Cisco "show ip ospf neighbor" Command Explained
show ip ospf neighbor — lists the router's OSPF neighbours and their adjacency state — the first stop in any OSPF troubleshoot. Runs in privileged EXEC mode.
Syntax and common variants
| Variant | Purpose |
|---|---|
show ip ospf neighbor | All neighbours and states |
show ip ospf neighbor detail | Timers, areas, addresses per neighbour |
show ip ospf interface brief | Which interfaces run OSPF, their areas and costs |
Reading the output
| Output field | Meaning |
|---|---|
Neighbor ID | The neighbour's router ID |
State | FULL = healthy; 2WAY = normal non-DR pairs; stuck EXSTART/EXCHANGE = usually MTU mismatch |
Dead Time | Countdown since last hello |
Address / Interface | Their IP and your interface |
When to use it
No neighbour listed? Check matching subnet, hello/dead timers, area ID and authentication. Stuck in EXSTART/EXCHANGE? Almost always an MTU mismatch. Every OSPF "routes are missing" case starts here — no FULL adjacency, no routes. Browse more in the command reference or practise in the free labs.
Frequently asked questions
What does FULL state mean?
Databases fully synchronized — a healthy adjacency. On multi-access networks, 2WAY between two non-DR routers is also normal.
Why is my neighbour stuck in EXSTART/EXCHANGE?
The classic cause is an MTU mismatch between the two interfaces — align MTUs or configure ip ospf mtu-ignore.
Why do I see no neighbours at all?
Mismatched area, subnet, timers or authentication — or OSPF isn't enabled on that interface (check show ip ospf interface).
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