A network engineer replaced a bad router with a spare, used router in an OSPF network. After the replacement, OSPF neighborship is not being established on one of the interfaces. Which two reasons…

If OSPF authentication is configured, a mismatch in authentication type (e.g., MD5 vs. plain text) or incorrect authentication keys/passwords between two routers will prevent OSPF neighborship from being established.

An MTU mismatch on the link between OSPF neighbors will cause the Database Description (DBD) packet exchange to fail, preventing the OSPF adjacency from progressing beyond the ExStart or Exchange state.

The OSPF process ID is locally significant to a router and does not need to match on neighboring routers for OSPF adjacency to form successfully.

Matching OSPF timers (such as hello and dead intervals) is a critical requirement for OSPF neighbors to establish an adjacency; therefore, if they match, it would facilitate, not prevent, neighborship.

Matching OSPF area numbers on a shared network segment is a fundamental requirement for OSPF neighbors to form an adjacency; thus, if they match, it contributes to successful neighborship rather than causing a failure.