OSPF: Database Description Packets

Once two routers exchange Hellos and verify parameters match, the begin building DBD ackets which contain only the headers of the LSAs the router is aware of with the revision number.  It compiles this list of LSAs into a DBD packet and transmits it to the neighbor.

If the neighboring router does not have a specific LSA listed in the index of the DBD message it will request the full LSA via an LSU subsequently.

DBD packets use a simple error recovery process, where each DBD packet contains a sequence number, the receiver acknowledges  the DBD packet by sending its own DBD packet with the same sequence number back to the sender.

 

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