192.168.2.1 0.0.0.0 EIGRP summarizes routes the same way RIP does, but because EIGRP is a classless protocol, we can disable this behavior with the no auto-summary command: Router-A(config-router)# no auto-summary There are very few instances where you'd want to leave auto-summary on, SO you should get into the habit of disabling it. EIGRP operates by sending out hello packets using the multicast IP address 224.0.0.10 on configured interfaces. When a router running EIGRP receives these hello packets, it checks to see if the hello contains a process number matching an EIGRP process run- ning locally. If it does, a handshake is performed. If the handshake is successful, the routers become neighbors. Unlike RIP, which broadcasts routes to anyone who'll listen, EIGRP routers exchange routes only with neighbors. Once a neighbor adjacency has been formed, update packets are sent to the neighbor directly using unicast packets. A useful command for EIGRP installations is the eigrp log-neighbor-changes com- mand. This command displays a message to the console/monitor/log (depending on your logging configuration) every time an EIGRP neighbor adjacency changes state: 1d11h: %DUAL-5-NBRCHANGE: IP-EIGRP 100: Neighbor 10.10.10.4 (Etherneto/0) is up: new adjacency On large networks, this can be annoying during a problem, but it can easily be disabled if needed. Specific Routing Protocols To see the status of EIGRP neighbors on a router, use the show ip eigrp neighbors command: R3# sho ip eigrp neighbors IP-EIGRP neighbors for process 100 H Address Interface Hold Uptime RTO 0 Seq Type (sec) Cnt Num 10.10.10.5 Eto/o 14 00:00:19 0 10.10.10.4 Eto/o 13 00:02:35 This command's output should be one of the first things you look at if you're having problems, because without a neighbor adjacency, EIGRP routers will not exchange routes. Routes learned via internal EIGRP have an administrative distance of 90, and are marked with a single D in the first column of the routing table. Routes learned via external EIGRP have an administrative di