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Difficulty: HardOSPFv2 Network Types and DR/BDR Selection

Match each OSPFv2 network type on the left to its corresponding DR/BDR election behavior, neighbor adjacency capability, and default Hello/Dead timer characteristics on the right.

  • Broadcast Network TypeElects a DR and BDR using interface priority and Router ID; default timers are Hello 10s and Dead 40s.
  • Point-to-Point Network TypeSuppresses DR/BDR election; automatically forms adjacencies; default timers are Hello 10s and Dead 40s.
  • Point-to-Multipoint Network TypeSuppresses DR/BDR election; treats neighbors as individual point-to-point links; default timers are Hello 30s and Dead 120s.
  • Loopback Interface Network TypeSuppresses DR/BDR election; forms no neighbor adjacencies; advertises the interface IP with a /32 prefix length regardless of configured subnet mask.

Answer

Broadcast Network Type matches with DR/BDR election and Hello 10s/Dead 40s. Point-to-Point Network Type matches with no DR/BDR election and Hello 10s/Dead 40s. Point-to-Multipoint Network Type matches with no DR/BDR election and Hello 30s/Dead 120s. Loopback Interface Network Type matches with no DR/BDR election, no neighbors, and /32 host route advertisement.
Each OSPF network type is designed for specific underlying link technologies. Broadcast multiaccess networks perform DR/BDR election with 10s/40s timers. Point-to-point bypasses DR election with 10s/40s timers. Point-to-multipoint bypasses DR election with 30s/120s timers. Loopback interfaces advertise /32 host routes without forming adjacencies.

Step-by-Step Solution

1
Analyze Broadcast multiaccess network characteristics.
Broadcast networks (e.g., Ethernet interfaces running OSPF) require DR and BDR elections to avoid N(N−1)/2N(N-1)/2 full mesh adjacencies. The standard Hello timer is 10 seconds, and the Dead timer is 40 seconds.
DR/BDR selection is mandatory on multiaccess media.
2
Analyze Point-to-Point network characteristics.
Point-to-Point networks connect two endpoints directly. DR/BDR election is bypassed because only two routers exist on the segment. Timers default to Hello 10s and Dead 40s.
Electing a DR/BDR on a two-node point-to-point connection adds unnecessary protocol overhead.
3
Analyze Point-to-Multipoint network characteristics.
Point-to-Multipoint treats the physical or logical multiaccess network as multiple point-to-point connections. It disables DR/BDR elections and defaults to longer timers (Hello 30s, Dead 120s).
Used primarily in WAN/hub-and-spoke topologies where direct spoke-to-spoke broadcast reachability is absent.
4
Analyze Loopback network characteristics.
In Cisco IOS OSPFv2, loopback interfaces automatically default to the Loopback network type, advertising the interface IP as a /32 host route regardless of the configured netmask, without participating in neighbor discovery.
Loopback interfaces represent logical local endpoints, not actual transit links.

Key Concept

OSPFv2 Network Types, Adjacencies, Timers, and DR/BDR Requirements
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Topics

OSPFv2 Network Types and DR/BDR Selection

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