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


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