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The characteristics you assign to an
area control the type of route information it can receive. The area
types possible are shown in the main figure and are described as
follows:
--- An area that operates as discussed in
"Configuring OSPF in a Single Area." This area can
accept link updates and route summaries.
Backbone area (transit area) --- When interconnecting
multiple areas, the backbone area is the central entity to which all
other areas connect. The backbone area is always labeled "area
0." All other areas must connect to this area in order to
exchange route information. The OSPF backbone has all of the
properties of a standard OSPF area.
Stub area --- Refers to an area that does not accept
information about routes external to the autonomous system (that is,
the OSPF internetwork), such as routes from non-OSPF sources. If
routers need to reach networks outside the autonomous system, they
will use a default route. A default route is noted as 0.0.0.0.
Totally stubby area --- An area that does not accept
external autonomous system (AS) routes and summary routes from other
areas internal to the autonomous system. Instead, if the router
needs to send a packet to a network external to the area, it sends
it using a default route.
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