OSPF NEIGHBORSHIP vs ADJACENCY
Difference between Neighborship and Adjacency
Neighbors are routers who have exchanged Hello packets, but not LSA information and don’t have same LSDB. Example : Two DROther routers.
Adjacent routers are routers who have exchanged Hello packet, LSA information and have same LSDB. Example: DR & BDR
Illustrating the difference
As you know, in a LAN environment you have a DR election. After this election, the DR and BDR are elected,
and all other routers( DROthers) form adjacencies with the DR/BDR.
Meaning, they pass the 2WAY state into ex-start and start exchanging LSA headers to begin the route exchange.
However, between two DROther routers, you will never pass beyond 2WAY. That is to say, they will exchange hello packets, but will never enter exstart, never exchange LSA headers, never converge into adjaceny neighbors