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Configuring gated
Configuring the OSPF Protocol
Chapter 3 61
Figure 3-3 Areas Defined in an Autonomous System
Internal routers have all their directly connected networks in the same
area. In Figure 3-3, routers A, B, and H are internal routers.
Routers that are connected to multiple areas are called area border
routers. In Figure 3-3, routers F and G are area border routers.
Routers that connect one AS to another are called AS boundary
routers. In Figure 3-3, router D is an AS boundary router.
Neighbor routers are routers that interface to a common network.
OSPF uses its own Hello subprotocol to determine which routers are
neighbors. In Figure 3-3, routers A, B, and C are a set of neighbor routers
that interface to network 1, while routers A and F are another set of
neighbor routers that interface to network 2.
NOTE The Hello subprotocol used with OSPF is not the same as the gated
HELLO protocol. The Hello subprotocol is still supported.
1
AB
23
F
Area 1
CD
E
Other AS
I
6
H
5G
4
Area 2 Area 3
Legend:
Network
Router
Area
Backbone