the sales department s servers whilst the sales department might require access to a similarly restricted set of applications on the finance department s network By deploying a single D Link Firewall between the two department s networks transparent but controlled access can be achieved using the Transparent Mode feature Another example might be an organisation allowing traffic between the external Internet and a range of public IP address on an internal network Transparent mode can control what kind of service is permitted to these IP addresses and in what direction For instance the only services permitted in such a situation may be HTTP access out to the Internet 4 6 2 Comparison with Routing mode The D Link Firewall can operate in two modes Routing Mode or Transparent Mode In Routing Mode the D Link Firewall performs all the functions of a Layer 3 router if the firewall is placed into a network for the first time or if network topology changes the routing configuration must therefore be thoroughly checked to ensure that the routing table is consistent with the new layout Reconfiguration of IP settings may be required for pre existing routers and protected servers This mode works well when complete control over routing is desired In Transparent Mode where Switch Route is used instead of Route the firewall acts in a way that has similarities to a switch it screens IP packets and forwards them transp
239. es 139 6 2 3 FTP Chapter 6 Security Mechanisms e Block Selected means that those filetypes marked will be automatically blocked as downloads A file s contents will be analyzed to identify the correct filetype If for example a file is found to contain exe data but the the filetype is not exe then the file will be blocked if exe files are blocked Blocking is the default action taken so if nothing in the list is marked no action is taken e Allow Selected means that only those filetypes marked will be allowed in downloads File contents are also examined to establish the true filetype Additional filetypes not included by default can be added to the Allow Block list however these cannot be subject to MIME type checking meaning that the file extension will be trusted as being correct for the contents of the file Additionally a size limit can be put on any single download operation Deploying an HTTP ALG As mentioned in the introduction the HTTP ALG object is brought into use by first associating it with a Service object and then associating that Service object with an IP rule in the IP rule set A number of pre defined HTTP Services could be used with the ALG For example the http service might be selected for this purpose As long as the associated Service is associated with an IP rule then the ALG will be applied to traffic targeted by that IP rule The https Service which is also included in the http all Service
240. es included in a NAT Pool NetDefendOS will need to send the correct ARP replies for this resolution to take place through its Proxy ARP mechanism so the external router can correctly build its routing table By default the administrator must specify in NAT Pool setup which interfaces will be used by NAT pools The option exists however to enable Proxy ARP for a NAT Pool on all interfaces but this can cause problems sometimes by possibly creating routes to interfaces on which packets shouldn t arrive It is therefore recommended that the interface s to be used for the NAT Pool Proxy ARP mechanism are explicitly specified Using NAT Pools NAT Pools are used in conjunction with a normal NAT IP rule When defining a NAT rule the dialog includes the option to select a NAT Pool to use with the rule This association brings the NAT Pool into use Example 7 2 Using NAT Pools This example creates a NAT pool which will be applied the external IP address range 10 6 13 10 to 10 16 13 15 and then uses it in a NAT IP rule for HTTP traffic on the Wan interface Web Interface A First create an object in the address book for the address range 1 Goto Objects gt Address Book gt Add gt IP address 208 7 2 NAT Pools Chapter 7 Address Translation Specify a suitable name for the IP range nat_pool_range Enter 70 6 13 10 10 16 13 15 in the IP Address textbox a network eg 10 6 13 0 24 could be used here the 0 and 255 addresses wi
241. et Key Exchange IKE protocol IKE is used as a method of distributing these session keys as well as providing a way for the VPN endpoints to agree on how the data should be protected IKE has three main tasks e Provide a means for the endpoints to authenticate each other e Establish new IPsec connections create SA pairs e Manage existing connections IKE keeps track of connections by assigning a set of Security Associations SAs to each connection An SA describes all parameters associated with a particular connection such as the IPsec protocol used ESP AH both as well as the session keys used to encrypt decrypt and or authenticate verify the transmitted data An SA is by nature unidirectional thus the need for more than one SA per connection In most cases where only one of ESP or AH is used two SAs will be created for each connection one describing the incoming traffic and the other the outgoing In cases where ESP and AH are used in conjunction four SAs will be created 240 9 3 2 Internet Key Exchange IKE Chapter 9 VPN IKE Negotiation The process of negotiating session parameters consists of a number of phases and modes These are described in detail in the below sections The flow of events can summarized as follows IKE Phase 1 e Negotiate how IKE should be protected IKE Phase 2 e Negotiate how IPsec should be protected e Derive some fresh keying material from the key exchange in phase 1 to p
242. et using the HTTP protocol through a D Link Firewall is an example of this where a username password combination is the primary authentication method In using this approach passwords are often subject to attacks by guesswork or systematic searches To counter this a password should be carefully chosen Ideally it should e Be more than 8 characters with no repeats e Use random character sequences not commonly found in phrases e Contain both lower and upper case alphabetic characters e Contain both digits and special characters To remain secure passwords should also e Not be recorded anywhere in written form e Never be revealed to anyone else e Changed on a regular basis such as every three months 220 8 2 Authentication Setup Chapter 8 User Authentication 8 2 Authentication Setup 8 2 1 Setup Summary The following list summarizes the steps for User Authentication setup with NetDefendOS e Set up a database of users each with a username password combination This can exist locally in a NetDefendOS User DB object or remotely on a RADIUS server and will be designated as the Authentication Source Membership of an Authentication Group can optionally be specified for each user e Define a User Authentication Rule which describes which traffic is to be authenticated and which Authentication Source will be used e Define an IP object for the IP addresses of the clients that will be authenticated Associate this wi
243. etDefendOS will wait for a short period 30 seconds by default during which a connection to the administrator must be re established As described previously if the configuration was activated via the CLI with the activate command then a commit command must be issued within that period If a lost connection could not be re established or if the commit command was not issued then NetDefendOS will revert to using the previous configuration This is a fail safe mechanism and amongst others things can help prevent a remote administrator from locking themselves out Example 2 10 Activating and Committing a Configuration This example shows how to activate and commit a new configuration CLI gw world gt activate The system will validate and start using the new configuration When the command prompt is shown again gw world gt commit The new configuration is now committed Web Interface 1 Go to Configuration gt Save and Activate in the menu bar 2 Click OK to confirm The web browser will automatically try to connect back to the web interface after 10 seconds If the connection succeeds this is interpreted by NetDefendOS that remote management is still working The new configuration is then automatically committed 33 2 1 5 Working with Configurations Chapter 2 Management and Maintenance Note gt The configuration must be committed before changes are saved All changes to a configuration can be ignored simpl
244. eters for the IPsec connection In phase 2 we will also extract new keying material from the Diffie Hellman key exchange in phase 1 to provide session keys to use in protecting the VPN data flow If PFS Perfect Forwarding Secrecy is used a new Diffie Hellman exchange is performed for each phase 2 negotiation While this is slower it makes sure that no keys are dependent on any other previously used keys no keys are extracted from the same initial keying material This is to make sure that in the unlikely event that some key was compromised no subsequent keys can be derived Once the phase 2 negotiation is finished the VPN connection is established and ready for use IKE Parameters There are a number of parameters used in the negotiation process Below is a summary of the configuration parameters needed to establish a VPN connection Understanding what these parameters do before attempting to configure the VPN endpoints is highly recommended since it is of great importance that both endpoints are able to agree on all of these parameters When installing two D Link Firewalls as VPN endpoints this process is reduced to comparing fields in two identical dialog boxes However it is not quite as easy when equipment from different vendors is involved Endpoint Identification The Local ID is a piece of data representing the identity of the VPN gateway With Pre Shared Keys this is a unique piece of data uniquely identifying the tunnel endp
245. ets that pass through NetDefendOS traffic shaping pipes have a precedence In the examples so far precedences have not been explicitly set and so all packets have had the same default precedence of 0 Eight precedences exist numbered from 0 to 7 Precedence 0 is the least important and 7 is the most important A precedence can be viewed as a separate traffic queue traffic in precedence 2 will be forwarded before traffic in precedence 0 precedence 4 forwarded before 2 The meaning of a precedence comes from the fact that it is either higher or lower than another precedence If for example two precedences are used in a scenario choosing 4 and 6 instead of 0 and 3 will makes no difference Figure 10 2 The Eight Pipe Precedences Allocating Precedence The way precedence is assigned to a packet is decided by the Pipe Rule that controls it and is done in one of three ways e Use the precedence of the first pipe Each pipe has a default precedence and packets take the default precedence of the first pipe they pass through e Use the allocated precedence The Pipe Rule explicitly allocates a precedence e Use the DSCP bits Take the precedence from the DSCP bits in the packet DSCP is a subset of the Diffserv architecture where the Type of Service ToS bits are included in the IP packet header Pipe Precedences When a pipe is configured a Default Precedence a Minimum Precedence and a Maximum Precedence can be specified The
246. etting 316 ConnLife_TCP_SYN setting 316 ConnLife_TCP setting 316 ConnLife_UDP setting 316 ConnReplace setting 314 content filtering 169 active content 169 categories 176 dynamic 172 phishing 180 spam 182 static 170 core interface 58 core routes 93 D date and time setting 82 default access rule 135 DefaultTTL setting 305 denial of service 198 DHCP 127 over ethernet 59 relaying 131 servers 128 static assignment 130 DHCP_AllowGlobalBcast setting 325 DHCP_DisableArpOnOffer setting 325 DHCP_MinimumLeaseTime setting 325 351 Alphabetical Index DHCP_UseLinkLocalIP setting 325 DHCP_ValidateBcast setting 325 DHCPRelay_AutoSaveRelayInterval setting 326 DHCPRelay_MaxAutoRoutes setting 326 DHCPRelay_MaxHops setting 326 DHCPRelay_MaxLeaseTime setting 326 DHCPRelay_MaxPPMPerlface setting 326 DHCPRelay_MaxTransactions setting 326 DHCPRelay_TransactionTimeout setting 326 DHCPServer_AutoSaveLeaselInterval setting 327 DHCPServer_SaveLeasePolicy setting 327 DHCPServer_SaveRelayPolicy setting 326 diffserv 267 DirectedBroadcasts setting 306 distance vector algorithm 103 distribution algorithms 282 DNS black lists see SPAM filtering DNS lookup 87 DoS attack see denial of service Drop IP rule 75 DroppedFrags setting 321 DSCP 267 in setting precedence 272 DuplicateFragData setting 320 DuplicateFrags setting 321 dynamic balancing in pipes 275 dynamic routing policy
247. etwork object named Jannet Default Gateway An IP Address object named wan_gw is auto generated and represents the default gateway of the system The wan_gw object is used primarily by the routing table but is also used by the DHCP client subsystem to store gateway address information acquired from an DHCP server If a default gateway address has been provided during the setup phase the wan_gw object will contain that address Otherwise the object will be left empty In other words the IP address is 0 0 0 0 all nets The all nets IP address object is initialized to the IP address 0 0 0 0 0 thus representing all possible IP addresses This object is used extensively throughout the configuration 51 3 2 Services Chapter 3 Fundamentals 3 2 Services 3 2 1 Overview A Service object is a reference to a specific IP protocol with associated parameters A Service definition is usually based on one of the major transport protocols such as TCP or UDP with the associated port number s The HTTP service for instance is defined as using the TCP protocol with associated port 80 However service objects are in no way restricted to TCP or UDP They can be used to define ICMP messages as well as any user definable IP protocol Services are passive objects in that they cannot carry out any action in the system on their own Instead Service objects are used frequently in the various security policies defined by rule sets For insta
248. etworks The NetDefendOS ALG provides an extra layer of security to TFTP in being able to put restrictions on its use General TFTP Options Allow Disallow Read The TFTP GET function can be disabled so that files cannot be retrieved by a TFTP client The default value is Allow Allow Disallow Write The TFTP PUT function can be disabled so that files cannot be written by a TFTP client The default value is Allow Remove Request Option Specifies if options should be removed from request The default is False which means don t remove Block Unknown Options This option allows the blocking of any option in a request other than the blocksize the timeout period and the file transfer size The default is False which means don t block TFTP Request Options As long as the Remove Request Option described above is set to false options aren t removed then the following request option settings can be applied Maximum Blocksize The maximum blocksize allowed can be specified The allowed range is 0 to 65464 bytes The default value is 65464 bytes Maxiumum File Size The maximum size of a file transfer can be restricted By default this is the absolute maximum allowed which 999 999 KBytes Allow Directory Traversal This option can disallow directory traversal through the use of filenames contaning consecutive periods Allowing Request Timeouts The NetDefendOS TFTP ALG blocks the repetition of an TFTP request coming from the s
249. ew uncategorized URLs sent to the D Link network are treated as anonymous submissions and no record of the source of new submissions is kept Categorizing Pages and Not Sites NetDefendOS dynamic filtering categorizes web pages and not sites In other words a web site may contain particular pages that should be blocked without blocking the entire site NetDefendOS provides blocking down to the page level so that users may still access parts of websites that aren t blocked by the filtering policy Activation Dynamic Content Filtering is a feature that is enabled by taking out a separate subscription to the service This is an addition to the normal NetDefendOS license For complete details of subscription services see Appendix A Subscribing to Security Updates Once a subscription is taken out an HTTP Application Layer Gateway ALG Object should be defined with Dynamic Content Filtering enabled This object is then associated with a Service object and the Service object is then associated with a rule in the IP rule set to determine which traffic should be subject to the filtering This makes possible the setting up of a detailed filtering policy based on the filtering parameters that are used for rules in the IP rule set Tip If you would like your content filtering policy to vary depending on the time of the day make use of a schedule object in the corresponding IP rule For more information please see Section 3 6 Schedules Ex
250. f an interface named dmz is connected to a wireless LAN it might be convenient to change the interface name to radio For maintenance and troubleshooting it is recommended to tag the corresponding physical port with the new name Note gt The startup process will enumerate all available Ethernet interfaces Each interface will be given a name of the form lanN wanN and dmz where N represents the number of the interface if your D Link Firewall has more than one of these interfaces In most of the examples in this guide lan is used for LAN traffic and wan is used for WAN traffic If your D Link Firewall does not have these interfaces please substitute the references with the name of your chosen interface Ethernet IP Addresses Each Ethernet interface is required to have an Interface IP Address which can be either a static address or an address provided by DHCP The interface IP address is used as the primary address for communicating with the system through the specific Ethernet interface The standard is to use IP4 Address objects to define the addresses of Ethernet interfaces Those objects are normally auto generated by the system For more information please see Section 3 1 5 Auto Generated Address Objects Tip Multiple IP addresses can be specified for an Ethernet interface by using the ARP Publish feature For more information see Section 3 4 ARP In addition to the interface IP address a Network address is al
251. f an existing connection is found the connection table entry includes information on where to route the packet so there is no need for lookups in the routing table This is far more efficient than traditional routing table lookups and is one reason for the high forwarding performance of NetDefendOS If an established connection cannot be found then the routing table is consulted It is important to understand that the route lookup is performed before the various rules sections get evaluated As a result the destination interface is known at the time NetDefendOS decides if the connection should be allowed or dropped This design allows for a more fine grained control in security policies NetDefendOS Route Notation NetDefendOS uses a slightly different way of describing routes compared to most other systems but this way is easier to understand making errors less likely Many other products do not use the specific interface in the routing table but specify the IP address of the interface instead The routing table below is from a Microsoft Windows XP workstation Interface List ok evoke ok E fsx eue hone A E e exons hor MS TCP Loopback interface MOTOS 2 0O0 1S da Sil Sel cel esocas Intel R PRO 1000 CT Network OxZO0004 2 600 53 45 00 OO OO caocses WAN PPP SLIP Interface Active Routes Network Destination Netmask Gateway Interface Metric OMORORO O 6050 0 UI92 168 0 1 192 168 0 LO 2
252. face to any user on the Internet Logging out from the Web Interface When you have finished working in the web interface you should always logout to prevent other users with access to your workstation to get unauthorized access to the system Logout by clicking on the Logout button at the right of the menu bar Tip If there is a problem with the management interface when communicating alongside VPN tunnels check the main routing table and look for an all nets route to the VPN tunnel If no specific route exists to the management interface then all management traffic coming from NetDefendOS will automatically be routed to the VPN tunnel If this is the case then a route should be added by the administrator to route management traffic destined for the management network to the correct interface 2 1 5 Working with Configurations The system configuration is built up by Configuration Objects where each object represents a configurable item of any kind Examples of configuration objects are routing table entries address book entries service definitions IP rules and so on Each configuration object has a number of properties that constitute the values of the object A configuration object has a well defined type The type defines the properties that are available for the configuration object as well as the constraints for those properties For instance the IP4Address type is used for all configuration objects representing a named IPv4 add
253. fic passing through to or from the system Without interfaces a NetDefendOS system has no means for receiving or sending traffic Several types of interfaces are supported Physical Interfaces Physical Sub Interfaces and Tunnel Interfaces Physical interfaces corresponds to actual physical Ethernet ports physical sub interfaces include VLAN and PPPoE interfaces while tunnel interfaces are used for receiving and sending traffic in VPN tunnels Interface Symmetry The NetDefendOS interface design is symmetric meaning that the interfaces of the device are not fixed as being on the insecure outside or secure inside of a network topology The notion of what is inside and outside is totally for the administrator to define Logical Objects Logical objects can be seen as pre defined building blocks for use by the rule sets The address book for instance contains named objects representing host and network addresses Another example of logical objects are services representing specific protocol and port combinations Also important are the Application Layer Gateway ALG objects which are used to define additional parameters on specific protocols such as HTTP FTP SMTP and H 323 NetDefendOS Rule Sets Finally rules which are defined by the administrator in the various rule sets are used for actually implementing NetDefendOS security policies The most fundamental set of rules are the JP Rules which are used to define the layer 3 IP filteri
254. flags and URG Urgent data flags both turned on The presence of a SYN flag indicates that a new connection is in the process of being opened and an URG flag means that the packet contains data requiring urgent attention These two flags should not be turned on in a single packet as they are used exclusively to crash computers with poorly implemented TCP stacks Default DropLog TCPSynPsh Specifies how NetDefendOS will deal with TCP packets with SYN and PSH Push flags both turned on The PSH flag means that the recipient stack should immediately send the information in the packet to the destination application in the computer These two flags should not be turned on at the same time as it could pose a crash risk for poorly implemented TCP stacks However many Macintosh computers do not implement TCP correctly meaning that they always send out SYN packets with the PSH flag turned on This is why NetDefendOS normally removes the PSH flag and allows the packet through despite the fact that the normal setting should be dropping such packets Default StripSilent TCPFinUrg Specifies how NetDefendOS will deal with TCP packets with both FIN Finish close connection and URG flags turned on This should normally never occur as you do not usually attempt to close a connection at the same time as sending important data This flag combination could be used to crash poorly implemented TCP stacks and is also used by OS Fingerprinting Default D
255. for accounting tasks e Multiple RADIUS servers can be configured in NetDefendOS to deal with the event when the primary server is unreachable 2 3 5 RADIUS Accounting Security Communication between NetDefendOS and any RADIUS accounting server is protected by the use of a shared secret This secret is never sent over the network but instead a 16 byte long Authenticator code is calculated using a one way MDS hash function and this is used to authenticate accounting messages The shared secret is case sensitive can contain up to 100 characters and must be typed exactly the same for NetDefendOS and for the RADIUS server Messages are sent using the UDP protocol and the default port number used is 1813 although this is user configurable 2 3 6 RADIUS Accounting and High Availability In an HA cluster accounting information is synched between the active and passive D Link Firewalls This means that accounting information is automatically updated on both cluster members whenever a connection is closed Two special accounting events are also used by the active unit to keep the passive unit synchronized 41 2 3 7 Handling Unresponsive Servers Chapter 2 Management and Maintenance e An AccountingStart event is sent to the inactive member in an HA setup whenever a response has been received from the accounting server This specifies that accounting information should be stored for a specific authenticated user e A problem with acc
256. for each phone This means that multiple external addresses have to be used However it is preferred to use a H 323 gatekeeper as in the H 323 with Gatekeeper scenario as this only requires one external address Example 6 6 Two Phones Behind Different D Link Firewalls This scenario consists of two H 323 phones each one connected behind the D Link Firewall on a network with public IP addresses In order to place calls on these phones over the Internet the following rules need to be added to the rule listings in both firewalls Make sure there are no rules disallowing or allowing the same kind of ports traffic before these rules QF Web Interface Outgoing Rule Go to Rules gt IP Rules gt Add gt IPRule Now enter Name H323AllowOut Action Allow Service H323 Source Interface lan Destination Interface any Source Network lannet Destination Network 0 0 0 0 0 all nets Comment Allow outgoing calls 3 Click OK Incoming Rule 6 2 8 H 323 Chapter 6 Security Mechanisms Go to Rules gt IP Rules gt Add gt IPRule Now enter Name H323Allowin Action Allow Service H323 Source Interface any Destination Interface lan Source Network 0 0 0 0 0 all nets Destination Network lannet Comment Allow incoming calls Click OK Example 6 7 Using Private IP Addresses This scenario consists of two H 323 phones each one connected behind the D Link Firewall on a network with private IP addresses In ord
257. found in plaintext but pattern matching is done in the same way on pure binary data Recognising Unknown Threats Attackers who build new intrusions often re use older code This means their new attacks can appear in the wild quickly To counter this D Link IDP uses an approach where the module scans for these reusable components with pattern matching looking for building blocks rather than the entire complete code patterns This means that known threats as well as new recently released unkown threats built with re used software components can be protected against Signature Advisories An advisory is a explanatory textual description of a signature Reading a signature s advisory will explain to the administrator what the signature will search for Due to the changing nature of the signature database advisories are not included in D Link documentation but instead are available on the D Link website at http security dlink com tw Advisories can be found under the NetDefend IDS option in the NetDefend Live menu IDP Signature types IDP offers three signature types which offer differing levels of certainty with regard to threats e Intrusion Protection Signatures IPS are highly accurate and a match is almost certainly an indicator of a threat Using the Protect action is recommended These signatures can detect administrative actions and security scanners e Intrusion Detection Signatures IDS can detect events that m
258. four VLAN interfaces Example 3 13 Creating an Interface Group CLI gw world gt add Interface InterfaceGroup examplegroup Members exampleif1 exampleif2 Web Interface 1 Go to Interfaces gt Interface Groups gt Add gt InterfaceGroup 2 Enter the following information to define the group Name The name of the group to be used later e Security Transport Equivalent If enabled the interface group can be used as a destination interface in rules where connections might need to be moved between the interfaces examples of such usage are Route Fail Over and OSPF Interfaces Select the interfaces to be in the group 66 3 3 6 Interface Groups Chapter 3 Fundamentals 3 Click OK 67 3 4 ARP Chapter 3 Fundamentals 3 4 ARP 3 4 1 Overview Address Resolution Protocol ARP is a protocol which maps a network layer protocol address to a data link layer hardware address and it is used to resolve an IP address into its corresponding Ethernet address It works at the OSI Data Link Layer Layer 2 see Appendix D The OSI Framework and is encapsulated by Ethernet headers for transmission A host in an Ethernet network can communicate with another host only if it knows the Ethernet address MAC address of that host Higher level protocols such as IP make use of IP addresses which are fundamentally different from a lower level hardware addressing scheme like the MAC address ARP is used to retrieve the Eth
259. ft blank If it is left blank then the sending IP address will default to the local host address of 127 0 0 1 Remote Network The remote network which the GRE tunnel will connect with e Remote Endpoint This is the IP address of the remote device which the tunnel will connect with e Use Session Key A unique number can optionally specified for this tunnel This allows more than one GRE tunnel to run between the same two endpoints The Session Key value is used to distinguish between them e Additional Encapsulation Checksum The GRE protocol allows for an additional checksum over and above the IPv4 checksum This provides an extra check of data integrity The Advanced settings for a GRE interface are e Automatically add route for remote network This option would normally be checked in order that the routing table is automatically updated The alternative is to manually create the required route e Address to use as source IP It is possible to specify a particular IP address as the source interface IP for the tunnel GRE and the IP Rule Set An established GRE tunnel does not automatically mean that all traffic coming from or to that GRE tunnel is trusted On the contrary network traffic coming from the GRE tunnel will be transferred to the NetDefendOS IP rule set for evaluation The source interface of the network traffic will be the name of the associated GRE Tunnel The same is true for traffic in the opposite direction
260. g Middle East Dubai Netherlands Norway Poland Portugal Russia Singapore South Africa Spain Sweden Switzerland Taiwan Turkey U S A FAX 972 9 9715601 Website www dlink co il Via Nino Bonnet n 6 b 20154 Milano Italy TEL 39 02 2900 0676 FAX 39 02 2900 1723 Website www dlink it Isidora Goyeechea 2934 Ofcina 702 Las Condes Santiago Chile TEL 56 2 232 3185 FAX 56 2 232 0923 Website www dlink cl Rue des Colonies 11 B 1000 Brussels Belgium TEL 32 0 2 517 7111 FAX 32 0 2 517 6500 Website www dlink be P O Box 500376 Office 103 Building 3 Dubai Internet City Dubai United Arab Emirates Tel 971 4 3916480 Fax 971 4 3908881 Website www dlink me com Weena 290 3012 NJ Rotterdam Netherlands Tel 31 10 282 1445 Fax 31 10 282 1331 Website www dlink nl Karihaugveien 89 N 1086 Oslo Norway TEL 47 99 300 100 FAX 47 22 30 95 80 Website www dlink no Budynek Aurum ul Walic w 11 PL 00 851 Warszawa Poland TEL 48 0 22 583 92 75 FAX 48 0 22 583 92 76 Website www dlink pl Rua Fernando Pahla 50 Edificio Simol 1900 Lisbon Portugal TEL 351 21 8688493 Website www dlink es Grafsky per 14 floor 6 Moscow 129626 Russia TEL 7 495 744 0099 FAX 7 495 744 0099 350 Website www dlink ru 1 International Business Park 03 12 The Synergy Singapore 609917 TEL 65 6774 6233 FAX 65 6774 6322 Website www dlink intl com Ei
261. g Table 0 108 4 7 Exporting the Default Route into an OSPF AS ssssseesssseerssresrrsresrrrrerrerrsrrerrereere 109 4 8 Forwarding of Multicast Traffic using the SAT Multiplex Rule 0 ee 112 4 9 Multicast Forwarding Address Translation cece ceeeceeece nec ece eee eeeeeeee ees 113 4 10 IGMP No Address Translation 2 0 00 00 eceeceee scence cece nsec neeeneeneeeneeeneeeeeeeees 115 4 11 Configuration ifl 208 cask Ga Ba i Gall eda bene Diab 116 4 12 Configuration if2 Group Translation cceeeeceeeceeeeeceeeceeueeeueeeeeeeceauerenaees 117 4 13 Setting up Transparent Mode Scenario 1 oo cece eee eee c eee ece eee eeeee ees 121 4 14 Setting up Transparent Mode Scenario 2 0 eee cee cence eee c eee ece eee eeeeeees 122 10 User Manual 5 12 Setting upa DACP Server mioni nesese ni io erior En ss Steee sss soendshesaaeas E SPTO ITR 128 5 2 Checking the status of a DHCP server eesssseeessessereeerrrrrsrreersrrererrerrrreerrerereeee 129 5 3 Setting Up Stance DACP svcd s eens poee dl acd ha uetadsy ieee Neat aed ascot ietaaeh Mees 130 54 Setting Upia DACP relayer ssc eines tery ea E E ea oh yeaa AE a test E 131 J gt Creating an LP Pool meene r aa cdot E e EA E E E E RAE 133 6 1 Setting up an Access Rulen renne ee e a E ty EE E a SeS 137 6 2 Protecting an FTP Server with an ALG 200 0 eee cence cence ence eeceeeeeeeeeeeeaeeenes 141 6 3 Protecting FIP Clients iiss
262. g a rule to the remote management policy CLI gw world gt add RemoteManagement RemoteMgmtSSH ssh Network lannet Interface lan LocalUserDatabase AdminUsers Web Interface Go to System gt Remote Management gt Add gt Secure Shell Management Enter a Name for the SSH remote management policy eg ssh_policy Select the following from the dropdown lists User Database AdminUsers Interface lan e Network lannet Click OK Logging on to the CLI When access to the CLI has been established to NetDefendOS through the serial console or an SSH client the administrator will need to logon to the system before being able to execute any CLI command This authentication step is needed to ensure that only trusted users can access the system as well as providing user information for auditing When accessing the CLI the system will respond with a login prompt Enter your username and press Enter followed by your password and then Enter again After a successful logon you will see the command prompt If a welcome message has been set then it will be displayed directly after the logon gw world gt For security reasons it can be advisable to disable or anonymize the CLI welcome message Changing the CLI Prompt The default CLI prompt is Device gt where Device is the model number of the D Link Firewall This can be customized for example to gw world gt by using the CLI command 25 2 1 4 The WebUI Chapter 2 Ma
263. g alternate tables in conjunction with the main table This is described further in Section 4 3 5 The Ordering parameter below 4 3 3 Policy based Routing Rules A tule in the Policy based Routing rule set can decide which routing table is selected A 98 4 3 4 Policy based Routing Table Chapter 4 Routing Selection Policy based Routing rule can be triggered by the type of Service HTTP for example in combination with the Source Destination Interface and Source Destination Network When looking up Policy based Rules it is the first matching rule found that is triggered 4 3 4 Policy based Routing Table Selection When a packet corresponding to a new connection first arrives the processing steps are as follows to determine which routing table is chosen 1 The PBR Rules must first be looked up but to do this the packet s destination interface must be determined and this is always done by a lookup in the main routing table It is therefore important a match for the destination network is found or at least a default all nets route exists which can catch anything not explicitly matched 2 A search is now made for a Policy based Routing Rule that matches the packets s source destination interface network as well as service If a matching rule is found then this determines the routing table to use If no PBR Rule is found then the main table will be used 3 Once the correct routing table has been located a check is made t
264. g trusted areas Before a new connection is checked against the IP rule set NetDefendOS checks the connection source against a set of Access Rules Access Rules can specify what traffic source is expected on a given interface and also to automatically drop traffic originating from specific sources AccessRules can provide an efficient and targeted initial filter of new connection attempts The Default Access Rule Even if the administrator doesn t explicitly specify any Access Rules a basic access rule is always in place which is known as the Default Access Rule This default rule always checks incoming traffic by performing a reverse lookup in the routing tables This lookup validates that the incoming traffic is coming from a source that the routing tables indicate is accessible via the interface on which the traffic arrived If this reverse lookup fails then the connection is dropped and a Default Access Rule log message will be generated For most configurations the Default Access Rule is sufficient and the administrator does not need to explicity specify other rules The default rule can for instance protect against IP spoofing which is described in the next section If Access Rules are explicitly specified then the Default Access Rule is still applied if a new connection doesn t match any of the specified rules 6 1 2 IP spoofing Traffic that pretends it comes from a trusted host can be sent by an attacker to try and get past a fire
265. ges in the following ways 35 2 2 3 Event Message Distribution Chapter 2 Management and Maintenance Memlog A D Link Firewall has a built in logging mechanism known as the Memory Log This retains all event log messages in memory and allows direct viewing of log messages through the web interface Syslog The de facto standard for logging events from network devices If other network devices are already logging to Syslog servers using syslog with NetDefendOS messages can simplify overall administration 2 2 3 1 Logging to Syslog Hosts Syslog is a standardized protocol for sending log data although there is no standardized format for the log messages themselves The format used by NetDefendOS is well suited to automated processing filtering and searching Although the exact format of each log entry depends on how a Syslog receiver works most are very much alike The way in which logs are read is also dependent on how the syslog receiver works Syslog daemons on UNIX servers usually log to text files line by line Most Syslog recipients preface each log entry with a timestamp and the IP address of the machine that sent the log data Feb 5 2000 09 45 23 gateway ourcompany com This is followed by the text the sender has chosen to send Feb 5 2000 09 45 23 gateway ourcompany com EFW DROP Subsequent text is dependent on the event that has occurred In order to facilitate automated processing of all messages NetDefendOS
266. gh Availability Clusters Updating the IDP databases for both the D Link Firewalls in an HA Cluster is performed automatically by NetDefendOS In a cluster there is always an active unit and an inactive unit Only the active unit in the cluster will perform regular checking for new database updates If a new database update becomes available the sequence of events will be as follows 1 The active unit determines there is a new update and downloads the required files for the update 2 The active unit performs an automatic reconfiguration to update its database 3 This reconfiguration causes a failover so the passive unit becomes the active unit 4 When the update is completed the newly active unit also downloads the files for the update and performs a reconfiguration 5 This second reconfiguration causes another failover so the passive unit reverts back to being active again These steps result in both D Link Firewalls in a cluster having updated databases and with the original active passive roles For more information about HA clusters refer to Chapter 11 High Availability 6 5 3 IDP Rules Rule Components An IDP Rule defines what kind of traffic or service should be analyzed An IDP Rule is similar in makeup to an IP Rule IDP Rules are constructed like other security policies in NetDefendOS such as IP Rules An IDP Rule specifies a given combination source destination interfaces addresses as well as being associated with a Ser
267. go to Add gt HTTP ALG URL Select Blacklist in the Action dropdown control Enter exe in the URL textbox Click OK Finally make an exception from the blacklist by creating a certain whitelist Go to Objects gt ALG In the grid click on the recently created HTTP ALG content_filtering and go to Add gt HTTP ALG URL Select Whitelist in the Action dropdown control In the URL textbox enter www D Link com exe Click OK Simply continue adding specfic blacklists and whitelists until the filter satifies the needs 171 6 3 4 Dynamic Web Content Filtering Chapter 6 Security Mechanisms 6 3 4 Dynamic Web Content Filtering Overview NetDefendOS supports Dynamic Web Content Filtering WCF of web traffic which enables an administrator to permit or block access to web pages based on the content of those web pages This functionality is automated and it is not necessary to manually specify which URLs to block or allow Instead D Link maintains a global infrastructure of databases containing massive numbers of current web site URL addresses grouped into a variety of categories such as shopping news sport and adult oriented on so on These databases are updated every hour with new categorized URLs while at the same time older invalid URLs are dropped The database content is global covering websites in many different languages and which are hosted in countries around the world Dynamic Web Content Filtering Availabilit
268. h a multicast group thus creating a distribution tree for packet flow Rather than aquiring new network information PIM uses the routing information from existing protocols such as OSPF to decide the optimal path A key mechanism in the Multicast Routing process is that of Reverse Path Forwarding For unicast traffic a router is concerned only with a packet s destination With multicast the router is also concerned with a packets source since it forwards the packet on paths which are known to be downstream away from the packet s source This approach is adopted to avoid loops in the distribution tree By default multicast packets are routed by NetDefendOS to the core interface SAT Mutliplex rules are set up in the IP rule set in order to perform forwarding to the correct interfaces This is demonstrated in the examples which follow Note For multicast to function with an Ethernet interface on any D Link Firewall that interface must have multicast handling set to On or Auto For further details on this see Section 3 3 2 Ethernet 4 5 2 Multicast Forwarding using the SAT Multiplex Rule The SAT Multiplex rule is used to achieve duplication and forwarding of packets through more than one interface This feature implements multicast forwarding in NetDefendOS where a multicast packet is sent through several interfaces Note that since this rule overrides the normal routing tables packets that should be duplicated by the multiplex rul
269. hat bottleneck passes through the defined NetDefendOS pipes If there is traffic going through your Internet connection that the pipes do not know about they cannot know when the Internet connection is full The problems resulting from leaks are exactly the same as in the cases described above Traffic leaking through without being measured by pipes will have the same effect as bandwidth consumed by parties outside of administrator control but sharing the same connection Troubleshooting For a better understanding of what is happening in a live setup the console command pipe u lt pipename gt can be used to display a list of currently active users in each pipe 10 1 11 A Summary of Traffic Shaping NetDefendOS traffic shaping provides a sophisticated set of mechanisms for controlling and prioritising network packets The following points summarize its use e Select the traffic to manage through Pipe Rules e Pipe Rules send traffic through Pipes 277 10 1 11 A Summary of Traffic Shaping Chapter 10 Traffic Management e A pipe can have a limit which is the maximum amount of traffic allowed e A pipe can only know when it is full if a limit is specified e A single pipe should handle traffic in only one direction although 2 way pipes are allowed e Pipes can be chained so that one pipe s traffic feeds into another pipe e Specific traffic types can be given a priority in a pipe e Priorities can be given a maximum
