The debug privileged EXEC commands can provide a wealth of information about the traffic and events being seen (or not seen) by OSPF. These traffic and events can include, but are not limited to, interface traffic, error messages generated by nodes on the network, protocol-specific diagnostic packets, and other useful troubleshooting data.
Exercise care when using debug commands. Many of these commands are processor intensive and can cause serious network problems (such as degraded performance or loss of connectivity). When you finish using a debug command, disable it with its specific no debug command (or use the no debug all command to turn off all debugging).
Use debug commands only ...