debug ip ospf events

To display information on OSPF-related events, such as adjacencies, flooding information, designated router selection, and shortest path first (SPF) calculation, use the debug ip ospf events command in privileged EXEC mode.

Examples：
The following is sample output from the debug ip ospf events command:

Router# debug ip ospf events
OSPF:hello with invalid timers on interface Ethernet0
hello interval received 10 configured 10
net mask received 255.255.255.0 configured 255.255.255.0
dead interval received 40 configured 30

Pay attention to the "received" and "configured" parameters, they must be accurately match with each others. "Received" means the parameter that you are receiving from your neighbor, and "Configured" means the parameter that you are configuring on your router (the debugging router). It's a useful command for you to find out the OSPF neighborship establishing problems by comparing if the parameters between "received" and "configured" are matched. If not, a neighborship will never up between these routers

The debug ip ospf events output shown might appear if any of the following situations occurs:

1. The IP subnet masks for routers on the same network do not match.
2. The OSPF hello interval for the router does not match that configured for a neighbor.
3. The OSPF dead interval for the router does not match that configured for a neighbor.

If a router configured for OSPF routing is not seeing an OSPF neighbor on an attached network, perform the following tasks:

1. Make sure that both routers have been configured with the same IP mask, OSPF hello interval, and OSPF dead interval.
2. Make sure that both neighbors are part of the same area type.

In the following example line, the neighbor and this router are not part of a stub area (that is, one is a part of a transit area and the other is a part of a stub area, as explained in RFC 1247)

OSPF: hello packet with mismatched E bit