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Routing & Switching · Intermediate

OSPF Network Types

OSPF interface modes - broadcast, non-broadcast, point-to-point, point-to-multipoint and loopback - controlling DR election, timers and neighbor discovery.

Definition

Broadcast (Ethernet default) elects a DR with 10/40 timers, while non-broadcast (NBMA) elects a DR with 30/120 timers and requires static neighbors. Point-to-point (serial, GRE default) has no DR with 10/40 timers. Point-to-multipoint has no DR, 30/120 timers and advertises /32 host routes for endpoints. Loopbacks are advertised as /32 unless set to point-to-point.

Example

ip ospf network point-to-point on an Ethernet link between two routers removes DR election.

Exam tip

Mismatched network types (broadcast vs point-to-point) can form adjacency but break routes because of inconsistent LSAs.

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