DR / BDR / DROther

• Desinated Router ( DR )

1. used on broadcast links to minimize adjacencies and LSA replication

• Backup Designated Router  ( BDR )

1. Used for redundancy of DR

• DROthers

1. For all other routers on the network
2. form adjacency w/ DR & BDR
3. Stop at 2-way adjacency with each other

• The DR and BDR are chosen through election process  

• DROther send LSUs to DR/BDR via multicast 224.0.0.6 
• DR forwards LSUs to DROthers via multicast 224.0.0.5 
• Prevents repeated forwarding of unneeded LSAs on the network
• BDR does not forward LSUs , it only waits for DR to fail