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: 224.0.0.6
  • from DR/BDR to DROTHER: 224.0.0.5
• 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.

Links

https://networklessons.com/ospf/ospf-drbdr-election-explained/