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OSPF Traffic Types

Three types of traffic may be defined in relation to areas:

Intra-area traffic consists of packets that are passed between routers within a single area.

Inter-area traffic consists of packets that are passed between routers in different areas.

External traffic consists of packets that are passed between a router within the OSPF domain and a router within another routing domain.


Area ID 0 (or 0.0.0.0) is reserved for the backbone. The backbone is responsible for summarizing the topologies of each area to every other area. For this reason, all inter-area traffic must pass through the backbone; non-backbone areas cannot exchange packets directly.


Ref: Routing TCP/IP volume 1

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