IP Routing

Troubleshooting EIGRP

EIGRP can be difficult to troubleshoot because of its complexity. As a reminder, the best preparation for troubleshooting a network is to be familiar with the network and its state during normal (trouble-free) conditions. Become familiar with the routing tables, their sizes, the summarization points, routing timers, etc. Also, plan ahead with “what-if” scenarios. What if router X failed or link Y dropped? How would connectivity recover? Will all the routes still be in every router’s table? Will the routes still be summarized?

Perhaps the second-best preparation for troubleshooting a network is the ability to track network implementations and changes. If network implementations/changes are made in a haphazard way with no central control, an implementation team may walk away from a change (unaware that their change caused an outage) and it may take the troubleshooting team hours, or even days, to unravel the events that led to the outage. Besides making the network more vulnerable, such loose methods of network operation create bad relationships between teams.

The following sections are a partial list of network states/conditions to check when looking for clues to routing problems in EIGRP.

Verifying Neighbor Relationships

If a router is unable to establish a stable relationship with its neighbors, it cannot exchange routes with those neighbors. The neighbor table can help check the integrity of neighbor relationships. Here is a sample of NewYork’s neighbor table: ...