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Routing & Switching · Intermediate

Autonomous System Boundary Router (ASBR)

An OSPF router that redistributes external routes into OSPF, originating Type 5 or Type 7 LSAs.

Definition

Any router running redistribution into OSPF becomes an ASBR. Its location is advertised to other areas by Type 4 LSAs from ABRs so routers can compute the cost to reach it. External summarization uses summary-address on the ASBR.

Example

redistribute static subnets under router ospf 1 makes the router an ASBR.

Exam tip

An ASBR in a normal area produces Type 5 LSAs; in an NSSA it produces Type 7.

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