Answer:
FULL neighbor state.
(FULL/DR or FULL/BDR)
Explanation:
The fact that the routers are neighbors is not enough to guarantee an exchange of link status updates; they must form adjacencies to exchange link status updates. Adjacency is the next step after the process of establishing neighbors. Adjacent routers are routers that go beyond a simple Greeting exchange and act in the database exchange process. To reduce the amount of information exchange in a given segment, OSPF selects a router as a designated router (DR) and a router as a designated backup router (BDR) in each multiple access segment. The BDR is chosen as the backup mechanism in case the DR fails. The idea behind this is that routers have a central point of contact for the exchange of information. In order to verify if two routers have established an adjacency, you can use the command: show ip ospf neighbor.
Here is an example:
R1#show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
203.250.12.1 1 2WAY/DROTHER 0:00:37 203.250.14.3 Ethernet0
203.250.15.1 1 FULL/DR 0:00:36 203.250.14.2 Ethernet0
203.250.13.41 1 FULL/BDR 0:00:34 203.250.14.1 Ethernet0
