Troubleshooting ISO CLNS

host% netstat -rn

Check the output of this command for a default gateway specification.

Step 2 If the default gateway specification is incorrect, or if it is not present at all, you can change or add a default gateway using the following UNIX command at the local host:

host% route add default address 1

where address is the IP address of the default gateway (the router local to the host). The value 1 indicates that the specified gateway is one hop away.

Step 3 It is recommended that you specify a default gateway as part of the boot process. Specify the ISO CLNS address of the gateway in the following UNIX host file:

/etc/defaultrouter

This filename might be different on your UNIX system.

Step 2 Make sure that there is at least one Level 1 router on the same network as the end system.

Step 2 Verify that all bytes of the NSAP address, up to but not including the system ID, are the same on both the router and the ES. The domain and area addresses must match, and the station IDs must be unique. (The value of the n-selector byte has no impact.)

Step 2 Check the adjacency database on the host and verify that it has an entry for its directly connected router.

Step 3 Use the debug clns packet privileged EXEC command on the Level 1 router to verify that it sees and forwards packets from the ES.

Step 4 If necessary, statically configure the router to recognize the ES by using the clns es-neighbor interface configuration command.

Step 2 If the trace fails at a router, use the show clns neighbors EXEC command to see which neighboring routers and ESs are recognized.

Step 3 If neighboring routers and end systems are up, perform one of the following procedures:

• For ISO-IGRP, check the routing table and see whether the routes are being learned. Use the show clns route EXEC command to display the routing tables.
• For IS-IS⁴, check the LSP⁵ database to see whether the links are being reported in link state advertisements. Check the IS-IS routing table to see whether the routes are being installed in the routing table. Use the show isis database detail EXEC command to display the routing tables.

Route redistribution problem

Step 2 Verify that the hosts are in the same area.

Step 3 Check that the NSAP address is entered correctly on the hosts.

Step 2 If multiple network addresses are configured, verify that the router is configured to support a multihomed area (a single area that has more than one area address).

Step 3 To communicate, routers must establish a Level 1 adjacency. Therefore, area addresses in a multihomed area must overlap across routers.

For example, in the multihomed area shown in Figure 10-1, to configure Area 1 and Area 2 as a multihomed area, both Router A and Router B must be configured to be in both areas.

Step 4 Alternatively, one router can be configured in both areas, while the other router remains configured for a single area. Provided that the area numbers on routers overlap, the routers will establish a Level 1 adjacency, allowing them to communicate.

Step 2 Check the adjacency database on the host and verify that it has an entry for its directly connected router.

Step 3 Use the debug clns packet privileged EXEC command on the Level 1 router to verify that it sees and forwards packets from the ES.

Step 4 If necessary, statically configure the router to recognize the ES by using the clns es-neighbor interface configuration command.

Step 2 Use the trace EXEC command to verify that Level 2 routers are routing packets to the correct destination area.

Step 3 If packets are not being routed to the correct area, check the Level 2 routing tables (ISO-IGRP) or the Level 2 link state databases (IS-IS) to see whether the packets are being forwarded to another area.

Step 4 If necessary, reconfigure routers with the correct area addresses and Level 2 (IS-IS) routing information.

Step 2 Check the adjacency database on the host and verify that it has an entry for its directly connected router.

Step 3 Use the debug clns packet privileged EXEC command on the Level 1 router to verify that it sees and forwards packets from the ES.

Step 4 If necessary, statically configure the router to recognize the ES by using the clns es-neighbor interface configuration command.

Step 2 If the trace fails at a router, use the show clns neighbors EXEC command to see which neighboring routers and ESs are recognized.

Step 3 If neighboring routers and end systems are up, perform one of the following procedures:

• For ISO-IGRP, check the routing table and see whether the routes are being learned. Use the show clns route EXEC command to display the routing tables.
• For IS-IS, check the LSP database to see whether the links are being reported in link state advertisements. Check the IS-IS routing table to see whether the routes are being installed in the routing table. Use the show isis database detail EXEC command to display the routing tables.

Step 2 If you discover a router that is stopping traffic, use the show access-lists privileged EXEC command to see if any access lists are configured on the router.

Step 3 Disable all access lists on the router using no access-group interface configuration commands on the appropriate interfaces.

Step 4 Determine whether hosts can now use the protocol in question. If traffic can get through, it is likely that an access list is blocking protocol traffic.

Step 5 Make sure the access list does not filter traffic from ports that are used by the protocol in question. Configure explicit permit statements for traffic that you want the router to forward normally.

Step 6 Enable the access list and verify that the protocol still functions correctly. If problems persist, continue isolating and analyzing access lists on all routers in the path from source to destination.

Step 2 Wait for the routing protocol to converge. Use the show clns route command again to see if the routes are now "up."

Note: ISO-IGRP does load balancing only for domain prefix routes. If you are doing Level 1 or Level 2 routing in ISO-IGRP, only a single path is maintained. If that path goes down, you must wait for the network to converge before the alternative path is available.

Step 2 If you discover a router that is stopping traffic, use the show access-lists privileged EXEC command to see if any access lists are configured on the router.

Step 3 Disable all access lists on the router using no access-group interface configuration commands on the appropriate interfaces.

Step 4 Determine whether hosts can now use the protocol in question. If traffic can get through, it is likely that an access list is blocking protocol traffic.

Step 5 Make sure the access list does not filter traffic from ports that are used by the protocol in question. Configure explicit permit statements for traffic that you want the router to forward normally.

Step 6 Enable the access list and verify that the protocol still functions correctly. If problems persist, continue isolating and analyzing access lists on all routers in the path from source to destination.

Step 1 Use the show running-config privileged EXEC command to display the router configuration. Look for route-map router configuration command entries.

Step 2 If route-map commands are configured, look at the sequence numbers that are assigned. Lower sequence numbers are tested before higher sequence numbers, regardless of the order in which they are listed in the configuration.

Step 3 If conditions are not being tested in the order you want, you must modify the sequence numbers to change the testing order.

Step 2 If the default-metric router configuration command or the distance router configuration command is missing, add the appropriate version of the missing command.

Refer to the Cisco IOS Network Protocols Configuration Guide, Part 2 and Network Protocols Command Reference, Part 2, for information about adjusting ISO CLNS default metrics.

Step 2 If the distance command is missing, configure a distance specification on the router.

If you must redistribute at another point, use default metrics to perform the redistribution in one direction only.

Refer to the Cisco IOS Network Protocols Configuration Guide, Part 2 and Network Protocols Command Reference, Part 2, for information about adjusting ISO CLNS default metrics.

Step 2 If multiple ISO-IGRP processes are configured on a single interface, different Level 2 updates are being sent out through the same interface.

Multiple Level 2 updates on the same interface can cause congestion problems, especially if the network is large and links are flapping outside of the damping intervals.

Step 3 Remove one of the ISO-IGRP processes from the interface configuration using the appropriate no clns router iso-igrp interface configuration command.

Step 1 Use the show clns is-neighbors detail and the show clns neighbors detail EXEC commands to see through which routers and protocols the router's adjacencies were learned.

Look for routers that are known to be on a remote network. A router listed in the adjacency table but that is not on a directly connected network indicates a problem.

You can also look for paths to networks (or areas) on multiple interfaces.

Step 2 If you determine that there is a parallel bridge or repeater, remove the device or configure filters that block routing updates from being learned from the device.