Verifying and Troubleshooting IGRP

Verifying and Troubleshooting IGRP
Now that you know how to configure IGRP, we need to focus on how to verify that it is operating
correctly and, if IGRP is not operating correctly, how to troubleshoot it.
There are two important items to keep in mind when working with IGRP:
 Remember that IGRP is a standard distance-vector routing protocol. What this means to
you as the engineer is that IGRP does not keep a topology table. So you need to look at the
routing table to verify most information.
 IGRP is a classful routing protocol. If you have implemented redistribution, or if IGRP is
automatically redistributing with EIGRP, the routes being redistributed must be on classful
boundaries or on the same non-classful boundary as a prefix of the exact same length and
value as configured on one or more of its own interfaces. If they are not, IGRP will not
accept the routes into its routing table. If you have implemented VLSM in another routing
protocol, you will want to make sure that you summarize the routes to the classful or similar
non-classful boundary that you want advertised into IGRP.