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Re: Weird BGP Issue
- From: Tatsuya Kawasaki
- Date: Tue Jul 21 23:51:08 1998
(Bwe have similar situation but it is rather complicate.
(BTo answer your question, it may be wrong or you obviously
(Bomit something but according to your explaination, you did not
(Bmention anyhing about ISP Y's routing policy.
(BAssume that A and B does not do anything on your BGP how about
(BISP Y? Did you talk to ISP Y about it? don't ask me why they do but
(Bit is mostly likely ? or am I missing all ?
(BI assume there is NO carrier btwn X and Y other than A and B.
(BIn theory, someone else other than you can change BGP route update
(Binfomation, but I don't think it is the case or perhaps?
(BP.S. please let me know if you hear better explanation.
(B= = = = = =
(BBusiness Network Telecom (BNT)
(BOn Tue, 21 Jul 1998, Jason L. Weisberger wrote:
(B> Lets say ISP X is peering with Tier One's A and B, as well as buying
(B> transit from them. ISP Y also peers with A and B, in another geographic
(B> region. While all routes for Y are best through A for X, it seems that 75%
(B> of X's routes have a return path of A for Y to reach X and the other 25%,
(B> although annouced in the EXACT SAME MANNER, use B for the return.
(B> ISPs A and B both claim they are distributing all of the routes in the
(B> exact same manner, there is no difference between a route for one of my
(B> /17's and there is for one of my /19's - yet some of my traffic is taking
(B> a different return path than the rest of it.
(B> Assymetry is cool and all, but this boggles the mind.
(B> I announce 22.214.171.124/17 and 126.96.36.199/19 to A and B.
(B> ISP A and B annouce them to both to Y, making no discrimination between
(B> the two routes.
(B> ISP Y takes A for 188.8.131.52/17 and B for 184.108.40.206/19
(B> Why doesn't take the route from A as best is 220.127.116.11/17 is best from A
(B> or why doesn't it choose B over A, as the 18.104.22.168/19 route appears
(B> I'd like to understand this c.p. and not just find an answer that is
(B> "prepend your routes to A and B will always be preferred."
(B> Any ideas?
(B> Jason Weisberger
(B> Chief Technology Officer
(B> SoftAware, Inc. - 310/305-0275
(B> ...but the wicked shall do wickedly...
(B> --Daniel 12:10