270. he event e Protect Drop the triggering connection Logging would be the preferred option if the appropriate triggering value cannot be determined beforehand Multiple Actions for a given rule might consist of Audit for a given threshold while the action might become Protect for a higher threshold 279 10 2 6 Exempted Connections Chapter 10 Traffic Management 10 2 5 Multiple Triggered Actions When a rule is triggered then NetDefendOS will perform the associated rule Actions that match the condition that has occured If more than one Action matches the condition then those matching Actions are applied in the order they appear in the user interface If several Actions that have the same combination of Type and Grouping see above for the definition of these terms are triggered at the same time only the Action with the highest threshold value will be logged 10 2 6 Exempted Connections It should be noted that some Advanced Settings known as BeforeRules settings can exempt certain types of connections for remote management from examination by the NetDefendOS rule set These settings will also exempt the connections from Threshold Rules 10 2 7 Threshold Rules and ZoneDefense Threshold Rules are used in the D Link ZoneDefense feature to block the source of excessive connection attmepts from internal hosts For more information on this refer to Chapter 12 Zone Defense 10 2 8 Threshold Rule Blacklisting If the Protect opt
271. he group total bandwidth for each user to some value such as 40 kbps There will be a problem if there are more than 5 users utilizing SSH simultaneously 16 kbps times 5 is more than 64 kbps The total limit for the pipe will still be in effect and each user will have to compete for the available precedence 2 bandwidth the same way they have to compete for the lowest precedence bandwidth Some users will still get their 16 kbps some will not Dynamic balancing can be enabled to improve this situation by making sure all of the 5 users get the same amount of limited bandwidth When the 5th user begins to generate SSH traffic balancing lowers the limit per user to about 13 kbps 64 kbps divided by 5 users Dynamic Balancing takes place within each precedence of a pipe individually This means that if users are allotted a certain small amount of high priority traffic and a larger chunk of best effort traffic all users will get their share of the high precedence traffic as well as their fair share of the best effort traffic 10 1 10 Recommendations The importance of setting a pipe limit Traffic shaping only comes into effect when a NetDefendOS pipe is full That is to say it is passing as much traffic as the total limit allows If a 500 kbps pipe is carrying 400 kbps of low priority traffic and 90 kbps of high priority traffic then there is 10 kbps of bandwidth left and there is no reason to throttle back anything It is therefore important t
272. he web server However if at a later point you add an interface that cannot be entrusted to communicate with the web server separate Drop rules would have to be placed before the rule granting all machines access to the web server Determining the best course of action must be done on a case by case basis taking all circumstances into account Example 7 4 Enabling Traffic to a Web Server on an Internal Network The example we have decided to use is that of a web server with a private address located on an internal network From a security standpoint this approach is wrong as web servers are very vulnerable to attack and should therefore be located in a DMZ However due to its simplicity we have chosen to use this model in our example In order for external users to access the web server they must be able to contact it using a public address In this example we have chosen to translate port 80 on the D Link Firewall s external address to port 80 on the web server These two rules allow us to access the web server via the D Link Firewall s external IP address Rule 1 states that address translation can take place if the connection has been permitted and rule 2 permits the connection Of course we also need a rule that allows internal machines to be dynamically address translated to the Internet In this example we use a rule that permits everything from the internal network to access the Internet via NAT hide The problem with th
273. header ESP Encapsulating Security Payload The ESP protocol inserts an ESP header after the original IP header in tunnel mode the ESP header is inserted after the outer header but before the original inner IP header All data after the ESP header is encrypted and or authenticated The difference from AH is that ESP also provides encryption of the IP packet The authentication phase also differs in that ESP only authenticates the data after the ESP header thus the outer IP header is left unprotected The ESP protocol is used for both encryption and authentication of the IP packet It can also be used to do either encryption only or authentication only Figure 9 2 The ESP protocol 247 9 3 5 NAT Traversal Chapter 9 VPN Original IP packet ESP in transport mode IP header ESP hdr IP data ESP trailer ESP auth Encrypted Authenticated ESP in tunnel mode Outer IP hdr ESP hdr IP hdr IP data ESP trailer ESP auth SSS Authenticated 9 3 5 NAT Traversal Both IKE and IPsec protocols present a problem in the functioning of NAT Both protocols were not designed to work through NATs and because of this a technique called NAT traversal has evolved NAT traversal is an add on to the IKE and IPsec protocols that allows them to function when being NATed NetDefendOS supports the RFC3947 standard for NAT Traversal with IKE NAT traversal is divided into two parts e Additions to IKE that lets IPsec peer
274. hem faster and more efficiently At the same time using a public IP network enables companies to reduce infrastructure related costs Unfortunately the same advantages that the Internet brings to business also benefit the hackers who use the same public infrastructure to mount attacks Attack tools are readily available on the Internet and development work on these tools is often split across groups of novice hackers known as script kiddies or larval hackers scattered across the globe providing around the clock progression of automated attack methods Many of the new attack methods utilize the distributed nature of the Internet to launch DoS attacks against organizations To be on the receiving end of a DoS attack is probably the last thing any network administrator wants to experience Attacks can appear out of thin air and the consequences can be devastating with crashed servers jammed Internet connections and business critical systems in overload This section deals with using the D Link Firewall to protect organizations against DoS attacks 6 6 2 DoS Attack Mechanisms A DoS attack can be perpetrated in a number of ways but there are three basic types of attack consumption of computational resources such as bandwidth disk space or CPU time e disruption of configuration information such as routing information e disruption of physical network components One of the most commonly used method is the consumption of computation
275. her words it is perfectly legal to specify one route for the destination address range 192 168 0 5 192 168 0 17 and another route for addresses 192 168 0 18 192 168 0 254 This is a feature that makes NetDefendOS highly suitable for routing in highly complex network topologies Displaying the Routing Table It is important to distinguish between the routing table that is active in the system and the routing table that you configure The routing table that you configure contains only the routes that you have added manually in other words the static routes The content of the active routing table however will vary depending on several factors For instance if dynamic routing has been enabled the routing table will be populated with routes learned by communicating with other routers in the network Also features such as route fail over will cause the active routing table to look different from time to time Example 4 1 Displaying the Routing Table This example illustrates how to display the contents of the configured routing table as well as the active routing table CLI To see the configured routing table gw world gt cc RoutingTable main ld main gt show nterface Network Gateway Local IP all nets 213 124 165 1 none lannet none none wannet none none To see the active routing table enter gw world gt routes Flags Network Gateway OGak IH Metric 92 4 2 2 Static Routing Chapter 4 Routing
276. herSubIPLen setting 319 MaxPipeUsers setting 336 max sessions services parameter 54 MaxSKIPLen setting 318 MaxTCPLen setting 318 MaxUDPLen setting 318 MinimumFragLength setting 322 multicast routing 110 multiple login authentication 222 N NAT 204 IP rules 75 pools 207 network address translation see NAT NTP see time synchronization O OSPF 104 aggregates 105 overriding content filtering 175 P packet flow diagram 19 phishing see content filtering pipe rules 268 268 pipes 268 268 policies 73 policy based routing 98 POP3 ALG 151 port address translation 216 PPoE 61 client configuration 62 PPP_L2TPBeforeRules setting 333 PPP_PPTPBeforeRules setting 333 PPTP 260 quickstart guide 236 precedences in pipes 272 pre shared keys 231 250 proposal lists 249 PseudoReass_MaxConcurrent setting 320 Q QoS see quality of service quality of service 267 R RADIUS accounting 39 authentication 221 ReassDoneLinger setting 322 Reassembly_MaxConnections setting 335 Reassembly_MaxProcessingMem setting 335 ReassIllegalLinger setting 322 ReassTimeLimit setting 322 ReassTimeout setting 322 Reject IP rule 75 reset to factory defaults 45 roaming clients 253 route failover 94 route notation 91 routing 89 dynamic 103 metrics 103 monitoring 94 static 90 S safestream 184 SAT 210 SAT IP rule 75 schedules 77 secure shell see SSH serial console port
277. his example we concentrate only on inbound traffic which is the direction that is the most likely to be the first one to fill up in client oriented setups Set the return chain of the port 22 rule to ssh in followed by std in Set the return chain of the port 23 rule to telnet in followed by std in Set the priority assignment for both rules to Use defaults from first pipe the default precedence of both the ssh in and telnet in pipes is 2 Using this approach rather than hard coding precedence 2 in the rule set you can easily change the precedence of all SSH and Telnet traffic by changing the default precedence of the ssh in and 274 10 1 9 Groups Chapter 10 Traffic Management telnet in pipes Notice that we did not set a total limit for the ssh in and telnet in pipes We do not need to since the total limit will be enforced by the std in pipe at the end of the respective chains The ssh in and telnet in pipes act as a priority filter they make sure that no more than the reserved amount 64 and 32 kbps respectively of precedence 2 traffic will reach std in SSH and Telnet traffic exceeding their guarantees will reach std in as precedence 0 the best effort precedence of the std in and ssh in pipes Note Here the ordering of the pipes in the return chain is important Should std in appear before ssh in and telnet in then traffic will reach std in at the lowest precedence only and hence compete for the 250 kbps of availa
278. ication of D Link Firewall s Proxy ARP feature where access between the parts needs to be controlled In such a scenario NetDefendOS can monitor and regulate all traffic passing between the two parts Note gt It is only possible to have Proxy ARP functioning for Ethernet and VLAN interfaces 97 4 3 Policy based Routing Chapter 4 Routing 4 3 Policy based Routing 4 3 1 Overview Policy based Routing PBR is an extension to the standard routing described previously It offers administrators significant flexibility in implementing routing decision policies by being able to define rules so alternative routing tables are used Normal routing forwards packets according to destination IP address information derived from static routes or from a dynamic routing protocol For example using OSPF the route chosen for packets will be the least cost shortest path derived from an SPF calculation Policy based Routing means that routes chosen for traffic can be based on specific traffic parameters Policy based Routing can allow Source based routing A different routing table may need to be chosen based on the source of traffic When more than one ISP is used to provide Internet services Policy based Routing can route traffic originating from different sets of users through different routes For example traffic from one address range might be routed through one ISP whilst traffic from another address range might be through a second
279. ication rules source net interface only see Chapter 8 User Authentication Specifying Any Interface or Network When specifying the filtering criteria in any of the rule sets specified above there are three useful pre defined options that can be used e For a Source or Destination Network the all nets option is equivalent to the IP address 0 0 0 0 0 which will mean that any IP address is acceptable e For Source or Destination Interface the any option can be used so that NetDefendOS will not care about the interface which the traffic is going to or coming from e The Destination Interface can be specified as core This means that traffic such as an ICMP Ping is destined for the D Link Firewall itself and it is NetDefendOS that will respond to it 73 3 5 2 IP Rule Evaluation Chapter 3 Fundamentals IP Rules The JP rule set is the most important of these security policy rule sets It determines the critical packet filtering function of NetDefendOS regulating what is allowed or not allowed to pass through the D Link Firewall and if necessary how address translations like NAT are applied There are two possible approaches to how traffic traversing a NetDefendOS could be dealt with e Everything is denied unless specifically permitted e Everything is permitted unless specifically denied To provide the best security the first of these approaches is adopted by NetDefendOS and the Drop action is the default policy of th
280. ich SNMP requests will come e Community The community string which provides password security for the accesses The Community String Security for SNMP Versions 1 and 2c is handled by the Community String which is the same as a password for SNMP access The Community String should be difficult to guess and therefore be constructed in the same way that any other password using combinations of upper and lower case letters with digits Enabling an IP Rule for SNMP The advanced setting SNMPBeforeRules in the RemoteAdmin section controls if the IP rule set checks all accesses by SNMP clients This is by default disabled and the recommendation is to always enable this setting The effect of enabling this setting is to add an invisible Allow rule at the top of the IP rule set which automatically permits accesses on port 161 from the network and on the interface specified for 43 2 4 1 SNMP Monitoring Chapter 2 Management and Maintenance SNMP access Port 161 is usually used for SNMP and NetDefendOS always expects SNMP traffic on that port Remote Access Encryption It should be noted that SNMP Version 1 or 2c access means that the community string will be sent as plain text over a network This is clearly insecure if a remote client is communicating over the public Internet It is therefore advisable to have remote access take place over an encrypted VPN tunnel or similarly secure means of communication Preventing SNMP Overload
281. ierra attacks ececeeeceee nec eeneceecereecnereeenereees 199 6 6 6 The WinNuke attack cceccecceeceeceeceecneeeeeeeeeeceeeeeeereeenereeeneneees 199 6 6 7 Amplification attacks Smurf Papasmurf Fraggle cooo 200 6 6 8 TCP SYN Flood Attacks eire a a ee r oe e EEA AEE 201 6 6 9 The Jolt2 Attack seinen ei pni iei e EE EEE 201 6 6 10 Distributed DoS Attacks 22 0 0 ececcee eee eecneeeeceereeeereeenereeenereees 201 6 7 Blacklisting Hosts and Networks 20 00 0000 cee ceecceeceeeceeeceeeceeeeeeeeeeeaeeeaeeeaes 202 T Address Translation nasi so sesecccevees jeved dues beets Dogo Pes een goevses Sota vets Soe ee sera eve need angers 204 7 1 Dynamic Network Address Translation cee ceeeceeeeeeeceeece teen eeea seen eenes 204 FD NAV POOLS 055 e535 cb san eects ere ces EA EEEE E ES EE EEE ES EEEE S SEs 207 7 3 Static Address Translation ceceeeeeceeeneceeeneceeeeceeeeeaeeneeeeeneresenenesenes 210 7 3 1 Translation of a Single IP Address 1 1 cceeceecceeeceeeceeeeeeneeees 210 7 3 2 Translation of Multiple IP Addresses M N eceeeeeceeeeeeeeeeenees 213 7 3 3 All to One Mappings N 1 cece cece n e a e t 215 7 3 4 Port Translationy oreert eeii iii e se EE sands ta EEN RA 216 7 3 5 Protocols handled by SAT oneensneseseessesrersesresrerersrerrsrereesresrerees 216 7 3 6 Multiple SAT rule matches eeeseeenseeeseseesreresrrerrsrrrrrreerreerereeers 217 RI T SAT and FwdEas
282. ignature Database seeseeseessesrsreerrsresrrrresrrrrsrrerrsrrerrrees 184 6 4 5 Subscribing to the D Link Anti Virus Service 2 0 0 0 ee eee eee 184 6 4 6 Anti Virus Options 20 0 0 cece ec cece rece ece nsec neeeeeeeeeeeeesaeeeaeeeaes 184 6 5 Intrusion Detection and Prevention ccceeeceeeeeceeenece eeu ereeeeeeeenereeener 188 ODI S OVERVIEW a eonace se cdaeies sa Senate ye vomecseewen teens E peices geeehecaneceetedomedwenmae 188 6 5 2 IDP Availability in D Link Models cece cece ceeeeeeeeeeeee scene 188 GSH LDP RUNES 65s seeded ES E dent Lacnaveds jacgdue E SST anzateetass 190 6 5 4 Insertion Evasion Attack Prevention cseceeeeeceeeeeceeeeeeeeeeenees 191 6 5 5 IDP Pattern Matching ieo teense sh sone sega E E E E A EE O 192 6 5 6 IDP Signature Groups sssesssessresessrerrsrrerrsresrreresrrresrreererrererees 192 6 5 7 TIDP ACHIOMS sos ioiei ipa e e abbot EAE E E sets ees 194 6 5 8 SMTP Log Receiver for IDP Events sseesessseseeseerrerrersrrerrerrerreees 194 6 6 Denial Of Service DoS Attacks cccccc ccc ecc cence cece ee eeeeceeeeeeeneneeeenenees 198 0 01 OVERVIEW sesciied late a E ateveans cringe av eusteewesy EESE lees 198 6 6 2 DoS Attack Mechanisms merisier a 198 6 6 3 Ping of Death and Jolt Attacks 10 0 0 cee ceee cece ee cence eeeeeeceeeeaeeeaes 198 6 6 4 Fragmentation overlap attacks Teardrop Bonk Boink and Nestea 199 6 6 5 The Land and LaT
283. igned Certificate based VPN tunnel for roaming clients 255 9 6 Setting up a CA Server issued Certificate based VPN tunnel for roaming clients 256 9 7 Setting Up Contig Mode lineis sien e e a Seon ee ated teri Seda ae lees dee 258 9 8 Using Config Mode with IPsec Tunnels eee cee ceeeceeeceeeee eee eeeeeeeeeeeaeeeaes 258 9 9 Setting upan LDAP Server aee e E E e eee side cheek go EE EE TE NE 259 9 10 Setting p A PPEP S6rVeR ssie e dau EE Savane E aE 260 9 11 Setting up an L2TP serv re eoon rituo seee aeee rE EEEE AEREE EEEn eSEE 261 9 12 Setting up n L2TP Tunnel soiis rieordi o obs oes seosaacssedeeesyssvtaagasegsaess seeaeogpease 262 10 1 Applying a Simple Bandwidth Limit 2 0 0 0 eee e cece eeca teen seca sean eenes 269 10 2 Limiting Bandwidth in Both Directions 0 0 00 0 e cence eeeceeecaeceueeee sean eeaes 270 10 32 Setting up SUB estasion aes ee nra SEEE EE ESTEEN EEE EKSENE EErEE 285 12 1 Asimple ZoneDefense Scenario 0c 5 cs csscesasgssesseessshvisadsasdsscaseeseesssseiasapenss 301 Preface Intended Audience The target audience for this reference guide is Administrators who are responsible for configuring and managing D Link Firewalls which are running the NetDefendOS operating system This guide assumes that the reader has some basic knowledge of networks and network security Text Structure and Conventions The text is broken down into chapters and sub sections Nu
284. il is not good Phone conversations might be secure enough e How many different keys should be used One key per user One per group of users One per LAN to LAN connection One key for all users and one key for all LAN to LAN connections It is probably better using more keys than is necessary today since it will be easier to adjust access per user group in the future e Should the keys be changed If so how often In cases where keys are shared by multiple users you may want to consider overlapping schemes so that the old keys work for a short period of time when new keys have been issued e What happens when an employee in possession of a key leaves the company If several users are using the same key it should be changed e In cases where the key is not directly programmed into a network unit such as a VPN firewall how should the key be stored On a floppy As a pass phrase to memorize On a smart card If it is a physical token how should it be handled 230 9 2 VPN Quickstart Guide Chapter 9 VPN 9 2 VPN Quickstart Guide Later sections in this chapter will explore VPN components in detail To help put those later sections in context this section is a quickstart summary of the key steps in VPN setup It outlines the individual steps in setting up VPNs for the most common VPN scenarios These are e IPsec LAN to LAN with Pre shared Keys e IPsec Roaming Clients with Pre shared Keys e IPsec Roaming Clients with Cer
285. ime Transport Protocol RFC3550 is used as the underlying packet format for delivering audio and video streaming via IP using the UDP protocol RTCP Real time Control Protocol RFC3550 is used in conjunction with RTP to provide out of band control flow management SIP Usage Scenarios The NetDefendOS SIP ALG supports the following usage scenarios 1 Internal to External The SIP session is between a peer on the protected side of a 2 Same Network D Link Firewall and a peer which is on the external unprotected side Communication typically takes place across the public Internet A refinement of the internal to internal scenario is the case where the two peers in a session reside on the same network In all these three scenarios the proxy server is assumed to be on the unprotected side of the D Link Firewall SIP Configuration Options The following options can be configured for a SIP ALG object 153 6 2 7 SIP Chapter 6 Security Mechanisms Maximum Sessions per ID The number of simultaneous sessions that a single peer can be involved with is restricted by this value The default number is 5 Maximum Registration Time The maximum time for registration with a SIP Registrar The default value is 3600 seconds SIP Request Response Timeout The maximum time allowed for responses to SIP requests A timeout condition occurs after this wait The default is 180 seconds SIP Signal Timeout The maximum time allowed for
286. implify setup The authentication source can be one of the following e A Local User DB object which is internal to NetDefendOS e An external authentication server An internal user database is easier to set up and is assumed here Changing this to an external server is simple to do later To implement user authentication with an internal database Define a Local User DB object let s call this object TrustedUsers e Add individual users to TrustedUsers This should consist of at least a username and password combination The Group string for a user can be specified if its group s access is to be restricted to certain source networks Group can be specified with the same text string in the 232 9 2 2 IPsec Roaming Clients with Chapter 9 VPN Pre shared Keys Authentication section of an IP object If that IP object is then used as the Source Network of a rule in the IP rule set that rule will only apply to a user if their Group string matches the Group string of the IP object note Group has no meaning in Authentication Rules Create a new User Authentication Rule with the Authentication Source set to TrustedUsers The other parameters for the rule are 2 The IPsec Tunnel object ipsec_tunnel should have the following parameters Set Local Network to annet Set Remote Network to all nets Set Remote Gateway to all nets Set Encapsulation mode to Tunnel Set the IKE and IPsec proposal lists to match the
287. ing This 258 9 4 4 Fetching CRLs from an alternate Chapter 9 VPN LDAP server message includes the two IP addresses as well as the client identity Optionally the affected SA can be automatically deleted if validation fails by enabling the advanced setting PsecDeleteSA On IPValidationFailure The default value for this setting is Disabled 9 4 4 Fetching CRLs from an alternate LDAP server An X 509 root certificate usually includes the IP address or hostname of the Certificate Authority to contact when certificates or Certificate Revocation Lists need to be downloaded to the D Link Firewall Lightweight Directory Access Protocol LDAP is used for these downloads However in some scenarios this information is missing or the administrator wishes to use another LDAP server The LDAP configuration section can then be used to manually specify alternate LDAP servers Example 9 9 Setting up an LDAP server This example shows how to manually setup and specify a LDAP server CLI gw world gt add LDAPServer Host 192 168 101 146 Username myusername Password mypassword Port 389 Web Interface Go to Objects gt VPN Objects gt LDAP gt Add gt LDAP Server Now enter IP Address 192 168 101 146 Username myusername Password mypassword Confirm Password mypassword Port 389 Click OK 259 9 5 PPTP L2TP Chapter 9 VPN 9 5 PPTP L2TP The access by a client using a modem link over dial up public s
288. ing GRE GRE is typically used to provide a method of connecting two networks together across a third network such as the Internet The two networks being connected together communicate with a common protocol which is tunneled using GRE through the intervening network Examples of GRE usage are e Traversing network equipment that blocks a particular protocol e Tunneling IPv6 traffic across an IPv4 network e Where a UDP data stream is to be multicast and it is necessary to transit through a network device which does not support multicasting GRE allows tunneling though the network device GRE Security and Performance A GRE tunnel does not use any encryption for the communication and is therefore not in itself secure Any security must come from the protocol being tunneled The advantage of GRE s lack of encryption is the high performance which is achievable because of the low traffic processing overhead The lack of encryption can be acceptable in some circumstances if the tunneling is done across an internal network that is not public Setting Up GRE Like other tunnels in NetDefendOS such as an IPsec tunnel a GRE Tunnel is treated as a logical interface by NetDefendOS with the same filtering traffic shaping and configuration capabilities as a standard interface The GRE options are 63 3 3 5 GRE Tunnels Chapter 3 Fundamentals e IP Address This is the IP address of the sending interface This is optional and can be le
289. ing in the conference call have to establish a connection with the MCU The MCU then manages the calls resources video and audio codecs used in the call The different protocols used in implementing H 323 are H 225 RAS signaling and Call Control Setup signaling H 245 Media Control and Transport T 120 H 323 ALG features Used for call signaling It used to establish a connection between two H 323 endpoints This call signal channel is opened between two H 323 endpoints or between a H 323 endpoint and a gatekeeper For communication between two H 323 endpoints TCP 1720 is used When connecting to a gatekeeper UDP port 1719 H 225 RAS messages are used Provides control of multimedia sessions established between two H 323 endpoints Its most important task is to negotiate opening and closing of logical channels A logical channel is for instance an audio channel used for voice communication Video and T 120 channels are also called logical channels during negotiation A suite of communication and application protocols Depending on the type of H 323 product T 120 protocol can be used for application sharing file transfer as well as for conferencing features such as whiteboards The H 323 ALG is a flexible application layer gateway that allows H 323 devices such as H 323 phones and applications to make and receive calls between each other when connected via private networks secured by D Link Firewalls The H 323 specifi
290. ion capabilities as regular interfaces with the IP rule set being applied to all traffic Network traffic arriving at the firewall through the PPPoE tunnel will have the PPPoE tunnel interface as its source interface For outbound traffic the PPPoE tunnel interface will be the destination interface As with any interface one or more routes are defined so NetDefendOS knows what IP addresses it should accept traffic from and which to send traffic to through the PPPoE tunnel The PPPoE client can be configured to use a service name to distinguish between different servers on the same Ethernet network IP address information PPPoE uses automatic IP address allocation which is similar to DHCP When NetDefendOS receives this IP address information from the ISP it stores it in a network object and uses it as the IP address of the interface User authentication If user authentication is required by the ISP the username and password can be setup in NetDefendOS for automatic sending to the PPPoE server Dial on demand If dial on demand is enabled the PPPoE connection will only be up when there is traffic on the PPPoE interface It is possible to configure how the firewall should sense activity on the interface either on outgoing traffic incoming traffic or both Also configurable is the time to wait with no activity before the tunnel is disconnected Example 3 12 Configuring a PPPoE client on the wan interface with traffic routed over PPPoE
291. ion groups This also includes bulletin boards message boards online forums discussion groups as well as URLs for downloading chat software Examples might be e www thetalkroom org e chat yazoo com Category 9 Dating Sites A web site may be classified under the Dating Sites category if its content includes facilities to submit and review personal advertisements arrange romantic meetings with other people mail order bride foreign spouse introductions and escort services Examples might be e adultmatefinder com e www marri agenow com Category 10 Game Sites A web site may be classified under the Game Sites category if its content focuses on or includes the review of games traditional or computer based or incorporates the facilities for downloading computer game related software or playing or participating in online games Examples might be e www gamesunlimited com e www gameplace com Category 11 Investment Sites A web site may be classified under the Investment Sites category if its content includes information services or facilities pertaining to personal investment URLs in this category include contents such as brokerage services online portfolio setup money management forums or stock quotes This category does not include electronic banking facilities refer to the E Banking category 12 Examples might be 178 6 3 4 Dynamic Web Content Filtering Chapter 6 Security Mechanisms e www loadsofmoney
292. ion is chosen and that table is an alternate routing table the Ordering parameter associated with the table is used to decide how the alternate table is combined with the main table to lookup the appropriate route The three available options are 1 Default The default behaviour is to first look up the route in the main table If no matching route is found or the default route is found the route with the destination all nets 0 0 0 0 0 a lookup for a matching route in the alternate table is done If no match is found in the alternate table then the default route in the main table will be used 2 First This behaviour is to first look up the connection s route in the alternate table If no matching route is found there then the main table is used for the lookup The default all nets route will be counted as a match in the alternate table if it exists there 3 Only This option ignores the existence of any other table except the alternate table so the alternate table is the only one used for the lookup One application of this is to give the administrator a way to dedicate a single routing table to one set of interfaces Only is the option to use when creating virtual systems since it can dedicate one routing table to a set of 99 4 3 5 The Ordering parameter Chapter 4 Routing interfaces The first two options can be regarded as combining the alternate table with the main table and assigning one route if there is a match in bo
293. ion is used Threshold Rules can be configured so that the source that triggered the tule is added automatically to a Blacklist of IP addresses or networks If several Protect Actions with blacklisting enabled are triggered at the same time only the first triggered blacklisting Action will be executed by NetDefendOS A host based Action with blacklisting enabled will blacklist a single host when triggered A network based action with blacklisting enabled will blacklist the source network associated with the rule If the Threshold Rule is linked to a service then it is possible to block only that service When Blacklisting is chosen then the administrator can elect that existing connections from the triggering source can be left unaffected or they can be dropped The length of time in seconds for which the source is blacklisted can also be set This option is discussed further in Section 6 7 Blacklisting Hosts and Networks 280 10 3 Server Load Balancing Chapter 10 Traffic Management 10 3 Server Load Balancing 10 3 1 Overview The Server Load Balancing SLB feature in NetDefendOS is a powerful tool that can improve the following aspects of network applications e Performance e Scalability e Reliability e Ease of administration SLB allows network service demands to be shared among multiple servers This improves both the performance and the scalability applications by allowing a cluster of multiple servers some
294. ions to servers in an orderly fashion It will also behave as the Round Robin algorithm if there are always clients with a new IP address that make one connection The real benefit is when using Connection Rate together with stickiness and clients make multiple connections Connection Rate will then ensure that the distribution of new connections is as even as possible among servers Before the interval reaches the specified Idle Timeout of stickiness new incoming connections from the same IP address as a previous connection are assigned to the same server The connection with a new address will be redirected to a server with the lowest connection rate The algorithm aims to minimize the new connection load for a server but the distribution may get uneven if a client from a single IP is sending lots of new connections in a short time and the other servers do not get as many new connections In the management interface the time window is variable for counting the number of seconds back in time to summarize the number of new connections for the connection rate algorithm As default value 10 is used so that the number of new connections which were made to each server in the last 10 seconds will be remembered An example is shown in the figure below In this example the D Link Firewall is responsible for balancing connections from 3 clients with different addresses to 2 servers Stickiness is set Figure 10 6 Connections from Three Clients F2
295. ious types of thresholds where to alarm or limit network traffic and Server Load Balancing enables a device running NetDefendOS to distribute network load to multiple hosts Chapter 10 Traffic Management provides more detailed information on the various traffic management capabilities To facilitate management of a NetDefendOS device administrative control is enabled through a Web based User Interface or via the Command Line Interface In addition NetDefendOS provides very detailed event and logging capabilities and support for monitoring using standards such as SNMP For more information please see Chapter 2 Management and Maintenance NetDefendOS can be used to control D Link switches using the ZoneDefense feature Reading through this documentation carefully will ensure that you get the most out of your NetDefendOS product In addition to this document the reader should also be aware of the companion volumes The NetDefendOS CLI Guide which details all NetDefendOS console commands e The NetDefendOS Log Reference Guide which details all NetDefendOS log event messages These documents together form the essential documentation for NetDefendOS operation Note gt High Availability Anti Virus Web Content Filtering and ZoneDefense are not available with some models as specified in the chapters relating to those features 15 1 2 NetDefendOS Architecture Chapter 1 Product Overview 1 2 NetDefendOS Architectur
296. iplex e Action Multiplex SAT e Service multicast_service Under Address Filter enter Source Interface wan Source Network 192 168 10 1 Destination Interface core Destination Network 239 192 10 0 24 Click the Multiplex SAT tab and add the output interfaces if1 if2 and if8 one at a time For each interface leave the IPAddress field blank since no destination address translation is wanted Make sure the forwarded using IGMP checkbox is set Click OK 4 5 2 2 Multicast Forwarding Address Translation Scenario Figure 4 5 Multicast Forwarding Address Translation 112 4 5 2 Multicast Forwarding using the Chapter 4 Routing SAT Multiplex Rule This scenario is based on the previous scenario but now we are going to translate the multicast group When the multicast streams 239 192 10 0 24 are forwarded through the if2 interface the multicast groups should be translated into 237 192 10 0 24 No address translation should be made when forwarding through interface if1 The configuration of the corresponding IGMP rules can be found below in Section 4 5 3 2 IGMP Rules Configuration Address Translation Caution 3 As previously noted remember to add an Allow rule matching the SAT Multiplex rule Example 4 9 Multicast Forwarding Address Translation The following SAT Multiplex rule needs to be configured to match the scenario described above Web Interface A Create a custom service for multicast called multic
297. irewall Comment Allow incoming calls to H 323 phone at ip phone Click OK To place a call to the phone behind the D Link Firewall place a call to the external IP address on the firewall If multiple H 323 phones are placed behind the firewall one SAT rule has to be configured for each phone This means that multiple external addresses have to be used However it is preferable to use an H 323 gatekeeper as as this only requires one external address Example 6 8 H 323 with Gatekeeper In this scenario a H 323 gatekeeper is placed in the DMZ of the D Link Firewall A rule is configured in the firewall to allow traffic between the private network where the H 323 phones are connected on the internal network and to the Gatekeeper on the DMZ The Gatekeeper on the DMZ is configured with a private address The following rules need to be added to the rule listings in both firewalls make sure there are no rules disallowing or allowing the same kind of ports traffic before these rules 162 6 2 8 H 323 Chapter 6 Security Mechanisms Web Interface Incoming Gatekeeper Rules Go to Rules gt IP Rules gt Add gt IPRule Now enter Name H323 In Action SAT Service H323 Gatekeeper Source Interface any Destination Interface core Source Network 0 0 0 0 0 all nets Destination Network wan_ip external IP of the firewall Comment SAT rule for incoming communication with the Gatekeeper located at ip gatekeeper For SAT enter Trans
298. is for NetDefendOS to mark a connection as alive not idle every time data is sent from the side that opened the connection Connections that don t receive any data from the opening side within the UDP lifetime will therefore be closed even if the other side continues to transmit data 316 AllowBothSidesToKeepConnAlive_UDP Chapter 13 Advanced Settings Default False 317 13 7 Size Limits by Protocol Chapter 13 Advanced Settings 13 7 Size Limits by Protocol This section contains information about the size limits imposed on the protocols directly under IP level ie TCP UDP ICMP etc The values specified here concern the IP data contained in packets In the case of Ethernet a single packet can contain up to 1480 bytes of IP data without fragmentation In addition to that there is a further 20 bytes of IP header and 14 bytes of Ethernet header corresponding to the maximum media transmission unit on Ethernet networks of 1514 bytes MaxTCPLen Specifies the maximum size of a TCP packet including the header This value usually correlates with the amount of IP data that can be accommodated in an unfragmented packet since TCP usually adapts the segments it sends to fit the maximum packet size However this value may need to be increased by 20 50 bytes on some less common VPN systems Default 71480 MaxUDPLen Specifies the maximum size of a UDP packet including the header This value may well need to be quite high
299. is known as UpstreamRouterIP Two rules are needed The first one is a report rule that allows the clients behind interfaces if1 if2 and if3 to subscribe for the multicast groups 239 192 10 0 24 The second rule is a query rule that allows the upstream router to query us for the multicast groups that the clients have requested The following steps need to be executed to create the two rules Web Interface A Create the first IGMP Rule Go to Routing gt IGMP gt IGMP Rules gt Add gt IGMP Rule Under General enter Name A suitable name for the rule eg Reports Type Report Action Proxy Output wan this is the relay interface Under Address Filter enter e Source Interface IfGrpClients 115 4 5 3 IGMP Configuration Chapter 4 Routing Source Network if1net if2net if3net Destination Interface core Destination Network auto Multicast Source 192 168 10 1 Multicast Group 239 192 10 0 24 Click OK B Create the second IGMP Rule 1 Again go to Routing gt IGMP gt IGMP Rules gt Add gt IGMP Rule 2 Under General enter Name A suitable name for the rule eg Queries Type Query Action Proxy Output IfGrpClients this is the relay interface Under Address Filter enter Source Interface wan Source Network UpstreamRouterlp Destination Interface core Destination Network auto Multicast Source 192 168 10 1 Multicast Group 239 192 10 0 24 Click OK 4 5 3 2 IGMP Rules Configuratio
300. is rule set is that it will not work at all for traffic from the internal network In order to illustrate exactly what happens we use the following IP addresses wan_ip 195 55 66 77 a public IP address lan_ip 10 0 0 1 the D Link Firewall s private internal IP address wwwsrv 10 0 0 2 the web servers private IP address PC1 10 0 0 3 a machine with a private IP address PC1 sends a packet to wan_ip to reach www ourcompany com 10 0 0 3 1038 gt 195 55 66 77 80 212 7 3 2 Translation of Multiple IP Chapter 7 Address Translation Addresses M N NetDefendOS translates the address in accordance with rule 1 and forwards the packet in accordance with rule 2 10 0 0 3 1038 gt 10 0 0 2 80 wwwsrv processes the packet and replies 10 0 0 2 80 gt 10 0 0 3 1038 This reply arrives directly to PC1 without passing through the D Link Firewall This causes problems The reason this will not work is because PC1 expects a reply from 195 55 66 77 80 not 10 0 0 2 80 The unexpected reply is discarded and PC1 continues to wait for a response from 195 55 66 77 80 which will never arrive Making a minor change to the rule set in the same way as described above will solve the problem In this example for no particular reason we choose to use option 2 PC1 sends a packet to wan_ip to reach www ourcompany com 10 0 0 3 1038 gt 195 55 66 77 80 NetDefendOS address translates this statically in accordance with rule 1
