An OSPF designated router (DR) is elected on a broadcast network segment to reduce the number of neighbor adjacencies and link-state advertisement exchanges. A backup designated router (BDR) provides a replacement role. The election occurs separately on each segment, not once for the entire OSPF area. section 18.3.2
On a broadcast network:
- Routers dynamically discover neighbors with OSPF hello messages; the default hello and dead timers are 10 and 40 seconds. section 18.3.2
Inspecting and influencing the election
On R2, configure interface G0/1 with `ip ospf priority 100`, then verify the interface and neighbors. `show ip ospf interface g0/1` displays the broadcast network type, priority, and current state. After resetting the OSPF process with `clear ip ospf process`, the neighbor output shows R2 as the BDR and R4 as the DR. The reset affects the OSPF process, so use it deliberately.
