Simple definition
OSPF neighbor states track adjacency formation, from discovery through full database synchronization.
Purpose and use
OSPF neighbor states show progress from discovering a router to synchronizing the link-state database.
How does it work?
Stages include Init, 2-Way, ExStart, Exchange, Loading and Full, according to the adjacency being formed.
Example and verification
An adjacency stuck in ExStart or Exchange warrants comparing interface settings, including MTU, and the exchanges actually received.
Points to watch
On a network using a DR and BDR, two DROther routers can normally remain in 2-Way. Not every pair must reach Full.
In short
Interpret state alongside network type and OSPF roles to avoid mistaking normal behavior for a synchronization failure.