301. it is the direction that becomes full first Now what if we want to limit outbound bandwidth in the same way Just inserting std in in the forward chain won t work since you probably want 2 Mbps limit for outbound traffic to be separate from the 2 Mbps limit for inbound traffic If we try to pass 2 Mbps of outbound traffic through the pipe in addition to 2 Mbps of inbound traffic it adds up to 4 Mbps Since the pipe limit is 2 Mbps you d get something close to 1 Mbps in each direction Raising the total pipe limit to 4 Mbps won t solve the problem since the single pipe will not know that 2 Mbps inbound and 2 Mbps outbound was intended 3 Mbps outbound and 1 Mbps inbound might be the result since that also adds up to 4 Mbps The recommended way to control bandwidth in both directions is to use two separate pipes one for inbound and one for outbound traffic In the secenario under discussion each pipe would have a 2 Mbps limit to achieve the desired result The following example goes through the setup for this Example 10 2 Limiting Bandwidth in Both Directions Create a second pipe for outbound traffic CLI 270 10 1 5 Creating Differentiated Limits Chapter 10 Traffic Management with Chains gw world gt add Pipe std out LimitKbpsTotal 2000 Web Interface Go to Traffic Management gt Traffic Shaping gt Pipes gt Add gt Pipe Specify a name for the pipe eg std out Enter 2000 in Total textbox Click OK After cr
302. ite may be classified under the Health Sites category if its content includes health related information or services including sexuality and sexual health as well as support groups hospital and surgical information and medical journals Examples might be www thehealthzone com e www safedrugs com Category 22 Clubs and Societies A web site may be classified under the Clubs and Societies category if its content includes information or services of relating to a club or society This includes team or conference web sites 180 6 3 4 Dynamic Web Content Filtering Chapter 6 Security Mechanisms Examples might be e www sietra org e www walkingclub org Category 23 Music Downloads A web site may be classified under the Music Downloads category if it provides online music downloading uploading and sharing facilities as well as high bandwidth audio streaming Examples might be e www onlymp3s com e www mp3space com Category 24 Business Oriented A web site may be classified under the Business Oriented category if its content is relevant to general day to day business or proper functioning of the Internet for example Web browser updates Access to web sites in this category would in most cases not be considered unproductive or inappropriate Category 25 Government Blocking List This category is populated by URLs specified by a government agency and contains URLs that are deemed unsuitable for viewing by the gen
303. ithin the category e Description A short textual description e Action What action is NetDefendOS taking This information can be cross referenced to the Log Reference Guide Note NetDefendOS sends SNMP Traps which are based on the SNMPv2c standard as defined by RFC1901 RFC1905 and RFC1906 Example 2 12 Sending SNMP Traps to an SNMP Trap Receiver To enable generation of SNMP traps for all events with a severity greater than or equal to Alert to an SNMP trap receiver with an IP address of 195 11 22 55 follow the steps outlined below 37 2 2 3 Event Message Distribution Chapter 2 Management and Maintenance CLI gw world gt add LogReceiver EventReceiverSNMP2c my_snmp IPAddress 195 11 22 55 Web Interface Goto Log amp Event Receivers gt Add gt EventReceiverSNMP2c Specify a name for the event receiver eg my_snmp Enter 195 11 22 55 as the IP Address Enter an SNMP Community String if needed by the trap receiver Click OK The system will now be sending SNMP traps for all events with a severity greater than or equal to Alert to an SNMP trap receiver at 195 11 22 55 38 2 3 RADIUS Accounting Chapter 2 Management and Maintenance 2 3 RADIUS Accounting 2 3 1 Overview Within a network environment containing large numbers of users it is advantageous to have one or a cluster of central servers that maintain user account information and are responsible for authentication and authorization tasks
304. ituations do not occur nearly as easily in NetDefendOS due to much better resource management and lack of restrictions normally placed upon a full blown operating system While a normal operating system can exhibit problems with as few as 5 outstanding half open connections NetDefendOS can fill its entire state table thousands or millions of connections depending on your product model before anything out of the ordinary happens When the state table fills up old outstanding SYN connections will be among the first to be dropped to make room for new connections TCP SYN Flood attacks will show up in NetDefendOS logs as excessive amounts of new connections or drops if the attack is targeted at a closed port The sender IP address is almost invariably spoofed It should ne noted that if Syn Flood Protection is enabled on a Service object and that Service object has an ALG associated with it then the ALG will be disabled 6 6 9 The Jo t2 Attack The Jolt2 attack works by sending a steady stream of identical fragments at the victim machine A few hundred packets per second will freeze vulnerable machines completely until the stream is ended NetDefendOS will protect completely against this attack The first fragment will be enqueued waiting for earlier fragments to arrive so that they may be passed on in order but this never happens so not even the first fragment gets through Subsequent fragments will be thrown away as they are identical to
305. ivating Anti Virus Scanning Association with an ALG Activation of Anti Virus scanning is achieved through an Application Layer Gateway ALG associated with the targeted protocol An HTTP ALG object should first be created with Anti Virus enabled The ALG must then be associated with the appropriate Service object for the protocol to be scanned This Service object is then associated with a rule in the IP rule set which defines the origin and destination of the traffic to which the ALG is to be applied Creating Anti Virus Policies Since IP rule set rules are the means by which the Anti Virus feature is deployed the deployment can be policy based IP rules can specify that the ALG and its associated Anti Virus scanning can apply to traffic going in a given direction and between specific source and destination IP addresses and or networks Scheduling can also be applied to virus scanning so that it takes place only at specific times 6 4 4 The Signature Database SafeStream NetDefendOS Anti Virus scanning is implemented by D Link using the SafeStream virus signature database The SafeStream database is created and maintained by Kaspersky a company which is a world leader in the field of virus detection The database provides protection against virtually all known virus threats including trojans worms backdoor exploits and others The database is also thoroughly tested to provide near zero false positives Database Updates The SafeSt
306. judgement as to the optimal initial size of the prefetch cache Example 5 5 Creating an IP Pool This example shows the creation of an IP Pool object that will use the DHCP server on IP address 28 70 14 7 with 10 prefetched leases It s assumed that this IP address is already defined in the address book as an IP object called jppool_dhcp CLI gw world gt add IPPool ip_pool_1 DHCPServerType ServerIP ServerIP ippool_dhcp Web Interface Go to Objects gt IP Pools gt Add gt IP Pool Now enter Name ip_pool_1 Select Specify DHCP Server Address Add jppool_dhcp to the Selected list Select the Advanced tab Set Prefetched Leases to 10 Click OK 133 5 5 IP Pools Chapter 5 DHCP Services 134 Chapter 6 Security Mechanisms This chapter describes NetDefendOS security features e Access Rules page 135 e Application Layer Gateways page 138 e Web Content Filtering page 169 e Anti Virus Scanning page 183 e Intrusion Detection and Prevention page 188 e Denial Of Service DoS Attacks page 198 e Blacklisting Hosts and Networks page 202 6 1 Access Rules 6 1 1 Introduction One of the principal functions of NetDefendOS is to allow only authorized connections access to protected data resources Access control is primarily addressed by the NetDefendOS IP rule set in which a range of protected LAN addresses are treated as trusted hosts and traffic flow from untrusted sources is restricted from enterin
307. ked up 2 5 3 Resetting to Factory Defaults A restore to factory defaults can be applied so that it is possible to return to the original hardware state that existed when the D Link Firewall was shipped by D Link When a restore is applied all data such as the IDP and Ant Virus databases are lost and must be reloaded 45 2 5 3 Resetting to Factory Defaults Chapter 2 Management and Maintenance Example 2 15 Complete Hardware Reset to Factory Defaults CLI gw world gt reset unit Web Interface 1 Goto Maintenance gt Reset 2 Select Restore the entire unit to factory defaults then confirm and wait for the restore to complete Reset alternative for the DFL 210 260 800 860 only To reset the DFL 210 260 800 860 you must hold down the reset button at the rear panel for 10 15 seconds while powering on the unit After that release the reset button and the DFL 210 800 will continue to load and startup in default mode that is to say with 192 168 1 1 on the LAN interface Reset alternatives for the DFL 1600 and DFL 2500 only Press any key on the keypad when the Press keypad to Enter Setup message appears on the display Select Reset firewall confirm by selecting Yes and wait for the process to complete Warning 4 DO NOT ABORT THE RESET TO FACTORY DEFAULTS PROCESS If aborted the D Link Firewall can cease to function properly 46 2 5 3 Resetting to Factory Defaults Chapter 2 Management and Maintenanc
308. ket was forwarded along the route These options do not occur in normal traffic Time stamps may also be used to record the route a packet has taken from sender to final destination NetDefendOS never enters information into these options regardless of this setting Default DropLog IPOPT_OTHER All options other than those specified above Default DropLog DirectedBroadcasts Indicates whether NetDefendOS will forward packets which are directed to the broadcast address of its directly connected networks It is possible to achieve this functionality by adding lines to the Rules section but it is also included here for simplicity s sake This form of validation is faster than entries in the Rules section since it is more specialized Default DropLog IPRF Indicates what NetDefendOS will do if there is data in the reserved fields of IP headers In normal circumstances these fields should read 0 Used by OS Fingerprinting Default DropLog StripDFOnSmall Strip the Don t Fragment flag for packets equal to or smaller than the size specified by this setting Default 65535 bytes 306 13 2 TCP Level Settings Chapter 13 Advanced Settings 13 2 TCP Level Settings TCPOptionSizes Verifies the size of TCP options This function acts in the same way as IPOptionSizes described above Default ValidateLogBad TCPMSSMin Determines the minimum permissible size of the TCP MSS Packets containing maximum segment
309. ks can be blocked by default or based on a schedule It is also possible to specify which protocols and protocol port numbers are to be blocked Exclude Lists can be created and used to exclude hosts from being blocked when a threshold rule limit is reached Good practice includes adding to the list the firewall s interface IP or MAC address connecting towards the ZoneDefense switch This prevents the firewall from being accidentally blocked out Example 12 1 A simple ZoneDefense scenario The following simple example illustrates the steps needed to set up ZoneDefense It is assumed that all interfaces on the firewall have already been configured An HTTP threshold of 10 connections second is applied If the connection rate exceeds this limitation the firewall will block the specific host in network range 192 168 2 0 24 for example from accessing the switch completely A D Link switch model DES 3226S is used in this case with a management interface address 192 168 1 250 connecting to the firewall s interface address 192 168 1 1 This firewall interface is added into the exclude list to prevent the firewall from being accidentally locked out from accessing the switch Web Interface Add a new switch into ZoneDefense section Go to Zone Defense gt Switches gt Add gt ZoneDefense switch Now enter Name switchi Switch model DES 3226S IP Address 192 168 1 250 For SNMP Community enter the Write Community String configured f
310. l ARP Transaction State entry and broadcasts the ARP request to all the other switch route interfaces except the interface the ARP request was received on If NetDefendOS receives an ARP reply from the destination within a configurable timeout period it will relay the reply back to the sender of the request using the information previously stored in the ARP Transaction State entry During the ARP transaction NetDefendOS learns the source address information for both ends from the request and reply NetDefendOS maintains two tables to store this information the Content Addressable Memory CAM and Layer 3 Cache The CAM table tracks the MAC addresses available on a given interface and the Layer 3 cache maps an IP address to MAC address and interface As the Layer 3 Cache is only used for IP traffic Layer 3 Cache entries are stored as single host entries in the routing table For each IP packet that passes through the D Link Firewall a route lookup for the destination is done If the route of the packet matches a Switch Route or a Layer 3 Cache entry in the routing table NetDefendOS knows that it should handle this packet in a transparent manner If a destination interface and MAC address is available in the route NetDefendOS has the necessary information to forward the packet to the destination If the route was a Switch Route no specific information about the destination is available and the firewall will have to discover where the destination is
311. l even though a corresponding ARP request has not been issued According to the ARP specification the recipient should accept these types of ARP replies However because this can facilitate hijacking of local connections NetDefendOS will normally drop and log such replies The behavior can be changed by modifying the Advanced Setting UnsolicitedA RPReplies ARP Requests The ARP specification states that a host should update its ARP Cache with data from ARP requests received from other hosts However as this procedure can facilitate hijacking of local connections NetDefendOS will normally not allow this To make the behavior compliant with the RFC 826 specification the administrator can modify the Adavnced Setting ARPRequests Even if ARPRequests is set to Drop meaning that the packet is discarded without being stored the system will provided that other rules approve the request reply to it Changes to the ARP Cache NetDefendOS provides a few settings controlling how to manage changes to the ARP cache Possibly a received ARP reply or ARP request would alter an existing item in the ARP cache Allowing this to take place may allow hijacking of local connections However not allowing this may cause problems if for example a network adapter is replaced as NetDefendOS will not accept the new address until the previous ARP cache entry has timed out The Advanced Setting ARPChanges can be adjusted to change the behavior The default
312. l will connect to wan_ip Furthermore the IPsec tunnel needs to be configured to dynamically add routes to the remote network when the tunnel is established B Continue setting up the IPsec Tunnel CLI gw world gt add Interface IPsecTunnel 12tp_ipsec LocalNetwork wan_ip RemoteNetwork all nets IKEAlgorithms ike roamingclients IPsecAlgorithms esp 12tptunnel PSK MyPSK EncapsulationMode Transport 262 9 5 2 L2TP Chapter 9 VPN DHCPOverIPsec Yes AddRouteToRemoteNet Yes IPsecLifeTimeKilobytes 250000 IPsecLifeTimeSeconds 3600 Web Interface Go to Interfaces gt IPsec gt Add gt IPsec Tunnel Enter a name for the IPsec tunnel eg 2tp_ipsec Now enter Local Network wan_ip Remote Network all nets Remote Endpoint none Encapsulation Mode Transport IKE Proposal List ike roamingclients IPsec Proposal List esp l2tptunnel Enter 3600 in the IPsec Life Time seconds control Enter 250000 in the IPsec Life Time kilobytes control Under the Authentication tab select Pre shared Key Select MyPSK in the Pre shared Key control Under the Routing tab check the following controls Allow DHCP over IPsec from single host clients Dynamically add route to the remote network when a tunnel is established Click OK Now it is time to setup the L2TP Server The inner IP address should be a part of the network which the clients are assigned IP addresses from in this lan_ip The outer interface filter is the interface that the L2TP
313. late Destination IP Address To New IP Address ip gatekeeper IP address of gatekeeper Click OK Go to Rules gt IP Rules gt Add gt IPRule Now enter Name H323 In Action Allow Service H323 Gatekeeper Source Interface any Destination Interface core Source Network 0 0 0 0 0 all nets Destination Network wan_ip external IP of the firewall Comment Allow incoming communication with the Gatekeeper Click OK Go to Rules gt IP Rules gt Add gt IPRule Now enter Name H323 In Action Allow Service Gatekeeper Source Interface lan Destination Interface dmz Source Network lannet Destination Network ip gatekeeper IP address of the gatekeeper Comment Allow incoming communication with the Gatekeeper Click OK 163 6 2 8 H 323 Chapter 6 Security Mechanisms Note There is no need to specify a specific rule for outgoing calls NetDefendOS monitors the communication between external phones and the Gatekeeper to make sure that it is possible for internal phones to call the external phones that are registered with the gatekeeper Example 6 9 H 323 with Gatekeeper and two D Link Firewalls This scenario is quite similar to scenario 3 with the difference that the D Link Firewall is protecting the external phones The D Link Firewall with the Gatekeeper connected to the DMZ should be configured exactly as in scenario 3 The other D Link Firewall should be configured as below The rules need to
314. lay The time it takes to move a packet from the source to the destination The time depends on various factors including bandwidth load and the length of the path 4 4 2 OSPF Overview Open Shortest Path First OSPF is a routing protocol developed for IP networks by the Internet Engineering Task Force IETF The NetDefendOS OSPF implementation is based upon RFC 2328 with compatibility to RFC 1583 The way OSPF works is that it routes IP packets based only on the destination IP address found in the IP packet header IP packets are routed as is that is they are not encapsulated in any further protocol headers as they transit the Autonomous System AS OSPF is a dynamic routing protocol it quickly detects topological changes in the AS such as router interface failures and calculates new loop free routes after a period of time OSPF is a link state routing protocol that calls for the sending of link state advertisements LSAs to all other routers within the same area In a link state routing protocol each router maintains a database describing the Autonomous System s topology This database is referred to as the link state database Each router in the same AS has an identical database From the information in the link state database each router constructs a tree of shortest paths with itself as root This shortest path tree gives the route to each destination in the Autonomous System OSPF allows sets of networks to be grouped togeth
315. layed select Undo Delete Listing Modified Objects After modifying several configuration objects you might want to see a list of the objects that were changed added and removed since the last commit Example 2 9 Listing Modified Configuration Objects This example shows how to list configuration objects that have been modified 2 1 5 Working with Configurations Chapter 2 Management and Maintenance CLI gw world gt show changes Object IP4Address ServiceTCPUDP telnet A character in front of the row indicates that the object has been added A character indicates that the object has been modified A character indicates that the object has been marked for deletion Web Interface 1 Go to Configuration gt View Changes in the menu bar A list of changes is displayed Activating and Committing a Configuration After changes to a configuration have been made the configuration has to be activated for those changes to have an impact on the running system During the activation process the new proposed configuration is validated and NetDefendOS will attempt to initialize affected subsystems with the new configuration data Committing IPsec Changes q The administrator should be aware that if any changes that effect the configurations of live IPsec tunnels are committed then those live tunnels connections WILL BE TERMINATED and must be re established If the new configuration is validated N
316. le to communicate In a large Internet like environment this means there has to be a different server on every network This problem is solved by the use of a DHCP relayer A DHCP relayer takes the place of the DHCP server in the local network to act as the link between the client and the remote DHCP server It intercepts requests from clients and relays them to the server The server then responds to the relayer which forwards the response to the client The DHCP relayers follow the BOOTP relay agent functionality and retain the BOOTP message format and communication protocol and hence they are often called BOOTP relay agents Example 5 4 Setting up a DHCP relayer This example allows clients on VLAN interfaces to obtain IP addresses from a DHCP server It is assumed the firewall is configured with VLAN interfaces vlani and vlan2 that use DHCP relaying and the DHCP server IP address is defined in the address book as ip dhcp NetDefendOS will install a route for the client when it has finalized the DHCP process and obtained an IP CLI Adding VLAN interfaces vlan1 and vian2 that should relay to an interface group named as ipgrp dhcp gw world gt add Interface InterfaceGroup ipgrp dhcp Members vlan1 vlan2 Adding a DHCP relay named as vian to dhcpserver gw world gt add DHCPRelay vlan to dhcpserver Action Relay TargetDHCPServer ip dhcp SourceInterface ipgrp dhcp AddRoute Yes ProxyARPInterfaces ipgrp dhcp Web Interface
317. lication attacks WEB_JSP FILE INCLUSION JSP file inclusion WEB_PACKAGES Popular web application packages WEB_PHP XML RPC PHP XML RPC WEB_SQL INJECTION SQL Injection WEB_XSS WINS_GENERAL Cross Site Scripting MS WINS Service WORM_GENERAL Worms X_GENERAL Generic X applications 343 Appendix C Checked MIME filetypes The HTTP Application Layer Gateway has the ability to verify that the contents of a file downloaded via the HTTP protocol is the type that the filetype in its filename indicates This appendix lists the MIME filetypes that can be checked by NetDefendOS to make sure that the content matches the filetype of a download Checking is done if the Check MIME Type option is enabled as described in Section 6 2 2 HTTP Checking also always done if the filetype is ticked in the Allow Selected list for an HTTP ALG Filetype extension Application 3ds 3d Studio files 3gp 3GPP multimedia file aac MPEG 2 Advanced Audio Coding File ab Applix Builder ace ACE archive ad3 Dec systems compressed Voice File ag Applix Graphic file aiff aif Audio Interchange file am Applix SHELF Macro arc Archive file alz ALZip compressed file avi Audio Video Interleave file arj Compressed archive ark QuArk compressed file archive arq Compressed archive as Applix
318. lient will itself act as the LAC L2TP is certificate based and therefore is simpler to administer with a large number of clients and arguably offers better security than PPTP Unlike PPTP it is possible to set up multiple virtual networks across a single tunnel Being IPsec based L2TP requires NAT traversal NAT T to be implemented on the LNS side of the tunnel Example 9 11 Setting up an L2TP server This example shows how to setup a L2TP Network Server The example presumes that you have created some address objects in the Address Book You will have to specify the IP address of the L2TP server interface an outer IP address that the L2TP server should listen to and an IP pool that the L2TP server will use to give out IP addresses to the clients from The interface that the L2TP server will accept connections on is a virtual IPsec tunnel not illustrated in this example CLI gw world gt add Interface L2TPServer MyL2TPServer ServerIP ip_12tp Interface 12tp_ipsec IP wan_ip IPPool L2TP_Pool TunnelProtocol L2TP AllowedRoutes all nets Web Interface 1 Goto Interfaces gt L2TP Servers gt Add gt L2TPServer 2 Enter a suitable name for the L2TP Server eg MyL2TPServer 261 9 5 2 L2TP Chapter 9 VPN Now enter Inner IP Address ip_ 2tp Tunnel Protocol L2TP e Outer Interface Filter 2tp_ipsec e Outer Server IP wan_ip Under the PPP Parameters tab select L2TP_Pool in the IP Pool control Under the Add
319. lies the ike lantolan and esp tn lantolan are suitable for LAN to LAN VPN solutions These proposal lists are trimmed to include only AES and 3DES based proposals Example 9 1 Using a Proposal List This example shows how to create and use an IPsec Proposal List for use in the VPN tunnel It will propose 3DES and DES as encryption algorithms The hash function SHA1 and MD5 will both be used in order to check if the data packet is altered while being transmitted Note that this example does not illustrate how to add the specific IPsec tunnel object It will also be used in a later example CLI First create a list of IPsec Algorithms gw world gt add IPsecAlgorithms esp 12tptunnel DESEnabled Yes DES3Enabled Yes SHA1Enabled Yes MD5Enabled Yes Then apply the proposal list to the IPsec tunnel gw world gt set Interface IPsecTunnel MyIPsecTunnel IPsecAlgorithms esp 12tptunnel Web Interface First create a list of IPsec Algorithms 249 9 3 7 Pre shared Keys Chapter 9 VPN Go to Objects gt VPN Objects gt IKE Algorithms gt Add gt IPsec Algorithms Enter a name for the list eg esp l2tptunnel Now check the following DES 3DES SHA1 MD5 4 Click OK Then apply the proposal list to the IPsec tunnel Go to Interfaces gt IPsec In the grid control click the target IPsec tunnel Select the recently created esp I2tptunnel in the IPsec Algorithms control Click OK 9 3 7 Pre shared Keys Pre Shared Keys
320. ll and it will not throttle lower precedences Limits should be slightly less than available bandwidth Pipe limits should be slightly below the network bandwidth A recommended value is to make the pipe limit 95 of the physical limit The need for this difference becomes less with increasing bandwidth since 5 represents an ever larger piece of the total The reason for the lower pipe limit is how NetDefendOS processes traffic For outbound connections where packets leave the D Link Firewall there is always the possibility that NetDefendOS might slightly overload the connection because of the software delays involved in deciding to send packets and the packets actually being dispatched from buffers For inbound connections there is less control over what is arriving and what has to be processed by the traffic shaping subsystem and it is therefore more important to set pipe limits slightly below the real connection limit to account for the time needed for NetDefendOS to adapt to changing conditions Attacks on Bandwidth Traffic shaping cannot protect against incoming resource exhaustion attacks such as DoS attacks or other flooding attacks NetDefendOS will prevent these extraneous packets from reaching the hosts behind the D Link Firewall but cannot protect the connection becoming overloaded if an attack floods it Watching for Leaks When setting out to protect and shape a network bottleneck make sure that all traffic passing through t
321. ll be automatically removed Click OK B Next create a Stateful NAT Pool object called stateful_natpool Go to Objects gt NAT Pools gt Add gt NAT Pool Now enter Name stateful_natpool Pool type stateful IP Range nat_pool_range Select the Proxy ARP tab and add the WAN interface Click OK C Now define the NAT rule in the IP rule set Go to Rules gt IP Rules gt Add gt IP Rule Under General enter Name Enter a suitable name Action NAT Under Address filter enter Source Interface int Source Network int net Destination Interface wan Destination Network all nets Service HTTP Select the Address Translation tab and enter Check the Use NAT Pool option e Select stateful_natpool from the drop down list Click OK 209 7 3 Static Address Translation Chapter 7 Address Translation 7 3 Static Address Translation NetDefendOS can translate entire ranges of IP addresses and or ports Such translations are transpositions that is each address or port is mapped to a corresponding address or port in the new range rather than translating them all to the same address or port This functionality is known as Static Address Translation SAT Unlike NAT SAT requires more than just a single SAT rule to function NetDefendOS does not terminate the rule set lookup upon finding a matching SAT rule Instead it continues to search for a matching Allow NAT or FwdFast rule Only when it has found su
322. ll not achieve the desired effect which is allocating a maximum of 125 kbps to inbound surfing traffic as part of the 250 kbps total Inbound traffic will pass through one of two pipes one that allows 250 kbps and one that allows 125 kbps giving a possible total of 375 kbps of inbound traffic To solve this we create a chain of the surf in pipe followed by the std in pipe in the surfing traffic Pipe Rule Inbound surf traffic will now first pass through surf in and be limited to a maximum of 125 kbps Then it will pass through the std in pipe along with other inbound traffic which will apply the 250 kbps total limit If surfing uses the full limit of 125 kbps those 125 kbps will occupy half of the std in pipe leaving 125 kbps for the rest of the traffic If no surfing is taking place then all of the 250 kbps allowed through std in will be available for other traffic This is not a bandwidth guarantee for web browsing but it is a 125 kbps bandwidth guarantee for everything except web browsing For web browsing the normal rules of first come first forwarded will apply when competing for bandwidth This may mean 125 kbps but it may also mean much slower speed if the connection is flooded 271 10 1 6 Precedences Chapter 10 Traffic Management Setting up pipes in this way only puts limits on the maximum values for certain traffic types It does not give priorities to different types of competing traffic 10 1 6 Precedences All pack
323. ll switch models require a short period of latency time to implement blocking once the rule is triggered Some models can activate blocking in less than a second while some models may require a minute or more A second difference is the maximum number of rules supported by different switches Some switches support a maximum of 50 rules while others support up to 800 usually in order to block a host or network one rule per switch port is needed When this limit has been reached no more hosts or networks will be blocked out Important 9 ZoneDefense uses a range of the ACL rule set on the switch To avoid potential conflicts in these rules and guarantee the firewall s access control it is strongly recommended that the administrator clear the entire ACL rule set on the switch before executing the ZoneDefense setup 302 12 3 4 Limitations Chapter 12 ZoneDefense 303 Chapter 13 Advanced Settings This chapter describes the configurable advanced setings for NetDefendOS The settings are divided up into the following categories gt pe advanced setting is changed a reconfiguration must be performed in order for the new NetDefendOS configuration to be uploaded to the D Link Firewall and the new value to take effect IP Level Settings page 304 e TCP Level Settings page 307 e ICMP Level Settings page 311 e ARP Settings page 312 e Stateful Inspection Settings page 314 e Connection Timeouts page 316 e Size Limits
324. llow H 323 phones on the Internet to call this phone we need to configure rules The following rules need to be added to the rule set make sure there are no rules disallowing or allowing the same kind of ports traffic before these rules 157 6 2 8 H 323 Chapter 6 Security Mechanisms Web Interface Outgoing Rule Go to Rules gt IP Rules gt Add gt IPRule Now enter Name H323AllowOut Action Allow Service H323 Source Interface lan Destination Interface any Source Network lannet Destination Network 0 0 0 0 0 all nets Comment Allow outgoing calls 3 Click OK Incoming Rule Go to Rules gt IP Rules gt Add gt IPRule Now enter Name H323AllowIn Action Allow Service H323 Source Interface any Destination Interface lan Source Network 0 0 0 0 0 all nets Destination Network lannet Comment Allow incoming calls Click OK 158 6 2 8 H 323 Chapter 6 Security Mechanisms Example 6 5 H 323 with private IP addresses In this scenario a H 323 phone is connected to the D Link Firewall on a network with private IP addresses To make it possible to place a call from this phone to another H 323 phone on the Internet and to allow H 323 phones on the Internet to call this phone we need to configure rules The following rules need to be added to the rule set make sure there are no rules disallowing or allowing the same kind of ports traffic before these rules As we are using private IPs on th
325. lmost correct the packets will arrive at wwwsrv but Return traffic from wwwsrv 80 to internal machines will be sent directly to the machines themselves This will not work as the packets will be interpreted as coming from the wrong address We will now try moving the NAT rule between the SAT and FwdFast rules What happens now External traffic to wan_ip 80 will match rules 1 and 4 and will be sent to wwwsrv Correct Return traffic from wwwsrv 80 will match rules 2 and 3 The replies will therefore be dynamically address translated This changes the source port to a completely different port which will not work The problem can be solved using the following rule set External traffic to wan_ip 80 will match rules 1 and 5 and will be sent to wwwsrv Return traffic from wwwsrv 80 will match rules 2 and 3 Internal traffic to wan_ip 80 will match rules 1 and 4 and will be sent to wwwsrv The sender address will be the D Link Firewall s internal IP address guaranteeing that return traffic passes through the D Link Firewall Return traffic will automatically be handled by the D Link Firewall s stateful inspection mechanism 218 7 3 7 SAT and FwdFast Rules Chapter 7 Address Translation 219 Chapter 8 User Authentication This chapter describes how NetDefendOS implements user authentication e Overview page 220 e Authentication Setup page 221 8 1 Overview In situations where individual use
326. located in the network Discovery is done by NetDefendOS sending out ARP as well as ICMP ping requests acting as the initiating sender of the original IP packet for the destination on the interfaces specified in the Switch Route If an ARP reply is received NetDefendOS will update the CAM table and Layer 3 Cache and forward the packet to the destination If the CAM table or the Layer 3 Cache is full the tables are partially flushed automatically Using the discovery mechanism of sending ARP and ICMP requests NetDefendOS will rediscover destinations that may have been flushed 4 6 4 Enabling Transparent Mode Two steps are normally required to have NetDefendOS operate in Transparent Mode 1 If desired create a group of the interfaces that are to be transparent Interfaces in a group can be marked as Security transport equivalent if hosts are to move freely between them 2 Create Switch Routes and if applicable use the interface group created earlier For the Network parameter specify the range of IP addresses that will be transparent between the interfaces When the entire firewall is working in Transparent Mode this range is normally all nets 4 6 5 High Availability with Transparent Mode Switch Routes cannot be used with High Availability and therefore true transparent mode cannot be implemented with a NetDefendOS High Availability Cluster Instead of Switch Routes the solution in a High Availability setup is to use Proxy ARP to
327. lt configuration it will simply compare arriving packets to the contents of the routing table if a packet arrives on an interface that is different from the interface where the system expects the source to be the packet will be dropped Land and LaTierra attacks will show up in NetDefendOS logs as drops with the rule name set to AutoAccess by default or if you have written custom Access rules the name of the Access rule that dropped the packet The sender IP address is of no interest here since it is always the same as the destination IP address 6 6 6 The WinNuke attack The WinNuke attack works by connecting to a TCP service that does not have handlers for out of band data TCP segments with the URG bit set but still accepts such data This will usually put the service in a tight loop that consumes all available CPU time One such service was the NetBIOS over TCP IP service on Windows machines which gave the attack its name NetDefendOS protects against this in two ways e With a careful inbound policy the attack surface is greatly reduced Only exposed services could possibly become victims to the attack and public services tend to be more well written than 199 6 6 7 Amplification attacks Smurf Chapter 6 Security Mechanisms Papasmurf Fraggle services expected to only serve the local network e By stripping the URG bit by default from all TCP segments traversing the system configurable via Advanced Settings
328. ltaneous scans 183 application layer gateways 138 deploying 138 FTP 140 H 323 155 HTTP 139 POP3 151 SIP 152 SMTP 146 SPAM filtering 147 TFTP 145 ARP 68 gratuitous 94 proxy 96 static 69 ARPBroadcast setting 313 ARPCacheSize setting 313 ARPChanges setting 312 ARPE xpire setting 312 ARPExpireUnknown setting 313 ARPHashSize setting 313 ARPHashSizeVLAN setting 313 ARPIPCollision setting 313 ARPMatchEnetSender setting 312 ARPMiulticast setting 313 ARPQueryNoSenderIP setting 312 ARPRequests setting 312 ARPSenderIP setting 312 authentication 220 databases 221 HTTP 223 local database 221 rules 222 servers 221 setup summary 221 auto update 45 bandwidth guarantees 274 blacklisting hosts and networks 202 IDP 194 threshold rules 280 URL 170 wildcarding 170 Block0000Srec setting 305 BlockONet setting 305 Block127Net setting 305 blocking applications with IDP 188 BlockMulticastSrc setting 305 BufFloodRebootTime setting 336 C certification authority 79 chains in traffic shaping 268 CLI 24 secure shell 24 CLI prompt change 25 cluster see high availability cluster ID see high availability command line interface see CLT config mode 257 configurations 29 connection limiting see threshold rules connection rate limiting see threshold rules ConnLife_IGMP setting 316 ConnLife_Other setting 316 ConnLife_Ping setting 316 ConnLife_TCP_FIN s
329. lude endpoint authentication which is what the PSKs are really for It also includes all the benefits of using IKE Instead of using a fixed set of encryption keys session keys will be used for a limited period of time where after a new set of session keys are used PSK Disadvantages One thing that has to be considered when using Pre Shared Keys is key distribution How are the Pre Shared Keys distributed to remote VPN clients and firewalls This is a major issue since the security of a PSK system is based on the PSKs being secret Should one PSK be compromised the configuration will need to be changed to use a new PSK Certificates Each VPN firewall has its own certificate and one or more trusted root certificates The authentication is based on several things e That each endpoint has the private key corresponding to the public key found in its certificate and that nobody else has access to the private key e That the certificate has been signed by someone that the remote gateway trusts Certificate Advantages Added flexibility Many VPN clients for instance can be managed without having the same pre shared key configured on all of them which is often the case when using pre shared keys and 246 9 3 4 IPsec Protocols ESP AH Chapter 9 VPN roaming clients Instead should a client be compromised the client s certificate can simply be revoked No need to reconfigure every client Certificate Disadvantages Added
330. ly directed at attacks against servers Anti Virus scanning is focussed on downloads by clients NetDefendOS Anti Virus is designed to be a compliment to the standard antivirus scanning normally carried out locally by specialised software installed on client computers IDP is not intended as a complete substitute for local scanning but rather as an extra shield to boost client protection Most importantly it can act as a backup for when local client antivirus scanning is for some reason not able to function NetDefendOS Anti Virus is enabled via the HTTP Application Layer Gateway see Section 6 2 2 HTTP Anti Virus Availability on D Link Models Anti Virus scanning is available on the D Link DFL 260 and DFL 860 only 6 4 2 Implementation Streaming As a file transfer is streamed through a D Link Firewall NetDefendOS will scan the data stream for the presence of viruses if the Anti Virus module is enabled Since files are being streamed and not being read completely into memory a minmum amount of memory is required and there is minimal effect on overall throughput Pattern Matching The inspection process is based on pattern matching against a database of known virus patterns and can determine with a high degree of certainty if a virus is in the process of being downloaded to a user behind a D Link Firewall Once a virus is recognized in the contents of a file the download can be terminated before it completes Types of Files
331. many connections NetDefendOS may keep open at any one time Each connection consumes approximately 150 bytes RAM When this setting is dynamic NetDefendOS will try to use as many connections as is allowed by product Default lt dynamic gt LogConnections Specifies how NetDefendOS will log connections 314 LogConnections Chapter 13 Advanced Settings e NoLog Does not log any connections consequently it will not matter if logging is enabled for either Allow or NAT rules in the Rules section they will not be logged However FwdFast Drop and Reject rules will be logged as stipulated by the settings in the Rules section e Log Logs connections in short form gives a short description of the connection which rule allowed it to be made and any SAT rules that apply Connections will also be logged when they are closed e LogOC As for Log but includes the two packets that cause the connection to be opened and closed If a connection is closed as the result of a timeout no ending packet will be logged e LogOCAll Logs all packets involved in opening and closing the connection In the case of TCP this covers all packets with SYN FIN or RST flags turned on e LogAll Logs all packets in the connection Default Log 315 13 6 Connection Timeouts Chapter 13 Advanced Settings 13 6 Connection Timeouts The settings in this section specify how long a connection can remain idle ie no data being sen
332. mary and one secondary DNS server having IP addresses 10 0 0 1 and 10 0 0 2 respectively CLI gw world gt set DNS DNSServer1 10 0 0 1 DNSServer2 10 0 0 2 Web Interface Goto System gt DNS Enter the following e Primary DNS 10 0 0 1 e Secondary DNS 10 0 0 2 Click OK 87 3 9 DNS Lookup Chapter 3 Fundamentals 88 Chapter 4 Routing This chapter describes how to configure IP routing in NetDefendOS e Overview page 89 e Static Routing page 90 e Policy based Routing page 98 e Dynamic Routing page 103 e Multicast Routing page 110 e Transparent Mode page 119 4 1 Overview IP routing capabilities belong to the most fundamental functionalities of NetDefendOS any IP packet flowing through the system will be subjected to at least one routing decision at some point in time and proper setup of routing is crucial for a NetDefendOS system to function as expected NetDefendOS offers support for the following types of routing mechanisms e Static routing e Dynamic routing NetDefendOS additionally supports route monitoring to achieve route and link redundancy with fail over capability 89 4 2 Static Routing Chapter 4 Routing 4 2 Static Routing The most basic form of routing is known as Static Routing The term static refers to the fact that entries in the routing table are manually added and are therefore permanent or static by nature Due to this manual approach stati
