OSPF is not behaving properly, and you want to debug it to isolate and solve the problem.
There are several OSPF debugging options. But usually, if there is an OSPF problem, you will see it as 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 particularly useful because it helps to diagnose problems when routers fail 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
Router Configuration and File Management
User Access and Privilege Levels
Handling Queuing and Congestion
Tunnels and VPNs
NTP and Time
Router Interfaces and Media
Simple Network Management Protocol
First Hop Redundancy Protocols
Appendix 1. External Software Packages
Appendix 2. IP Precedence, TOS, and DSCP Classifications