Hi Samuel,
The neighbor 10.51.254.2 is flapping up and down due to holding time expired. This means the router did not receive an eigrp packet from its neighbor and the hold time expired,causing the neighbor to reset.
%DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 10.51.254.2 (Vlan1)) is down: holding time expired
"If no hellos are received within the hold time, which is 15 seconds by default on most links, the router informs the neighbor that the neighbor relationship has been torn down and logs a syslog message."
1. Send a stream of 10000 count, once using 100 byte and once using 1500 byte packets,using extended
ping, to the neighbor's directly connected interface IP address. Are there any packet drops or time
outs?
Does the neighbor respond if you ping the EIGRP multicast address 224.0.0.10?
2. Perform "debug eigrp packet hello" on both routers to verify that the neighbors are ending and receiving EIGRP hello packets.
Check the routing table entry to verify the next-hop address is correct for the neighbor.
3. Other possibilities that can bring the neighbor relationship down are unidirectional links, uncommon subnet mismatches, mismatched masks, layer 2 problems, ACL deny statement, etc.
The detailed steps can be found here:
Troubleshooting EIGRP - Neighbor Check
http://www.cisco.com/warp/public/103/trouble_eigrp.html#nc
HTH,Please rate if it does.
-amit singh
