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OSPF Neighbors and Adjacency

What would cause a router to be able to establish a Neighbor relationship but not become Adjacencies and exchange Link State Databases?

2 REPLIES
Silver

Re: OSPF Neighbors and Adjacency

For example, If there are a four or more routers in a broadcast network then not all routers would become adjacent to the others. Adjacency is required only to DR and BDR.

Thanks.

Bronze

Re: OSPF Neighbors and Adjacency

Fomation of adjacency mean the neighbors are ready for exchange of path routing informations/link states.They reach FULL state once they have done this and have similar views on the topology.Reasons for adjacency issues could be ::

* Neigbor sees the other neighbor as down after the periodic hello's arent received even till the dead interval.OSPF hello intervals may not be proper on both.

Or hellos are not processed due to memory/CPU issues.

*OSPF area might be stub configured in one neighbor but the other neighbor in same area is not configured for Stub role.

*Adjacency is only formed by neighbors on primary interfaces and not on secondary.

*OSPF might be manually configured as passive for the interface pointing to neighbor.

*MTU issues.

*One neighbor doesnt see its router id on the other neigbors hello packet.

*They would be trying to exchange Bad LSA.

In a typical broadcast scenario involving DR/BDR the routers other than DR/BDR will never form adjacency with each other, they wud be attaining a 2-way state with each other.This is b'cos the DR/BDR is the one interacting with each of other members for dissemination of updates.

Pls rate/mark if this helps!!!

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