Troubleshooting Route Flapping Problem in IGRP

Running IGRP in a complex environment sometimes can cause flapping of routes. Route flapping means that the routes keep coming and going from the routing table. To see whether the routes are indeed flapping, check the routing table and look at the age of the routes. If the ages are constantly getting reset to 00:00:00, the routes are flapping. There could be several reasons for this. This section discusses one of the most common reasons ‚ packet loss. Packet loss prevents an IGRP update from reaching the other side.

The example in this section considers Frame Relay because it is the most common medium in which this problem occurs. The packet loss can be verified through the interface statistics by looking at the number of packet drops and seeing if it is con-stantly incrementing.