What does adjacency mean in OSPF?

Adjacency in OSPF (Open Shortest Path First) refers to the state of a full routing relationship established between two OSPF routers. This relationship is crucial for OSPF to function correctly, as it allows routers to exchange routing information efficiently. When two routers form an adjacency, they have successfully completed the OSPF neighbor discovery process, communicated their respective OSPF parameters, and agreed upon the Link State Database (LSDB) contents.

Once an adjacency is formed, the routers will share their routing updates, allowing them to synchronize their routing tables. This synchronization aids in creating a cohesive and updated network view, which is essential for effective routing decisions. Therefore, adjacency signifies a robust and fully-functional connection between two OSPF routers, in contrast to other states that might indicate partial or non-existent communications.