To verify the OSPF adjacencies, use the show ip ospf neighbor command as shown in Figure 1.
Unlike serial links that only display a state of FULL/-, the state of neighbors in multiaccess networks can be:
- FULL/DROTHER - This is a DR or BDR router that is fully adjacent with a non-DR or BDR router. These two neighbors can exchange Hello packets, updates, queries, replies, and acknowledgments.
- FULL/DR - The router is fully adjacent with the indicated DR neighbor. These two neighbors can exchange Hello packets, updates, queries, replies, and acknowledgments.
- FULL/BDR - The router is fully adjacent with the indicated BDR neighbor. These two neighbors can exchange Hello packets, updates, queries, replies, and acknowledgments.
- 2-WAY/DROTHER - The non-DR or BDR router has a neighbor relationship with another non-DR or BDR router. These two neighbors exchange Hello packets.
The normal state for an OSPF router is usually FULL. If a router is stuck in another state, it is an indication that there are problems in forming adjacencies. The only exception to this is the 2-WAY state, which is normal in a multiaccess broadcast network.
In multiaccess networks, DROTHERs only form FULL adjacencies with the DR and BDR. However, DROTHERs will still form a 2-WAY neighbor adjacency with any DROTHERs that join the network. This means that all DROTHER routers in the multiaccess network still receive Hello packets from all other DROTHER routers. In this way, they are aware of all routers in the network. When two DROTHER routers form a neighbor adjacency, the neighbor state displays as 2-WAY/DROTHER.
The output generated by R1 confirms that R1 has adjacencies with router:
- R2 with router ID 2.2.2.2 is in a Full state and the role of R2 is BDR. (1)
- R3 with router ID 3.3.3.3 is in a Full state and the role of R3 is DR. (2)
The output generated by R2 in Figure 2 confirms that R2 has adjacencies with router:
- R1 with router ID 1.1.1.1 is in a Full state and R1 is neither the DR nor BDR. (1)
- R3 with router ID 3.3.3.3 is in a Full state and the role of R3 is DR. (2)
The output generated by R3 in Figure 3 confirms that R3 has adjacencies with router:
- R1 with router ID 1.1.1.1 is in a Full state and R1 is neither the DR nor BDR. (1)
- R2 with router ID 2.2.2.2 is in a Full state and the role of R2 is BDR. (2)