Routing-Bits

With EIGRP, as you might know neighbor sessions are established by using reliable multicast, to the destination address 224.0.0.10 and a TTL=0.

The neighbor command can used in EIGRP to define a unicast session to neighbor, with which to exchange routing information. This is configured at an interface level, that need to be configured on both ends to work. Care should be taken in production environments when planning on using this command, if there are multiple neighbors connected to the interface.

This because, EIGRP stops processing all multicast packets that come inbound on that interface. Also, EIGRP stops sending multicast packets on that interface. Any neighbor session previously established via multicast discovery, will be dropped and will have to be manually specified individually with the neighbor command.

(config)# int ser0
(config-if)# neighbor [Neighbor address] [Interface]