Troubleshooting XNS

Step 2 If the status line indicates that an interface that should be up is "administratively down," use the no shutdown interface configuration command on the interface.

Step 3 If the status line indicates that the interface or line protocol is in any other state, refer to the "Troubleshooting Hardware and Booting Problems" and "Troubleshooting LAN Media Problems" chapters.

Step 2 If XNS routing is not enabled, add the xns routing router configuration command and related commands as necessary.

For more information on configuring XNS routing, see the Network Protocols Configuration Guide, Part 2.

Step 1 Check the network numbers of network servers.

Step 2 Use the show xns interface EXEC command to obtain the network number specified on the server side of the router.

Step 3 Compare the network numbers. If they do not match, reconfigure the router or the server, as appropriate, with the correct network number.

Step 4 If the network numbers match, check the router interface on the client side and make sure that the assigned network number is unique with respect to all network numbers in the XNS internetwork.

Step 2 Disable all access lists that are configured on the router using no xns access-group commands.

Step 3 Test the connection from the client to the server to see whether connections are now possible. If the connection is successful, an access list is blocking traffic.

Step 4 To isolate the problem access list, apply one access list statement at a time until you can no longer create connections.

Step 5 When the problem list is identified, alter it so that necessary traffic is allowed to pass. Configure explicit permit statements for traffic that you want to be forwarded by the router.

Step 6 If problems persist, continue testing for problem access lists on all routers in the path from source to destination.

Step 2 If this counter is increasing, use a network analyzer to look for packet loops on suspect segments. Look for routing updates. If a backdoor bridge exists, you will probably see hop counts that increment up to 15, at which point the route will disappear. The route reappears unpredictably.

Step 3 Use a network analyzer to examine the traffic on each segment. Look for known remote network numbers that appear on the local network. That is, look for packets from a remote network whose source address is not the source address of the router.

Step 4 The back door is located on the segment on which a packet from a remote network appears whose source address is not the source address of a local router.

Step 2 Use the show running-config privileged EXEC command to view the router configuration. Check the configuration of the client-side interface to see if an xns helper-address interface configuration command entry is present.

Step 3 If the xns helper-address command is not present, add it to the client-side interface.

Step 4 If the command is present, make sure that the MAC address specified in this command is a type of broadcast.

Following is an example of an all-nets broadcast:

interface ethernet 0
xns helper-address -1.ffff.ffff.ffff

Following is an example of a directed broadcast:

interface ethernet 1
xns helper-address 40.ffff.ffff.ffff

Depending on the network configuration, the helper address specification will differ. For more information, refer to the Cisco IOS Network Protocols Configuration Guide, Part 2 and Network Protocols Command Reference, Part 2.

Step 2 Use the show running-config privileged EXEC command to view the router configuration. Look for an xns forward-protocol global configuration command entry.

Step 3 If the xns forward-protocol command is not present, add it as appropriate.

Step 2 Disable any access lists that are enabled on the router.

Step 3 Test the connection to see whether connections are now possible. If the connection is successful, an access list is blocking traffic.

Step 4 Enable access lists one at a time until connections are no longer possible.

Step 5 Alter the problem list so that traffic can pass. Configure explicit permit statements for traffic that you want to be forwarded by the router.

Step 6 If problems persist, continue testing for problem access lists on all routers in the path from source to destination.

Step 2 If you are running X.25, make sure that x25 map xns interface configuration commands are properly configured. Make sure that MAC addresses and X.121 addresses are correctly specified.

Step 3 If you are running Frame Relay, make sure that frame-relay map xns interface configuration commands are properly configured. Make sure that MAC addresses and DLCIs are correctly specified.

Step 2 Check the network number specified on the server side of the router.

Step 3 Compare the network numbers. If they do not match, reconfigure the router or servers as appropriate with the correct network number.

Step 4 If the network numbers match, check the router interface on the client side and make sure that the assigned network number is unique with respect to all network numbers in the XNS internetwork.

Step 2 If an encapsulation command is not present, the default is HDLC¹ encapsulation. For PSN interconnection, you must explicitly specify an encapsulation type.