3Com 4007, Implementation Manual, Page: 480 / 684

480 C
HAPTER
19: O
PEN
S
HORTEST
P
ATH
F
IRST
(OSPF) R
OUTING
Neighbors
Neighbor routers are those that are physically attached to the same
network segment. The OSPF Hello protocol establishes adjacencies
among neighboring routers to facilitate the exchange of routing
information. An
adjacency describes the relationship between two
routers that exchange network topology information. A router attached
to multiple network segments may have different sets of neighbors on
each segment.
For example, Figure 54 earlier in this chapter includes several sets of OSPF
neighbor routers. In backbone area 0:
■
Routers 2 and 3 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.