show ip ospf neighbor
Displays the current state of all OSPF adjacencies formed with directly connected routers. This is the primary diagnostic tool used to verify that OSPF Hello packets are successfully passing between interfaces and that link-state databases have been synchronized.
Quick Reference
Router#show ip ospf databaseReading the Output Table
Column Breakdown
- Neighbor ID: The OSPF Router ID of the neighbor (not necessarily their physical IP address).
- Pri: The interface OSPF Priority (default is 1). Used to rig the DR/BDR election. A priority of 0 completely removes the router from the election.
- State: Displays the adjacency status (e.g., FULL) and the network role (DR, BDR, or DROTHER). If a dash (
-) appears, the connection is a point-to-point link that doesn't use DR/BDR elections. - Dead Time: A countdown timer (default 40s on Ethernet). If this hits 00:00:00 before receiving a Hello packet, OSPF drops the neighbor.
CCNA Exam Gotchas
The 2WAY State Illusion
If you look at the 3.3.3.3 output above, the state is 2WAY/DROTHER. Junior engineers often panic thinking the link is broken because it isn't "FULL".
This is normal. On broadcast multi-access networks (like an Ethernet switch), OSPF routers only form a FULL adjacency with the Designated Router (DR) and Backup (BDR) to save bandwidth. Two normal routers (DROTHERs) will intentionally stop at the 2WAY state and refuse to sync databases directly with each other.
Stuck in EXSTART / EXCHANGE
If the state column is permanently stuck in EXSTART or EXCHANGE, the routers are talking, but their databases are crashing during the sync. This is almost universally caused by an MTU Mismatch on the physical interfaces. The CCNA will heavily test your ability to recognize this specific failure code.