Why Do Routers Form Full Adjacencies Only with the DR or BDR?
Introduction:
In a large Broadcast OSPF network, If all routers formed adjacencies with every other attached router, a large number of link-state advertisements (LSAs) would be sent over the network. To be exact, The advertisement of LSA UPDATE is done over n * (n-1) / 2 neighbor pairs which can be an enormous number in large networks.
Please refer to this post where we explain the need for DR-BDR and the process of election.
Why Do Routers Form Full Adjacencies Only with the DR or BDR?
By electing a Designated Router and a Backup Designated Router, Full OSPF adjacencies are formed only to the DR and BDR, and the number of LSAs sent over the network is reduced by far.
