OSPF is not behaving properly and you want to debug it to isolate and solve the problem.
There are several OSPF debugging options. The most common symptoms of OSPF problems are instabilities in the neighbor relationships. So the most useful debugging option traces the formation of adjacencies:
Router3#debug ip ospf adj OSPF adjacency events debugging is on Router3#
This particular debug output is especially useful because it helps to diagnose problems when routers refuse to form adjacencies with one another. For example, the following debug message indicates that there is an authentication problem. The neighbor router in this case is configured for MD5 authentication, while this router is configured for no authentication:
Dec 21 16:00:14.341: OSPF: Rcv pkt from 172.25.1.7, FastEthernet0/0.1 : Mismatch Authentication type. Input packet specified type 2, we use type 0
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