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TCP/IP Tutorial and Technical Overview - IBM Redbooks

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Intra-area, area border, <strong>and</strong> AS boundary routers<br />

There are three classifications of routers in an OSPF network. Figure 5-14<br />

illustrates the interaction of these devices.<br />

Figure 5-14 OSPF router types<br />

Where:<br />

Intra-area routers This class of router is logically located entirely<br />

within an OSPF area. Intra-area routers<br />

maintain a topology database for their local<br />

area.<br />

Area border routers (ABR) This class of router is logically connected to two<br />

or more areas. One area must be the backbone<br />

area. An ABR is used to interconnect areas.<br />

They maintain a separate topology database for<br />

each attached area. ABRs also execute<br />

separate instances of the SPF algorithm for<br />

each area.<br />

198 <strong>TCP</strong>/<strong>IP</strong> <strong>Tutorial</strong> <strong>and</strong> <strong>Technical</strong> <strong>Overview</strong><br />

IA<br />

Area 2<br />

AS 10<br />

ABR<br />

AS External Links<br />

ASBR<br />

Area 1<br />

ABR<br />

Area 0<br />

ABR<br />

Area 3<br />

ASBR<br />

AS External Links<br />

ABR<br />

IA<br />

Area 4<br />

Key<br />

ASBR - AS Border Router<br />

ABR - Area Border Router<br />

IA - Intra-Area Router

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