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Difficulty: MediumOSPFv2 Network Types and DR/BDR Selection

Match each OSPFv2 network type or interface configuration on the left to its corresponding election behavior and default timer characteristics on the right.

  • Broadcast Multiaccess interfaceElects DR and BDR with default Hello/Dead timers of 10s/40s
  • Point-to-Point interfaceSuppresses DR/BDR election with default Hello/Dead timers of 10s/40s
  • Interface configured with ip ospf priority 0Disqualifies the interface from DR/BDR election, forcing DROTHER state
  • Non-Broadcast (NBMA) interfaceElects DR and BDR with default Hello/Dead timers of 30s/120s

Answer

Broadcast Multiaccess matches electing DR/BDR with 10s/40s timers; Point-to-Point matches suppressing DR/BDR election with 10s/40s timers; Interface priority 0 matches disqualifying from DR/BDR election; Non-Broadcast matches electing DR/BDR with 30s/120s timers.
Broadcast multiaccess interfaces use 10s/40s timers and elect a DR/BDR. Point-to-Point interfaces use 10s/40s timers but suppress DR/BDR elections. Configuring priority 0 explicitly disqualifies an interface from election eligibility. Non-Broadcast interfaces elect a DR/BDR but use 30s/120s timers by default.

Step-by-Step Solution

1
Determine DR/BDR election requirements for each network type.
Broadcast Multiaccess and Non-Broadcast networks require DR/BDR elections to manage multiaccess adjacencies, while Point-to-Point interfaces bypass DR/BDR elections completely.
Direct peer-to-peer topologies do not suffer from the N(N−1)/2N(N-1)/2 adjacency scaling problem of multiaccess media.
2
Evaluate default Hello and Dead timers for OSPF network types.
Broadcast and Point-to-Point network types use 10-second Hello and 40-second Dead timers. Non-Broadcast (NBMA) networks use 30-second Hello and 120-second Dead timers.
NBMA interfaces default to longer timers to account for WAN link characteristics.
3
Analyze the role of interface priority zero in DR/BDR selection.
An interface assigned a priority value of 0 is ineligible for election to DR or BDR status.
A priority value of 0 acts as an explicit override to prevent a router interface from becoming DR or BDR regardless of Router ID.

Key Concept

OSPFv2 Network Types, DR/BDR Selection Rules, and Default Timers
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Topics

OSPFv2 Network Types and DR/BDR Selection

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