333. mbered sub sections are shown in the table of contents at the beginning An index is included at the end of the document to aid with alphabetical lookup of subjects Where a See chapter section link such as see is provided in the main text this can be clicked to take the reader directly to that reference Text that may appear in the user interface of the product is designated by being in bold case Where is term is being introduced for the first time or being stressed it may appear in a italics Where console interaction is shown in the main text outside of an example this will appear in a box with a gray background Where a web address reference is shown in the text this will open the specified URL in a browser in a new window when clicked some systems may not allow this For example http www dlink com Examples Examples in the text are denoted by the header Example and appear with a gray background as shown below They contain a CLI example and or a Web Interface example as appropriate The accompanying CLI Reference Guide documents all CLI commands Example 1 Example Notation Information about what the example is trying to achieve is found here sometimes with an explanatory image CLI The Command Line Interface example would appear here It would start with the command prompt followed by the command gw world gt somecommand someparameter somevalue Web Interface The Web Interface actions for the example are sh
334. me TCP stacks optimize their connection by measuring the time it takes for a packet to travel to and from its destination This information can then be used to generate resends faster than is usually the case It is also used by OS Fingerprinting TSOPT is a common occurrence in modern networks Default ValidateLogBad TCPOPT_ALTCHKREQ Determines how NetDefendOS will handle alternate checksum request options These options were initially intended to be used in negotiating for the use of better checksums in TCP However these are not understood by any today s standard systems As NetDefendOS cannot understand checksum algorithms other than the standard algorithm these options can never be accepted The ALTCHKREQ option is normally never seen on modern networks Default StripLog TCPOPT_ALTCHKDATA Determines how NetDefendOS will handle alternate checksum data options These options are used 308 TCPOPT_CC Chapter 13 Advanced Settings to transport alternate checksums where permitted by ALTCHKREQ above Normally never seen on modern networks Default StripLog TCPOPT_CC Determines how NetDefendOS will handle connection count options Default StripLogBad TCPOPT_OTHER Specifies how NetDefendOS will deal with TCP options not covered by the above settings These options usually never appear on modern networks Default StripLog TCPSynUrg Specifies how NetDefendOS will deal with TCP packets with SYN Synchronize
335. means that all subsequent traffic coming from a blacklisted source with be automatically dropped by NetDefendOS For more details of how blacklisting functions see Section 6 7 Blacklisting Hosts and Networks IDP ZoneDefense The Protect action includes the option that the particular D Link switch that triggers the IDP Rule can be de activated through the D Link ZoneDefense feature For more details on how ZoneDefense functions see Chapter 12 ZoneDefense 6 5 8 SMTP Log Receiver for IDP Events In order to receive notifications via email of IDP events a SMTP Log receiver can be configured This email will contain a summary of IDP events that have occurred in a user configurable period of time When an IDP event occurrs the NetDefendOS will wait for Hold Time seconds before sending the notification email However the email will only be sent if the number of events occurred in this period of time is equal to or bigger than the Log Threshold When this email has been sent NetDefendOS will wait for Minimum Repeat Time seconds before sending a new email Example 6 19 Configuring an SMTP Log Receiver In this example an IDP Rule is configured with an SMTP Log Receiver Once an IDP event occurs the Rule is 194 6 5 8 SMTP Log Receiver for IDP Chapter 6 Security Mechanisms Events triggered At least one new event occurs within the Hold Time of 120 seconds thus reaching the log threshold level at least 2 events have oc
336. ming client VPN scenarios L2TP is usually encapsulated in IPsec to provide encryption with IPsec running in transport mode instead of tunnel mode The steps for L2TP over IPsec setup are 1 Create an IP object let s call it 2tp_pool which defines the range of IP addresses which can be handed out to clients The range chosen could be of two types e A range taken from the internal network to which clients will connect If the internal network is 192 168 0 0 24 then we might use the address range 192 168 0 10 to 192 168 0 20 The danger here is that an IP address might be accidentally used on the internal network and handed out to a client e Use a new address range that is totally different to any internal network This prevents any chance of an address in the range also being used on the internal network 2 Define two other IP objects e ip_ext which is the external public IP address through which clients connect let s assume this is on the ext interface e ip_int which is the internal IP address of the interface to which the internal network is connected let s call this interface int 234 9 2 4 L2TP Roaming Clients with Chapter 9 VPN Pre Shared Keys 3 Define a Pre shared Key for the IPsec tunnel 4 Define an IPsec Tunnel object let s call this object ipsec_tunnel with the following parameters Set Local Network to ip_ext specify all nets instead if NetDefendOS is behind a NATing device Set Remote Netw
337. mode for FTP clients though some advice may recommend the opposite FTP Security Issues Both modes of FTP operation present problems for firewalls Consider a scenario where an FTP 140 6 2 3 FTP Chapter 6 Security Mechanisms client on the internal network connects through the firewall to an FTP server on the Internet The IP tule is then configured to allow network traffic from the FTP client to port 21 on the FTP server When active mode is used NetDefendOS is not aware that the FTP server will establish a new connection back to the FTP client Therefore the incoming connection for the data channel will be dropped As the port number used for the data channel is dynamic the only way to solve this is to allow traffic from all ports on the FTP server to all ports on the FTP client Obviously this is not a good solution When passive mode is used the firewall does not need to allow connections from the FTP server On the other hand NetDefendOS still does not know what port the FTP client tries to use for the data channel This means that it has to allow traffic from all ports on the FTP client to all ports on the FTP server Although this is not as insecure as in the active mode case it still presents a potential security threat Furthermore not all FTP clients are capable of using passive mode The Solution The FTP ALG solves this problem by fully reassembling the TCP stream of the command channel and examining its contents
338. n Address Translation The following examples illustrates the IGMP rules needed to configure IGMP according to the Address Translation scenario described above in Section 4 5 2 2 Multicast Forwarding Address Translation Scenario We need two IGMP report rules one for each client interface If1 uses no address translation and if2 translates the multicast group to 237 192 10 0 24 We also need two query rules one for the translated address and interface and one for the original address towards if1 Two examples are provided one for each pair of report and query rule The upstream multicast router uses IP UpstreamRouterIP Example 4 11 Configuration if1 The following steps needs to be executed to create the report and query rule pair for if1 which uses no address translation Web Interface A Create the first IGMP Rule 1 Goto Routing gt IGMP gt IGMP Rules gt Add gt IGMP Rule 2 Under General enter 116 4 5 3 IGMP Configuration Chapter 4 Routing Name A suitable name for the rule eg Reports _if1 Type Report Action Proxy Output wan this is the relay interface Under Address Filter enter Source Interface if1 Source Network ifinet Destination Interface core Destination Network auto Multicast Source 192 168 10 1 Multicast Group 239 192 10 0 24 Click OK B Create the second IGMP Rule Again go to Routing gt IGMP gt IGMP Rules gt Add gt IGMP Rule Under General enter
339. n IGMP_GENERAL IGMP IMAP_GENERAL IMAP protocol implementation IM_AOL AOL IM IM_GENERAL Instant Messenger implementations IM_MSN MSN Messenger IM_YAHOO Yahoo Messenger IP_GENERAL IP protocol and implementation IP_OVERFLOW Overflow of IP protocol implementation IRC_GENERAL Internet Relay Chat LDAP_GENERAL LDAP_OPENLDAP General LDAP clients servers Open LDAP LICENSE_CA LICENSE License management for CA software LICENSE_GENERAL General License Manager MALWARE_GENERAL Malware attack METASPLOIT_FRAME Metasploit frame attack METASPLOIT_GENERAL Metasploit general attack MISC_GENERAL General attack MSDTC_GENERAL Ms DTC MSHELP_GENERAL Microsoft Windows Help NETWARE_GENERAL NetWare Core Protocol NFS_FORMAT Format NFS_GENERAL NFS protocol implementation NNTP_GENERAL NNTP implementation protocol OS_SPECIFIC AIX AIX specific OS_SPECIFIC GENERAL OS general OS_SPECIFIC HPUX HP UX related OS_SPECIFIC LINUX Linux specific OS_SPECIFIC SCO SCO specific OS_SPECIFIC SOLARIS OS_SPECIFIC WINDOWS Solaris specific Windows specific P2P_EMULE eMule P2P tool P2P_GENERAL General P2P tools P2P_GNUTELLA Gnutella P2P tool PACKINGTOOLS_GENERAL PBX_GENERAL General packing tools attack PBX 341 Appendix B IDP Signature Groups Group Name Intrusion Type PO
340. n High Availability Clusters Updating the Anti Virus databases for both the D Link Firewalls in an HA Cluster is performed automatically by NetDefendOS In a cluster there is always an active unit and an inactive unit Only the active unit in the cluster will perform regular checking for new database updates If a new database update becomes available the sequence of events will be as follows 1 The active unit determines there is a new update and downloads the required files for the update 2 The active unit performs an automatic reconfiguration to update its database 3 This reconfiguration causes a failover so the passive unit becomes the active unit 4 When the update is completed the newly active unit also downloads the files for the update and performs a reconfiguration 5 This second reconfiguration causes another failover so the passive unit reverts back to being active again These steps result in both D Link Firewalls in a cluster having updated databases and with the original active passive roles For more information about HA clusters refer to Chapter 11 High Availability Example 6 18 Activating Anti Virus Scanning This example shows how to setup an Anti Virus scanning policy for HTTP traffic from lannet to all nets We will assume there is already a NAT rule defined in the IP rule set to handle this traffic CLI First create an HTTP Application Layer Gateway ALG Object with Anti Virus scanning enabled gw world
341. n of how well the victim s IP stack is implemented NetDefendOS will never allow fragments through that would result in the total size exceeding 65535 bytes In addition to that there are configurable limits for IP packet sizes in the Advanced Settings section Ping of death will show up in NetDefendOS logs as drops with the rule name set to LogOversizedPackets The sender IP address may be spoofed 6 6 4 Fragmentation overlap attacks Teardrop Bonk Boink and Nestea Teardrop and its followers are fragment overlap attack Many IP stacks have shown erratic behavior excessive resource exhaustion or crashes when exposed to overlapping fragments NetDefendOS protects fully against fragmentation overlap attacks Overlapping fragments are never allowed to pass through the system Teardrop and its followers will show up in NetDefendOS logs as drops with the rule name set to TllegalFrags The sender IP address may be spoofed 6 6 5 The Land and LaTierra attacks The Land and LaTierra attacks works by sending a packet to a victim and making the victim respond back to itself which in turn generates yet another response to itself etc This will either bog the victim s machine down or make it crash The attack is accomplished by using the victim s IP address in the source field of an IP packet as well as in the destination field NetDefendOS protects against this attack by applying IP spoofing protection to all packets In its defau
342. nagement and Maintenance Device gt set device name gw world The CLI Reference Guide uses the command prompt gw world gt throughout Note When the command line prompt is changed to a new string value this string also appears as the new device name in the top level node of the WebUI tree view Activate and Committing Changes If any changes are made to the current configuration through the CLI those changes won t be uploaded to NetDefendOS until the command gw world gt activate is issued Immediately following the activate command the command gw world gt commit should be issued to make those changes permanent If a commit command is not issued within a default time period of 30 seconds then the changes are automatically undone and the old configuration restored Logging off from the CLI After finishing working with the CLI you should logout to avoid other people getting unauthorized access to the system Log off by using the exit or the logout command 2 1 4 The WebUIl NetDefendOS provides a highly versatile web user interface WebUI for management of the system using a standard web browser This allows the administrator to perform remote management from virtually anywhere in the world without having to install any third party clients Logging on to the Web Interface To access the web interface launch a standard web browser and point the browser at the IP address of the firewall The factory default addre
343. namicRoutingRuleAddRoute Destination MainRoutingTable Web Interface Go to Routing gt Dynamic Routing Rules Click on the recently created ImportOSPFRoutes Go to OSPF Routing Action gt Add gt DynamicRountingRuleAddRoute In Destination add the main routing table to the Selected list Click OK Example 4 7 Exporting the Default Route into an OSPF AS In this example the default route from the main routing table will be exported into an OSPF AS named as0 First add a dynamic routing policy filter that matches the main routing table and the default route CLI gw world gt add DynamicRoutingRule OSPFProcess as0 name ExportDefRoute RoutingTable MainRoutingTable DestinationInterface wan DestinationNetworkExactly all nets Web Interface Go to Routing gt Dynamic Routing Rules gt Add gt Dynamic routing policy rule Specify a suitable name for the filter eg ExportDefRoute For From Routing Table select Main Routing Table Choose wan for Destination Interface Choose all nets in the Exactly Matches list Click OK Then create an OSPF Action that will export the filtered route to the specified OSPF AS CLI gw world gt cc DynamicRoutingRule ExportDefRoute gw world ExportDefRoute gt add DynamicRoutingRuleExportOSPF ExportToProcess as0 Web Interface Go to Routing gt Dynamic Routing Rules Click on the newly created ExportDefRoute Go to OSPF Action gt Add gt DynamicRoutingRuleExportOSPF For Export to pro
344. nce a rule in the IP rule set can use a Service object as a filter to decide whether or not to allow certain traffic through the D Link Firewall For more information on how service objects are being used wit IP rules see Section 3 5 The IP Rule Set A large number of Service objects come pre defined with NetDefendOS These include common services such as HTTP FTP Telnet and SSH Pre defined Services can be used and also modified just like user defined Services However it is recommended NOT to make any changes to pre defined services but instead create new ones with the desired parameters Example 3 6 Listing the Available Services To produce a listing of the available services in the system CLI gw world gt show Service The output will look similar to the following listing ServiceGroup Comments all_services All ICMP TCP and UDP services all_tcpudp All TCP and UDP services ipsec suite The IPsectIKE suite 12tp ipsec L2TP using IPsec for encryption and authentication 12tp raw L2TP control and transport unencrypted pptp suite PPTP control and transport ServiceICMP Web Interface 1 Goto Objects gt Services Example 3 7 Viewing a Specific Service To view a specific service in the system CLI gw world gt show Service ServiceTCPUDP echo The output will look similar to the following listing Property Value 3 2 2 TCP and UDP Based Services Chapter 3 Fundamentals DestinationPorts Type
345. nce this command is issued an ICMP ping can be then sent to the D Link Firewall from the other end of the tunnel This will cause ikesnoop verbose to output details of the tunnel setup Incompatibilities in the proposal lists for IKE and or IPsec can often cause problems which show up in this output If there are multiple tunnels in a setup or mutiple clients on a single tunnel then the output from ikesnoop verbose can be overwhelming It is therefore better to specify that the output come from a single tunnel by specifying the client s IP address ikesnoop verbose lt ip address gt Management Interface Failure with VPN If any VPN tunnel is set up and then the management interface no longer operates then it is likely to be a problem with the management traffic being routed back through the VPN tunnel instead of the correct interface This happens when a route is established in the main routing table which routes any traffic for all nets through the VPN tunnel If the management interface is not reached by the VPN tunnel then the administrator needs to create a specific route that routes management interface traffic leaving the D Link Firewall back to the management subnet When any VPN tunnel is defined an all nets route is automatically defined in the routing table so the administrator should always set up a specific route for the management interface to be correctly routed 239 9 3 IPsec Chapter 9 VPN 9 3 IPsec 9 3 1 O
346. nd can also significantly impair throughput performance Default Disabled ConnReplace Allows new additions to NetDefendOS s connection list to replace the oldest connections if there is no available space Default ReplaceLog LogOpenFails In some instances where the Rules section determines that a packet should be allowed through the stateful inspection mechanism may subsequently decide that the packet cannot open a new connection One example of this is a TCP packet that although allowed by the Rules section and not being part of an established connection has its SYN flag off Such packets can never open new connections In addition new connections can never be opened by ICMP messages other than ICMP ECHO Ping This setting determines if NetDefendOS is to log the occurrence of such packets Default Enabled LogReverseOpens Determines if NetDefendOS logs packets that attempt to open a new connection back through one that is already open This only applies to TCP packets with the SYN flag turned on and to ICMP ECHO packets In the case of other protocols such as UDP there is no way of determining whether the remote peer is attempting to open a new connection Default Enabled LogStateViolations Determines if NetDefendOS logs packets that violate the expected state switching diagram of a connection for instance getting TCP FIN packets in response to TCP SYN packets Default Enabled MaxConnections Specifies how
347. nd packets destined for the shared address The only delay in failover therefore is detecting that the active unit is down ARP queries are also broadcast periodically to ensure that switches don t forget where to send 291 11 2 High Availability Mechanisms Chapter 11 High Availability packets destined for the shared hardware address 292 11 3 High Availability Setup Chapter 11 High Availability 11 3 High Availability Setup This section provides a step by step guide for setting up an HA Cluster 11 3 1 Hardware Setup 1 Start with two physically similar D Link Firewalls Both may be newly purchased or one may have been purchased to be the back up unit in other words to be the slave unit 2 Make the physical connections e Connect the matching interfaces of master and slave through a common switch e Select an interface on the master and slave which is to be used by the units for monitoring each other and connect them together with an Ethernet crossover cable This will be the NetDefendOS sync interface It is recommended that the same interface is used on both master and slave assuming they are similar systems Figure 11 1 High Availability Setup Master Firewall Slave Firewall Internal Z LAN N x Extema router The illustration above shows the typical HA Cluster connections All interfaces of the master would normally also be present on the slave and be connected to the same netw
348. nect to Remote Network all nets Remote Endpoint None Encapsulation Mode Tunnel For Algorithms enter IKE Algorithms Medium or High IPsec Algorithms Medium or High For Authentication enter e Pre Shared Key Select the pre shared key created earlier 254 9 4 3 Roaming Clients Chapter 9 VPN 5 Under the Routing tab Enable the option Dynamically add route to the remote network when a tunnel is established 6 Click OK C Finally configure the IP rule set to allow traffic inside the tunnel 9 4 3 2 Self signed Certificate based client tunnels Example 9 5 Setting up a Self signed Certificate based VPN tunnel for roaming clients This example describes how to configure an IPsec tunnel at the head office D Link Firewall for roaming clients that connect to the office to gain remote access The head office network uses the 10 0 1 0 24 network span with external firewall IP wan_ip Web Interface A Create a Self signed Certificate for IPsec authentication The step to actually create self signed certificates is performed outside the WebUI using a suitable software product The certificate should be in the PEM Privacy Enhanced Mail file format B Upload all the client self signed certificates Go to Objects gt Authentication Objects gt Add gt Certificate Enter a suitable name for the Certificate object Select the X 509 Certificate option Click OK C Create Identification Lists Go to
349. neeees 28 2 3 Listing Contig uratlon OBects css 2s seed nEn EEE EER TES EAEE EE e sean seey 29 2 4 Displaying a Configuration Object eee ee ccee cence eece seca cece een eeeaeeea eens eeaneees 30 2 5 Editing a Configuration Object 2 0 0 0 cece cece cc ence ence eeceeeeeeeceeseaeeea sees eens eeae esas 31 2 6 Adding a Configuration Object 2 0 0 0 cece cc eecc ence ence eeceeeceeeceeeeaeeeueeea sean sean eegs 31 2 7 Deleting a Configuration Object sssr cece eee nec c ence eeeeeeeeeeceeeea essa eeaa eens eeae esas 32 2 8 Undeleting a Configuration Object cece cee cence eeceeeeeeeeaeeea essa sean eeu eees 32 2 9 Listing Modified Configuration Objects 2 0 0 0 cece cece ee ceeeceeece seca eeea sean ecueeees 32 2 10 Activating and Committing a Configuration ccc cece nee ce eee ceneeeneeeneeeenees 33 2 11 Enable Logging to a Syslog Host cee eesceseccsscnescnsecnsenneseneseserna sven ssensoes 36 2 12 Sending SNMP Traps to an SNMP Trap Receiver ccc ceee cece eee en eeee een een eens 37 2 13 Enabling SNMP Monitoring 20 00 00 onite ence eece neces ceeecaeseaesea sean sean eean eens 44 2 14 Configuration Backup and Restore 0 e cece cece cee ceeeceeeee ceca ceca eeu eeeneeea sean ecu eegs 45 2 15 Complete Hardware Reset to Factory Defaults cee ceeeeeeneeceeeeeceeecenueeeene eee 46 ST nAdding an IP HOSti t s3 core e a a a a dace ae eh oe dau sede teu antaieyen
350. ng policy as well as carrying out address translation and server load balancing The Traffic Shaping Rules define the policy for bandwidth management the IDP Rules control the behavior of the intrusion prevention engine and so on 1 2 3 Basic Packet Flow Chapter 1 Product Overview 1 2 3 Basic Packet Flow This section outlines the basic flow in the state engine for packets received and forwarded by NetDefendOS Please note that this description is simplified and might not be fully applicable in all scenarios The basic principle however is still valid in all applications 1 An Ethernet frame is received on one of the Ethernet interfaces in the system Basic Ethernet frame validation is performed and the packet is dropped if the frame is invalid 2 The packet is associated with a Source Interface The source interface is determined as follows e If the Ethernet frame contains a VLAN ID Virtual LAN identifier the system checks for a configured VLAN interface with a corresponding VLAN ID If one is found that VLAN interface becomes the source interface for the packet If no matching interface is found the packet is dropped and the event is logged e If the Ethernet frame contains a PPP payload the system checks for a matching PPPoE interface If one is found that interface becomes the source interface for the packet If no matching interface is found the packet is dropped and the event is logged e If none the above is true
351. ng web sites to conduct company assessments If the corporate policy blocks gambling web sites he won t be able to do his job For this reason NetDefendOS supports a feature called Allow Override With this feature enabled the content filtering component will present a warning to the user that he is about to enter a web site that is restricted according to the corporate policy and that his visit to the web site will be logged This page is known as the restricted site notice The user is then free to continue to the URL or abort the request to prevent being logged By enabling this functionality only users that have a valid reason to visit inappropriate sites will normally do so Other will avoid those sites due to the obvious risk of exposing their surfing habits a Caution 2 Enabling override can result in a user being able to surf to sites that are linked to by x the visited site Reclassification of Blocked Sites As the process of classifying unknown web sites is automated there is always a small risk that some sites are given an incorrect classification NetDefendOS provides a mechanism for allowing users to manually propose a new classification of sites This mechanism can be enabled on a per HTTP ALG level which means that you can choose to enable this functionality for regular users or for a selected user group only If reclassification is enabled and a user requests a web site which is disallowed the block web page will inclu
352. ngs tab Create IDP Action 196 6 5 8 SMTP Log Receiver for IDP Chapter 6 Security Mechanisms Events When this IDP Rule has been created an action must also be created specifying what signatures the IDP should use when scanning data matching the IDP Rule and what NetDefendOS should do in case an intrusion is discovered Intrusion attempts should cause the connection to be dropped so Action is set to Protect Severity is set to Attack in order to match all SMTP attacks Signatures is set to IPS_MAIL_SMTP in order to use signatures that describe attacks from the external network dealing with the SMTP protocol 1 Goto IDP gt IDP Rules gt IDPMailSrvRule gt Add gt IDP Rule Action 2 Now enter Action Protect Severity All Signatures IPS_MAIL_SMTP Click OK In summary the following will occur If traffic from the external network to the mail server occurs IDP will be activated If traffic matches any of the signatures in the IPS_MAIL_SMTP signature group the connection will be dropped thus protecting the mail server 197 6 6 Denial Of Service DoS Attacks Chapter 6 Security Mechanisms 6 6 Denial Of Service DoS Attacks 6 6 1 Overview By embracing the Internet enterprises experience new business opportunities and growth The enterprise network and the applications that run over it are business critical Not only can a company reach a larger number of customers via the Internet it can serve t
353. nitiated with the command gw world gt updatecenter update Antivirus 338 Database Console Commands Appendix A Subscribing to Security Updates Querying Update Status To get the status of IDP updates use the command gw world gt updatecenter status IDP To get the status of AV updates gw world gt updatecenter status Antivirus Querying Server Status To get the status of the D Link network servers use the command gw world gt updatecenter servers Deleting Local Databases Some technical problem in the operation of either IDP or the Anti Virus modules may be resolved by deleting the database and reloading For IDP this is done with the command gw world gt removedb IDP To remove the Anti Virus database use the command gw world gt removedb Antivirus Once removed the entire system should be rebooted and a database update initiated Removing the database is also recommended if either IDP or Anti Virus is not used for longer periods of time Note Anti Virus database updates require a couple of seconds to be optimized once an update is downloaded This will cause the firewall to momentarily pause in its operation It can therefore be best to set the timing of updates to be at times of low traffic such as in the early hours of the morning Deleting a database can cause a similar pause in operation 339 Appendix B IDP Signature Groups For IDP scanning the following signature groups a
354. nization are used Example 3 27 Enabling the D Link NTP Server To enable the use of the D Link NTP server CLI gw world gt set DateTime TimeSynchronization D Link Web Interface 1 Goto System gt Date and Time 2 Select the D Link TimeSync Server radio button 3 Click OK As mentioned above it is important to have an external DNS server configured so that the D Link Time Server URLs can be resolved during the access process 86 3 9 DNS Lookup Chapter 3 Fundamentals 3 9 DNS Lookup A DNS server can resolve a Fully Qualified Domain Name FQDN into the corresponding numeric IP address FQDNs are unambiguous textual domain names which specify a node s unique position in the Internet s DNS tree hierarchy FQDN resolution allows the actual physical IP address to change while the FQDN can stay the same A Uniform Resource Locator URL differs from an FQDN in that the URL includes the access protocol along with the FQDN For example the protocol might be specified http for world wide web pages FQDNs are used in many aspects of a NetDefendOS configuration where IP addresses are unknown or where it makes more sense to make use of DNS resolution instead of using static IP addresses To accomplish DNS resolution NetDefendOS has a built in DNS client that can be configured to make use of up to three DNS servers Example 3 28 Configuring DNS Servers In this example the DNS client is configured to use one pri
355. nnection to the backbone e Linking the backbone in case of a partitioned backbone Areas without direct connection to the backbone The backbone always need to be the center of all other areas In some rare case where it is impossible to have an area physically connected to the backbone a virtual link is used This virtual link will provide that area with a logical path to the backbone area This virtual link is established between two ABRs that are on one common area with one of the ABRs connected to the backbone area In the example below two routers are connected to the same area Area 1 but just one of them fw1 is connected physically to the backbone area Figure 4 2 Virtual Links Example 1 In the above example the Virtual Link is configured between fw1 and fw2 on Area 1 as it is used as the transit area In this configuration only the Router ID has to be configured The diagram shows that fw2 needs to have a Virtual Link to fwl with Router ID 192 168 1 1 and vice versa These Virtual Links need to be configured in Area 1 A Partitioned Backbone OSPF allows for linking a partitioned backbone using a virtual link The virtual link should be configured between two separate ABRs that touch the backbone are from each side and having a 106 4 4 3 Dynamic Routing Policy Chapter 4 Routing common area in between Figure 4 3 Virtual Links Example 2 The Virtual Link is configured between fw1 and fw2 on Area 1 as it
356. nnections SAT requires a second Allow rule Go to Rules gt IP Rules gt Add gt IPRule Now enter Name Allow ftp Action Allow e Service ftp inbound For Address Filter enter Source Interface any Destination Interface core Source Network all nets Destination Network wan_ip 143 6 2 3 FTP Chapter 6 Security Mechanisms 4 Click OK Example 6 3 Protecting FTP Clients In this scenario shown below the D Link Firewall is protecting a workstation that will connect to FTP servers on the Internet To make it possible to connect to these servers from the internal network using the FTP ALG the FTP ALG and rules should be configured as follows Web Interface A Create the FTP ALG Go to Objects gt ALG gt Add gt FTP ALG Enter Name ftp outbound Uncheck Allow client to use active mode Check Allow server to use passive mode Click OK B Create the Service Go to Objects gt Services gt Add gt TCP UDP Service Now enter Name ftp outbound Type select TCP from the dropdown list 144 6 2 4 TFTP Chapter 6 Security Mechanisms Destination 21 the port the ftp server resides on e ALG select the newly created ftp outbound 3 Click OK Rules Using Public IPs The following rule needs to be added to the IP rules if using public IP s make sure there are no rules disallowing or allowing the same kind of ports traffic before these rules The service in use is the ftp ou
357. ns to the network and sends data to another connected device when no other is sending If 2 devices broadcast simultaneously algorithms allow them to re send at different times Devices broadcast data as frames and the other devices listen to determine if they are the intended destination for any of these frames A frame is a sequence of bits which specify the originating device plus the destination device the data payload along with error checking bits A pause between the broadcasting of individual frames allows devices time to process each frame before the next arrives and this pause becomes progressively smaller as the transmission rates get faster from normal to Fast and then Gigabit Ethernet Each Ethernet interface in a D Link Firewall corresponds to a physical Ethernet port in the system The number of ports their link speed and the way the ports are realized is dependent on the hardware model Note Some systems use an integrated layer 2 switch for providing additional physical Ethernet ports Such additional ports are seen as a single interface by NetDefendOS Ethernet Interface Names 58 3 3 2 Ethernet Chapter 3 Fundamentals The names of the Ethernet interfaces are pre defined by the system and are mapped to the names of the physical ports a system with a wan port will have an Ethernet interface named wan and so on The names of the Ethernet interfaces can be changed to better reflect their usage For instance i
358. nstein Park II Block B 102 106 Witch Hazel Avenue Highveld Technopark Centurion Gauteng Republic of South Africa TEL 27 12 665 2165 FAX 27 12 665 2186 Website www d link co za Avenida Diagonal 593 95 9th floor 08014 Barcelona Spain TEL 34 93 4090770 FAX 34 93 4910795 Website www dlink es P O Box 15036 S 167 15 Bromma Sweden TEL 46 0 8564 61900 FAX 46 0 8564 61901 Website www dlink se Glatt Tower 2 0G CH 8301 Glattzentrum Postfach 2 0G Switzerland TEL 41 0 1 832 11 00 FAX 41 0 1 832 11 01 Website www dlink ch No 289 Sinhu 3rd Rd Neihu District Taipei City 114 Taiwan TEL 886 2 6600 0123 FAX 886 2 6600 1188 Website www dlinktw com tw Cetin Emec Bulvari 74 sokak ABC Plaza No 9 3 Ovecler Ankara TURKEY TEL 0090 312 473 40 55 FAX 0090 312 473 40 58 Website www dlink com tr 17595 Mt Herrmann Street Fountain Valley CA 92708 TEL 1 800 326 1688 Website www dlink com 350 Alphabetical Index A access rules 135 accounting 39 interim messages 41 limitations with NAT 42 messages 39 system shutdowns 42 address book 48 ethernet addresses in 50 IP addresses in 48 address groups 51 address translation 204 administration accounts 23 ALG see application layer gateway all nets IP object 51 AllowBothSidesToKeepConnAlive_UDP 316 Allow IP rule 75 anti virus scanning 183 activating 184 database 184 memory requirements 183 simu
359. nt message whenever a new connection is established given that the matching security policy rule has defined that event messages should be generated for that connection An example of a low level event would be the startup_normal event which generates a mandatory event message as soon as the system starts up All event messages have a common format with attributes that include category severity recommended actions These attributes enable easy filtering of messages either within NetDefendOS prior to sending to an event receiver or as part of the analysis after logging and storing messages on an external log server A list of all event messages can be found in the Log Reference Guide That guide also describes the design of event messages and explains the various attributes available The severity of each event is predefined and in order of severity can be one of Emergency Alert Critical Error Warning Notice Info Debug By default all messages of level Info and above are sent The Debug category of designed for troubleshooting only and should only be turned on if required to try and solve a problem Messages of all severity levels are found listed in the NetDefendOS Log Reference Guide 2 2 3 Event Message Distribution To distribute and log the event messages generated it is necessary to define one or more event receivers that specify what events to capture and where to send them NetDefendOS can distribute event messa
360. ntent_filtering Select the TCP in the Type dropdown list Enter 80 in the Destination Port textbox Select the HTTP ALG you just created in the ALG list Click OK Finally modify the NAT rule to use the new service Go to Rules gt IP Rules In the grid control click the NAT rule handling your HTTP traffic Click the Service tab Select your new service http_content_filtering in the pre defined Service list Click OK Dynamic content filtering is now activated for all web traffic from lannet to all nets Validate the functionality by following these steps On a workstation on the lannet network launch a standard web browser Try to browse to a search site for instance www google com If everything is configured correctly your web browser will present a web page that informs you about that the requested site is blocked Audit Mode In Audit Mode the system will classify and log all surfing according to the content filtering policy but restricted web sites will still be accessible to the users This means the content filtering feature of NetDefendOS can then be used as an analysis tool to analysis what categories of websites are being accessed by a user community and how often After running in Audit Mode for some weeks it is then easier to have a good understanding of surfing behaviour and also the potential time savings that can be made by enabling content filtering It is recommended that the administrator gradually introduce
361. nterface 2tp_tunnel Originator IP all nets Terminator IP wan_ip Under the Authentication Options tab enter UserDB as the Local User DB Click OK When the other parts are done all that is left is the rules To let traffic through from the tunnel two IP rules should be added E Finally set up the rules CLI gw world gt add IPRule action Allow Service all_services SourceInterface 12tp_ tunnel SourceNetwork 12tp_pool DestinationInterface any DestinationNetwork all nets name AllowL2TP gw world gt add IPRule action NAT Service all_services SourceInterface 12tp tunnel SourceNetwork 12tp_pool DestinationInterface any DestinationNetwork all nets name NATL2TP Web Interface 1 Goto Rules gt IP Rules gt Add gt IPRule 2 Enter a name for the rule eg AllowL2TP 3 Now enter Action Allow Service all_services Source Interface I2tp_tunnel Source Network 2tp_pool Destination Interface any Destination Network all nets 264 9 5 2 L2TP Chapter 9 VPN Click OK Go to Rules gt IP Rules gt Add gt IPRule Enter a name for the rule eg NATL2TP Now enter Action NAT Service all_services Source Interface I2tp_tunnel Source Network 2tp_pool Destination Interface any Destination Network all nets Click OK 265 9 5 2 L2TP Chapter 9 VPN 266 Chapter 10 Traffic Management This chapter describes how NetDefendOS can manage network traffic e Traffic
362. ny more requests until it the server recovers to full functionality SLB will use the default routing table unless the administrator sets a specific routing table location D Link Server Load Balancing provides the following monitoring modes ICMP Ping This works at OSI layer 3 SLB will ping the IP address of each individual server in the server farm This will detect any failed servers TCP Connection This works at OSI layer 4 SLB attempts to connect to a specified port on each server For example if a server is specified as running web services on port 80 the SLB will send a TCP SYN request to that port If SLB does not receive a TCP SYN ACK back it will mark port 80 on that server as down SLB recognizes the conditions no response normal response or closed port response from servers 10 3 6 SLB_SAT Rules 284 10 3 6 SLB_SAT Rules Chapter 10 Traffic Management The key component in setting up SLB is the SLB_SAT rule in the IP rule set The steps that should be followed are 1 Define an Object for each server for which SLB is to be done 2 Define a Group which included all these objects 3 Define an SLB_SAT Rule in the IP rule set which refers to this Group and where all other SLB parameters are defined 4 Define a further rule that duplicates the source destination interface network of the SLB_SAT rule that allows traffic through The could be one or combination of e ForwardFast e Allow e NAT The table bel
363. o make sure that the source IP address in fact belongs on the receiving interface The Access Rules are firstly examined to see if they can provide this check see Section 6 1 Access Rules for more details of this feature If there are no Access Rules or a match with the rules cannot be found a reverse lookup in the previously selected routing table is done using the source IP address If the check fails then a Default access rule log error message is generated 4 At this point using the routing table selected the actual route lookup is done to find the packet s destination interface At this point the ordering parameter is used to determine how the actual lookup is done and the options for this are described in the next section To implement virtual systems the Only ordering option should be used 5 The connection is then subject to the normal IP rule set If a SAT rule is encountered address translation will be performed The decision of which routing table to use is made before carrying out address translation but the actual route lookup is performed on the altered address Note that the original route lookup to find the destination interface used for all rule look ups was done with the original untranslated address 6 If allowed by the IP rule set the new connection is opened in the NetDefendOS state table and the packet forwarded through this connection 4 3 5 The Ordering parameter Once the routing table for a new connect
364. o specify a total limit for a pipe so that it knows what its capacity is and the precedence mechanism is totally dependent on this Pipe limits for VPN Traffic shaping measures the traffic inside VPN tunnels This is the raw unencrypted data without any protocol overhead so it will be less than the actual VPN traffic VPN protocols such as IPsec can add significant overhead to the data and for this reason it is recommended that the limits specified in the traffic shaping pipes for VPN traffic are set at around 20 below the actual available bandwidth Relying on the group limit A special case when a total pipe limit isn t specified is when a group limit is used instead The bandwidth limit is then placed on for example each user of a network where the users must share a fixed bandwidth resource An ISP might use this approach to limit individual user bandwidth by 276 10 1 11 A Summary of Traffic Shaping Chapter 10 Traffic Management specifying a Per DestinationIP grouping Knowing when the pipe is full is not important since the only constraint is on each user If precedences were used the pipe maximum would have to be used Limits shouldn t be higher than the available bandwidth If pipe limits are set higher than the available bandwidth the pipe will not know when the physical connection has reached its capacity If the connection is 500 kbps but the total pipe limit is set to 600 kbps the pipe will believe that it is not fu
