Full form: Designated Router
Also known as: Designated Router
Quick Definition
The elected OSPF router on a multi-access network that collects and distributes LSAs on behalf of all neighbours.
On multi-access networks (such as Ethernet LANs), OSPF routers elect a Designated Router (DR) and a Backup Designated Router (BDR) to reduce the number of OSPF adjacencies. Instead of each router forming full adjacency with every other router (N × (N-1)/2 adjacencies), all routers form full adjacency only with the DR and BDR. The DR collects LSAs from all routers and floods them to the multicast address 224.0.0.5. DR election is based on highest OSPF priority (default 1), then highest Router ID as a tiebreaker.
ip ospf priority 200 ! on the interface — higher wins DR election show ip ospf neighbor
Setting OSPF priority to 0 prevents a router from becoming DR or BDR. DR/BDR election is non-preemptive — the DR does not change unless it fails, even if a higher-priority router joins later.
A link-state routing protocol that calculates the best path using cost based on bandwidth.
The OSPF router elected to take over as DR if the current DR fails.
The information packets OSPF routers flood to share their link state with all other OSPF routers.
A 32-bit value that uniquely identifies an OSPF router within an OSPF domain.
On multi-access networks (such as Ethernet LANs), OSPF routers elect a Designated Router (DR) and a Backup Designated Router (BDR) to reduce the number of OSPF adjacencies. Instead of each router forming full adjacency with every other router (N × (N-1)/2 adjacencies), all routers form full adjacency only with the DR and BDR. The DR collects LSAs from all routers and floods them to the multicast address 224.0.0.5. DR election is based on highest OSPF priority (default 1), then highest Router ID as a tiebreaker.
Setting OSPF priority to 0 prevents a router from becoming DR or BDR. DR/BDR election is non-preemptive — the DR does not change unless it fails, even if a higher-priority router joins later.
DR falls under the Routing domain of the 200-301 exam. Understanding it in context with related terms like bdr and ospf is essential for answering scenario-based questions correctly.