Categories of Multi-area Components
F I G U R E 5 . 2
Starting at the core of the given network and working our way outward,
consider RouterA. Notice that RouterA is part of Area 0. As we learned in
the previous chapter, Area 0 is referred to as the backbone area. Therefore,
we can make the following definition:
Backbone router A backbone router is any router that exists (wholly or
in part) in OSPF Area 0.
Another distinction that we can make about RouterA is that it is con-
tained completely within a single area, in this case Area 0. Since all of
RouterA's interfaces are internal to a single area, we can make the following
Internal router An internal router is any router that has all of its inter-
faces as members of the same area.
Remember that a router can play more than one role. In our example, RouterA
is both a backbone router and an internal router.
Now consider RouterB. Notice that RouterB meets the requirement to be
classified as a backbone router (i.e., RouterB has one or more interfaces that
are part of Area 0). However, unlike RouterA, RouterB is partially in Area 0 and
Area Border Router
Autonomous System Boundary Router
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