Backbone routers

Figure 12-2 uses the network depicted in Figure 12-1 to identify the three different types of routers in the network.

Figure 12-2: Area border routers, internal routers, and backbone routers in an OSPF network.

Figure 12-2: Area border routers, internal routers, and backbone routers in an OSPF network.

As shown in Figure 12-2, a router with multiple interfaces may belong to two or more areas. Such routers become area border routers. That is, they interconnect the backbone and its area members. A backbone router is one that has at least one interface defined as belonging to Area 0. It is possible for an area border router to also be a backbone router. Any area border router that interconnects a numbered area with Area 0 is both an area border and a backbone router. An internal router features interfaces that are all defined as the same area, but not Area 0. Using these three basic types of routers, it is possible to construct highly efficient and scalable OSPF networks.

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