365. oint Authentication using Pre Shared Keys is based on the Diffie Hellman algorithm Local and Remote These are the subnets or hosts between which IP traffic will Networks Hosts be protected by the VPN In a LAN to LAN connection these will be the network addresses of the respective LANs If roaming clients are used the remote network will most likely be set to all nets meaning that the roaming client may connect from anywhere Tunnel Transport Mode IPsec can be used in two modes tunnel or transport Tunnel mode indicates that the traffic will be tunneled to a remote device which will decrypt authenticate the data extract it from its tunnel and pass it on to its final destination This way an eavesdropper will only see encrypted traffic going from one of VPN endpoint to another In transport mode the traffic will not be tunneled and is hence not applicable to VPN tunnels It can be used to secure a connection from a VPN client directly to the D Link Firewall for example for IPsec protected remote configuration This setting will typically be set to tunnel in most 242 9 3 2 Internet Key Exchange IKE Chapter 9 VPN Remote Gateway Main Aggressive Mode IPsec Protocols IKE Encryption configurations The remote gateway will be doing the decryption authentication and pass the data on to its final destination This field can also be set to none forcing the D Link VPN to treat the remote address
366. ols such as TCP but also by means of pseudo connections to stateless protocols such as UDP and ICMP This approach means that evaluation against the IP rule set is only done in the initial opening phase of a connection The size of the IP rule set consequently has negligible effect on overall throughput The First Matching Principle If several rules match the same parameters the first matching rule in a scan from top to bottom is the one that decides how the connection will be handled The exception to this is SAT rules since these rely on a pairing with a second rule to function After encountering a matching SAT rule the search will therefore continue on looking for a matching second rule see Section 7 3 Static Address Translation for more information on this Non matching Traffic Incoming packets that don t match any rule in the rule set and that don t have an already opened matching connection in the state table will automatically be subject to a Drop action For explicitness there should be a rule called DropAll as the final rule in the rule set with an action of Drop with Source Destination Network all nets and Source Destination Interface all 74 3 5 3 IP Rule Actions Chapter 3 Fundamentals 3 5 3 IP Rule Actions A rule consists of two parts the filtering parameters and the action to take if there is a match with those parameters As described above the parameters of any NetDefendOS rule including IP rules
367. ommended instead of the Drop action because a polite reply is required from NetDefendOS An example of such a situation is when responding to the IDENT user identification protocol 3 5 4 Editing IP rule set Entries After adding various rules to the rule set editing any line can be achieved in the Web UI by right clicking on that line A context menu will appear with the following options Edit This allows the contents of the rule to be changed Delete This will remove the rule permanently from the rule set Disable Enable This allows the rule to be disabled but left in the rule set While disabled the rule set line will not effect traffic flow and will appear grayed out in the user interface It can be re enabled at any time Move options The last section of the context menu allows the rule to be moved to a different position in the rule set and therefore have a different precedence 76 3 6 Schedules Chapter 3 Fundamentals 3 6 Schedules In some scenarios it might be useful to control not only what functionality is enabled but also when that functionality is being used For instance the IT policy of an enterprise might stipulate that web traffic from a certain department is only allowed access outside that department during normal office hours Another example might be that authentication using a specific VPN connection is only permitted on weekdays before noon NetDefendOS addresses this requirement by providing Sch
368. on with routers in other Autonomous Systems are called Autonomous System Boundary Router ASBRs They advertise externally learned routes throughout the Autonomous System Backbone Areas All OSPF networks need to have at least the backbone area that is the area with ID 0 This is the area that all other areas should be connected to and the backbone make sure to distribute routing information between the connected areas When an area is not directly connected to the backbone it needs a virtual link to it Stub Areas Stub areas are areas through which or into which AS external advertisements are not flooded When an area is configured as a stub area the router will automatically advertises a default route so that routers in the stub area can reach destinations outside the area Transit Areas Transit areas are used to pass traffic from a area that is not directly connect to the backbone area The Designated Router Each OSPF broadcast network has a designated router and a backup designated router The routers uses OSPF hello protocol to elect the DR and BDR for the network based on the priorities advertised by all the routers If there already are a DR on the network the router will accept that one regardless of its own router priority Neighbors Routers that are in the same area become neighbors in that area Neighbors are elected via the Hello protocol Hello packets are sent periodically out of each interface using IP multicast Routers
369. one tries to connect to the public address of the web server the destination address will be changed to its private address In this instance both rules are set to translate the destination address meaning that only one of them will be carried out If an attempt is made internally to communicate with the web servers public address it will instead be redirected to an intranet server If any other attempt is made to communicate with the web servers public address it will be redirected to the private address of the publicly accessible web server Again note that the above rules require a matching Allow rule at a later point in the rule set in order to work 7 3 7 SAT and FwdFast Rules It is possible to employ static address translation in conjunction with FwdFast rules although return traffic must be explicitly granted and translated The following rules make up a working example of static address translation using FwdFast rules to a web server located on an internal network We add a NAT rule to allow connections from the internal network to the Internet 217 7 3 7 SAT and FwdFast Rules Chapter 7 Address Translation What happens now External traffic to wan_ip 80 will match rules 1 and 3 and will be sent to wwwsrv Correct Return traffic from wwwsrv 80 will match rules 2 and 4 and will appear to be sent from wan_ip 80 Correct Internal traffic to wan_ip 80 will match rules 1 and 3 and will be sent to wwwsrv A
370. or example SSH for remote management of the D Link Firewalls in an HA Cluster the individual IP addresses of the firewalls should be used 11 3 2 NetDefendOS Setup The remaining steps to configure the NetDefendOS software through the WebUI are as follows 1 Connect to the master unit with the WebUIL 2 Go to System gt High Availability 3 Check the Enable High Availability checkbox 4 Set the Cluster ID This must be unique for each cluster 5 Choose the Sync Interface 6 Select the node type to be Master 7 Go to Objects gt Address book and create an IP4 HA address object for each interface Each object must contain the master and slave IP address 8 Go to Interfaces gt Ethernet going through each interface in the list and entering the shared IP address for that interface in the IP Address field Also select the Advanced tab for each interface and set the High Availability Private IP Address field to be the name of the IP4 HA object defined in the previous step for the interface NetDefendOS will automatically select the appropriate address from the master and slave IP addresses defined for the object 9 Repeat the above steps for the other D Link Firewall but select the node type to be Slave The configuration on both D Link Firewalls needs to be the same Configurations between the units are automatically synchronized To change something in a configuration logon to either the master or the slave make the change th
371. or the switch Press Check Switch to verify the firewall can communicate with the switch and the community string is correct Click OK Add the firewall s management interface into the exclude list 1 Goto Zone Defense gt Exclude list 301 12 3 4 Limitations Chapter 12 ZoneDefense 2 For Addresses choose the object name of the firewall s interface address 192 168 1 1 from the Available list and put it into the Selected list 3 Click OK Configure an HTTP threshold of 10 connections second Go to Traffic Management gt Threshold Rules gt Add gt Threshold Rule For the Threshold Rule enter Name HTTP Threshold e Service http For Address Filter enter Source Interface The firewall s management interface Destination Interface any Source Network 192 168 2 0 24 or the object name Destination Network all nets Click OK Specify the threshold the threshold type and the action to take if exceeded Go to Add gt Threshold Action Configure the Theshold Action as follows Action Protect Group By Host based Threshold 10 Set the units for the threshold value to be Connections Second Tick the Use ZoneDefense checkbox Click OK 12 3 4 Limitations There are some differences in ZoneDefense operation depending on switch model The first difference is the latency between the triggering of a blocking rule to the moment when switch es actually starts blocking out the traffic matched by the rule A
372. ork to all nets Set Remote Gateway to none For Authentication select the Pre shared Key object defined in the first step Set Encapsulation Mode to Transport Select the IKE and IPsec proposal lists to be used Enable the routing option Dynamically add route to the remote network when tunnel established 5 Define an PPTP L2TP Server object let s call this object 2tp_tunnel with the following parameters Set Inner IP Address to ip_int Set Tunnel Protocol to L2TP Set Outer Interface Filter to ipsec_tunnel Set Outer Server IP to ip_ext Select the Microsoft Point to Point Encryption allowed Since IPsec encryption is used this can be set to be None only otherwise double encryption will degrade throughput Set IP Pool to 2tp_pool Enable Proxy ARP on the int interface to which the internal network is connected Make the interface a member of a specific routing table so that routes are automatically added to that table Normally the main table is selected 6 For user authentication Define a Local User DB object let s call this object TrustedUsers Add individual users to TrustedUsers This should consist of at least a username and password combination The Group string for a user can also be specified This is explained in the same step in the IPsec Roaming Clients section above Define a User Authentication Rule 7 To allow traffic through the L2TP tunnel the following rules should be defined in the IP rule se
373. orks This is achieved by connecting the same interfaces on both master and slave via a switch to other network portions The lan interface on the master and the lan interface on the slave would be connected to the same switch which then connects to an internal network Similarly the wan interface on the master and the wan interface would connect to a switch which then connects to the external Internet 293 11 3 2 NetDefendOS Setup Chapter 11 High Availability 3 Decide on a shared IP address for each interface in the cluster Some interfaces could have shared addresses only with others having unique individual addresses as well The shared and unique addresses are used as follows e The unique non shared IP addresses are used to communicate with the D Link Firewalls themselves for functions such as remote control and monitoring They can also be pinged They should not be associated with the traffic flowing through the cluster If either unit is inoperative the associated IP address will be unreachable ARP queries for the respective addresses are answered by the firewall that owns the IP address using the normal hardware address just like normal IP units e One shared IP address is used for routing and it is also the address used by dynamic address translation unless the configuration explicitly specifies another address Note The shared IP address should not be used for remote management or monitoring purposes When using f
374. ounting information synchronization could occur if an active unit has an authenticated user for whom the associated connection times out before it is synchronized on the inactive unit To get around this problem a special AccountingUpdate event is sent to the passive unit on a timeout and this contains the most recent accounting information for connections 2 3 7 Handling Unresponsive Servers A question arises in the case of a client that sends an AccountingRequest START packet which the RADIUS server never replies to NetDefendOS will re send the request after the user specified number of seconds This will however mean that a user will still have authenticated access while NetDefendOS is trying to contact to the accounting server Only after NetDefendOS has made three attempts to reach the server will it conclude that the accounting server is unreachable The administrator can use the NetDefendOS advanced setting AllowAuthIfNoAccountingResponse to determine how this situation is handled If this setting is enabled then an already authenticated user s session will be unaffected If it is not enabled any effected user will automatically be logged out even if they have already been authenticated 2 3 8 Accounting and System Shutdowns In the case that the client for some reason fails to send a RADIUS AccountingRequest STOP packet the accounting server will never be able to update its user statistics but will most likely believe that the session
375. ounting server with the current status of an authenticated user An Interim Accounting Message can be seen as a snapshot of the network resources that an authenticated user has used up until a given point With this feature the RADIUS server can track how many bytes and packets an authenticated user has sent and received up until the point when the last message was sent An Interim Accounting Message contains the current values of the statistics for an authenticated user It contains more or less the same parameters as found in an AccountingRequest Stop message except that the Acct Terminate Cause is not included as the user has not disconnected yet The frequency of Interim Accounting Messages can be specified either on the authentication server or in NetDefendOS Switching on the setting in NetDefendOS will override the setting on the accounting server 2 3 4 Activating RADIUS Accounting In order to activate RADIUS accounting a number of steps must be followed e The RADIUS accounting server must be specified e A user authentication object must have a rule associated with it where a RADIUS server is specified Some important points should be noted about activation e RADIUS Accounting will not function where a connection is subject to a FwdFast rule in the IP tule set e The same RADIUS server does not need to handle both authentication and accounting one server can be responsible for authentication while another is responsible
376. oup type is one of the values IDS IPS or Policy These types are explained above 2 Signature Group Category This second level of naming describes the type of application or protocol Examples are e BACKUP e DB e DNS e FTP e HTTP 3 Signature Group Sub Category The third level of naming further specifies the target of the group and often specifies the application for example MSSQL The Sub Category may not be necessary if the Type and Category are sufficient to specify the group for example APP_ITUNES Listing of IDP Groups A listing of IDP groupings can be found in Appendix B IDP Signature Groups The listing shows groups names consisting of the Category followed by the Sub Category since the Type could be any of IDS IPS or POLICY Processing Multiple Actions For any IDP rule it is possible to specify multiple actions and an action type such as Protect can be repeated Each action will then have one or more signatures or groups associated with it When signature matching occurs it is done in a top down fashion with matching for the signatures for the first action specified being done first IDP signature wildcarding When selecting IDP signature groups it is possible to use wildcarding to select more than one group The character can be used to wildcard for a single character in a group name Alternatively the character can be used to wildcard for any set of characters of any length in a 193 6 5 7 IDP
377. oute is as a means to reach its destination When two routes offer a means to reach the same destination NetDefendOS will select the one with the lowest Metric value for sending data if two routes have the same Metric the route found first in the routing table will be chosen A primary preferred route should have a lower Metric for example 10 and a secondary failover route should have a higher Metric value for example 20 Multiple Failover Routes It is possible to specify more than one failover route For instance the primary route could have two other routes as failover routes instead of just one In this case the Metric should be different for each of the three routes 10 for the primary route 20 for the first failover route and 30 for the second failover route The first two routes would have Route Monitoring enabled in the routing table but the last one with the highest Metric would not since it has no route to failover to Failover Processing Whenever monitoring determines that a route is not available NetDefendOS will mark the route as disabled and instigate Route Failover for existing and new connections For already established connections a route lookup will be performed to find the next best matching route and the connections will then switch to using the new route For new connections route lookup will ignore disabled routes and the next best matching route will be used instead The table below defines two d
378. ow shows the rules that would be defined for a typical scenario of a set of webservers behind a D Link Firewall for which the load is being balanced The ALLOW rule allows external clients to access the webservers If there are clients on the same network as the webservers that also need access to those webservers then an NAT rule would also be used Note that the destination interface is specified as core meaning NetDefendOS itself deals with this The key advantage of having a separate ALLOW rule is that the webservers can log the exact IP address that is generating external requests Using only a NAT rule which is possible means that webservers would see only the IP address of the D Link Firewall Example 10 3 Setting up SLB In this example server load balancing is to be done between 2 HTTP webservers which are situated behind a D Link Firewall The 2 webservers have the private IP addresses 192 168 1 10 and 192 168 1 11 respectively The default SLB values for monitoring distribution method and stickiness are used A NAT tule is used in conjunction with the SLB_SAT rule so that clients behind the firewall can access the webservers An ALLOW rule is used to allow access by external clients Web Interface A Create an Object for each the webservers Go to Objects gt Address Book gt Add gt IP Address Enter a suitable name eg server1 Enter the IP Address as 192 168 1 10 285 10 3 6 SLB_SAT Rules Chapter 10 Tr
379. owed Wildcarding can also be used for these URLs It iss important to note that whitelisting a URL will mean that no checks such as virus scanning or content filtering will be applied to the HTTP traffic NetDefendOS will assume that the traffic from the URL can be trusted These features are described in depth in Section 6 3 3 Static Content Filtering e Dynamic Content Filtering Access to specific URLs can be allowed or blocked according to policies for certain types of web content Access to news sites might be allowed whereas access to gaming sites might be blocked This feature is described in depth in Section 6 3 4 Dynamic Web Content Filtering e Anti Virus Scanning The contents of HTTP file downloads can be checked for viruses The feature is described in depth in Section 6 4 Anti Virus Scanning e Verify File Integrity This part of the ALG deals with the filetype of downloaded files e Verify MIME type This is used to check that the filetype of the filename for file downloads agree with the contents of the file All filetypes that are checked in this way by NetDefendOS are listed in Appendix C Checked MIME filetypes These filetypes are also listed in the Allow Block list described below Any file download that fails verfication is aborted by NetDefendOS e Allow Block Selected Types This list option operates independently of the MIME verification option described above The list operates in two mod
380. own here They are typically a numbered list showing what items in the tree view list at the left of the interface or in the menu bar or in a context menu need to be opened followed by information about the data items that need to be entered 1 Goto Item X gt Item Y gt Item Z 2 Now enter Dataltem1 datavalue1 Dataltem2 datavalue2 12 Highlighted Content Preface Highlighted Content Special sections of text which the reader should pay special attention to are indicated by icons on the left hand side of the page followed by a short paragraph in italicized text Such sections are of the following types with the following purposes Note This indicates some piece of information that is an addition to the preceding text It may concern something that is being emphasized or something that is not obvious or explicitly stated in the preceding text Tip This indicates a piece of non critical information that is useful to know in certain situations but is not essential reading Caution This indicates where the reader should be careful with their actions as an undesirable situation may result if care is not exercised Important This is an essential point that the reader should read and understand Warning This is essential reading for the user as they should be aware that a serious situation may result if certain actions are taken or not taken OO OG 13 Chapter 1 Product Overview This chapter o
381. own in the previous example Set up the switch route with the new interface group created earlier Configure the rules Go to Rules gt New Rule The Rule Properties dialog will be displayed Specify a suitable name for the rule for instance HTTP LAN to DMZ Enter following Action Allow Source Interface lan Destination Interface dmz Source Network all nets Destination Network 10 1 4 10 Under the Service tab choose http in the Pre defined control Click OK Go to Rules gt New Rule The Rule Properties dialog will be displayed Specify a suitable name for the rule for instance HTTP WAN to DMZ Enter following Action SAT Source Interface wan Destination Interface dmz Source Network all nets Destination Network wan_ip Under the Service tab choose http in the Pre defined control Under the Address Translation tab choose Destination IP Address and enter 10 1 4 170 in the New IP Address control Click OK Go to Rules gt New Rule The Rule Properties dialog will be displayed Specify a suitable name for the rule for instance HTTP LAN to DMZ Enter following Action Allow Source Interface wan Destination Interface dmz Source Network all nets Destination Network wan_ip 18 Under the Service tab choose http in the Pre defined control 19 Click OK Web Interface Configure the interfaces 123 4 6 6 Transparent Mode Scenarios Chapter 4 Routing Go to Interfaces gt Ethernet gt Edit lan No
382. parameters are directly configured on both sides of the VPN tunnel Note D Link Firewalls do not support Manual Keying Manual Keying Advantages Since it is very straightforward it will be quite interoperable Most interoperability problems encountered today are in IKE Manual keying completely bypasses IKE and sets up its own set of IPsec SAs Manual Keying Disadvantages It is an old method which was used before IKE came into use and is thus lacking all the functionality of IKE This method therefore has a number of limitations such as having to use the same encryption authentication key always no anti replay services and it is not very flexible There is also no way of assuring that the remote host firewall really is the one it says it is This type of connection is also vulnerable for something called replay attacks meaning a malicious entity which has access to the encrypted traffic can record some packets store them and send them to its destination at a later time The destination VPN endpoint will have no way of telling if this packet is a replayed packet or not Using IKE eliminates this vulnerability PSK Using a Pre shared Key PSK is a method where the endpoints of the VPN share a secret key This is a service provided by IKE and thus has all the advantages that come with it making it far more flexible than manual keying PSK Advantages Pre Shared Keying has a lot of advantages over manual keying These inc
383. plished by encryption Authentication and Integrity Proof for the recipient that the communication was actually sent by the expected sender and that the data has not been modified in transit This is accomplished by authentication often by use of cryptographic keyed hashes Non repudiation Proof that the sender actually sent the data the sender cannot later deny having sent it Non repudiation is usually a side effect of authentication VPNs are normally only concerned with confidentiality and authentication Non repudiation is normally not handled at the network level but rather on a transaction document by document basis 9 1 3 VPN Planning An attacker targeting a VPN connection will typically not attempt to crack the VPN encryption since this requires enormous work Rather they will see VPN traffic as an indication that there is something worth targeting at the other end of the connection Typically mobile clients and branch offices are far more attractive targets than the main corporate networks Once inside those getting to the corporate network becomes easier In designing a VPN there are many non obvious issues that need to be addressed This includes 229 9 1 4 Key Distribution Chapter 9 VPN e Protecting mobile and home computers e Restricting access through the VPN to needed services only since mobile computers are vulnerable e Creating DMZs for services that need to be shared with other companies through
384. pressed file the specified Action should be taken The Action can be one of e Allow The file is allowed through without virus scanning e Scan Scan the file for viruses as normal e Drop Drop the file In all three of the above cases the event is logged Verifying the MIME Type The ALG File Integrity options can be utilized with Anti Virus scanning to check that the file s contents matches the MIME type it claims to be The MIME type identifies a file s type For instance a file might be identified as being of type gif and therefore should contain image data of that type Some viruses can try to hide inside files by using a misleading file type A file might pretend to be a gif file but the file s data will not match that type s data pattern because it is infected with a virus 185 6 4 6 Anti Virus Options Chapter 6 Security Mechanisms Enabling of this function is recommended to make sure this form of attack cannot allow a virus to get through The possible MIME types that can be checked are listed in Appendix C Checked MIME filetypes Setting the Correct System Time It is important that a NetDefendOS has the correct system time set if the auto update feature in the Anti Virus module can function correctly An incorrect time can mean the auto updating is disabled The console command gt updatecenter status will show the current status of the auto update feature This can also be done through the WebUI Updating i
385. r Terminal software included in some Microsoft Windows editions The serial console port uses the following default settings 9600 baud No parity 8 bits and I stop bit e A RS 232 cable with appropriate connectors An appliance package includes a RS 232 null modem cable To connect a terminal to the console port follow these steps 1 Set the terminal protocol as described previously 2 Connect one of the connectors of the RS 232 cable directly to the console port on your system hardware 3 Connect the other end of the cable to the terminal or the serial connector of the computer running the communications software 4 Press the enter key on the terminal The NetDefendOS login prompt should appear on the terminal screen 24 2 1 3 The CLI Chapter 2 Management and Maintenance SSH Secure Shell CLI Access The SSH Secure Shell protocol can be used to access the CLI over the network from a remote host SSH is a protocol primarily used for secure communication over insecure networks providing strong authentication and data integrity Many SSH clients are feely available for almost all hardware platforms NetDefendOS supports version 1 1 5 and 2 of the SSH protocol and SSH access is regulated by the remote management policy in NetDefendOS and is disabled by default Example 2 1 Enabling SSH Remote Access This example shows how to enable remote SSH access from the annet network through the lan interface by addin
386. r name and password please see Section 2 1 2 Default Administrator Accounts Note Access to the web interface is regulated by the remote management policy By default the system will only allow web access from the internal network Interface Layout The main web interface page is divided into three major sections Menu bar The menu bar located at the top of the web interface contains a number of buttons and drop down menus that are used to perform configuration tasks as well as for navigation to various tools and status pages 27 2 1 4 The WebUI Chapter 2 Management and Maintenance e Home Navigates to the first page of the web interface e Configuration e Save and Activate Saves and activates the configuration e Discard Changes Discards any changes made to the configuration during the current session e View Changes List the changes made to the configuration since it was last saved e Tools Contains a number of tools that are useful for maintaining the system e Status Provides various status pages that can be used for system diagnostics e Maintenance e Update Center Manually update or schedule updates of the intrusion detection and antivirus signatures e License View license details or enter activation code e Backup Make a backup of the configuration to your local computer or restore a previously downloaded backup e Reset Restart the firewall or reset to factory defa
387. rate sites can communicate with a level of security comparable to that existing if they communicated through a dedicated private link Secure communication is achieved through the use of IPsec tunneling with the tunnel extending from the VPN gateway at one location to the VPN gateway at another location The D Link Firewall is therefore the implementor of the VPN while at the same time applying normal security surveillance of traffic passing through the tunnel This section deals specifically with setting up Lan to Lan tunnels created with a Pre shared Key PSK A number of steps are required to set up LAN to LAN tunnels with PSK e Set up a Pre shared Key or secret for the VPN tunnel e Set up the VPN tunnel properties e Set up the Route e Set up the Rules 2 way tunnel requires 2 rules 9 4 3 Roaming Clients An employee who is on the move who needs to access a central corporate server from a notebook 253 9 4 3 Roaming Clients Chapter 9 VPN computer from different locations is a typical example of a roaming client Apart from the need for secure VPN access the other major issue with roaming clients is that the mobile user s IP address is often not known beforehand To handle the unknown IP address the NetDefendOS can dynamically add routes to the routing table as tunnels are established Dealing with Unknown IP addresses If the IP address of the client is not known before hand then the D Link Firewall needs to crea
388. rce destination network interface can be specified for a rule and a type of service such as HTTP can be associated with it Each rule can have associated with it one or more Actions which specify how to handle different threshold conditions A Threshold has the following parameters e Action The response to exceeding the limit either Audit or Protect e Group By Either Host or Network based e Threshold The numerical limit which must be exceeded to trigger a response e Threshold Type Limiting connections per second or limiting total number of concurrent connections These parameters are described below 10 2 2 Connection Rate Total Connection Limiting Connection Rate Limiting allows an administrator to put a limit on the number of new connections being opened to the D Link Firewall per second Total Connection Limiting allows the administrator to put a limit on the total number of connections opened to the D Link Firewall This function is extremely useful when NAT pools are required due to the large number of connections generated by P2P users 10 2 3 Grouping The two groupings are as follows e Host Based The threshold is applied separately to connections from different IP addresses e Network Based The threshold is applied to all connections matching the rules as a group 10 2 4 Rule Actions When a Threshold Rule is triggered one of two responses are possible e Audit Leave the connection intact but log t
389. rder to correctly configure it 2 2 3 2 SNMP Traps The SNMP protocol Simple Network Management Protocol SNMP is a means for communicating between a Network Management System NMS and a managed device SNMP defines 3 types of messages a Read command for an NMS to examine a managed device a Write command to alter the state of a managed device and a Trap which is used by managed devices to send messages asynchronously to an NMS about a change of state SNMP Traps in NetDefendOS NetDefendOS takes the concept of an SNMP Trap one step further by allowing any event message to be sent as an SNMP trap This means that the administrator can set up SNMP Trap notification of events that you consider significant for the operation of a network The file DFLNNN TRAP MIB where NNN indicates the model number of the firewall is provided by D Link and defines the SNMP objects and datatypes that are used to describe an SNMP Trap received from NetDefendOS Note gt There is a different MIB file for each model of D Link Firewall Make sure that the correct file is used For each D Link Firewall model there is one generic trap object called DLNNNosGenericTrap that is used for all traps where NNN indicates the model number This object includes the following parameters e System The system generating the trap e Severity Severity of the message e Category What NetDefendOS subsystem is reporting the problem e ID Unique identification w
390. re available for selection These groups are available only for the D Link Advanced IDP Service There is a version of each group under the three Types of IDS IPS and Policy For further information see Section 6 5 Intrusion Detection and Prevention Group Name Intrusion Type APP_AMANDA Amanda a popular backup software APP_ETHEREAL Ethereal APP_ITUNES Apple iTunes player APP_REALPLAYER Media player from RealNetworks APP_REALSERVER RealNetworks RealServer player APP_WINAMP WinAMP APP_WMP MS Windows Media Player AUTHENTICATION_GENERAL Authenticantion AUTHENTICATION_KERBEROS Kerberos AUTHENTICATION_XTACACS XTACACS BACKUP_ARKEIA Network backup solution BACKUP_BRIGHTSTOR Backup solutions from CA BACKUP_GENERAL General backup solutions BACKUP_NETVAULT BACKUP_VERITAS NetVault Backup solution Backup solutions BOT_GENERAL Activities related to bots including those controlled by IRC channels BROWSER_FIREFOX Mozilla Firefox BROWSER_GENERAL General attacks targeting web browsers clients BROWSER_IE BROWSER_MOZILLA Microsoft IE Mozilla Browser COMPONENT_ENCODER Encoders as part of an attack COMPONENT_INFECTION Infection as part of an attack COMPONENT_SHELLCODE Shell code as part of the attacks DB_GENERAL Database systems DB_MSSQL MS SQL Server DB_MYSQL MySQL DBMS DB_ORACLE Oracle D
391. ream database is updated on a daily basis with new virus signatures Older signatures are seldom retired but instead are replaced with more generic signatures covering several viruses The local NetDefendOS copy of the SafeStream database should therefore be updated regularly and this updating service is enabled as part of the subscription to the D Link Anti Virus subscription 6 4 5 Subscribing to the D Link Anti Virus Service The D Link Anti Virus feature is purchased as an additional component to the base D Link license and is bought in the form of a renewable subscription An Anti Virus subscription includes regular updates of the Kaspersky SafeStream database during the subscription period with the signatures of the latest virus threats To subscribe to the Anti Virus service please refer to the details described in Appendix A Subscribing to Security Updates 6 4 6 Anti Virus Options When configuring Anti Virus scanning in an ALG the following parameters can be set 184 6 4 6 Anti Virus Options Chapter 6 Security Mechanisms 1 General options Mode This must be one of A Enabled which means Anti Virus is active B Audit which means it is active but logging will be the only action Fail mode behaviour If a virus scan fails for any reason then the transfer can be dropped or allowed with the event being logged 2 File Type Blocking Allowing Action When a particular download file type is encountered the administra
392. red when using SLB 1 The target servers across which the load is to be balanced 2 The load distribution mode 3 The SLB algorithm used 4 The monitoring method Each of these topics is discussed further in the sections that follow 10 3 2 Identifying the Servers The first step is to identify the servers across which the load is to be balanced This might be a server farm which is a cluster of servers set up to work as a single virtual server The servers that are to be treated as a single vitual server by SLB must be specified 10 3 3 The Load Distribution Mode No single method of distributing the server load is ideal for all services Different types of services have different needs In the IP rule set the administrator can configure rules for specific services SLB will then filter the packet flow according to these rules NetDefendOS SLB supports the following distribution modes Per state Distribution In this mode SLB records the state of every connection The entire session will then be distributed to the same server This guarantees reliable data transmission for that session IP Address Stickiness In this mode all connections from a specific client will be sent to the same server This is particularly important for SSL services such as HTTPS which require a consistent connection to the same host Network Stickiness This mode is similar to IP stickiness except that by using a subnet mask a range of hosts in a subnet
393. response after the timeout for example every 2 seconds This will be retried a maximum of 3 times Shared Secret Enter a text string here for basic encryption of the RADIUS messages Confirm Secret Retype the string to confirm the one typed above 3 Click OK 228 Chapter 9 VPN This chapter describes VPN usage with NetDefendOS e Overview page 229 e VPN Quickstart Guide page 231 e IPsec page 240 e IPsec Tunnels page 253 e PPTP L2TP page 260 9 1 Overview 9 1 1 The Need for VPNs Most networks are connected to each other through the Internet Business increasingly utilizes the Internet since it offers efficient and inexpensive communication A means is needed for data to travel across the Internet to its intended recipient without another party being able to read or alter it It is equally important that the recipient can verify that no one is falsifying information in other words pretending to be someone else Virtual Private Networks VPNs meet this need providing a highly cost effective means of establishing secure links so that data can be exchanged in a secure manner 9 1 2 VPN Encryption Cryptography provides the means to create VPNs across the Internet with no additional investments in connectivity Cryptography is an umbrella expression covering 3 techniques and benefits Confidentiality No one but the intended recipients is able to receive and understand the communication Confidentiality is accom
394. ress In the web user interface the configuration objects are organized into a tree like structure based on the type of the object In the CLI similar configuration object types are grouped together in a category These categories are different from the structure used in the web user interface to allow quick access to the configuration objects in the CLI The IP4Address IP4Group and EthernetAddress types are for instance grouped in a category named Address as they all represent different addresses Consequently Ethernet and VLAN objects are all grouped in a category named Interface as they are all interface objects The categories have actually no impact on the system configuration they are merely provided as means to simplify administration The following examples show how to manipulate objects Example 2 3 Listing Configuration Objects To find out what configuration objects exist you can retrieve a listing of the objects This example shows how to list all service objects CLI 29 2 1 5 Working with Configurations Chapter 2 Management and Maintenance gw world gt show Service A list of all services will be displayed grouped by their respective type Web Interface 1 Goto Objects gt Services 2 A web page listing all services will be presented A list contains the following basic elements Add Button Displays a dropdown menu when clicked The menu will list all types of configuration items that can b
395. rity Mechanisms Prevention 6 5 Intrusion Detection and Prevention 6 5 1 Overview Intrusion Definition Computer servers can sometimes have vulnerabilites which leave them exposed to attacks carried by network traffic Worms trojans and backdoor exploits are examples of such attacks which if successful can potentially compromise or take control of a server A generic term that can be used to describe these server orientated threats are intrusions Intrusion Detection Intrusions differ from viruses in that a virus is normally contained in a single file download and this is normally downloaded to a client system An intrusion manifests itself as a malicious pattern of Internet data aimed at bypassing server security mechanisms Intrusions are not uncommon and they can constantly evolve as their creation can be automated by the attacker NetDefendOS IDP provides an important line of defense against these threats Intrusion Detection and Prevention IDP is a NetDefendOS module that is designed to protect against these instrusion attempts It operates by monitoring network traffic as it passes through the D Link Firewall searching for patterns that indicate an intrusion is being attempted Once detected NetDefendOS IDP allows steps to be taken to neutralize both the intrusion attempt as well as its source IDP Issues In order to have an effective and reliable IDP system the following issues have to be addressed 1 What kinds of tr
396. rnal host Once the state is removed then subsequent communication from the host will result in a new state table entry and may be allocated to a different extternal IP address in the NAT Pool The state table itself takes up memory so it is possible to limit its size using the Max States value in a NAT Pool object The state table is not allocated all at once but is incremented in size as needed One entry in the state table tracks all the connections for a single host behind the D Link Firewall no matter which external host the connection concerns If Max States is reached then an existing state with the longest idle time is replaced If all states in the table is active then the new connection is dropped As a rule of thumb the Max States value should be at least the number of local hosts or clients that will connect to the Internet There is only one state table per NAT Pool so that if a single NAT Pool is re used in multiple NAT IP rules they share the same state table 207 7 2 NAT Pools Chapter 7 Address Translation Stateless NAT Pools The Stateless option means that no state table is maintained and the external IP address chosen for each new connection is the one that has the least connections already allocated to it This means two connections between one internal host to the same external host may use two different external IP addresses The advantage of a Stateless NAT Pool is that there is good spreading of new connections
