Dynamic routing

Designated router

Also called DR, BDR, backup designated router, DROther, OSPF priority, DR election, 2-Way, 224.0.0.6, AllDRouters

The OSPF router a shared segment elects to sync with everyone, so routers need not all sync with each other.

On a broadcast segment, routers elect a DR and a BDR: the highest priority (default 1) wins, then the highest router ID; priority 0 never stands. Others (DROthers) become Full with the DR and BDR and stop at 2-Way with each other, send updates to 224.0.0.6 for the DR to flood to 224.0.0.5, and the DR writes the segment's network LSA. The election is not preemptive: a better router waits until the DR leaves, and the BDR takes over.

See it on real machines

Learn it on real machines.