OSPF Neighbor States Explained
A walkthrough of the seven OSPF neighbor states, from Down to Full.
OSPF routers progress through a well-defined sequence of states while forming an adjacency: Down, Attempt, Init, 2-Way, ExStart, Exchange, Loading, and Full.
Early states
The Down state means no hellos have been heard from a neighbor recently. Init means a hello was received but the router’s own ID was not seen in it yet.
2-Way is reached once bidirectional communication is confirmed – this is as far as DR/BDR election candidates need to go on broadcast networks.
Database synchronization
- ExStart – master/slave relationship is negotiated
- Exchange – Database Description (DBD) packets are exchanged
- Loading – Link State Request packets fetch missing LSAs
- Full – link-state databases are fully synchronized
R1# show ip ospf neighbor
Neighbor ID Pri State Dead Time Address
10.0.0.2 1 FULL/DR 00:00:38 10.0.0.2