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Routing & Switching · Intermediate

OSPF Type 3 Summary LSA

The LSA an ABR originates to advertise prefixes from one area into another.

Definition

Type 3 LSAs carry a prefix and cost but not the underlying topology, so inter-area routing behaves like distance vector. ABRs regenerate them at each area boundary. Totally stubby areas block Type 3 LSAs except a default route, and filter-list or area range can control them.

Example

area 1 filter-list prefix BLOCK in on an ABR filters Type 3 LSAs into area 1.

Exam tip

Inter-area routes appear as O IA in show ip route and come from Type 3 LSAs.

Related terms