2.3 Single Area OSPF Configuration  
  2.3.7 Common OSPF configuration issues  
An OSPF router must establish a neighbor or adjacency relationship with another OSPF router to exchange routing information. Failure to establish a neighbor relationship is caused by any of the following reasons:
  • Hellos are not sent from both neighbors.
  • Hello and dead interval timers are not the same.
  • Interfaces are on different network types.
  • Authentication passwords or keys are different.

In OSPF routing it is also important to ensure the following:

  • All interfaces have the correct addresses and subnet mask.
  • network area statements have the correct wildcard masks.
  • network area statements put interfaces into the correct area.
  
 

Web Links

Troubleshooting OSPF

http://www.cisco.com/en/US/ tech/tk826/ tk365/technologies_ tech_ note09186a00800949f7.shtml