Thanks in advance for the recommendations to my issue, I'm running a multihome environment with two different ISP's (A and B) and two different routers, we are PI ASN which I advertise to both ISP's, 126.96.36.199/24 thought ISP-A and 188.8.131.52 though ISP-B and in reverse each respective secondary IP blocks which I AS prepend to influence the return traffic, typical setup, nothing fancy...everything works fine until I enable iBGP to complete this multihome setup, at that time 184.108.40.206 shows a better BGP metric via ISP-B even with the AS prepend on (which shows in a looking glass router show IP bgp command), I would like my traffic to remain symmetric and by AS prepending I should be accomplishing that, well is not working, I welcome any ideas and suggestions on what else I can try to accomplish my goals.
You need to increase the number of AS prepending in the BGP AS prepend statement. Let's say you are prepending your own AS 5 times from router B for 220.127.116.11/24 subnet so increase it to 10 times and see the result. if it don't solve the problem increase the AS prepending it to 15-20 times till the time 18.104.22.168/24 is best path from router A.
For ex:- Issue is reachability from BGP looking Glass server through ISP-B to your network could be 10 hops and 15 hops through ISP-A so if you prepend own AS for 22.214.171.124/24 route through ISP-B 4 times still ISP B is best path because it is still 14 hops away as compared to ISP-A which is 15 hops Away.
I hope it answers your question. Please rate the post if you find it useful.
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