OSPF Neighbor Stuck? Use the State to Narrow the Cause
Troubleshoot OSPF neighbors stuck in Down, Init, ExStart, Exchange or another incomplete state.
Let the neighbor state guide the first check
OSPF states tell you how far adjacency formation progressed. A neighbor stuck in Init points toward a different fault than one stuck in ExStart or Exchange. Start with the current state and the last transition rather than using one generic checklist.
Confirm that you are looking at the intended interface, area, and peer before changing anything.
Compare the parameters that must agree
Verify area, authentication, hello/dead timers, network type, subnet consistency, and any platform-specific area flags. Mismatched required parameters can prevent a Full adjacency even when both devices see OSPF packets.
MTU mismatch is a common reason for neighbors that reach ExStart or Exchange and then fail. Compare interface MTU before assuming a database problem.
Verify two-way protocol traffic and the final topology
Check that each side receives hellos from the other and that ACLs, VLAN state, tunnels, or one-way media faults are not interfering with protocol traffic.
After the fix, confirm the neighbor reaches Full and remains stable, then verify installed routes and cost. Repeatedly clearing the process as a first step can hide the state information that would have identified the problem.