This video explains the OSPF parameters that must match between two routers to become neighbors or form an adjacency. The OSPF parameter checks are demonstrated on the CLI using debug output and verification commands. This video also contains a bit-level investigation of OSPF operation and analyzing an OSPF packet dump.
After two routers discover each other by receiving Hellos from the other router, the routers perform the following parameter checks:
- Must pass the authentication process
- Must be in the same primary subnet, including the same subnet mask
- Must be in the same OSPF area
- Must be of the same area type
- Must not have duplicate RIDs
- OSPF Hello and Dead timers must be equal
If any of these items do not match, the two routers simply do not form a neighbor relationship.
NOTE: The OSPF process ID does not have to match.
All of the listed parameter checks (except authentication) are investigated in detail in this video.
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