You are advertising a summary route that represents your local network (172.20.0.0716) to both ISP A and ISPB. You want to influence all traffic sent to you from ISP C to go through R2.
How would you accomplish this task?
A.
On R1, prepend your AS number three times on the 172.20.0.0/16 route when advertising It to ISP 1.
B.
On R1, change the local preference value to 250.
C.
On R2. prepend your AS number three times on the 172.20.0.0/16 route when advertising it to ISP 2.
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.
[References:, Juniper Networks documentation on BGP: BGP Path Selection and Configuration, ]
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