3Com 4007, Руководство по внедрению, Страница: 464 / 684

464 C
HAPTER
19: O
PEN
S
HORTEST
P
ATH
F
IRST
(OSPF) R
OUTING
Area Border Routers Each area (including the backbone area) includes all border routers that
are connected to the area. In Figure 54, for example, you define:
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Area border routers 1, 2, and 3 as being in backbone area 0
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Area border routers 2 and 4 as being in area 1
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Area border router 1 as being in area 2
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Area border routers 3 and 4 as being in area 3
Routers must communicate with each other through interfaces that are
defined as being in the same area. An area, however, may contain virtual
links from area border routers to the backbone area. For example, in
Figure 54, area border routers 3 and 4 terminate a virtual link between
area 1 and the backbone area. For more information, see “Virtual Links”
later in this chapter.
Routing Databases All routers that are connected to an area maintain identical routing
databases about the area. Routers that are connected to multiple areas
maintain a separate routing database for each attached area. For
example, in Figure 54:
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Routers 1, 2, 3, and 4 maintain identical routing databases about
backbone area 0.
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Routers 5 and 6 maintain identical routing databases about area 1.
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Area border router 1 maintains separate routing databases about
backbone area 0 and area 2.
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Area border router 2 maintains separate routing databases about
backbone area 0 and area 1.
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Area border router 3 maintains separate routing databases about
backbone area 0 and area 3.
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Area border router 4 maintains separate routing databases about
areas 1 and 3. It also maintains a separate routing database about
area 0 due to its virtual link to this backbone area through area border
router 3.
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Autonomous system boundary routers 1 and 2 maintain separate
routing databases about autonomous systems A and B.