BDR

In OSPF (Open Shortest Path First), the system elects a designated router (DR) and a backup designated router (BDR). The BDR smooths the transition to the DR, and each multi-access network has a BDR. The BDR is adjacent to all routers on the network and becomes the DR when the previous DR fails. The period of disruption in transit traffic lasts only as long as it takes to flood the new LSA (Link State Advertisement)s (which announce the new DR). The BDR is elected by the protocol; each hello packet has a field that specifies the BDR for the network.