A good writing about OSPF exchange process.
Initial Database Exchange
For the SPF algorithm to work properly, all routers in the area should have the same database information on which the SPF algorithm works. The process of synchronization includes the “Initial Database Exchange” which is done when the adjacency is coming up and the asynchronous flooding when the Adjacencies are up.
– A master-slave relation is established to do the database exchange. Besides the MTU is exchanged in the database description packets before any database exchange starts.
– The database exchange begins once the adjacency state reaches Exstart. On a broadcast links, the DR and BDR form adjacencies with all other routers on the network.
– Only one DB Description packet can be unacknowledged at a time that is, the window size is 1. Each DB Description packet from the master is acknowledged by the slave. The slave sends its own DB Description packet with similar identifiers as the masters. This is important because…
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