The area number must match
Interfaces must be in the same subnet
OSPF process must not be shutdown
OSPF Router IDs must be unique
Hello and Dead timers must match
The authentication setting must match
IP MRU setting must match
Can become OSPF neighbors, but OSPF doesn't operate properly.
The OSPF Network Type must match
Can become OSPF neighbors, but OSPF doesn't operate properly.