397. ropLog TCPUrg Specifies how NetDefendOS will deal with TCP packets with the URG flag turned on regardless of any other flags Many TCP stacks and applications deal with Urgent flags in the wrong way and can in the worst case scenario cease working Note however that some programs such as FTP and MS SQL Server nearly always use the URG flag Default StripLog TCPECN 309 TCPRF Chapter 13 Advanced Settings Specifies how NetDefendOS will deal with TCP packets with either the Xmas or Ymas flag turned on These flags are currently mostly used by OS Fingerprinting Note an upcoming standard called Explicit Congestion Notification also makes use of these TCP flags but as long as there are only a few operating systems supporting this standard the flags should be stripped Default StripLog TCPRF Specifies how NetDefendOS will deal with information present in the reserved field in the TCP header which should normally be 0 This field is not the same as the Xmas and Ymas flags Used by OS Fingerprinting Default DropLog TCPNULL Specifies how NetDefendOS will deal with TCP packets that do not have any of the SYN ACK FIN or RST flags turned on According to the TCP standard such packets are illegal and are used by both OS Fingerprinting and stealth port scanners as some firewalls are unable to detect them Default DropLog TCPSequenceNumbers This setting determines if the sequence number range occupied
398. rovide session keys to be used in the encryption and authentication of the VPN data flow IKE and IPsec Lifetimes Both the IKE and the IPsec connections have limited lifetimes described both in terms of time seconds and data kilobytes These lifetimes prevent a connection from being used too long which is desirable from a crypto analysis perspective The IPsec lifetime must be shorter than the IKE lifetime The difference between the two must be a minimum of 5 minutes This allows for the IPsec connection to be re keyed simply by performing another phase 2 negotiation There is no need to do another phase 1 negotiation until the IKE lifetime has expired IKE Proposals An IKE proposal is a suggestion of how to protect data The VPN device initiating an IPsec connection the initiator will send a list of proposals a proposal list suggesting different methods of how to protect the connection The connection being negotiated can be either an IPsec connection protecting the data flow through the VPN or it can be an IKE connection protecting the IKE negotiation itself The responding VPN device upon receiving this proposal list will choose the most suitable proposal according to its own security policy and respond by specifying which one of the proposal it has chosen If no acceptable proposal can be found it will respond by saying that no proposal could be accepted and possibly provide a reason why The proposals contain all p
399. rred because the master s operation has been impaired Inter connection In a cluster the master and slave units must be directly connected to each other by a synchronization connection which is known to NetDefendOS as the sync interface One of the normal interfaces on the master and the slave are dedicated for this purpose and are connected together with a crossover cable Cluster Management An HA Cluster of two D Link Firewalls is managed as a single unit with a unique cluster name which appears in the management interface as a single logical D Link Firewall Administration operations such as changing rules in the IP rule set are carried out as normal with the changes automatically being made to the configurations of both the master and the slave Load sharing D Link HA clusters do not provide load sharing since only one unit will be active while the other is inactive and only two D Link Firewalls the master and the slave can exist in a single cluster The only processing function the inactive unit fulfills is to replicate the state of the active unit and to take over all traffic processing if it detects the active unit is not responding Hardware Duplication 289 11 1 Overview Chapter 11 High Availability D Link HA will only operate between two D Link Firewalls As the internal operation of different security gateway manufacturer s software is completely dissimilar there is no common method available to communicating sta
400. rs connect to protected resources through a D Link Firewall the administrator will often require that each user goes through a process of authentication before access is allowed This chapter deals with setting up authentication for NetDefendOS but first the general issues involved in authentication are examined Proving Identity The aim of authentication is to have the user prove their identity so that the network administrator can allow or deny access to resources based on that identity Possible types of proof could be A Something the user is Unique attributes that are different for every person such as a fingerprint B Something the user has such a passcard a X 507 Digital Certificate or Public and Private Keys C Something the user knows such as a password Method A may require a special biometric reader Another problem is that the feature often can t be replaced if it is lost Methods B and C are therefore the most common in network security However these have drawbacks Keys might be intercepted passcards might be stolen passwords might be guessable or people may simply be bad at keeping a secret Methods B and C are sometimes combined for example in a passcard that requires a password or pincode for use Using Username Passwords This chapter deals specifically with user authentication through validation of username password combinations manually entered by a user attempting to gain access to resources Access to the Intern
401. rvers public address port 80 will result in a connection to the web servers private address port 1080 e Attempts to communicate with the web servers public address port 84 will result in a connection to the web servers private address port 1084 Note In order to create a SAT Rule that allows port transation a Custom Service must be used with the SAT Rule 7 3 5 Protocols handled by SAT Generally static address translation can handle all protocols that allow address translation to take place However there are protocols that can only be translated in special cases and other protocols that simply cannot be translated at all Protocols that are impossible to translate using SAT are most likely also impossible to translate using NAT Reasons for this include e The protocol cryptographically requires that the addresses are unaltered this applies to many VPN protocols e The protocol embeds its IP addresses inside the TCP or UDP level data and subsequently requires that in some way or another the addresses visible on IP level are the same as those embedded in the data Examples of this include FTP and logons to NT domains via NetBIOS e Either party is attempting to open new dynamic connections to the addresses visible to that party In some cases this can be resolved by modifying the application or the firewall 216 7 3 6 Multiple SAT rule matches Chapter 7 Address Translation configuration There is no defini
402. rvice http SourceInterface lan SourceNetwork lannet DestinationInterface any DestinationNetwork all nets Schedule OfficeHours name AllowHTTP Web Interface Go to Objects gt Schedules gt Add gt Schedule Enter the following Name OfficeHours Select 08 17 Monday to Friday in the grid Click OK Go to Rules gt IP Rules gt Add gt IPRule Enter the following e Name AllowHTTP Select the following from the dropdown lists 77 3 6 Schedules Chapter 3 Fundamentals Action NAT Service http Schedule OfficeHours Sourcelnterface lan SourceNetwork lannet DestinationInterface any DestinationNetwork all nets Click OK 78 3 7 X 509 Certificates Chapter 3 Fundamentals 3 7 X 509 Certificates NetDefendOS supports digital certificates that comply with the ITU T X 509 standard This involves the use of an X 509 certificate hierarchy with public key cryptography to accomplish key distribution and entity authentication 3 7 1 Overview An X 509 certificate is a digital proof of identity It links an identity to a public key in order to establish whether a public key truly belongs to the supposed owner By doing this it prevents data transfer interception by a malicious third party who might post a phony key with the name and user ID of an intended recipient Certificates with VPN Tunnels The predominate usage of certificates in NetDefendOS is with VPN tunnels The simplest and fastest
403. s MS rors rne erain a EE E E A EES Gee 135 61 Access RUNES orreen pr oe E EEE N E E A SE ERS NEE wanes 135 6 1 Introd UCth oii e EE E EE coves ANEA ETNE 135 6 12 TP Spooning on n AE R RE A NEA DEEDE 135 6 1 3 Access Rule Settings a oh is tee ea 136 6 2 Application Layer Gateways c iccs 2ssiesssossads serors Esi Esa ISE SSS EEES EREE aS 138 0 2 1 Over vie Wasso iens en e A ER E E E NEE weete ds 138 6 2 2 TEETER o ea eea es E E E E EEES 139 6 253 FIP E A E E E EE E EE 140 EA ATER EE E E E E ET 145 0 23 SMTP pern a Gaon r e Te e Seb acct S aE aes Seen ae 146 6 2 6 POPS E E E Ree Saya E E ae aes 151 6 27 SIP aot acs deca e shone cevendasioss Samos de NE ee vous ch eked eats S A EDE caved tes ss wanes 152 User Manual 6 2 8 323 E sss stands EE sans cosaschss voand saepaaesseeeimagshess 155 6 32 Web Content Filtering sesiis sense esir an e sees Dede bares has geek des 169 63T OVERVIEW aed eed A he lids eee ae anh Gee ees 169 6 3 2 Active Content Handling sssrin eee E R a E 169 6 3 3 Static Content Filtering noiseen ec cee cee E E EE R SA 170 6 3 4 Dynamic Web Content Filtering 2 0 0 0 cece ceeeceee ce eeeeeeneeenee 172 G4 Anti Vir s Scant aici ised nn a SH coe ee das as adel EEE see R eee 183 OA MOVERVICW onai omaes e ERE RAA E ETE EEE E EGES 183 6 4 2 Implementation srs iinne eno e ne Ene IO EEEE AE E ES 183 6 4 3 Activating Anti Virus Scanning e sseesseseesrsrrsrrerrsrrrrsrrerrerrerreees 184 6 4 4 The S
404. s Translation for a detailed description Drop This tells NetDefendOS to immediately discard the packet This is an impolite version of Reject in that no reply is sent back to the sender It is often preferable since it gives a potential attacker no clues about what happened to their packets Reject This acts like Drop but will return a TCP RST or ICMP Unreachable message informing the sending computer that the packet was disallowed This is a polite version of the Drop action Bi directional Connections A common mistake when setting up IP Rules is to define two rules one rule for traffic in one direction and another rule for traffic coming back in the other direction In fact nearly all IP Rules types allow bi directional traffic flow once the initial connection is set up The Source Network and Source Interface in the rule means the source of the initial connection request Once a connection is permitted and established traffic can then flow in either direction over it The exception to this bi directional flow is FwdFast rules If the FwdFast action is used then the tule will not allow traffic to flow from the destination back to the source If bi directional flow is required then two FwdFast rules are needed one for either direction This is also the case if a FwdFast rule is used with a SAT rule 75 3 5 4 Editing IP rule set Entries Chapter 3 Fundamentals Using Reject In certain situations the Reject action is rec
405. s addressing and routing Protocols IP OSPF ICMP IGMP etc Data Link Layer Creates frames of data for transmission over the physical layer and includes error checking correction Protocols Ethernet PPP etc Physical Layer Defines the physical hardware connection 348 Appendix E D Link worldwide offices Below is a complete list of D Link worldwide sales offices Please check your own country area s local website for further details regarding support of D Link products as well as contact details for local support Australia Belgium Brazil Canada China Czech Republic Denmark Egypt Europe UK Finland France Germany Greece Hungary India Israel 1 Giffnock Avenue North Ryde NSW 2113 Australia TEL 61 2 8899 1800 FAX 61 2 8899 1868 Website www dlink com au Rue des Colonies 11 B 1000 Brussels Belgium Tel 32 0 2 517 7111 Fax 32 0 2 517 6500 Website www dlink be Av das Nacoes Unidas 11857 14 andar cj 141 142 Brooklin Novo Sao Paulo SP Brazil CEP 04578 000 Zip Code TEL 55 11 21859300 FAX 55 11 21859322 Website www dlinkbrasil com br 2180 Winston Park Drive Oakville Ontario L6H 5W1 Canada TEL 1 905 8295033 FAX 1 905 8295223 Website www dlink ca No 202 C1 Building Huitong Office Park No 71 Jianguo Road Chaoyang District Beijing 100025 China TEL 86 10 58635800 FAX 86 10 58635799 Website www dlink com cn Vaclav
406. s and using NAT Pools to allocate new connections across them Types of NAT Pools A NAT Pool can be one of three types each allocating new connections in a different way e Stateful e Stateless e Fixed These three types are discussed below Stateful NAT Pools When the Stateful option is selected NetDefendOS allocates a new connection to the external IP address that currently has the least number of connections routed through it with the assumption that it is the least loaded NetDefendOS keeps a record in memory of all such connections Subsequent connections involving the same internal client host will then use the same external IP address The advantage of the stateful approach is that it can balance connections across several external ISP links while ensuring that an external host will always communicate back to the same IP address which will be essential with protocols such as HTTP when cookies are involved The disadvantage is the extra memory required by NetDefendOS to track the usage in its state table and the small processing overhead involved in processing a new connection To make sure that the state table does not contain dead entries for communications that are no longer active a State Keepalive time can be specified This time is the number of seconds of inactivity that must occur before a state in the state table is removed After this period NetDefendOS assumes no more communication will originate from the associated inte
407. s comparable to H 323 but a design goal with SIP is to make it more scalable that H 323 For 152 6 2 7 SIP Chapter 6 Security Mechanisms VOIP see also Section 6 2 8 H 323 SIP Components The following components are the logical building blocks for SIP communication User Agents Proxy Servers Registrars These are the end points or peers that are involved in the peer to peer communication These would typically be the workstation or device used in an IP telephony conversation The word peer will often be used in this section in this context These act as routers in the SIP protocol performing both as peer and server when receiving peer requests They forward requests to a peer s current location as well as authenticating and authorizing access to services They also implement provider call routing policies The proxy is typically located on the unprotected side of the D Link Firewall and this is the proxy location supported by the NetDefendOS SIP ALG A server that handles SIP REGISTER requests is given the special name of Registrar The Registrar server has the task of locating the host where the other peer is reachable The Registrar and Proxy Server are logical entities and my in fact reside in the same physical server SIP Media related Protocols SIP sessions make use of a number of sub protocols SDP Session Description Protocol RFC4566 is used for media session initialization RTP Real t
408. s in the above example are added for both inbound and outbound connections 102 4 4 Dynamic Routing Chapter 4 Routing 4 4 Dynamic Routing 4 4 1 Dynamic Routing overview Dynamic routing is different to static routing in that the D Link Firewall will adapt to changes of network topology or traffic load automatically NetDefendOS first learns of all the directly connected networks and gets further route information from other routers Detected routes are sorted and the most suitable routes for destinations are added into the routing table and this information is distributed to other routers Dynamic Routing responds to routing updates on the fly but has the disadvantage that it is more susceptible to certain problems such as routing loops In the Internet two types of dynamic routing algorithm are used the Distance Vector DV algorithm and the Link State LS algorithm How a router decides the optimal or best route and shares updated information with other routers depends on the type of algorithm used Distance Vector Algorithms The Distance vector DV algorithm is a decentralized routing algorithm that computes the best path in a distributed way Each router computes the costs of its own attached links and shares the route information only with its neighbor routers The router will gradually learns the least cost path by iterative computation and information exchange with its neighbors The Routing Information Protocol RIP
409. s or disallow the entire packet is governed by two factors e Itis safer to discard the whole packet e If as the result of receiving an illegal fragment you choose to discard the whole packet attackers will be able to disrupt communication by sending illegal fragments during a reassembly and in this way block almost all communication Default DropLog discards individual fragments and remembers that the reassembly attempt is suspect DuplicateFragData If the same fragment arrives more than once this can mean either that it has been duplicated at some point on its journey to the recipient or that an attacker is trying to disrupt the reassembly of the packet In order to determine which is more likely NetDefendOS compares the data components of the fragment The comparison can be made in 2 to 512 random locations in the fragment four bytes of each location being sampled If the comparison is made in a larger number of samples it is more likely to find mismatching duplicates However more comparisons result in higher CPU load 320 FragReassemblyFail Chapter 13 Advanced Settings Default Check8 compare 8 random locations a total of 32 bytes FragReassemblyFail Reassemblies may fail due to one of the following causes e Some of the fragments did not arrive within the time stipulated by the ReassTimeout or ReassTimeLimit settings This may mean that one or more fragments were lost on their way across the Interne
410. s tell each other that they support NAT traversal and the specific versions supported NetDefendOS supports the RFC3947 standard for NAT Traversal with IKE e Changes to the ESP encapsulation If NAT traversal is used ESP is encapsulated in UDP which allows for more flexible NATing Below is a more detailed description of the changes made to the IKE and IPsec protocols NAT traversal is only used if both ends has support for it For this purpose NAT traversal aware VPNs send out a special vendor ID telling the other end that it understand NAT traversal and which specific versions of the draft it supports NAT detection Both IPsec peers send hashes of their own IP addresses along with the source UDP port used in the IKE negotiations This information is used to see whether the IP address and source port each peer uses is the same as what the other peer sees If the source address and port have not changed then the traffic has not been NATed along the way and NAT traversal is not necessary If the source address and or port has changed then the traffic has been NATed and NAT traversal is used Once the IPsec peers have decided that NAT traversal is necessary the IKE negotiation is moved away from UDP port 500 to port 4500 This is necessary since certain NAT devices treat UDP packet on port 500 differently from other UDP packets in an effort to work around the NAT problems with IKE The problem is that this special handling of IKE packe
411. s the blocking of particular categories one at a time This allows individual users time to get used to the notion that blocking exists and can avoid the widespread protests that might occur if everything is blocked at once Gradual introduction also makes for better evaluation as to whether the goals of blocking are being met Example 6 16 Enabling Audit Mode This example is based on the same scenario as the previous example but now with audit mode enabled CLI First create an HTTP Application Layer Gateway ALG Object gw world gt add ALG ALG_HTTP content_filtering WebContentFilteringMode Audit 174 6 3 4 Dynamic Web Content Filtering Chapter 6 Security Mechanisms FilteringCategories SEARCH_SITES Web Interface First create an HTTP Application Layer Gateway ALG Object Go to Objects gt ALG gt Add gt HTTP ALG Specify a suitable name for the ALG eg content_filtering Click the Web Content Filtering tab Select Audit in the Mode list In the Blocked Categories list select Search Sites and click the gt gt button Click OK The steps to then create a Service object using the new HTTP ALG and modifing the NAT rule to use the new service are described in the previous example Allowing Override On some occasions Active Content Filtering may prevent users carrying out legitimate tasks Consider a stock broker dealing with on line gaming companies In his daily work he might need to browse gambli
412. same The Intrusion Detection and Prevention IDP Rules are now evaluated in a similar way to the IP rules If a match is found the IDP data is recorded with the state By doing this NetDefendOS will know that IDP scanning is supposed to be conducted on all packets belonging to this connection The Traffic Shaping and the Threshold Limit rule sets are now searched If a match is found the corresponding information is recorded with the state This will enable proper traffic management on the connection From the information in the state NetDefendOS now knows what to do with the incoming packet e If ALG information is present or if IDP scanning is to be performed the payload of the packet is taken care of by the TCP Pseudo Reassembly subsystem which in turn makes use of the different Application Layer Gateways layer 7 scanning engines and so on to further analyze or transform the traffic e If the contents of the packet is encapsulated such as with IPsec L2TP PPTP or some other type of tunneled protocol then the interface lists are checked for a matching interface If one is found the packet is decapsulated and the payload the plaintext is sent into NetDefendOS again now with source interface being the matched tunnel interface In other words the process continues at step 3 above e If traffic management information is present the packet might get queued or otherwise be subjected to actions related to traffic management Ev
413. se hosts For more information about the IDP capabilities of NetDefendOS please see Section 6 5 Intrusion Detection and Prevention NetDefendOS features integrated gateway anti virus functionality Traffic passing through the gateway can be subjected to in depth scanning for viruses and attacking hosts can be blocked and black listed at your choice Section 6 4 Anti Virus Scanning provides more information about how to use the integrated anti virus feature NetDefendOS provides various mechanisms for filtering web content that is deemed inappropriate according to your web usage policy Web content can be blocked based on category malicious objects can be removed and web sites can be whitelisted or blacklisted in multiple policies For more information please see Section 6 3 Web Content Filtering A device running NetDefendOS is highly suitable for participating in a Virtual Private Network VPN NetDefendOS supports IPsec L2TP and PPTP based VPNs concurrently can act as either server or client for all of the VPN types and can provide individual security policies for each VPN tunnel Virtual Private Networking is covered in detail by Chapter 9 VPN With the support of Traffic Shaping Threshold Rules and Server Load Balancing features NetDefendOS is optimal for traffic management The Traffic Shaping feature enables fine granular limiting and balancing of bandwidth Threshold Rules allows for implementing var
414. separate two networks This is described further in Section 4 2 4 Proxy ARP The key disadvantage with this approach is that clients will not be able to roam between NetDefendOS interfaces retaining the same IP address 4 6 6 Transparent Mode Scenarios Scenario 1 The firewall in Transparent Mode is placed between an Internet access router and the internal network The router is used to share the Internet connection with a single public IP address The internal NAT ed network behind the firewall is in the 10 0 0 0 24 address space Clients on the internal network are allowed to access the Internet via the HTTP protocol 120 4 6 6 Transparent Mode Scenarios Chapter 4 Routing Figure 4 8 Transparent mode scenario 1 Example 4 13 Setting up Transparent Mode Scenario 1 Web Interface Configure the interfaces Go to Interfaces gt Ethernet gt Edit wan Now enter IP Address 10 0 0 1 Network 10 0 0 0 24 Default Gateway 10 0 0 1 Transparent Mode Enable Click OK Go to Interfaces gt Ethernet gt Edit lan Now enter IP Address 10 0 0 2 e Network 10 0 0 0 24 Transparent Mode Enable 6 Click OK Configure the rules 1 Goto Rules gt IP Rules gt Add gt IPRule 2 Now enter Name HTTPAllow Action Allow Service http Source Interface lan 121 4 6 6 Transparent Mode Scenarios Chapter 4 Routing Destination Interface any e Source Network 10 0 0 0 24 Destina
415. separate IP addresses one from each ISP However this difference does not matter for the policy routing setup itself Note that for a single organization Internet connectivity through multiple ISPs is normally best done with the BGP protocol where you do not need to worry about different IP spans or policy routing Unfortunately this is not always possible and this is where Policy Based Routing becomes a necessity We will set up the main routing table to use ISP A and add a named routing table r2 that uses the default gateway of ISP B Contents of the named Policy based Routing table r2 The table r2 has its Ordering parameter set to Default which means that it will only be consulted if the main routing table lookup matches the default route al nets Contents of the Policy based Routing Policy To configure this example scenario Web Interface Add the routes found in the list of routes in the main routing table as shown earlier Create a routing table called r2 and make sure the ordering is set to Default Add the route found in the list of routes in the routing table r2 as shown earlier Add two VR policies according to the list of policies shown earlier Go to Routing gt Routing Rules gt Add gt Routing Rule Enter the information found in the list of policies displayed earlier e Repeat the above to add the second rule 101 4 3 5 The Ordering parameter Chapter 4 Routing Note gt Rule
416. site may be categorised under the Swimsuit Lingerie Models category if its content includes information pertaining to or images of swimsuit lingerie or general fashion models Examples might be e www vickys secret com e sportspictured cnn com features 2002 swimsuit Category 31 Spam A web site may be classified under the Spam category if it is found to be contained in bulk or spam emails Examples might be e kaqsovdij gjibhgk info e www pleaseupdateyourdetails com Category 32 Non Managed Unclassified sites and sites that don t fit one of the other categories will be placed in this category It is unusual to block this category since this could result in most harmless URLs being blocked 182 6 4 Anti Virus Scanning Chapter 6 Security Mechanisms 6 4 Anti Virus Scanning 6 4 1 Overview The NetDefendOS Anti Virus module protects against malicious code carried in file downloads Files may be downloaded as part of a web page in an HTTP transfer in an FTP download or perhaps as an attachment to an email delivered through SMTP Malicious code in such downloads can have different intents ranging from programs that merely cause annoyance to more sinister aims such as sending back passwords credit card numbers and other sensitive information The term Virus can be used as a generic description for all forms of malicious code carried in files Combining with Client Anti Virus Scanning Unlike IDP which is primari
417. ske namesti 36 Praha 1 Czech Republic TEL 420 603 276 589 Website www dlink cz Naverland 2 DK 2600 Glostrup Copenhagen Denmark TEL 45 43 969040 FAX 45 43 424347 Website www dlink dk 47 El Merghany street Heliopolis Cairo Egypt TEL 202 2919035 202 2919047 FAX 202 2919051 Website www dlink me com 4th Floor Merit House Edgware Road Colindale London NW9 SAB UK TEL 44 20 8731 5555 FAX 44 20 8731 5511 Website www dlink co uk Latokartanontie 7A FIN 00700 HELSINKI Finland TEL 358 10 309 8840 FAX 358 10 309 8841 Website www dlink fi No 2 Allee de la Fresnerie 78330 Fontenay le Fleury France TEL 33 1 30238688 FAX 33 1 30238689 Website www dlink fr Schwalbacher Strasse 74 D 65760 Eschborn Germany TEL 49 6196 77990 FAX 49 6196 7799300 Website www dlink de 101 Panagoulis Str 163 43 Helioupolis Athens Greece TEL 30 210 9914 512 FAX 30 210 9916902 Website www dlink gr R k czi t 70 72 HU 1074 Budapest Hungary TEL 36 0 1 461 30 00 FAX 36 0 1 461 30 09 Website www dlink hu D Link House Kurla Bandra Complex Road Off CST Road Santacruz East Mumbai 400098 India TEL 91 022 26526696 56902210 FAX 91 022 26528914 Website www dlink co in 11 Hamanofim Street Ackerstein Towers Regus Business Center P O B 2148 Hertzelia Pituach 46120 Israel TEL 972 9 9715700 349 Appendix E D Link worldwide offices Italy LatinAmerica Luxembur
418. so specified for the Ethernet interface The Network address provides information to NetDefendOS about what IP addresses are directly reachable through the interface in other words those residing on the same LAN segment as the interface itself In the routing table associated with the interface NetDefendOS will automatically create a direct route to the specified network over the actual interface The Default Gateway A Default Gateway address can optionally be specified for an Ethernet interface This setting tells NetDefendOS how to reach hosts for which no routes exist In other words if a Default Gateway address has been specified NetDefendOS will automatically create a default route destination network all nets over the actual interface using the specified gateway For natural reasons only one Ethernet interface at a time can be assigned a default gateway Using DHCP on Ethernet Interfaces NetDefendOS includes a DHCP client for dynamic assignment of address information The information that can be set using DHCP includes the IP address of the interface the local network that the interface is attached to and the default gateway All addresses received from the DHCP server are assigned to corresponding IP4Address objects In this way dynamically assigned addresses can be used throughout the configuration in the same way as static addresses By default the objects in use are the same ones as defined in Section 3 1 5 Auto Generated A
419. ss 192 168 10 15 and Ethernet address 4b 86 f6 c5 a2 14 on the lan interface CLI gw world gt add ARP Interface lan IP 192 168 10 15 Mode Static MACAddress 4b 86 f 6 c5 a2 14 Web Interface Go to Interfaces gt ARP gt Add gt ARP Select the following from the dropdown lists Mode Static Interface lan Enter the following IP Address 192 168 10 15 e MAC 4b 86 f6 c5 a2 14 Click OK Published ARP Entries NetDefendOS supports publishing ARP entries meaning that you can define IP addresses and optionally Ethernet addresses for an interface NetDefendOS will then provide ARP replies for ARP requests related to those IP addresses This can serve two purposes e To give the impression that an interface in NetDefendOS has more than one IP address e To aid nearby network equipment responding to ARP in an incorrect manner This use is however less common The first purpose is useful if there are several separate IP spans on a single LAN The hosts on each IP span may then use a gateway in their own span when these gateway addresses are published on the corresponding NetDefendOS interface Another use is publishing multiple addresses on an external interface enabling NetDefendOS to statically address translate communications to these addresses and send it onwards to internal servers with private IP addresses 70 3 4 5 Advanced ARP Settings Chapter 3 Fundamentals There are two publishing modes P
420. ss for all D Link Firewalls is 792 168 1 1 When performing this initial connection to NetDefendOS the administrator MUST use https as the URL protocol in the browser for example https 192 168 1 1 Using HTTPS as the protocol protects the username and password with encryption when they are sent to NetDefendOS If communication with the NetDefendOS is successfully established a user authentication dialog similar to the one shown below will then be shown in the browser window Authentication Required Please enter your username and password Username Password Language English v Login Optimized for Internet Explorer 6 and later Firefox and Netscape 3 26 2 1 4 The WebUI Chapter 2 Management and Maintenance Enter your username and password and click the Login button If the user credentials are correct you will be transferred to the main web interface page This page with its essential parts highlighted is shown below Multi language Support The WebUI login dialog offers the option to select a language other than english for the interface Language support is provided by a separate set of resource files provided with NetDefendOS It may occasionally be the case that a NetDefendOS upgrade might contain features that temporarily lack a complete non english translation because of time constraints In this case the original english will be used as a temporary solution The Web Browser Interface
421. ss myhost Address 192 168 10 10 Show the new object gw world gt show Address IP4Address myhost Property Value Address 192 5 SE 10 5 10 UserAuthGroups none NoDefinedCredentials No Comments none Web Interface 31 2 1 5 Working with Configurations Chapter 2 Management and Maintenance Go to Objects gt Address Book Click on the Add button In the dropdown menu displayed select IP4 Address In the Name text box enter myhost Enter 192 168 10 10 in the IP Address textbox Click OK Verify that the new IP4 address object has been added to the list Example 2 7 Deleting a Configuration Object This example shows how to delete the newly added IP4Address object CLI gw world gt delete Address IP4Address myhost Web Interface 1 Goto Objects gt Address Book 2 Right click on the row containing the myhost object 3 Inthe dropdown menu displayed select Delete The row will be rendered with a strike through line indicating that the object is marked for deletion Example 2 8 Undeleting a Configuration Object A deleted object can always be restored until the configuration has been activated and committed This example shows how to restore the deleted IP4Address object shown in the previous example CLI gw world gt undelete Address IP4Address myhost Web Interface 1 Goto Objects gt Address Book 2 Right click on the row containing the myhost object 3 In the dropdown menu disp
422. st from launching the spoof 6 1 3 Access Rule Settings The configuration of an access rule is similar to other types of rules It contains Filtering Fields as well as the Action to take If there is a match the rule is triggered and NetDefendOS will carry out the specified Action Access Rule Filtering Fields The Access Rule filtering fields used to trigger a rule are e Interface The interface that the packet arrives on e Network The IP span that the sender address should belong to Access Rule Action The Access Rule actions that can be specified are e Drop Discard the packets that match the defined fields e Accept Accept the packets that match the defined fields for further inspection in the rule set e Expect If the sender address of the packet matches the Network specified by this rule the receiving interface is compared to the specified interface If the interface matches the packet is accepted in the same way as an Accept action If the interfaces do not match the packet is dropped in the same way as a Drop action Note Logging can be enabled on demand for these Actions Turning Off Default Access Rule Messages If for some reason the Default Access Rule log message is continuously being generated by some source and needs to be turned off then the way to do this is to specify an Access Rule for that source with an action of Drop Troubleshooting Access Rule Related Problems It should be noted that
423. st scenarios require only a handful of pipes It is possible dozens of pipes may be needed in scenarios where individual pipes are used for individual protocols or in ISP cases clients Pipe Rules Pipe Rules make up the Pipe Rule set Each Rule is defined much like other NetDefendOS policies by specifying the source destination interface network as well as the Service to which the rule is to apply Once a new connection is permitted by the IP rule set the Pipe rule set is always checked for matching rules and in the same way by going from top to bottom The first matching Pipe Rule if any is used for traffic shaping The Pipe rule set is initially empty When a Pipe Rule is defined the pipes to be used with that rule are also specified and they are placed into one of two lists in the Pipe Rule These lists are e The Forward Chain These are the pipes that will be used for outgoing leaving traffic from the D Link Firewall One none or a series of pipes may be specified The Return Chain These are the pipes that will be used for incoming arriving traffic One none or a series of pipes may be specified 268 10 1 3 Simple Bandwidth Limiting Chapter 10 Traffic Management Figure 10 1 Pipe rule set to Pipe Packet Flow Where one pipe is specified in a list then that is the pipe whose characteristics will be applied to the traffic If a series of pipes are specified then these will form a Chain of pipes through whi
424. streams should only be forwarded if some host has requested the streams using the IGMP protocol The example below only covers the multicast forwarding part of the configuration The IGMP configuration can be found below in Section 4 5 3 1 IGMP Rules Configuration No Address Translation Figure 4 4 Multicast Forwarding No Address Translation Note Remember to add an Allow rule matching the SAT Multiplex rule 111 4 5 2 Multicast Forwarding using the Chapter 4 Routing SAT Multiplex Rule Example 4 8 Forwarding of Multicast Traffic using the SAT Multiplex Rule In this example we will create a multiplex rule in order to forward the multicast groups 239 192 10 0 24 1234 to the interfaces if1 if2 and if8 All groups have the same sender 192 168 10 1 which is located somwhere behind the wan interface The multicast groups should only be forwarded to the out interfaces if clients behind those interfaces have requested the groups using IGMP The following steps need to be executed to configure the actual forwarding of the multicast traffic IGMP has to be configured seperately Web Interface A Create a custom service for multicast called multicast_service Go to Objects gt Services gt Add gt TCP UDP Now enter Name multicast_service Type UDP Destination 1234 B Create an IP rule Go to Rules gt IP Rules gt Add gt IP Rule Under General enter Name a name for the rule eg Multicast_Mult
425. t 235 9 2 5 L2TP Roaming Clients with Chapter 9 VPN Certificates The second rule would be included to allow clients to surf the Internet via the ext interface on the D Link Firewall The client will be allocated a private internal IP address which must be NATed if connections are then made out to the public Internet via the D Link Firewall 8 Set up the client Assuming Windows XP the Create new connection option in Network Connections should be selected to start the New Connection Wizard The key information to enter in this wizard is the resolvable URL of the D Link Firewall or alternatively its ip_ext IP address Then choose Network gt Properties In the dialog that opens choose the L2TP Tunnel and select Properties In the new dialog that opens select the Networking tab and choose Force to L2TP Now go back to the L2TP Tunnel properties select the Security tab and click on the IPsec Settings button Now enter the pre shared key 9 2 5 L2TP Roaming Clients with Certificates If certificates are used with L2TP roaming clients instead of pre shared keys then the differences in the setup described above are 1 Load a Gateway Certificate and Root Certificate into NetDefendOS 2 When setting up the IPsec Tunnel object specify the certificates to use under Authentication This is done by a Enable the X 509 Certificate option b Select the Gateway Certificate c Add the Root Certificate to use 3 If using the
426. t through it before it is automatically closed Please note that each connection has two timeout values one for each direction A connection is closed if either of the two values reaches 0 ConnLife_TCP_SYN Specifies how long a not yet been fully established TCP connection may idle before being closed Default 60 seconds ConnLife_TCP Specifies how long a fully established TCP connection may idle before being closed Connections become fully established once packets with their SYN flags off have traveled in both directions Default 262144 seconds ConnLife_TCP_FIN Specifies how long a TCP connection about to close may idle before finally being closed Connections reach this state when a packet with its FIN flag on has passed in any direction Default SO seconds ConnLife_UDP Specifies how long UDP connections may idle before being closed This timeout value is usually low as UDP has no way of signaling when the connection is about to close Default 130 seconds ConnLife_Ping Specifies how long a Ping CMP ECHO connection can remain idle before it is closed Default 8 seconds ConnLife_Other Specifies how long connections using an unknown protocol can remain idle before it is closed Default 130 seconds ConnLife_IGMP Connection lifetime for IGMP Default 72 seconds AllowBothSidesToKeepConnAlive_UDP The UDP Bidirectional keep alive setting allows both sides to keep a UDP connection alive The default
427. t which is a quite common occurrence e NetDefendOS was forced to interrupt the reassembly procedure due to new fragmented packets arriving and the system temporarily running out of resources In situations such as these old reassembly attempts are either discarded or marked as failed e An attacker has attempted to send an incorrectly fragmented packet Under normal circumstances you would not want to log failures as they occur frequently However it may be useful to log failures involving suspect fragments Such failures may arise if for example the IllegalFrags setting has been set to Drop rather than DropPacket The following settings are available for FragReassemblyFail e NoLog No logging is done when a reassembly attempt fails e LogSuspect Logs failed reassembly attempts only if suspect fragments have been involved e LogSuspectSubseq As LogSuspect but also logs subsequent fragments of the packet as and when they arrive e LogAll Logs all failed reassembly attempts e LogAliSubseq As LogAll but also logs subsequent fragments of the packet as and when they arrive Default LogSuspectSubseq DroppedFrags If a packet is denied entry to the system as the result of the settings in the Rules section it may also be worth logging individual fragments of that packet The DroppedFrags setting specifies how NetDefendOS will act Possible settings for this rule are as follows e NoLog No logging is carried out
428. t Rules aoimo me oia e a pa aasa P ELE EP GARRI 217 8 User Authentication iorri iseni i ene tE E Tee E AE E E E 220 glr OVERVIEW coha e E a E E a E A ANE A 220 8 2 Authentication Setup cece eecc ence ence EEEE EEEE KES EN ES EE 221 8 2 1 Setup SUMMALY scissor pai easa EEE I OEI PESES E ETARE sess 221 8 22 The Local Database meron e ena ar A a aE 221 8 2 3 External Authentication Servers seceeeeeceeeneceeeeeceeeeeeeeeueeeeenes 221 8 2 4 Authentication Rules 2 2 0 eee isped epia eei i p 222 8 2 5 Authentication Processing cece cece ceeecneece cece eee ceca tena een eeueeees 223 2 6 HTTP Authentication 2224 sscccgeend code vectes nae E a E a tact 223 OV PIN sides Sas eave Ra eRe ieee aE UL GT aad nase A aaa a 229 OT OVERVIEW pe aeaeaie nina EEE OAE coadds ved saatha ESIR OEE sip ads vee EEEE ERRA S 229 9 1 1 The Need f t VENS narine a E EA EEE E 229 9 1 2 VPN Enery puny isosti sins cheg des sede sab aaa EEE EEE E EEES 229 9 1 3 VPN Planning oeiee nesar Se EE vt E EEE ENES 229 9 14 Key Distribution iinis oi errores E eei oS EREE PIOS OSERE EP Oit 230 9 2 VPN Quickst rt Guide ien a a a a a yi sak Sais 231 9 2 1 IPsec LAN to LAN with Pre shared Keys ccc cceceeeeeeeeeeeee teen es 231 9 2 2 IPsec Roaming Clients with Pre shared Keys cccceeeeee sees eeeeee 232 6 User Manual 9 2 3 IPsec Roaming Clients with Certificates 1 0 00 cee ceee eee este ee e
