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Cisco IOS Cookbook, 2nd Edition by Ian Brown, Kevin Dooley

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Logging EIGRP Neighbor State Changes

Problem

You want to log EIGRP neighbor state changes.

Solution

To enable the logging of EIGRP neighbor state changes, use the eigrp log-neighbor-changes configuration command:

Router1#configure terminal 
Enter configuration commands, one per line.  End with CNTL/Z.
Router1(config)#router eigrp 55
Router1(config-router)#eigrp log-neighbor-changes
Router1(config-router)#exit
Router1(config)#end
Router1#

Another closely related feature is the eigrp log-neighbor-warnings configuration command:

Router1#configure terminal 
Enter configuration commands, one per line.  End with CNTL/Z.
Router1(config)#router eigrp 55
Router1(config-router)#eigrp log-neighbor-warnings 300
Router1(config-router)#exit
Router1(config)#end
Router1#

Discussion

When a neighbor relationship is lost, you also lose all of the routing entries for that neighbor. And the effects of this lost routing information are often felt throughout the network. Therefore, it can be extremely useful to have a good log of neighbor change events for troubleshooting strange intermittent network problems. However, this feature also gives you a good way of looking for faults on links that don’t have a way of telling you about loss of connectivity.

Two important examples of this are tunnels and LAN extensions. In many cases, when the network breaks, bringing down a tunnel, the two tunnel end points are unable to see the problem. Similarly, in a LAN extension service, the two end point routers are both connected ...

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