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Routing & Switching · Intermediate

OSPF Neighbor States

The progression an OSPF adjacency follows: Down, Attempt, Init, 2-Way, ExStart, Exchange, Loading, Full.

Definition

Init means a hello was received but the router's own ID is not yet listed; 2-Way means bidirectional communication, the final state between DROthers. ExStart negotiates master/slave and initial DBD sequence, Exchange swaps DBD summaries, Loading requests missing LSAs, and Full means databases are synchronized. Attempt applies only to manually configured NBMA neighbors.

Example

show ip ospf neighbor shows FULL/DR or 2WAY/DROTHER.

Exam tip

2-Way between two DROthers is normal, not a fault; stuck in ExStart/Exchange usually means MTU mismatch.

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