When enabled, the first thing that an OSPF (Open Shortest Path First) routing protocol router does is look to create a formal neighbor relationship with its directly connected OSPF peers. This adjacency is created by exchanging OSPF Hello packets. There are several fields which make up the Hello packet and four of these fields must match between neighbors before an adjacency occurs.
- Hello/Dead Intervals – These values determine how often the Hello packets are exchanged and how long a router waits without receiving a Hello from a neighbor before that neighbor and its associated routes are removed from the OSPF database.
- Area ID – This is the area number a router’s interface is configured to be a part of.
- Authentication Password – This optional parameter requires neighbors authenticate themselves with a shared password.
- Stub Area Flag – This flag is set if the area that an OSPF router’s interface is a part of is configured as a stub, totally stub, or not-so-stub area.
The Cisco IOS commands to verify the values of each of these fields include:
Are you running OSPF? Which commands do you find useful when troubleshooting OSPF neighbor relationships?
Implementing and Operating Cisco Enterprise Network Core Technologies (ENCOR)