Summary

This chapter focuses on troubleshooting methodology for common IS-IS problems. Two broad classes of troubleshooting problems are identified at the start of the chapter:

• Misconfiguration and interoperability problems

• Problems caused by malfunctioning of software or hardware

The primary objectives of the troubleshooting techniques discussed involve identifying both categories of problems. However, problems that seem to fall in the later class normally require special tools and deeper understanding of the Cisco IOS implementation and should, therefore, be referred to Cisco for further diagnosis.

Misconfiguration and interoperability issues are broken down into adjacency formation problems and routing update problems.

Table 11-1 provides a summary of adjacency problems and lists possible causes. Subsequent coverage on adjacency problems provides detailed descriptions of troubleshooting method-ology and flowcharts, along with show commands and debugging examples.

Later sections of the chapter are dedicated to reviewing routing update problems and flowcharts; relevant debugging information for troubleshooting such problems is also provided.

The final sections review some common IS-IS errors that are logged to flag potential problems. The ping clns and traceroute clns commands are also discussed.

At the end of the chapter, a case study for troubleshooting a basic setup of IS-IS routing over an ISDN connection is discussed.