Which of the following transport multiple types of networks. Which of the following types of networks need to elect DR and BDR? (Multiple choice)

Question

Options

• AP2P
• BBROADCAST
• CP2S
• DNBMA

• A
  4% (1)
• B
  83% (20)
• C
  13% (3)

Explanation

In OSPF, DR (Designated Router) and BDR (Backup Designated Router) elections are only needed on multi-access network types - where more than two routers share the same segment and full mesh adjacency would be inefficient. Broadcast (e.g., Ethernet) and NBMA (Non-Broadcast Multi-Access, e.g., Frame Relay, ATM) both qualify: multiple routers exist on a shared medium, so OSPF elects a DR to centralize LSA flooding and reduce overhead.

P2P (A) is wrong because point-to-point links connect exactly two routers - there's no need for election since full adjacency forms directly. P2S (C) (Point-to-Multipoint) is wrong because OSPF treats each path as a separate point-to-point link, so no shared segment exists and no DR/BDR is needed.

Memory tip: Think "multi-access = election." If the network type allows multiple routers to share the same wire or virtual circuit and uses that shared medium to exchange LSAs, it needs a DR/BDR. Broadcast and NBMA both fit that profile - Broadcast can, NBMA can't (hence "Non-Broadcast"), but both are still multi-access.

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