OSPF DR BDR election and neighbor adjacencies

When OSPF is configured in a multi-access network such as Ethernet, the following guidelines should be considered:

  • A DR/BDR election will take place on a per segment basis and not on a per OSPF area basis. A segment is a single broadcast domain, that is, a single IP subnet.
  • Neighbor adjacencies will form only between the following types of OSPF routers:
    • DR and BDR
    • DR and DROTHER
    • BDR and DROTHER
  • DROTHER to DROTHER adjacencies will not form.
  • hello and LSA exchanges take place like so:
    • from DROTHER to DR/BDR:
    • from DR/BDR to DROTHER:
  • In the OSPF DR BDR election process, the BDR is selected first.

Whether OSPF attempts a DR/BDR election depends on the OSPF network types.