You would prefer to view proper domain names rather than see the raw IP addresses in the output of your OSPF show commands.
You can configure OSPF to resolve IP addresses into router names with the following global configuration command:
Router3#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router3(config)#ip ospf name-lookup Router3(config)#end Router3#
When you configure OSPF name-lookup, the router will use its locally configured host table, if it has one, or DNS to resolve the names. If both are present, the router will check the local host table first. You can enable DNS on a router with the ip domain-lookup and ip name-server commands, as we discussed in Chapter 2.
Enabling name resolution can be useful when displaying information like OSPF neighbor tables. For example, if we look at the neighbor table without name-lookup enabled, we see IP addresses:
Router3#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 172.20.220.1 1 FULL/DR 00:00:34 172.20.10.2 Ethernet0 172.25.25.1 1 FULL/ - 00:00:31 172.20.1.1 Serial0.1 Router3#
But with name lookup, the router replaces the router IDs with names:
Router3#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface Router6 1 FULL/DR 00:00:37 172.20.10.2 Ethernet0 Router1 1 FULL/ - 00:00:36 172.20.1.1 Serial0.1 Router3#
The output will show an IP address rather than a name if the router can't resolve the address into a name, either because it can't reach the name server or because the name server doesn't include this address.