429. t crror nios arses red oss oes pbs ngs SEDEER E S PERESEIS REE POSEST 267 10 1 Traffic Shaping iesise eisa e eoe ei EEE E EE SIOE eE 267 10 1 1 Introduction zieker e inne r eaa a a Eh 267 10 1 2 Traffic Shaping in NetDefendOS 1 0 0 0 ceeeceeseeceeeeeeeeeeeneeeeees 268 10 1 3 Simple Bandwidth Limiting 0 0 0 0 eee ceeeceeeeaeeeeeeneeenee 269 10 1 4 Limiting Bandwidth in Both Directions 20 00 00 eee cece cence eee 270 10 1 5 Creating Differentiated Limits with Chains 2 0 0 0 cece eeee eee 271 10 1 6 Precedentes sorpena a geepy OEE E une EEREN A ESN 272 10 1 7 G arante eS eee a s O nE E E A E ERA eed OSA 274 10 1 8 Differentiated Guarantees eseeeeseeereeeserrerrrrresrrerrsrrerrrreseee 274 10 1 9 GTOUpS ici sese ccs vieeccae dies eorr uE E EEEE IDETE EEEIEE E SSIES SET VETESSE EEEa 275 10 1 10 Recommendations sissies soati veosasssssetangasedssesstoseassstotataneeds 276 10 1 11 A Summary of Traffic Shaping e eseeseeesseeersererreresrrreerrerrsrree 277 10 2 Threshold Rules cies secs sectsaess pevei kinesio eee aaa E TEE TEE 279 10 2 1 OVERVIEW ornes eeo re a e aa des panne rii haves 279 10 2 2 Connection Rate Total Connection Limiting seeecesresrrrrerrerrerse 279 10 2 3 Grouping spot e es tdact ey Tah s ag a a n anv eades tease teed 279 10 24 RULE ACtONS asus sete Bk Sse hue aA A wat Salem 279 10 2 5 Multiple Triggered Actions 20 00 00 cece cece cece eece eee eeceeeeeeeeneeenes 280 10 2 6
430. t that allow traffic to pass through the tunnel Setup for D Link Firewall B Assuming that the network 92 168 11 0 24 is lannet on the lan interface the steps for setting up NetDefendOS on B are as follows 65 3 3 6 Interface Groups Chapter 3 Fundamentals 1 In the address book set up the following IP objects e remote_net_A 192 168 10 0 24 e remote_gw 172 16 0 1 e ip_GRE 192 168 0 2 2 Create a GRE Tunnel object called GRE_to_A with the following parameters e IP Address ip_GRE e Remote Network remote_net_A e Remote Endpoint remote_gw e Use Session Key 1 e Additional Encapulation Checksum Enabled 3 Define a route in the main routing table which routes all traffic to remote_net_A on the GRE_to_A GRE interface This is not necessary if the option Add route for remote network is enabled in the Advanced tab since this will add the route automatically 4 Create the following rules in the IP rule set that allow traffic to pass through the tunnel 3 3 6 Interface Groups Multiple NetDefendOS interfaces can be grouped together to form an Interface Group Such a logical group can then be subject to common policies and be referred to using a group name in the IP rule set and User Authentication Rules A group can consist of regular Ethernet interfaces VLAN interfaces or VPN Tunnels and the members of a group need not be of the same type A group might consist for instance of two Ethernet interfaces and
431. t to ReconfShutTimer Default 56400 327 13 13 IPsec Settings Chapter 13 Advanced Settings 13 13 IPsec Settings IKESendinitialContact Determines whether or not IKE should send the Initial Contact notification message This message is sent to each remote gateway when a connection is opened to it and there are no previous IPsec SA using that gateway Default Enabled IKESendCRLs Dictates whether or not CRLs Certificate Revocation Lists should be sent as part of the IKE exchange Should typically be set to ENABLE except where the remote peer does not understand CRL payloads Default Enabled IKECRLValidityTime A CRL contains a next update field that dictates the time and date when a new CRL will be available for download from the CA The time between CRL updates can be anything from a few hours and upwards depending on how the CA is configured Most CA software allow the CA administrator to issue new CRLs at any time so even if the next update field says that a new CRL is available in 12 hours there may already be a new CRL for download This setting limits the time a CRL is considered valid A new CRL is downloaded when IKECRLVailityTime expires or when the next update time occurs Whichever happens first Default 90000 IKEMaxCAPath When the signature of a user certificate is verified NetDefendOS looks at the issuer name field in the user certificate to find the CA certificate the certifi
432. t up by the administrator Dropping SPAM Email If the calculated sum is greater than or equal to the Drop threshold value then the email is not forwarded to the intended recipient Instead the administrator can choose one of two alternatives for dropped email e A special email address can be configured to receive all dropped email If this is done then any TXT messages mentioned earlier sent by the DNSBL servers that identified the email as SPAM can be optionally appended by NetDefendOS as an attachment to the forwarded email e If no receiver email address is configured for dropped emails then they are discarded by NetDefendOS and an error message sent back to the sender address along with the TXT messages from the DNSBL servers that failed the email Allowing for Failed DNSBL Servers If a query to a DNSBL server times out then NetDefendOS will consider that the query has failed and the weight given to that server will be automatically subtracted from both the SPAM and Drop thresholds for the scoring calculation done for that email If enough DNSBL servers don t respond then this subtraction could mean that the threshold values become negative Since the scoring calculation will always produce a value of zero or greater servers can t have negative weights then all email will be allowed through if both the SPAM and Drop thresholds become negative A log message is generated whenever a configured DNSBL server does not respond within the r
433. tDefendOS it can still be reused with any number of other different VPN tunnels 3 7 2 X 509 Certificates in NetDefendOS X 509 certificates can be uploaded to the D Link Firewall for use in IKE IPsec authentication Webauth etc There are two types of certificates that can be uploaded self signed certificates and remote certificates belonging to a remote peer or CA server Example 3 18 Uploading an X 509 Certificate The certificate may either be self signed or belonging to a remote peer or CA server Web Interface 1 Goto Objects gt Authentication Objects gt Add gt Certificate 2 Specify a suitable name for the certificate 80 3 7 2 X 509 Certificates in Chapter 3 Fundamentals NetDefendOS 3 Now select one of the following Upload self signed X 509 Certificate Upload a remote certificate 4 Click OK and follow the instructions Example 3 19 Associating X 509 Certificates with IPsec Tunnels To associate an imported certificate with an IPsec tunnel Web Interface Go to Interfaces gt IPsec Display the properties the IPsec tunnel Select the Authentication tab Select the X509 Certificate option Select the correct Gateway and Root certificates Click OK 81 3 8 Setting Date and Time Chapter 3 Fundamentals 3 8 Setting Date and Time Correctly setting the date and time is important for NetDefendOS to operate properly Time scheduled policies auto update of the IDP and
434. tbound which should be using the ALG definition ftp outbound as described earlier C Allow connections to ftp servers on the outside Go to Rules gt IP Rules gt Add gt IPRule Now enter Name Allow ftp outbound Action Allow e Service ftp outbound For Address Filter enter Source Interface lan Destination Interface wan Source Network lannet Destination Network all nets Click OK Rules Using Private IPs If the firewall is using private IP s the following NAT rule need to be added instead Go to Rules gt IP Rules gt Add gt IPRule Now enter Name NAT ftp outbound Action NAT e Service ftp outbound For Address Filter enter Source Interface lan Destination Interface wan Source Network lannet Destination Network all nets Check Use Interface Address Click OK 6 2 4 TFTP Trivial File Transfer Protocol TFTP is a much simpler version of FTP with more limited capabilities Its purpose is to allow a client to upload files to or download files from a host system TFTP data transport is based on the UDP protocol and therefore it supplies its own transport and session control protocols which are layered onto UDP 145 6 2 5 SMTP Chapter 6 Security Mechanisms TFTP is widely used in enterprise environments for updating software and backing up configurations on network devices TFTP is recognised as being an inherently insecure protocol and its usage is often confined to internal n
435. te IP addresses in an internal network and it is desirable that outbound connections appear as though they originate from the D Link Firewall itself instead of the internal addresses NAT is a many to one translation meaning that each NAT rule will translate several source IP addresses into a single source IP address To maintain session state information each connection from dynamically translated addresses must use a unique port number and IP address combination as its sender Therefore NetDefendOS will perform an automatic translation of the source port number as well The source port used will be the next free port usually one above 32768 This means that there is a limitation of about 30000 simultaneous connections using the same translated source IP address NetDefendOS supports two strategies for how to translate the source address Use Interface Address When a new connection is established the routing table is consulted to resolve the egress interface for that connection The IP address of that resolved interface is then being used as the new source IP address when NetDefendOS performs the address translation Specify Sender Address A specific IP address can be specified as the new source IP address The specified IP address needs to have a matching ARP 204 7 1 Dynamic Network Address Chapter 7 Address Translation Translation Publish entry configured for the egress interface Otherwise the return traffic will not be re
436. te a route in its routing table dynamically as each client connects In the example below this is the case and the IPsec tunnel is configured to dynamically add routes If clients are to be allowed to roam in from everywhere irrespective of their IP address then the Remote Network needs to be set to all nets IP address 0 0 0 0 0 which will allow all existing IPv4 addresses to connect through the tunnel When configuring VPN tunnels for roaming clients it is usually not necessary to add to or modify the proposal lists that are pre configured in NetDefendOS 9 4 3 1 PSK based client tunnels Example 9 4 Setting up a PSK based VPN tunnel for roaming clients This example describes how to configure an IPsec tunnel at the head office D Link Firewall for roaming clients that connect to the office to gain remote access The head office network uses the 10 0 1 0 24 network span with external firewall IP wan_ip Web Interface A Create a pre shared key for IPsec authentication Go to Objects gt Authentication Objects gt Add gt Pre Shared Key Now enter Name Enter a name for the pre shared key SecretKey for instance Shared Secret Enter a secret passphrase Confirm Secret Enter the secret passphrase again Click OK B Configure the IPsec tunnel Go to Interfaces gt IPsec gt Add gt IPsec Tunnel Now enter Name Roaming PsecTunnel Local Network 10 0 1 0 24 This is the local network that the roaming users will con
437. te a Pre shared Key 250 9 3 8 Identification Lists Chapter 9 VPN Go to Objects gt Authentication Objects gt Add gt Pre shared key Enter a name for the pre shared key eg MyPSK Choose Hexadecimal Key and click Generate Random Key to generate a key to the Passphrase textbox Click OK Then apply the pre shared key to the IPsec tunnel Go to Interfaces gt IPsec In the grid control click the target IPsec tunnel object Under the Authentication tab choose Pre shared Key and select MyPSK Click OK 9 3 8 Identification Lists When X 509 certificates are used as authentication method for IPsec tunnels the D Link Firewall will accept all remote firewalls or VPN clients that are capable of presenting a certificate signed by any of the trusted Certificate Authorities This can be a potential problem especially when using roaming clients Consider the scenario of travelling employees being given access to the internal corporate networks using VPN clients The organization administers their own Certificate Authority and certificates have been issued to the employees Different groups of employees are likely to have access to different parts of the internal networks For instance members of the sales force need access to servers running the order system while technical engineers need access to technical databases Since the IP addresses of the travelling employees VPN clients cannot be known beforehand the incoming VP
438. te information to a dissimilar device It is also strongly recommended that the D Link Firewalls used in cluster have identical configurations They must also have identical licenses which allow identical capabilities including the ability to run in an HA cluster Extending Redundancy Implementing an HA Cluster will eliminate one of the points of failure in a network Routers switches and Internet connections can remain as potential points of failure and redundancy for these should also be considered The following sections describe the High Availability feature in greater detail 290 11 2 High Availability Mechanisms Chapter 11 High Availability 11 2 High Availability Mechanisms D Link HA provides a redundant state synchronized hardware configuration The state of the active unit such as the connection table and other vital information is continuously copied to the inactive unit via the sync interface When cluster failover occurs the inactive unit knows which connections are active and traffic can continue to flow The inactive system detects that the active system is no longer operational when it no longer detects sufficient Cluster Heartbeats Heartbeats are sent over the sync interface as well as all other interfaces NetDefendOS sends 5 heartbeats per second from the active system and when three heartbeats are missed that is to say after 0 6 seconds a failover will be initiated By sending heartbeats over all int
439. tekeeper on DMZ from the Branch network Click OK 166 6 2 8 H 323 Chapter 6 Security Mechanisms Go to Rules gt IP Rules gt Add gt IPRule Now enter Name BranchToGW Action Allow Service H323 Gatekeeper Source Interface vpn remote Destination Interface dmz Source Network remote net Destination Network ip gatekeeper Comment Allow communication with the Gatekeeper on DMZ from the Remote network Click OK Example 6 11 Configuring remote offices for H 323 If the branch and remote office H 323 phones and applications are to be configured to use the H 323 Gatekeeper at the head office the D Link Firewalls in the remote and branch offices should be configured as follows this rule should be in both the Branch and Remote Office firewalls Web Interface Go to Rules gt IP Rules gt Add gt IPRule Now enter Name ToGK Action Allow Service H323 Gatekeeper Source Interface lan Destination Interface vpn hq Source Network lannet Destination Network hq net Comment Allow communication with the Gatekeeper connected to the Head Office DMZ Click OK Example 6 12 Allowing the H 323 Gateway to register with the Gatekeeper The branch office D Link Firewall has a H 323 Gateway connected to its DMZ In order to allow the Gateway to register with the H 323 Gatekeeper at the Head Office the following rule has to be configured Web Interface 1 Goto Rules gt IP Rules gt Add gt IPRule 2 Now enter
440. ter Name http2fw Action Allow Service HTTP Source Interface lan 226 8 2 6 HTTP Authentication Chapter 8 User Authentication e Source Network lannet Destination Interface core Destination Network lan_ip Click OK B Set up the Authentication Rule Go to User Authentication gt User Authentication Rules gt Add gt User Authentication Rule Now enter Name HTTPLogin Agent HTTP Authentication Source Local Interface lan Originator IP lannet For Local User DB choose annet_auth_users For Login Type choose HTMLForm Click OK C Set up an IP rule to allow authenticated users to browse the Web Go to Rules gt IP Rules gt Add gt IP rule Now enter Name Allow_http_auth Action NAT Service HTTP Source Interface lan Source Network lannet_users Destination Interface any Destination Network all nets Click OK Example 8 3 Configuring a RADIUS server Web Interface 1 User Authentication gt External User Databases gt Add gt External User Database 2 Now enter a Name Enter a name for the server b Type Select RADIUS c IP Address Enter the IP address of the server or enter the symbolic name if the server has been defined in the Address Book 227 8 2 6 HTTP Authentication Chapter 8 User Authentication Port 1812 RADIUS service uses UDP port 1812 by default Retry Timeout 2 NetDefendOS will resend the authentication request to the sever if there is no
441. ter is replaced as NetDefendOS will not accept the new address until the previous ARP table entry has timed out Default AcceptLog StaticARPChanges Determines how NetDefendOS will handle situations where a received ARP reply or ARP request would alter a static item in the ARP table Of course this is never allowed to happen However this setting does allow you to specify whether or not such situations are to be logged Default DropLog 312 ARPExpireUnknown Chapter 13 Advanced Settings ARPExpire Specifies how long a normal dynamic item in the ARP table is to be retained before it is removed from the table Default 900 seconds 15 minutes ARPExpireUnknown Specifies how long NetDefendOS is to remember addresses that cannot be reached This is done to ensure that NetDefendOS does not continuously request such addresses Default 3 seconds ARPMulticast Determines how NetDefendOS is to deal with ARP requests and ARP replies that state that they are multicast addresses Such claims are usually never correct with the exception of certain load balancing and redundancy devices which make use of hardware layer multicast addresses Default DropLog ARPBroadcast Determines how NetDefendOS is to deal with ARP requests and ARP replies that state that they are broadcast addresses Such claims are usually never correct Default DropLog ARPCacheSize How many ARP entrys there can be in the cache in total Def
442. th an ALG The default value varies according to the ALG it is associated with If the default is for example 700 this would mean that only 100 connections are allowed in total for this Service across all interfaces For a Service involving for instance an HTTP ALG the default value can often be too low if there are large numbers of clients connecting through the D Link Firewall It is therefore recommended to consider if a higher value is required for a particular scenario Using All Services 54 3 2 3 ICMP Services Chapter 3 Fundamentals When setting up rules that filter by services it is possible to use the service grouping all_services to refer to all protocols If just referring to the main protocols of TCP UDP and ICMP then the service group all_tepudpicmp can be used 3 2 3 ICMP Services Internet Control Message Protocol ICMP is a protocol integrated with IP for error reporting and transmitting control information The PING service for example uses ICMP to test an Internet connectivity ICMP messages is delivered in IP packets and includes a Message Type that specifies the type that is the format of the ICMP message and a Code that is used to further qualify the message For example the message type Destination Unreachable uses the Code parameter to specify the exact reason for the error The ICMP message types that can be configured in NetDefendOS are listed as follows e Echo Request sent by PING to a
443. th an Authentication Group if required e Set up IP rules to allow the authentication to take place and also to allow access to resources by the clients belonging to the IP object set up in the previous step The following sections describe the components of these steps in detail Authentication Sources The database that an Authentication Rule uses to check a user s username password combination can be one of two types e The local user database internal to NetDefendOS e A RADIUS server which is external to the D Link Firewall 8 2 2 The Local Database The Local User Database is a built in registry inside NetDefendOS which contains the profiles of authorized users and user groups Usernames and passwords can be entered into this database and users with the same privileges can be collected together into groups to make administration easier There are two default user groups the administrators group and the auditors group Users that are members of the administrators group are allowed to change the NetDefendOS configuration while users that belong to the auditors group are only allowed to view the configuration Press the buttons under the Groups edit box to grant these group memberships to a user 8 2 3 External Authentication Servers The Need for Servers In a larger network topology with a larger administration workload it is often preferable to have a central authentication database on a dedicated server When there is more
444. th tables Important Ensuring all nets appears in the main table q A common mistake with Policy based routing is the absence of the default route with a destination interface of all nets in the default main routing table If there is no route that is an exact match then the absence a default all nets route will mean that the connection will be dropped Example 4 3 Creating a Policy Based Routing table In this example we create a Policy based Routing table named TestPBRTable Web Interface 1 Go to Routing gt Routing Tables gt Add gt RoutingTable 2 Now enter Name TestPBRTable e For Ordering select one of First the named routing table is consulted first of all If this lookup fails the lookup will continue in the main routing table Default the main routing table will be consulted first If the only match is the default route all nets the named routing table will be consulted If the lookup in the named routing table fails the lookup as a whole is considered to have failed Only the named routing table is the only one consulted If this lookup fails the lookup will not continue in the main routing table 3 If Remove Interface IP Routes is enabled the default interface routes are removed that is to say routes to the core interface which are routes to NetDefendOS itself 4 Click OK Example 4 4 Creating the Route After defining the routing table TestPBRTable we add routes into the table
445. than one D Link Firewall in the network and thousands of users maintaining separate authentication databases on each device becomes problematic Instead an external authentication server can validate username password combinations by responding to requests from NetDefendOS To provide this NetDefendOS supports the Remote Authentication Dial in User Service RADIUS protocol RADIUS with NetDefendOS 221 8 2 4 Authentication Rules Chapter 8 User Authentication NetDefendOS acts as a RADIUS client sending user credentials and connection parameter information as a RADIUS message to a nominated RADIUS server The server processes the requests and sends back a RADIUS message to accept or deny them One or more external servers can be defined in NetDefendOS RADIUS Security To provide security a common shared secret is configured on both the RADIUS client and the server This secret enables encryption of the messages sent from the RADIUS client to the server and is commonly configured as a relatively long text string The string can contain up to 100 characters and is case sensitive RADIUS uses PPP to transfer username password requests between client and RADIUS server as well as using PPP authentication schemes such as PAP and CHAP RADIUS messages are sent as UDP messages via UDP port 1812 8 2 4 Authentication Rules Authentication Rules are set up in a way that is similar to other NetDefendOS security policies by specifying
446. that we created to the return chain This means that the packets travelling in the return direction of this connection outside in should pass through the std in pipe 269 10 1 4 Limiting Bandwidth in Both Chapter 10 Traffic Management Directions CLI gw world gt add PipeRule ReturnChain std in SourceInterface lan SourceNetwork lannet DestinationInterface wan DestinationNetwork all nets Service all_services name Outbound Web Interface Go to Traffic Management gt Traffic Shaping gt Pipes gt Add gt Pipe Rule Specify a suitable name for the pipe for instance outbound Now enter Service all_services Source Interface lan Source Network lannet Destination Interface wan Destination Network all nets Under the Traffic Shaping tab make std in selected in the Return Chain control Click OK This setup limits all traffic from the outside the Internet to 2 megabits per second No priorities are applied nor any dynamic balancing 10 1 4 Limiting Bandwidth in Both Directions A single pipe doesn t care which direction the traffic through it is coming from when it calculates total throughout Using the same pipe for both outbound and inbound traffic is allowed by NetDefendOS but it will not neatly partition pipe limits between the two directions The following scenario clarifies this In the previous example only bandwidth in the inbound direction is limited We chose this direction because in most setups
447. thenticated user is closed When a new client session is started by a user establishing a new connection through the D Link Firewall NetDefendOS sends an AccountingRequest START message to a nominated RADIUS server to record the start of the new session User account information is also delivered to the RADIUS server The server will send back an AccountingResponse message to NetDefendOS acknowledging that the message has been received When a user is no longer authenticated for example after the user logs out or the session time expires an AccountingRequest STOP message is sent by NetDefendOS containing the relevant session statistics The information included in these statistics is user configurable The contents of the START and STOP messages are described in detail below START Message Parameters Parameters included in START messages sent by NetDefendOS are e Type Marks this AccountingRequest as signaling the beginning of the service START e ID A unique identifier to enable matching of an AccountingRequest with Acct Status Type set to STOP e User Name The user name of the authenticated user e NAS IP Address The IP address of the D Link Firewall e NAS Port The port of the NAS on which the user was authenticated this is a physical port and not a TCP or UDP port e User IP Address The IP address of the authenticated user This is sent only if specified on the authentication server How Authenticated
448. this response Example 3 25 Modifying the Maximum Adjustment Value CLI gw world gt set DateTime TimeSyncMaxAdjust 40000 Web Interface Go to System gt Date and Time For the setting Maximum time drift that a server is allowed to adjust enter the maximum time drift in seconds that a server is allowed to adjust for Click OK Sometimes it might be necessary to override the maximum adjustment for instance if time synchronization has just been enabled and the inital time difference is greater than the maximum adjust value It is then possible to manually force a synchronization and disregard the maximum adjustment parameter Example 3 26 Forcing Time Synchronization This example demonstrates how to force time synchronization overiding the maximum adjustment setting CLI gw world gt time sync force Synchronization Intervals The interval between each synchronization attempt can be adjusted if needed By default this value is 86 400 seconds 1 day meaning that the time synchronization process is executed once in a 24 hour period 85 3 8 2 Time Servers Chapter 3 Fundamentals D Link Time Servers Using D Link s own Time Servers is an option in NetDefendOS and this is the recommended way of synchronizing the firewall clock These servers communicate with NetDefendOS using the SNTP protocol When the D Link Server option is chosen a pre defined set of recommended default values for the synchro
449. though the arrival of too many fragments that are too small may cause problems for IP stacks it is usually not possible to set this limit too high It is rarely the case that senders create very small fragments However a sender may send 1480 byte fragments and a router or VPN tunnel on the route to the recipient subsequently reduce the effective MTU to 1440 bytes This would result in the creation of a number of 1440 byte fragments and an equal number of 40 byte fragments Because of potential problems this can cause the default settings in NetDefendOS has been designed to allow the smallest possible fragments 8 bytes to pass For internal use where all media sizes are known this value can be raised to 200 bytes or more Default 8 bytes ReassTimeout A reassembly attempt will be interrupted if no further fragments arrive within ReassTimeout seconds of receipt of the previous fragment Default 65 seconds ReassTimeLimit A reassembly attempt will always be interrupted ReassTimeLimit seconds after the first received fragment arrived Default 90 seconds ReassDoneLinger Once a packet has been reassembled NetDefendOS is able to remember this for a short period of time in order to prevent further fragments for example old duplicate fragments of that packet from arriving Default 20 seconds ReasslllegalLinger 322 ReasslllegalLinger Chapter 13 Advanced Settings Once a whole packet has been marked as illegal NetD
450. tificates e L2TP Roaming Clients with Pre Shared Keys e L2TP Roaming Clients with Certificates e PPTP Roaming Clients 9 2 1 IPsec LAN to LAN with Pre shared Keys 1 Create a Pre shared Key object 2 Optionally create a new IKE Proposal List object and or an IPsec Proposal List object if the default list settings are not satisfactory This will depend on the capabilities of the device at the other side of the tunnel 3 In Hosts amp Networks create IP objects for e The remote VPN gateway which is the IP address of the network device at the other end of the tunnel let s call this object remote_gw e The remote network which lies behind the remote VPN gateway let s call this object remote_net e The local network behind the D Link Firewall which will communicate across the tunnel Here we will assume that this is the pre defined address annet and this network is attached to the NetDefendOS lan interface 4 Create an IPsec Tunnel object let s call this object ipsec_tunnel Specify the following tunnel parameters Set Local Network to lannet e Set Remote Network to remote_net e Set Remote Gateway to remote_gw e Set Encapsulation mode to Tunnel e Choose the IKE and IPsec proposal lists to be used e For Authentication select the Pre shared Key object defined in step 1 above The IPsec Tunnel object can be treated exactly like any NetDefendOS Interface object in later steps 5 Set up two IP rules in the I
451. times called a server farm to handle many more requests than a single server The image below illustrates a typical SLB scenario with Internet access to applications being controlled by a D Link Firewall The SLB feature is available on the D Link DFL 800 1600 2500 only Figure 10 5 A Server Load Balancing configuration Besides improving performance SLB increases the reliability of network applications by actively monitoring the servers sharing the load SLB can detect when a server fails or becomes congested and will not direct any further requests to that server until it recovers or has less load 281 10 3 2 Identifying the Servers Chapter 10 Traffic Management SLB also means that network administrators can perform maintenance tasks on servers or applications without disrupting services Individual servers can be restarted upgraded removed or replaced and new servers and applications can be added or moved without affecting the rest of a server farm or taking down applications The combination of network monitoring and distributed load sharing also provides an extra level of protection against Denial Of Service DoS attacks NetDefendOS SLB is implemented through the use of SLB_SAT rules in the IP rule set and these rules offer administrators a choice of several different algorithms to distribute the load This allows the tailoring of SLB to best suit the needs of the network There are four issues to be conside
452. ting Policy 20 0 0 cece cc eee neceneene een eeneeeeeeeaees 107 4 5 Multicast ROUMNG essesi nisor sags sevens sessdsnessssotstapsedsdeasss bina gs esaseusesvotes seeds 110 ASD OVERVIEW eiee sen gobs aust SS Goleta gece ieee Soak CRESS TERESI Sa oe FEAE e EE 110 4 5 2 Multicast Forwarding using the SAT Multiplex Rule 0 0 00 110 4 5 3 IGMP Configuration 0 cece cece cece cece ne cenceeeeae een eeneeeaeeeeees 114 4 6 Transparent Mode mensen red iat aE a E E A wee Mareen eerie 119 4 6 1 Overview of Transparent Mode cee ceeeeeeeeeceeneeeueeeeeeneenueeeenees 119 4 6 2 Comparison with Routing mode eee eee ce eeceeeeeeeeeeeen ees 119 4 6 3 Transparent Mode Implementation cece cece cece c eee ce teen erent ee 119 4 6 4 Enabling Transparent Mode 0 eee eee ce cece neceeec ee ceneeneeeeeeeeees 120 4 6 5 High Availability with Transparent Mode cece eeee eee eens 120 4 6 6 Transparent Mode Scenarios ccc eceeeseceeece nsec eecee een eeeeceeeeeees 120 9 DHCP Services sssosess ss ess ra eenas eai o PETEERE POSET ES EE Pai OPERERET SPES aapeess 127 SL Oyeryl EW o aa a er E re E RE E E NEEESE I EREE EE dees 127 J2 DHCP SeryerS on e E a E E o EES 128 5 3 Static DHCP Assignment 20 0 0 eee srst aiii sores Kss EE I REEE E ea 130 9 4 DHCP Relaying oseere ir repar e a ear PESA SEEE POESIES EE EEE EA IS 131 SE l A 00 KAE A A E E EE ue saas 132 6 Security Mechani
453. tion e Route 1 All packets going to hosts on the 192 168 0 0 24 network should be sent out on the lan interface As no gateway is specified for the route entry the host is assumed to be located on the network segment directly reachable from the lan interface e Route 2 All packets going to hosts on the 10 4 0 0 16 network are to be sent out on the dmz interface Also for this route no gateway is specified e Route 3 All packets going to hosts on the 195 66 77 0 24 network will be sent out on the wan interface No gateway is required to reach the hosts e Route 4 All packets going to any host the all nets network will match all hosts will be sent out on the wan interface and to the gateway with IP address 195 66 77 4 That gateway will then consult its routing table to find out where to send the packets next A route with destination all nets is often referred to as the Default Route as it will match all packets for which no specific route has been configured When a routing table is evaluated the ordering of the routes is important In general a routing table is evaluated with the most specific routes first In other words if two routes have destination networks that overlap the more narrow network will be evaluated prior to the wider one In the above example a packet with a destination IP address of 192 168 0 4 will theoretically match both the first route and the last one However the first route entry is a more specific match
454. tion Network all nets 0 0 0 0 0 3 Click OK Scenario 2 Here the D Link Firewall in Transparent Mode separates server resources from an internal network by connecting them to a separate interface without the need for different address ranges Figure 4 9 Transparent mode scenario 2 All hosts connected to LAN and DMZ the lan and dmz interfaces share the 10 0 0 0 24 address space As this is configured using Transparent Mode any IP address can be used for the servers and there is no need for the hosts on the internal network to know if a resource is on the same network or placed on the DMZ The hosts on the internal network are allowed to communicate with an HTTP server on DMZ while the HTTP server on the DMZ can be reached from the Internet The firewall is transparent between the DMZ and LAN while traffic can subjected to the IP rule set Example 4 14 Setting up Transparent Mode Scenario 2 Configure a Switch Route over the LAN and DMZ interfaces for address range 10 0 0 0 24 assume the WAN interface is already configured Configure the interfaces Similar as shown in the previous example first we need to specify the involving interfaces lan and dmz using the example IP addresses for this scenario Interface Groups Similar as shown in the previous example Configure both interfaces Janand dmzinto the same group 122 4 6 6 Transparent Mode Scenarios Chapter 4 Routing Switch Route Similar as sh
455. tion process to take place and assumes the client is trying to access the an_ip IP address which is the IP address of the interface on the D Link Firewall where the local network connects The second rule allows normal surfing activity but we cannot just use annet as the source network since the rule would trigger for any unauthenticated client from that network Instead the source network is an administrator defined IP object called trusted_users which is the same network as lannet but has additionally either the Authentication option No Defined Credentials enabled or has an Authentication Group assigned to it which is the same group as that assigned to the users The third rule allows DNS lookup of URLs Forcing Users to a Login Page With this setup when users that aren t authenticated try to surf to any IP except an_ip they will fall through the rules and their packets will be dropped To always have these users come to the authentication page we must add a SAT rule and its associated Allow rule The rule set will now look like this 224 8 2 6 HTTP Authentication Chapter 8 User Authentication The SAT rule catches all unauthenticated requests and must be set up with an all to one address mapping that directs them to the address 727 0 0 1 which corresponds to core NetDefendOS itself 225 8 2 6 HTTP Authentication Chapter 8 User Authentication Example 8 1 Creating an authentication user group In the exampl
456. tive list of what protocols that can or cannot be address translated A general rule is that VPN protocols cannot usually be translated In addition protocols that open secondary connections in addition to the initial connection can be difficult to translate Some protocols that are difficult to address translate may be handled by specially written algorithms designed to read and or alter application data These are commonly referred to as Application Layer Gateways or Application Layer Filters NetDefendOS supports a number of such Application Layer Gateways and for more information please see Section 6 2 Application Layer Gateways 7 3 6 Multiple SAT rule matches NetDefendOS does not terminate the rule set lookup upon finding a matching SAT rule Instead it continues to search for a matching Allow NAT or FwdFast rule Only when it has found such a matching rule does the firewall execute the static address translation Despite this the first matching SAT rule found for each address is the one that will be carried out Each address above means that two SAT rules can be in effect at the same time on the same connection provided that one is translating the sender address whilst the other is translating the destination address The two above rules may both be carried out concurrently on the same connection In this instance internal sender addresses will be translated to addresses in the pubnet in a 1 1 relation In addition if any
457. to be used then specify the loopback address 727 0 0 1 as the DHCP server IP address 233 9 2 3 IPsec Roaming Clients with Chapter 9 VPN Certificates e Create a Config Mode Pool object there can only be one associated with a NetDefendOS installation and associate with it the IP Pool object defined in the previous step e Enable the IKE Config Mode option in the IPsec Tunnel object ipsec_tunnel Configuring the IPsec Client In both cases A and B above the IPsec client will need to configured with the URL of the D Link Firewall as well as the pre shared key 9 2 3 IPsec Roaming Clients with Certificates If certificates are used with IPsec roaming clients instead of pre shared keys then no Pre shared Key object is needed and the other differences in the setup described above are 1 Load a Gateway Certificate and Root Certificate into NetDefendOS 2 When setting up the IPsec Tunnel object specify the certificates to use under Authentication This is done by a Enable the X 509 Certificate option b Select the Gateway Certificate c Add the Root Certificate to use 3 The IPsec client software will need to appropriately configured with the certificates and remote IP addresses The step to set up user authentication is optional since this is additional security to certificates 9 2 4 L2TP Roaming Clients with Pre Shared Keys Due to the inbuilt L2TP client in Microsoft Windows L2TP is a popular choice for roa
458. to specific traffic based on source destination network interface as well as service Two types of IP rules NAT rules and SAT rules are used to specify address translation within the IP rule set There are two main reasons for employing address translation e Functionality Perhaps you use private IP addresses on your protected network and your protected hosts to have access to the Internet This is where dynamic address translation may be used You might also have servers with private IP addresses that need to be publicly accessible This is where static address translation may be the solution e Security Address translation does not in itself provide any greater level of security but it can make it more difficult for intruders to understand the exact layout of the protected network and which machines are susceptible to attack In the worst case scenario employing address translation will mean that an attack will take longer which will also make it more visible in NetDefendOS s log files In the best case scenario an intruder will just give up This section describes dynamic as well as static address translation how they work and what they can and cannot do It also provides examples of configuring NAT and SAT rules 7 1 Dynamic Network Address Translation Dynamic Network Address Translation NAT provides a mechanism for translating original source IP addresses to a different addresses The most common usage for NAT is when using priva
459. tor can explicitly state if the file is to be allowed or blocked as a download File types The file type to be blocked or allowed can be added into the list For example GIF could be added If a filetype is on the allowed list then it should be noted that MIME matching will still take place even if MIME matching is switched off providing the filetype is part of the list in Appendix C Checked MIME filetypes This is done to guard against an attack that tries to exploit the fact the filetype is on the allowed list 3 Scan Exclude Option Certain filetypes may be explicitly excluded from virus scanning if that is desirable This can increase overall throughput if an excluded filetype is a type which is commonly encountered in a particular scenario 4 Compression Ratio Limit When scanning compressed files NetDefendOS must apply decompression to examine the file s contents Some types of data can result in very high compression ratios where the compressed file is a small fraction of the original uncompressed file size This can mean that a comparatively small compressed file attachment might need to be uncompressed into a much larger file which can place an excessive load on NetDefendOS resources and noticeably slowdown throughput To prevent this situation the administrator should specify a Compression Ratio limit If the limit of the ration is specified as 10 then this will mean that if the uncompressed file is 10 times larger than the com
