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220 Chapter 7: OSPF, EIGRP, and IGRP

Autonomous System Boundary Router (ASBR)--A router that exchanges routing
information with routers that are not running OSPF (RIP, IGRP, EIGRP, and so on). ASBR
routers inject external link-state advertisements into the OSPF database.

Figure 7-3 illustrates the router classifications for OSPF.

Figure 7-3

OSPF Router Classifications

Link-State Advertisements (LSAs)

Every router in an area contains a link-state database, which consists of link-state
advertisements (LSAs). LSAs describe the router's local state. All of the routers in an area have
the same link-state database. The database consists of information gathered from all the LSAs
received. The LSAs are sent to all routers in an area. The LSAs are produced by routers and
include all the router's links, interfaces, state of links, and cost.

Types of Link-State Advertisements

LSAs present the state of the OSPF link. Different types of LSAs perform different
assignments. An LSA can describe the state of the router interface inside a particular area. Some

Backbone routers

AS boundary router

Area border router

Internal

routers

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