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solemdoms5
Beginner

When was DBD(database descriptor) packets sent ?

I know DBD packets would be exchanged when establishing adjacency after booting the router .

However after that ,Im not sure how DBD works .So

DBD packets was sent every 30 minutes ?  I mean .

When Router exchange LSDB every 30 minutes , First Do OSPF routers exchange DBD(database descriptor ) packets ?

thank you .

23 REPLIES 23
John Blakley
Advisor

My understanding is when the routers go into an exchange state, the dbd packets are sent to describe the networks that the router knows about to its neighbor. The dbd packet has the lsa headers of its lsdb and it's sent to the neighbor. I believe the master of the master/slave relationship is the one that starts the exchange. After the exchange is done and the neighbors settle into a FULL state, and it would not be sent again unless a topology change happens (a change in the lsdb) or the 30 minute window lapses.

HTH,
John

*** Please rate all useful posts ***

HTH, John *** Please rate all useful posts ***
Peter Paluch
Hall of Fame Cisco Employee

Hello,

The DBD packets are exchanged only during the initial database synchronization between routers. After the databases have been synchronized, new LSAs are flooded and acknowledged without the need of more DBD packets. That also goes for refreshing and reflooding LSAs.

John, the DBD packets do not describe networks. What they describe are the contents of the sender's link-state database. You have stated correctly that DBD packets contain headers of individual LSAs in the sender's database. Basically, if you think in terms of database systems, every record in a database can be uniquely identified by its primary key. If you want to compare two databases, you do not need to transfer the entire database - rather, you just take the keys and check whether both databases have the same set of keys. If any key is missi