300-410 ENARSI: Implementing Cisco Enterprise Advanced Routing and ServicesDemo

Question

Refer to the exhibit.

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AS111 is receiving its own routes from AS200, causing a loop in the network. Which configuration provides loop prevention?

A router bgp 111 neighbor 195.1.1.1 as-override no neighbor 195.1.2.2 allowas-in
B router bgp 111 no neighbor 195.1.1.1 allowas-in no neighbor 195.1.2.2 allowas-in
C router bgp 111 neighbor 195.1.2.2 as-override no neighbor 195.1.1.1 allowas-in
D router bgp 111 neighbor 195.1.1.1 as-override neighbor 195.1.2.2 as-override

Explanation

BGP normally rejects an update when its own ASN appears in the AS_PATH, preventing AS-path routing loops. allowas-in disables that protection for the local ASN; removing it from both AS111 neighbors restores the default loop check. Cisco documents that allowas-in permits prefixes even when the local ASN occurs in the AS path.

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Cisco: Configure Allowas-in Feature in BGP

300-410 ENARSI: Implementing Cisco Enterprise Advanced Routing and ServicesDemo

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