packets are sent to the neighbor directly using unicast packets. A useful command for EIGRP installations is eigrp log-neighbor-changes. This com- mand displays a message to the console/monitor/log (depending on your logging con- figuration) every time an EIGRP neighbor adjacency changes state: 1d11h: %DUAL -NBRCHANGE: IP-EIGRP 100: Neighbor 10.10.10.4 (Etherneto/o) is up: new adjacency On large networks, this can be annoying during a problem, but it can easily be disabled if needed. 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 Seq Type (sec) Cnt Num 10.10.10.5 Eto/o 14 00:00:19 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 distance of 170 and are marked with the letters D EX at the beginning of the route: R3#sho ip route [text removed] Gateway of last resort is 192.168.1.2 to network 0.0.0.0 5.0.0.0/32 is subnetted, 1 subnets 5.5.5.5 [170/409600] via 10.10.10.5, 00:00:03, Etherneto/o 10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks 10.10.10.0/24 is directly connected, Etherneto/o 10.100.100.100/32 is directly connected, Loopback0 192.168.1.0/24 is directly connected, Ethernet1/0 Chapter 10: Routing Protocols 192.168.3.0/24 [90/2195456] via 10.10.10.5, 00:08:42, Etherneto/o 0.0.0.0/0 [254/0] via 192.168.1.2 EIGRP stores its information in three databases: the route database, the topology da- tabase, and the neighbor database. Viewing the topology database can be a tremendous help when troubleshooting routing problems. Not only can you see what EIGRP has put into the routing table, but you can also see what EIGRP considers