An OSPF DROther is a router on a broadcast segment that is neither the designated router (DR) nor the backup designated router (BDR). The DR and BDR form full adjacencies with every router, while DROthers form full adjacencies only with the DR and BDR and remain in the 2-Way state with one another. section 18.3.2 section 18.5
This arrangement reduces OSPF traffic and resource use by concentrating LSA exchanges through the DR and BDR. DROthers send packets addressed to those routers to multicast 224.0.0.6; the election occurs per segment, not per area. section 18.3.2
Recognizing a DROther in Cisco output
The command show ip ospf neighbor identifies roles in the State column. FULL/DROTHER indicates a full adjacency with a DROther, while 2WAY/DROTHER indicates that two DROthers remain neighbors without exchanging LSAs directly. Configure interface priority with ip ospf priority; changing priority alone does not preempt an existing DR or BDR, so clear ip ospf process can trigger a new election.
