Viewing Neighbor Information

Viewing Neighbor Information
Knowing what’s going on between the router and its neighbor can be a very useful tool in verifying
and troubleshooting the operation of EIGRP. The following command displays all of the
routers with which the router has formed neighbor relationships:
Dallas#show ip eigrp neighbor
IP-EIGRP neighbors for process 100
H Address Interface Hold Uptime SRTT RTO Q Seq Type
(sec) (ms) Cnt Num
0 10.10.10.1 Se2/0.1 13 00:09:36 717 4302 0 2
The show ip eigrp neighbor command lists only a summary of the router’s neighbors. In
order to view more detailed information about the neighbors, you can add the detail keyword
to the end of the command line:
Dallas#show ip eigrp neighbor detail
IP-EIGRP neighbors for process 100
H Address Interface Hold Uptime SRTT RTO Q Seq Type
(sec) (ms) Cnt Num
0 10.10.10.1 Se2/0.1 12 00:10:05 717 4302 0 2
Version 12.0/1.0, Retrans: 0, Retries: 0
As you can see, this command also displays the number of retransmissions that have occurred
and the number of retries for a packet currently being sent to the neighbor.
You can also enter a command that will allow any changes that occur to a neighbor
to be logged. The command to accomplish this is eigrp log-neighbor-changes and it
must be entered in router configuration mode. With this command, the following logs are
generated:
16:01:31: %DUAL-5-NBRCHANGE: IP-EIGRP 100: Neighbor 10.10.10.1 (Serial2/0.1) is
up: new adjacency
The preceding log informs you that the router has formed a new adjacency with 10.10.10.1.
16:02:33: %DUAL-5-NBRCHANGE: IP-EIGRP 100: Neighbor 10.10.10.1 (Serial2/0.1) is
down: holding time expired
The preceding log informs you that the router has lost the adjacency with 10.10.10.1.
You can also view neighbor information with the debug eigrp neighbors command. This
command also informs you when new neighbors are discovered and when current neighbors are
lost. As with IGRP, in order to view debug information, you must configure logging. Note,
Enhanced Interior Gateway Routing Protocol 137
however, that logging console debugging is enabled by default. Here is an example of the
output of the debug eigrp neighbors command:
Dallas#debug eigrp neighbors
EIGRP Neighbors debugging is on
15:54:10: EIGRP: Holdtime expired
15:54:10: EIGRP: Neighbor 10.10.10.1 went down on Serial2/0.1
15:54:13: EIGRP: New peer 10.10.10.1
All of the commands described so far give information about EIGRP on the particular router and
information about its neighbors. This is important information, but if a route is not there that should
be or a neighbor relationship hasn’t been formed that you believe should have, all the commands
covered so far might not give you the detailed information needed to resolve the issue. The next section
explains how to view and interpret the EIGRP information being sent between routers.