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Routing & Switching · Foundational

OSPF Area 0

The OSPF backbone area to which all other areas must connect and through which all inter-area traffic passes.

Definition

Area 0 (0.0.0.0) carries inter-area routing information between ABRs. Inter-area routes are distance-vector-like: an ABR only accepts Type 3 LSAs from area 0 for re-flooding into other areas, which prevents loops. If an area cannot physically attach to area 0, a virtual link is required.

Example

network 10.0.0.0 0.0.0.255 area 0

Exam tip

A discontiguous (partitioned) area 0 breaks inter-area routing; virtual links or GRE tunnels can repair it.

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