Chapter 5. Troubleshooting IGRP

This chapter covers the following key topics:

• Troubleshooting IGRP route installation

• Troubleshooting IGRP route advertisement

• Troubleshooting IGRP redistribution problems

• Troubleshooting dial-on-demand (DDR) routing issues in IGRP

• Troubleshooting route flapping in IGRP

• Troubleshooting variance problem

This chapter discusses common problems in IGRP networks and how to solve those problems. IGRP is a Cisco proprietary protocol. IGRP fixes some of the problems with RIP, but still it has similar characteristics as RIP. IGRP also does not support discontiguous networks or VLSM; however, it does have good features, such as variance, and its metric is based on bandwidth and delay instead of hop count.

Most of the issues in IGRP are very similar to RIP, so those issues are repeated here again in this chapter from an IGRP perspective. As mentioned in Chapter 3, "Troubleshooting RIP," you must be careful with the debugs when dealing with large networks (for example, more than 100 subnets in a network) because debugging sometimes can have an adversarial effect on a router. The flowcharts that follow document how to address common problems with IGRP with the methodology used in this chapter.