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Understanding the network.pdf - Back to Home

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Figure 8.11. The OSPF router class tree.<br />

• <strong>Back</strong>bone routers—These routers maintain complete routing<br />

information for all <strong>the</strong> <strong>network</strong>s (all <strong>the</strong> areas or domains) that<br />

are connected <strong>to</strong> <strong>the</strong> backbone.<br />

• Area border routers—These are routers that connect two or<br />

more areas (inter-area routing). These routers usually sit on <strong>the</strong><br />

<strong>network</strong> backbone and connect <strong>the</strong> branch areas <strong>to</strong> <strong>the</strong> root<br />

area. They are different from backbone routers because <strong>the</strong>y<br />

traditionally do not redistribute o<strong>the</strong>r AS routing information<br />

and belong <strong>to</strong> only one AS. These routers only maintain<br />

information about <strong>the</strong> backbone and <strong>the</strong> areas <strong>to</strong> which <strong>the</strong>y are<br />

attached.

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