7-6 CHAPTER 7: ROUTING WITH OSPF
Neighbors Neighbor routers are physically attached to the same network segment. A
router attached to multiple network segments may have different sets of
neighbors on each segment. For example, Figure 7-1 includes several sets
of OSPF neighbor routers.
In backbone area 0:
■ Router 2 and area border routers 1 and 3 are neighbors on segment 1
(the backbone network).
■ Routers 1 and 2 are neighbors on a point-to-point link.
■ Routers 3 and 4 and area border router 2 are neighbors on segment 4.
■ No routers are neighbors on segments 2, 3, 5, and 6.
In area 1:
■ Router 5 and area border router 2 are neighbors on segment 7.
■ Routers 5 and 6, area border router 4, and autonomous system
boundary router 1 are neighbors on segment 9.
■ No routers are neighbors on segment 8.
In area 3:
■ Area border routers 3 and 4 are neighbors on a virtual link between
the backbone area 0 and area 1.
Routers use OSPF hello packets to learn neighbor addresses dynamically
on interfaces that support multicast routing. Define static neighbors only
on nonmulticast interfaces.
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