Troubleshooting IS-IS Routing Problems

The discussions in the previous sections of this chapter focus on tools and commands, ranging from simple to complex, needed for troubleshooting IS-IS problems. These sections provide a good foundation for discussing actual problems and troubleshooting methodology. Common IS-IS routing problems fall under the following two broad categories:

  • Adjacency formation problems

  • Route maintenance problems

During normal operation, IS-IS routers form and maintain adjacencies with each other by using hello packets. Routing information is then exchanged by flooding LSPs, which are stored in appropriate Link-State databases (Level 1 or Level 2). Sequence number packets (CSNPs and PSNPs) provide control for the flooding ...

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