The OSPFv2 process ID must be the same on each router.
The two routers must include the inter-router link network in an OSPFv2 network command.
The link interface subnet masks must match.
The OSPFv2 process is enabled on the interface by entering the ospf process area-id command.
The link interface on each router must be configured with a link-local address.
The OSPF hello or dead timers on each router must match.