Verifying the IS-IS Protocol

Purpose

If your MPLS network is configured with IS-IS as the IGP, and the output of the show mpls lsp extensive command shows that there is a problem, check the IP and IS-IS layers. Because IS-IS and IP are independent of each other, you can check either layer first. For more information on checking the IP layer, see Verifying the IP Layer.

After you have checked the IP layer and determined that there is still a problem, check the IS-IS layer, verify that IS-IS adjacencies are up, and make sure that the interfaces and IS-IS protocol are configured correctly.

Figure 18: MPLS Network Broken at the IS-IS Protocol Layer

The crosses in Figure 18 indicate where the LSP is not working because IS-IS levels are mismatched.

Steps To Take

To check the IS-IS protocol, follow these steps:

1. Verify the LSP
2. Verify IS-IS Adjacencies and Interfaces
3. Verify the IS-IS Configuration
4. Take Appropriate Action
5. Verify the LSP Again