460. ts as group members Now a single policy can be used with this group thereby greatly reducing the administrative workload Address Group objects are not restricted to contain members of the same subtype In other words IP host objects can be teamed up with IP ranges IP networks and so on All addresses of all group members are combined effectively resulting in a union of the addresses As an example a group containing two IP ranges one with addresses 192 168 0 10 192 168 0 15 and the other with addresses 192 168 0 14 192 168 0 19 will result in a single IP range with addresses 192 168 0 10 192 168 0 19 Keep in mind however that for obvious reasons IP address objects can not be combined with Ethernet addresses 3 1 5 Auto Generated Address Objects To simplify the configuration several address objects are automatically generated when the system is run for the first time These objects are being used by other parts of the configuration already from start The following address objects are auto generated Interface Addresses For each Ethernet interface in the system two IP Address objects are pre defined one object for the IP address of the actual interface and one object representing the local network for that interface Interface IP address objects are named interfacename_ip and network objects are named interfacenamenet As an example an interface named Jan will have an associated interface IP object named lan_ip and a n
461. ts may in fact break the IKE negotiations which is why the UDP port used by IKE has changed Another problem NAT traversal resolves is that the ESP protocol is an IP protocol There is no port information like in TCP and UDP which makes it impossible to have more than one NATed client connected to the same remote gateway and the same time Because of this ESP packets are encapsulated in UDP The ESP UDP traffic is sent on port 4500 the same port as IKE when NAT traversal is used Once the port has been changed all following IKE communications are done over port 4500 Keepalive packets are also being sent periodically to keep the NAT mapping alive NAT Traversal Configuration Most NAT traversal functionality is completely automatic and in the initiating firewall no special 248 9 3 6 Proposal Lists Chapter 9 VPN configuration is needed However for responding firewalls two points should be noted e On responding firewalls the Remote Gateway field is used as a filter on the source IP of received IKE packets This should be set to allow the NATed IP address of the initiator e When individual pre shared keys are used with multiple tunnels connecting to one remote firewall which are then NATed out through the same address it is important to make sure the Local ID is unique for every tunnel The Local ID can be one of e Auto The local ID is taken as the IP address of the outgoing interface This is the recommended setting unless
462. ts that are not part of an existing connection This provides the firewall administrator with a way to detect any traffic that appears to be an intrusion With this option the only possible IDP Rule Action is logging Caution should of course be exercised with this option since the processing load can be much higher when all data packets are checked 6 5 4 Insertion Evasion Attack Prevention Overview When defining an IDP Rule the administrator has the option to enable or disable the ability to Protect against Insertion Evasion attack Insertion Evasion Attack is a form of attack which is specifically aimed at IDP systems It exploits the fact that in a TCP IP data transfer the data stream must often be reassembled from smaller pieces of data because the individual pieces either arrive in the wrong order or are fragmented in some way Insertions or Evasions are designed to exploit this reassembly process Insertion Attacks An Insertion attack consists of inserting data into a stream so that the resulting sequence of data packets is accepted by the IDP subsystem but will be rejected by the targeted application This results is two different streams of data As an example consider a data stream broken up into 4 packets pl p2 p3 and p4 The attacker might first send packets p1 and p4 to the targeted application These will be held by both the IDP subsystem and the application until packets p2 and p3 arrive so that reassembly can be done Th
463. ttings Default 7000 bytes TCPZeroUnusedACK Determines whether NetDefendOS should set the ACK sequence number field in TCP packets to zero if it is not used Some operating systems reveal sequence number information this way which can make it easier for intruders wanting to hijack established connections Default Enabled TCPZeroUnusedURG Strips the URG pointers from all packets Default Enabled TCPOPT_WSOPT Determines how NetDefendOS will handle window scaling options These are used to increase the size of the windows used by TCP that is to say the amount of information that can be sent before the sender expects ACK They are also used by OS Fingerprinting WSOPT is a common occurrence in modern networks Default ValidateLogBad TCPOPT_SACK Determines how NetDefendOS will handle selective acknowledgement options These options are used to ACK individual packets instead of entire series which can increase the performance of connections experiencing extensive packet loss They are also used by OS Fingerprinting SACK is a common occurrence in modern networks Default ValidateLogBad TCPOPT_TSOPT Determines how NetDefendOS will handle time stamp options As stipulated by the PAWS Protect Against Wrapped Sequence numbers method TSOPT is used to prevent the sequence numbers a 32 bit figure from exceeding their upper limit without the recipient being aware of it This is not normally a problem Using TSOPT so
464. tual LANs Route Monitoring Proxy ARP and Transparency For more information please see Chapter 4 Routing Address Translation For functionality as well as security reasons NetDefendOS supports policy based address translation Dynamic Address Translation NAT as well as Static Address Translation SAT is supported and resolves most types of address translation needs This feature is covered in Chapter 7 Address Translation Firewalling At the heart of the product NetDefendOS features stateful inspection based firewalling for common protocols such as TCP UDP and ICMP As an administrator you have the possibility to define detailed firewalling policies based on source and destination network and interface protocol ports user credentials time of day and much more Section 3 5 The IP Rule Set describes how to use the firewalling aspects of NetDefendOS Intrusion Detection and To mitigate application layer attacks towards vulnerabilities Prevention in services and applications NetDefendOS provides a powerful Intrusion Detection and Prevention IDP engine The IDP engine is policy based and is able to perform high performance scanning and detection of attacks and can perform blocking and optional black listing of attacking 14 1 1 About D Link NetDefendOS Chapter 1 Product Overview Anti Virus Web Content Filtering Virtual Private Networking Traffic Management Operations and Maintenance ZoneDefen
465. typically work by queuing up immense amounts of data and then sorting out the prioritized traffic to send before sending non prioritized traffic Instead the amount of prioritized traffic is measured and the non prioritized traffic is limited dynamically so that it won t interfere with the throughput of prioritized traffic 10 1 2 Traffic Shaping in NetDefendOS NetDefendOS offers extensive traffic shaping capabilities for the packets passing through a D Link Firewall Different rate limits and traffic guarantees can be created as policies based on the traffic s source destination and protocol similar to the way in which IP rule set policies are created The two key components for traffic shaping in NetDefendOS are e Pipes e Pipe Rules Pipes A Pipe is the fundamental object for traffic shaping and is a conceptual channel through which packets of data can flow It has various characteristics that define how traffic passing through it is handled As many pipes as are required can be defined by the administrator None are defined by default Pipes are simplistic in that they do not care about the types of traffic that pass through them nor the direction of that traffic They simply measure the data that passes through them and apply the administrator configured limits for the pipe as a whole or for Precedences and or Groups these are explained below NetDefendOS is capable of handling hundreds of pipes simultaneously but in reality mo
466. ublish and XPublish The difference between the two is that XPublish lies about the sender Ethernet address in the Ethernet header this is set to be the same as the published Ethernet address rather than the actual Ethernet address of the Ethernet interface If a published Ethernet address is the same as the Ethernet address of the interface it will make no difference if you select Publish or XPublish the result will be the same Tip In the configuration of ARP entires addresses may only be published one at a time However you can use the ProxyARP feature to handle publishing of entire networks see Section 4 2 4 Proxy ARP 3 4 5 Advanced ARP Settings This section presents some of the advanced settings related to ARP In most cases these settings need not to be changed but in some deployments modifications might be needed Most can be found in the WebUI by going to ARP gt Advanced Settings Multicast and Broadcast ARP requests and ARP replies containing multicast or broadcast addresses are usually never correct with the exception of certain load balancing and redundancy devices which make use of hardware layer multicast addresses The default behaviour of NetDefendOS is to drop and log such ARP requests and ARP replies This can however be changed by modifying the Advanced Settings ARPMulticast and ARPBroadcast Unsolicited ARP Replies It is fully possible for a host on the LAN to send an ARP reply to the firewal
467. uent and unusually complex patterns of data in the stream Recommended Configuration By default Insertion Evasion protection is enabled for all IDP rules and this is the recommended setting for most configurations There are two motivations for disabling the option 191 6 5 5 IDP Pattern Matching Chapter 6 Security Mechanisms e Increasing throughput Where the highest throughout possible is desirable then turning the option off can provide a slight increase in processing speed e Excessive False Positives If there is evidence of an unusually high level of Insertion Evasion false positives then disabling the option may be prudent while the false positive causes are investigated 6 5 5 IDP Pattern Matching Signatures In order for IDP to correctly identify an attack it uses a profile of indicators or pattern associated with different types of attack These pre defined patterns also known as signatures are stored in a local NetDefendOS database and are used by the IDP module to analyze traffic for attack patterns Each IDP signature is designated by a unique number Consider the following simple attack example involving an exchange with an FTP server A rogue user might try to retrieve the password file passwd from an FTP server using the FTP command RETR passwd A signature looking for the ASCII text strings RETR and passwd would find a match in this case indicating a possible attack In this example the pattern is
468. uitable name for the Certificate object Select the X 509 Certificate option Click OK B Create Identification Lists 1 Goto Objects gt VPN Objects gt ID List gt Add gt ID List 2 Enter a descriptive name eg sales 256 9 4 3 Roaming Clients Chapter 9 VPN Click OK Go to Objects gt VPN Objects gt ID List gt Sales gt Add gt ID Enter the name for the client Select Email as Type In the Email address field enter the email address selected when you created the certificate on the client Create a new ID for every client that you want to grant access rights according to the instructions above C Configure the IPsec tunnel Go to Interfaces gt IPsec gt Add gt IPsec Tunnel Now enter Name Roaming PsecTunnel Local Network 10 0 1 0 24 This is the local network that the roaming users will connect to Remote Network all nets Remote Endpoint None Encapsulation Mode Tunnel For Algorithms enter IKE Algorithms Medium or High IPsec Algorithms Medium or High For Authentication enter Choose X 509 Certificate as authentication method Root Certificate s Select your CA server root certificate imported earlier and add it to the Selected list Gateway Certificate Choose your newly created firewall certificate Identification List Select your ID List that you want to associate with your VPN Tunnel In our case that will be sales Under the Routing tab Enable the option Dynamically
469. ult e Upgrade Upgrade the firewall s firmware Navigator The navigator located on the left hand side of the web interface contains a tree representation of the system configuration The tree is divided into a number of sections corresponding to the major building blocks of the configuration The tree can be expanded to expose additional sections Main Window The main window contains configuration or status details corresponding to the section selected in the navigator or the menu bar Controlling Access to the Web Interface By default the web interface is accessible only from the internal network If you need to enable access from other parts of the network you can do so by modifying the remote management policy Example 2 2 Enabling remote management via HTTPS CLI gw world gt add RemoteManagement RemoteMgmtHTTP https Network all nets Interface any LocalUserDatabase AdminUsers HTTPS Yes Web Interface Go to System gt Remote Management gt Add gt HTTP HTTPS Management Enter a Name for the HTTP HTTPS remote management policy eg https Check the HTTPS checkbox Select the following from the dropdown lists 28 2 1 5 Working with Configurations Chapter 2 Management and Maintenance User Database AdminUsers Interface any Network all nets 5 Click OK f Caution L The above example is provided for informational purposes only It is never recommended to expose any management inter
470. ulticastSrc Block multicast both source addresses 224 0 0 0 255 255 255 255 Default DropLog TTLMin The minimum TTL value accepted on receipt Default 3 TTLOnLow Determines the action taken on packets whose TTL falls below the stipulated TTLMin value Default DropLog DefaultTTL Indicates which TTL NetDefendOS is to use when originating a packet These values are usually between 64 and 255 Default 255 LayerSizeConsistency 305 IPOptionSizes Chapter 13 Advanced Settings Verifies that the size information contained in each layer Ethernet IP TCP UDP ICMP is consistent with that of other layers Default ValidateLogBad IPOptionSizes Verifies the size of IP options These options are small blocks of information that may be added to the end of each IP header This function checks the size of well known option types and ensures that no option exceeds the size limit stipulated by the IP header itself Default ValidateLogBad IPOPT_SR Indicates whether source routing options are to be permitted These options allow the sender of the packet to control how the packet is to be routed through each router and firewall These constitute an enormous security risk NetDefendOS never obeys the source routes specified by these options regardless of this setting Default DropLog IPOPT_TS Time stamp options instruct each router and firewall on the packet s route to indicate at what time the pac
471. us ARP Generation By default NetDefendOS generates a gratuitous ARP request when a route failover occurs The reason for this is to notify surrounding systems that there has been a route change This behaviour can be controlled by the advanced setting RFO_GratuitousARPOnFail 4 2 4 Proxy ARP As explained previously in Section 3 4 ARP the ARP protocol facilitates a mapping between an IP address and the MAC address of a node on an Ethernet network However situations may exist where a network running Ethernet is separated into two parts with a routing device such as an installed D Link Firewall in between In such a case NetDefendOS itself can respond to ARP requests directed to the network on the other side of the D Link Firewall using the feature known as Proxy ARP For example host A on one subnet might send an ARP request to find out the MAC address of the 96 4 2 4 Proxy ARP Chapter 4 Routing IP address of host B on another separate network The proxy ARP feature means that NetDefendOS responds to this ARP request instead of host B The NetDefendOS sends its own MAC address instead in reply essentially pretending to be the target host After receiving the reply Host A then sends data directly to NetDefendOS which acting as a proxy forwards the data on to host B In the process the device has the opportunity to examine and filter the data The splitting of an Ethernet network into two distinct parts is a common appl
472. usands of simultaneous connections then it may be necessary to set a value above the automatic value Much higher values have the disadvantage of possibly increasing thoughput latency 295 11 4 High Availability Issues Chapter 11 High Availability 11 4 High Availability Issues The following points should be kept in mind when managing and configuring an HA Cluster SNMP SNMP statistics are not shared between master and slave SNMP managers have no failover capabilities Therefore both firewalls in a cluster need to be polled separately Using Individual IPs The unique individual IP addresses of the master and slave cannot safely be used for anything but management Using them for anything else such as for source IPs in dynamically NATed connections or publishing services on them will inevitably cause problems as unique IPs will disappear when the firewall it belongs to does Failed Interfaces Failed interfaces will not be detected unless they fail to the point where NetDefendOS cannot continue to function This means that failover will not occur if the active unit can still send am alive heartbeats to the inactive unit through any of its interfaces even though one or more interfaces may be inoperative Changing the Cluster ID Changing the cluster ID in a live environment is not recommended for two reasons Firstly this will change the hardware address of the shared IPs and will cause problems for all units attached to th
473. use damage is when NetDefendOS sends a log message to a server whose log receiver is not active The server will send back an ICMP UNREACHABLE message which may cause NetDefendOS to send another log message which in turn will result in another ICMP UNREACHABLE message and so on By limiting the number of log messages NetDefendOS sends every second you avoid encountering such devastating bandwidth consuming scenarios Default 3600 seconds once an hour 330 13 15 Time Synchronization Settings Chapter 13 Advanced Settings 13 15 Time Synchronization Settings TimeSync_Synclinterval Seconds between each resynchronization Default 56400 TimeSync_MaxAdjust Maximum time drift that a server is allowed to adjust Default 3600 TimeSync_ServerType Type of server for time synchronization UDPTime or SNTP Simple Network Time Protocol Default SNTP TimeSync_GrouplintervalSize Interval according to which server responses will be grouped Default 0 TimeSync_TimeServerIP1 DNS hostname or IP Address of Timeserver 1 Default none TimeSync_TimeServerlP2 DNS hostname or IP Address of Timeserver 2 Default none TimeSync_TimeServerlIP3 DNS hostname or IP Address of Timeserver 3 Default none TimeSync_TimeZoneOffs Time zone offset in minutes Default 0 TimeSync_DSTEnabled Perform DST adjustment according to DSTOffs DSTS tartDate DSTEndDate Default OFF TimeSync_DSTOffs 331 TimeSync
474. utlines the key features of NetDefendOS e About D Link NetDefendOS page 14 e NetDefendOS Architecture page 16 e NetDefendOS State Engine Packet Flow page 19 1 1 About D Link NetDefendOS D Link NetDefendOS is the firmware the software engine that drives and controls all D Link Firewall products Designed as a network security operating system NetDefendOS features high throughput performance with high reliability plus super granular control In contrast to products built on standard operating systems such as Unix or Microsoft Windows NetDefendOS offers seamless integration of all subsystems in depth administrative control of all functionality as well as a minimal attack surface which helps negate the risk of being a target for security attacks From the administrator s perspective the conceptual approach of NetDefendOS is to visualize operations through a set of logical building blocks or objects which allow the configuration of the product in an almost limitless number of different ways This granular control allows the administrator to meet the requirements of the most demanding network security scenario NetDefendOS is an extensive and feature rich network operating system The list below presents the most essential features IP Routing NetDefendOS provides a variety of options for IP routing including static routing dynamic routing as well as multicast routing capabilities In addition NetDefendOS supports features such as Vir
475. utomatic dynamic classification process In a scenario where goods have to be purchased from a particular on line store Dynamic Content Filtering might be set to prevent access to shopping sites by blocking the Shopping category By entering the on line store s URL into the HTTP Application Layer Gateway s whitelist access to that URL is always allowed taking precedence over Dynamic Content Filtering Wildcarding Both the URL blacklist and URL whitelist support wildcard matching of URLs in order to be more flexible This wildcard matching is also applicable to the path following the URL hostname which means that filtering can be controlled to a file and directory level Below are some good and bad blacklist example URLs used for blocking example com Good This will block all hosts in the example com domain and all web pages served by those hosts www example com Good This will block the www example com website and all web pages served by that site gif Good This will block all files with gif as the file name extension www example com Bad This will only block the first request to the web site Surfing to www example com index html for instance will not be blocked example com Bad This will also cause www myexample com to be blocked since it blocks all sites ending with example com 170 6 3 4 Dynamic Web Content Filtering Chapter 6 Security Mechanisms Note Web content filtering URL blacklisting is
476. utton Check the Allow Reclassification control Click OK Then continue setting up the service object and modifing the NAT rule as we have done in the previous eae filtering is now activated for all web traffic from lannet to all nets and the user is able to propose reclassification of blocked sites Validate the functionality by following these steps On a workstation on the lannet network launch a standard web browser Try to browse to a search site for instance www google com If everything is configured correctly your web browser will present a block page where a dropdown list containing all available categories is included The user is now able to select a more proper category and propose a reclassification 6 3 4 1 Content Filtering Categories This section lists all the categories used with Dynamic Content Filtering and describes the purpose of each category Category 1 Adult Content A web site may be classified under the Adult Content category if its content includes the description or depiction of erotic or sexual acts or sexually oriented material such as pornography Exceptions to this are web sites that contain information relating to sexuality and sexual health which may be classified under the Health Sites Category 21 Examples might be e www naughtychix com e www fullonxxx com 176 6 3 4 Dynamic Web Content Filtering Chapter 6 Security Mechanisms Category 2 News A web site may be classified und
477. ved through Ethernet frames on a physical interface by NetDefendOS are examined for a VLAN ID If a VLAN ID is found and a matching VLAN interface has been defined for that interface NetDefendOS will use the VLAN interface as the source interface in further processing with rule sets If there is no VLAN ID attached to an Ethernet frame received on the physical interface then the frame is treated as being received on the physical interace and not on any VLAN interface that may be defined License Limitations The number of VLAN interfaces that can be defined for a NetDefendOS installation is limited by the parameters of the license used Different hardware models have different licenses and different limits on VLANs Summary of VLAN Setup It s important to understand that the administrator should treat a VLAN interface just like a physical interface in that they require at least IP rules and routes to be defined in order to function If for instance no Allow rule is defined in the IP rule set for a VLAN interface then packets arriving on that interface will be dropped Below are the key steps for setting up a VLAN interface 1 Assign a name to the VLAN interface 2 Select the physical interface for the VLAN 60 3 3 4 PPPoE Chapter 3 Fundamentals 3 Assign a VLAN ID that is unique on the physical interface 4 Optionally specify an IP address for the VLAN 5 Optionally specify an IP broadcast address for the VLAN 6
478. verview Internet Protocol Security IPsec is a set of protocols defined by the Internet Engineering Task Force IETF to provide IP security at the network layer An IPsec based VPN is made up by two parts e Internet Key Exchange protocol IKE e IPsec protocols AH ESP both The first part IKE is the initial negotiation phase where the two VPN endpoints agree on which methods will be used to provide security for the underlying IP traffic Furthermore IKE is used to manage connections by defining a set of Security Associations SAs for each connection SAs are unidirectional so there are usually at least two for each IPsec connection The second part is the actual IP data being transferred using the encryption and authentication methods agreed upon in the IKE negotiation This can be accomplished in a number of ways by using IPsec protocols ESP AH or a combination of both The flow of events can be briefly described as follows e IKE negotiates how IKE should be protected e IKE negotiates how IPsec should be protected e IPsec moves data in the VPN The following sections will describe each of these steps in detail 9 3 2 Internet Key Exchange IKE This section describes IKE the Internet Key Exchange protocol and the parameters that are used with it Encrypting and authenticating data is fairly straightforward the only things needed are encryption and authentication algorithms and the keys used with them The Intern
479. vice object which defines which protocols to scan A time schedule can also be associated with an IDP Rule Most importantly an IDP Rule specifies the Action to take on detecting an intrusion in the traffic targeted by the rule Initial Packet Processing The initial order of packet processing with IDP is as follows 1 A packet arrives at the firewall and NetDefendOS performs normal verification If the packet is part of a new connection then it is checked against the IP rule set before being passed to the IDP module If the packet is part of an existing connection it is passed straight to the IDP system If the packet is not part of an existing connection or is rejected by the IP rule set then it is dropped 2 The source and destination information of the packet is compared to the set of IDP Rules defined by the administrator If a match is found it is passed on to the next level of IDP processing which is pattern matching described in step below If there is no match against an IDP rule then the packet is accepted and the IDP system takes no further actions although further actions defined in the IP rule set are applied such as address translation logging Checking Dropped Packets 190 6 5 4 Insertion Evasion Attack Chapter 6 Security Mechanisms Prevention The option exists in NetDefendOS IDP to look for intrusions in all traffic even the packets that are rejected by the IP rule set check for new connections as well as packe
480. vice will be presented Note When accessing object via the CLI you can omit the category name and just use the type name The CLI command in the above example for instance could be simplified to gw world gt show ServiceTCPUDP telnet 30 2 1 5 Working with Configurations Chapter 2 Management and Maintenance Example 2 5 Editing a Configuration Object When you need to modify the behavior of NetDefendOS you will most likely need to modify one or several configuration objects This example shows how to edit the Comments property of the te net service CLI gw world gt set Service ServiceTCPUDP telnet Comments Modified Comment Show the object again to verify the new property value gw world gt show Service ServiceTCPUDP telnet Property Value telnet DestinetionPorts 22 Type TCE SourcePorts SYNRelay PassICMPReturn ALG MaxSessions Comments Modified Comment Web Interface Go to Objects gt Services Click on the telnet hyperlink in the list In the Comments textbox enter your new comment Click OK Verify that the new comment has been updated in the list Important 9 Changes to a configuration object will not be applied to a running system until you activate and commit the changes Example 2 6 Adding a Configuration Object This example shows how to add a new P4Address object here creating the IP address 192 168 10 10 to the Address Book CLI gw world gt add Address IP4Addre
481. vides QoS control by allowing the administrator to apply limits and guarantees to the network traffic passing through a D Link Firewall This approach is often referred to as traffic shaping and is well suited to managing bandwidth for LANs as well as to managing the bottlenecks that might be found in larger WANs It can be applied to any traffic including that passing through VPN tunnels Traffic Shaping Objectives Traffic shaping operates by measuring and queuing IP packets with respect to a number of configurable parameters The objectives are e Applying bandwidth limits and queuing packets that exceed configured limits then sending them later when bandwidth demands are lower e Dropping packets if packet buffers are full The packets to be dropped should be chosen from those that are responsible for the jam e Prioritizing traffic according to administrator decisions If traffic with a high priority increases while a communications line is full traffic with a low priority can be temporarily limited to make room for the higher priority traffic 267 10 1 2 Traffic Shaping in Chapter 10 Traffic Management NetDefendOS e Providing bandwidth guarantees This is typically accomplished by treating a certain amount of traffic the guaranteed amount as high priority Traffic exceeding the guarantee then has the same priority as any other traffic and competes with the rest of the non prioritized traffic Traffic shaping doesn t
482. w enter IP Address 10 0 0 1 Network 10 0 0 0 24 Transparent Mode Disable Add route for interface network Disable Click OK Go to Interfaces gt Ethernet gt Edit dmz Now enter IP Address 10 0 0 2 Network 10 0 0 0 24 Transparent Mode Disable Add route for interface network Disable 6 Click OK Configure the interface groups Go to Interfaces gt Interface Groups gt Add gt InterfaceGroup Now enter Name TransparentGroup Security Transport Equivalent Disable e Interfaces Select lan and dmz 3 Click OK Configure the routing Go to Routing gt Main Routing Table gt Add gt SwitchRoute Now enter e Switched Interfaces TransparentGroup e Network 10 0 0 0 24 Metric 0 3 Click OK Configure the rules Go to Rules gt IP Rules gt Add gt IPRule Now enter Name HTTP LAN to DMZ Action Allow Service http Source Interface lan Destination Interface dmz Source Network 10 0 0 0 24 Destination Network 10 1 4 10 124 4 6 6 Transparent Mode Scenarios Chapter 4 Routing Click OK Go to Rules gt IP Rules gt Add gt IPRule Now enter Name HTTP WAN to DMZ Action SAT Service http Source Interface wan Destination Interface dmz Source Network all nets Destination Network wan_ip Translate Select Destination IP New IP Address 10 1 4 10 Click OK Go to Rules gt IP Rules gt Add gt IPRule Now enter Name HTTP WAN to DMZ Action Allow Service
483. wall s security mechanisms Such an attack is commonly known as Spoofing IP spoofing is one of the most common spoofing attacks Trusted IP addresses are used to bypass filtering The header of an IP packet indicating the source address of the packet is modified by the attacker to be a local host address The firewall will believe the packet came from a trusted source Although the packet source cannot be responded to correctly there is the potential for unnecessary network congestion to be created and potentially a Denial of Service DoS condition could occur Even if the firewall is able to detect a DoS condition it is hard to trace or stop it because of its nature 135 6 1 3 Access Rule Settings Chapter 6 Security Mechanisms VPNs provide one means of avoiding spoofing but where a VPN is not an appropriate solution then Access Rules can provide an anti spoofing capability by providing an extra filter for source address verification An Access Rule can verify that packets arriving at a given interface do not have a source address which is associated with a network of another interface In other words e Any incoming traffic with a source IP address belonging to a local trusted host is NOT allowed e Any outgoing traffic with a source IP address belonging to an outside untrusted network is NOT allowed The first point prevents an outsider from using a local host s address as its source address The second point prevents any local ho
484. way to provide security between the ends of a tunnel is to use Pre shared Keys PSKs As a VPN network grows so does the complexity of using PSKs Certificates provide a means to better manage security in much larger networks Certificate Components A certificate consists of the following e A public key The identity of the user such as name user ID e Digital signatures A statement that tells the information enclosed in the certificate has been vouched for by a Certificate Authority CA By binding the above information together a certificate is a public key with identification attached coupled with a stamp of approval by a trusted party Certification Authorities A certification authority CA is a trusted entity that issues certificates to other entities The CA digitally signs all certificates it issues A valid CA signature in a certificate verifies the identity of the certificate holder and guarantees that the certificate has not been tampered with by any third party A certification authority is responsible for making sure that the information in every certificate it issues is correct It also has to make sure that the identity of the certificate matches the identity of the certificate holder A CA can also issue certificates to other CAs This leads to a tree like certificate hierarchy The highest CA is called the root CA In this hierarchy each CA is signed by the CA directly above it except for the root CA whi
485. witched networks possibly with an unpredictable IP address to protected networks via a VPN poses particular problems Both the PPTP and L2TP protocols provide two different means of achieving VPN access from remote clients 9 5 1 PPTP Overview Point to Point Tunneling Protocol PPTP is designed by the PPTP Forum a consortium of companies that includes Microsoft It is an OSI layer 2 data link protocol see Appendix D The OSI Framework and is an extension of the older Point to Point Protocol PPP used for dial up Internet access It was one of the first protocols designed to offer VPN access to remote servers via dial up networks and is still widely used Implementation PPTP can be used in the VPN context to tunnel different protocols across the Internet Tunneling is achieved by encapsulating PPP packets in IP datagrams using Generic Routing Encapsulation GRE IP protocol 47 The client first establishes a connection to an ISP in the normal way using the PPP protocol and then establishes a TCP IP connection across the Internet to the D Link Firewall which acts as the PPTP server TCP port 1723 is used The ISP is not aware of the VPN since the tunnel extends from the PPTP server to the client The PPTP standard does not define how data is encrypted Encryption is usually achieved using the Microsoft Point to Point Encryption MPPE standard Deployment PPTP offers a convenient solution to client access that is simple to deplo
486. y PPTP doesn t require the certificate infrastructure found in L2TP but instead relies on a username password sequence to establish trust between client and server The level of security offered by a non certificate based solution is arguably one of PPTP s drawbacks PPTP also presents some scalability issues with some PPTP servers restricting the number of simultaneous PPTP clients Since PPTP doesn t use IPsec PPTP connections can be NATed and NAT traversal is not required PPTP has been bundled by Microsoft in its operating systems since Windows95 and therefore has a large number of clients with the software already installed Troubleshooting PPTP A common problem with setting up PPTP is that a router and or switch in a network is blocking TCP port 1723 and or IP protocol 47 before the PPTP connection can be made to the D Link Firewall Examining the log can indicate if this problem occurred with a log message of the following form appearing Error PPP lcp_negotiation_stalled ppp_terminated Example 9 10 Setting up a PPTP server This example shows how to setup a PPTP Network Server The example assumes that you have already created certain address objects in the Address Book You will have to specify the IP address of the PPTP server interface an outer IP address that the PPTP server should listen to and an IP pool that the PPTP server will use to give out IP addresses to the clients from CLI 260 9 5 2 L2TP Chapter 9
487. y by not committing a changed configuration 34 2 2 Events and Logging Chapter 2 Management and Maintenance 2 2 Events and Logging 2 2 1 Overview The ability to log and analyze system activities is an essential feature of NetDefendOS Logging enables not only monitoring of system status and health but also allows auditing of network usage and assists in trouble shooting NetDefendOS defines a number of event messages which are generated as a result of corresponding system events Examples of such events are the establishment and teardown of connections receipt of malformed packets as well as the dropping of traffic according to filtering policies Whenever an event message is generated it can be filtered and distributed to all configured Event Receivers Multiple event receivers can be configured by the administrator with each event receiver having its own customizable event filter The sophisticated design of the event and logging mechanisms of NetDefendOS ensures that enabling logging is simple and straightforward while it still allows granular control of all the activities in the system for the more advanced deployments 2 2 2 Event Messages NetDefendOS defines several hundred events for which event messages can be generated The events range from high level customizable user events down to low level and mandatory system events The conn_open event for instance is a typical high level event that generates an eve
488. y in the various subystems and policies The result of this is a very high flexibility in how traffic can be controlled and routed in the system Each interface in NetDefendOS is given a unique name to be able to select it into other subsystems Some of the interface types provide relevant default names that are possible to modify should that be needed while other interface types require a user provided name Warning 0 If an interface definition is removed from a NetDefendOS configuration it is important to first remove or change any references to that interface For instance rules in the IP rule set that refer to that interface should be removed or changed The any and core interfaces In addition NetDefendOS provides two special logical interfaces named core and any e any represents all possible interfaces including the core interface e core indicates that it is NetDefendOS itself that will deal with the traffic Examples of the use of core would be when the D Link Firewall acts as a PPTP or L2TP server or is to respond to ICMP Ping requests By specifying the Destination Interface of a route as core NetDefendOS will then know that it is itself that is the ultimate destination of the traffic 3 3 2 Ethernet The IEEE 802 3 Ethernet standard allows various devices to be attached at arbitrary points or ports to a physical transport mechanism such as a coaxial cable Using the CSMA CD protocol each Ethernet connected device liste
489. y on D Link Models Dynamic Content Filtering is available on the D Link DFL 260 and DFL 860 only URL Processing Flow When a user requests access to a web site NetDefendOS sends a query to these databases to retrieve the category of the requested site The user is then granted or denied access to the site based on the filtering policy in place for that category If access is denied a web page will be presented to the user explaining that the requested site has been blocked To make the lookup process as fast as possible NetDefendOS maintains a local cache of recently accessed URLs Caching can be highly efficient since a given user community such as a group of university students often surfs to a limited range of websites Figure 6 2 Dynamic Content Filtering Flow ob Ss oN 3 AN y7 2a ivy Q User requests a a jatat f for s i D he roa V j j Si If the requested web page URL is not present in the databases then the webpage content at the URL will automatically be downloaded to D Link s central data warehouse and automatically analyzed using a combination of techniques including neural networks and pattern matching Once categorized the URL is distributed to the global databases and NetDefendOS receives the category for the URL Dynamic Content Filtering therefore requires a minimum of administration effort 172 6 3 4 Dynamic Web Content Filtering Chapter 6 Security Mechanisms Note N
490. y s IP address is not specified directly in the ALG Instead its location is either entered directly into the client software used by the peer or in some cases the peer will have a way of retrieving the proxy s IP address automatically such as through DHCP Handling Data Traffic The setup steps above take care of the SIP communication for establishing peer to peer communications The two IP rules are always needed so that peers can access the SIP proxy but no rules are needed to handle the actual data traffic involved in for example a VOIP call The SIP ALG automatically takes care of establishing the NetDefendOS objects required for allowing the data traffic to traverse the D Link Firewall and these are invisible to the administrator Tip Make sure there are no preceding rules already in the IP rule set disallowing or allowing the same kind of traffic Depending on the SIP environment the NetDefendOS SIP ALG can operate in hidden topology environments with private IP addresses as well as open environments with public IP addresses SIP is a highly configurable protocol and the following describes the configuration required 6 2 8 H 323 H 323 is a standard approved by the International Telecommunication Union ITU to allow compatibility in video conference transmissions over IP networks It is used for real time audio video and data communication over packet based networks such as the Internet It specifies the components protocols an
491. y than packet filtering since they are capable of scrutinizing all traffic for a specific protocol and perform checks at the higher levels of the TCP IP stack The following protocols are supported by NetDefendOS ALGs e HTTP e FTP e TFTP e SMTP e POP3 e SIP e H 323 Deploying an ALG Once an ALG is defined by the administrator it is brought into use by first associating it with a Service object and then associating that Service with an IP rule in the NetDefendOS IP rule set Maximum Connection Sessions The Service associated with an ALG has a configurable parameter associated with it called Max Sessions and the default value varies according to the type of ALG For instance the default value for the HTTP ALG is 7000 This means that a 1000 connections are allowed in total for the HTTP Service across all interfaces The full list of default maximum session values are HTTP ALG 1000 sessions e FTP ALG 200 sessions TFTP ALG 200 sessions e SMTP ALG 200 sessions e POP3 ALG 200 sessions e H 323 ALG 100 sessions Note This default value can often be too low for HTTP if there are large number of clients connecting through the D Link Firewall and it is therefore recommended to consider using a higher value 138 6 2 2 HTTP Chapter 6 Security Mechanisms ALGs and Syn Flood Protection It should be noted that user defined custom Service objects have the option to enable Syn Flood Protection a

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