There are seven different states that an OSPF router transitions through until ultimately synchronizing OSPF databases with its neighbors:
- Down – There is no active neighbor detected on the interface.
- INIT – A hello packet has been received; this is the first state in which you would see a neighbor ID appear in the neighbor table.
- 2-WAY – The local router has received a hello packet from a neighbor that contains its own router ID, signifying 2-way communications have been established.
- Exstart – (Exchange Start.) The two routers have agreed on the master and slave roles for transmission of database description (DBD) packets in the subsequent Exchange state. Initial sequence numbers are established.
- Exchange – The database description packets for the LSDB are exchanged. Packets may be flooded to other interfaces on the router.
- Loading – After DBD exchange, the two routers send LSUs and LSRs to exchange information about missing routes, using request and retransmission lists.
- Full – Once databases have been fully synchronized between the two routers and they are capable of running the SPF algorithm, the adjacency is completed and transitions to the “Full” state.
The only permanent states you will see in the show ip ospf neighbor table are Full and 2-WAY. A non-DR/BDR router will only form a 2-WAY relationship with a DROTHER because it does not fully synchronize its databases with them. (All other states are transient/temporary).
Stuck-in-Active: Journal of an IT-Network Administrator 