OSPF Areas

As a network grows, the initial flooding and database maintenance of LSAs can burden the CPU of a router. OSPF uses areas to reduce these effects. An area is a logical grouping of routers and links that divides the network. Routers share link-state information with only those routers in their area. This reduces the size of the database.

Area 0 is reserved for the backbone area, which is responsible for distributing routing information between areas. As you can see in Figure 6-4, communication between Area 1 and Area 2 must flow through Area 0. In intra-area traffic, packets are passed between routers in a single area. In inter-area traffic, packets are passed between routers in different areas.

Figure 6-4 OSPF Areas

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