JN0-363 Exam - Question 36

Question

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You are advertising a summary route that represents your local network (172.20.0.0/16) to both ISP A and ISP B. You want to influence all traffic sent to you from ISP C to go through R2.

How would you accomplish this task?

Examice · Accepted Answer

To influence traffic from ISP C to prefer the path through R2, you should make the path through R1 appear less preferable. This can be achieved by prepending your AS number three times on the route advertisement to ISP A via R2. By doing so, the AS path through R1 will appear longer and thus less desirable to ISP C, making it more likely for ISP C to choose the path through R2. AS path length is a significant factor in BGP route selection, with shorter paths being preferred.

GolanZemach · Answer

Answer C

theeprosemaestro · Answer

I am thinking it should be B. Changing the routing preference on R1 to 250 will prompt all traffic routing into the network to chose R2 as the preferred route.

ZeeZaidi · Answer

To influence ISP C to prefer the path through R2 for the 172.20.0.0/16 network, R2 should make its path less preferable to ISP B by prepending its AS number multiple times. This makes the path through R2 appear longer and less desirable to ISP C, which would receive these updates from ISP B. AS path length is a well-known attribute in BGP and is used to determine the best path; paths with a longer AS path are considered less preferable.

JN0-363 Exam - Question 36

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