Full form: Backup Designated Router
Also known as: Backup Designated Router
Quick Definition
The OSPF router elected to take over as DR if the current DR fails.
The BDR is the second router elected in an OSPF multi-access network. It monitors the DR and takes over its role instantly if the DR fails, preventing a full re-election and minimising convergence time. The BDR also has full adjacency with all DROTHER routers and receives all LSAs. Routers that are neither DR nor BDR are called DROTHER routers.
DROTHER routers (non-DR, non-BDR) form adjacency only with the DR and BDR — not with each other. Their neighbour state with other DROTHERs stays at 2-Way, not Full.
The BDR is the second router elected in an OSPF multi-access network. It monitors the DR and takes over its role instantly if the DR fails, preventing a full re-election and minimising convergence time. The BDR also has full adjacency with all DROTHER routers and receives all LSAs. Routers that are neither DR nor BDR are called DROTHER routers.
DROTHER routers (non-DR, non-BDR) form adjacency only with the DR and BDR — not with each other. Their neighbour state with other DROTHERs stays at 2-Way, not Full.
BDR falls under the Routing domain of the 200-301 exam. Understanding it in context with related terms like dr and ospf is essential for answering scenario-based questions correctly.