System information

Troubleshooting ISO CLNS
Book Title
12-282
ISO CLNS: Connections Fail Using Certain Protocols
Symptom: Host connections fail using certain protocols. Hosts might be able to connect to other
hosts using some protocols but are unable to connect using others.
Table 12-6 outlines the problems that might cause this symptom and describes solutions to those
problems.
Table 12-6 ISO CLNS: Connections Fail Using Certain Protocols
ISO CLNS: Users Cannot Make Connections over Parallel Path
Symptom: In environments with multiple paths between networks, when one link goes down,
connections across a parallel link are not possible.
Note IS-IS has equal-cost load balancing for both Level 1 and Level 2 routes. If there are parallel
paths in an IS-IS network and one goes down, the other should serve as a backup that is ready to be
used immediately.
Table 12-7 outlines the problems that might cause this symptom and describes solutions to those
problems.
Table 12-7 ISO CLNS: Users Cannot Make Connections over Parallel Path
Possible Problem Solution
Host is not configured to
support the service
Verify that the needed protocols are correctly installed and configured on the host
system. Consult your vendor’s documentation for information on configuring hosts.
Misconfigured access list
Step 1 Use the trace exec command to determine the path taken to reach remote hosts.
Step 2 If you discover a router that is stopping traffic, use the show access-lists
privileged exec command to see whether 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.