Troubleshooting OSPF Neighbor Relationships

This section discusses the problems related to establishing OSPF neighbor relationships. OSPF neighbor relationship problems can be of any type. Sometimes, the neighbor list is empty (that is, an OSPF neighbor might not even see the Hellos from each other). Sometimes, the problem is that the neighbor is stuck in a specific state. Recall from Chapter 8, "Understanding Open Shortest Path First (OSPF)," that the normal state of an OSPF neighbor is FULL. If the state is something other than FULL for a long period of time, this indicates a problem.

This section comes first because this is the most important step in using the OSPF protocol. If no neighbor relationships are established or the neighbors are stuck in a state other than FULL, OSPF will not install any routes in the routing table. Therefore, it is very important in OSPF to make sure that the neighbors are up.

OSPF neighbor relationship problems can be of any of these types:

• The OSPF neighbor list is empty.

• An OSPF neighbor is stuck in ATTEMPT.

• An OSPF neighbor is stuck in INIT.

• An OSPF neighbor is stuck in 2-WAY.

• An OSPF neighbor is stuck in EXSTART/EXCHANGE.

• An OSPF neighbor is stuck in LOADING.

None of the states mentioned in this list is an indication of a problem, but if a neighbor is stuck in one of these states for a long time, this is a problem and must be corrected; otherwise , OSPF will not function properly.