Troubleshooting IS-IS Neighbor Relationships

There are two instances where IS-IS will not form neighbor adjacencies correctly. The first is with misconfigured NSAPs. For example, Router C has just been attached to the network in Figure 6-8, and it isn't forming L1 adjacencies with Routers A and B as was expected.

Figure 6-8. IS-IS Neighbors in Different Areas

On Router A, you see the following:

A#sh clns neiSystem Id   SNPA                Interface   State  Holdtime  Type ProtocolB        00C0.174A.08FD           Et0       Up     27     L1  IS-ISC        00C0.0c76.f096         Et0        Up     26     L2  IS-IS

It's easy to see from this ...

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