Roles Of A Router

DR – reduces the number of adjacencies required on a multi-access network, which in turn reduces the amongst of routing traffic and the size of the topological database.

BDR - A router that becomes the designated router if the designated router fails

DROther - The router with the highest priority becomes the designated router (DR). If the priorities are the same, then the router with the highest router ID becomes the DR. By default, priorities are set to 1. A router with a priority of 0 never becomes a DR or a backup designated router (BDR); it is always a DROTHER, meaning a router that is neither the DR or the BDR.

DR Selection Process

OSPF chooses the designated router (DR) on a LAN as the device that has the highest IP address. If routers are added or removed from the LAN, or if a router gains an interface with a higher address than that of the existing DR, the DR likely will change if the DR or backup designated router (BDR) fails.