31 Days Before Your CCNA Exam

240 31 Days Before Your CCNA ExamOSPF external routes fall into one of two categories:■■External Type 1 (E1): OSPF accumulates cost for an E1 route as the route is being propagatedthroughout the OSPF area.External Type 2 (E2): The cost of an E2 route is always the external cost, irrespective of theinterior cost to reach that route.In this topology, because the default route has an external cost of 1 on the R1 router, R2 and R3 alsoshow a cost of 1 for the default E2 route. E2 routes at a cost of 1 are the default OSPF configuration.You can verify that expected neighbors have established adjacency with the show ip ospf neighborcommand. Example 12-7 shows the neighbor tables for all three routers.Example 12-7Verifying Neighbor Adjacency with the show ip ospf neighbor CommandR1#show ip ospf neighborNeighbor ID Pri State Dead Time Address Interface10.3.3.3 0 FULL/ - 00:00:19 192.168.10.6 Serial0/0/110.2.2.2 0 FULL/ - 00:00:18 192.168.10.2 Serial0/0/0R2#show ip ospf neighborNeighbor ID Pri State Dead Time Address Interface10.3.3.3 0 FULL/ - 00:00:16 192.168.10.10 Serial0/0/1172.30.1.1 0 FULL/ - 00:00:15 192.168.10.1 Serial0/0/0R3#show ip ospf neighborNeighbor ID Pri State Dead Time Address Interface172.30.1.1 0 FULL/ - 00:00:19 192.168.10.5 Serial0/0/010.2.2.2 0 FULL/ - 00:00:19 192.168.10.9 Serial0/0/1For each neighbor, this command displays the following output:■■■■■■Neighbor ID: The router ID of the neighboring router.Pri: The OSPF priority of the interface. These all show 0 because point-to-point links do notelect a DR or BDR.State: The OSPF state of the interface. FULL state means that the router’s interface is fullyadjacent with its neighbor and they have identical OSPF link-state databases.Dead Time: The amount of time remaining that the router will wait to receive an OSPF Hellopacket from the neighbor before declaring the neighbor down. This value is reset when theinterface receives a Hello packet.Address: The IP address of the neighbor’s interface to which this router is directly connected.Interface: The interface on which this router has formed adjacency with the neighbor.As shown in Example 12-8, you can use the show ip protocols command as a quick way to verifyvital OSPF configuration information, including the OSPF process ID, the router ID, networks the