Troubleshooting EIGRP
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Typical Problems
Because IGRP is a distance-vector protocol, you will not encounter prob-
lems with neighbor relationships or different databases that link-state pro-
tocols use.
For IGRP, the most typical problems are caused by access lists, improper
configuration, or the line to an adjacent router being down. The easiest way
to tell if the router is receiving and sending IGRP information is to use the
two debugging tools.
The primary symptom of a problem with IGRP is the lack of IGRP learned
routes. This can be verified through the use of the show commands listed in
Table 6.6.
Troubleshooting EIGRP
E
nhanced IGRP was created to resolve some of the problems with
IGRP. These problems include the fact that the entire route table is sent when
changes are made in the network, and that there is a lack of formal neighbor
relationships with connected routers. EIGRP is a hybrid of both link-state
and distance-vector routing algorithms, which brings the best of both worlds
together.
EIGRP allows for equal-cost load balancing, incremental routing updates,
and formal neighbor relationships, overcoming the limitations of IGRP. This
enhanced version uses the same distance-vector information as IGRP, yet
with a different algorithm. EIGRP uses DUAL (diffused update algorithm)
for metric calculation.
EIGRP's specific features are detailed in Table 6.7. The features offered by
EIGRP make it a stable and scalable protocol. EIGRP is also a Cisco propri-
etary protocol.
T A B L E 6 . 7
EIGRP Features
Feature
Description
Route tagging
Distinguishes routes learned via different EIGRP
sessions.
Formal neighbor
relationships
Uses the Hello protocol to establish peering.
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