In OSPF on multi-access networks, a Designated Router (DR) is elected to reduce the number of required adjacencies. A Backup Designated Router (BDR) is also elected at the same time. The BDR establishes full adjacencies with all other routers on the segment, just like the DR, and receives all Link-State Advertisements (LSAs). It acts as a hot standby. If the DR fails, the BDR immediately and without a new election process takes over the role of the DR, minimizing downtime and ensuring the stability of OSPF adjacencies on the segment.

B. All routers in an OSPF area synchronize their databases; this is not a unique function of the BDR, although it participates.

C. All OSPF routers are responsible for detecting failures on their directly connected links, not just the BDR.

D. OSPF's use of the SPF algorithm prevents routing loops. The DR/BDR mechanism is for efficiency and scalability, not loop prevention.

1. Juniper Networks TechLibrary. (2023). Junos OS Routing Protocols Configuration Guide. "OSPF Designated Router Election

" Section: Overview of the OSPF Designated Router. "The backup designated router takes over if the designated router fails. The backup designated router minimizes the transition time if the designated router fails."

2. Moy

J. (1998). OSPF Version 2 (RFC 2328). Internet Engineering Task Force. Section 7.4

"The Backup Designated Router." "The Backup Designated Router also establishes adjacencies with all routers on the network. It is promoted to Designated Router when the current Designated Router fails."