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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Weird BGP Issue
Lets say ISP X is peering with Tier One's A and B, as well as buying transit from them. ISP Y also peers with A and B, in another geographic region. While all routes for Y are best through A for X, it seems that 75% of X's routes have a return path of A for Y to reach X and the other 25%, although annouced in the EXACT SAME MANNER, use B for the return. ISPs A and B both claim they are distributing all of the routes in the exact same manner, there is no difference between a route for one of my /17's and there is for one of my /19's - yet some of my traffic is taking a different return path than the rest of it. Assymetry is cool and all, but this boggles the mind. Basically: I announce 207.155.0.0/17 and 209.151.224.0/19 to A and B. ISP A and B annouce them to both to Y, making no discrimination between the two routes. ISP Y takes A for 207.155.0.0/17 and B for 209.151.224.0/19 Why doesn't take the route from A as best is 207.155.0.0/17 is best from A or why doesn't it choose B over A, as the 209.151.224.0/19 route appears better. I'd like to understand this c.p. and not just find an answer that is "prepend your routes to A and B will always be preferred." Any ideas? -- Jason Weisberger Chief Technology Officer SoftAware, Inc. - 310/305-0275 ...but the wicked shall do wickedly... --Daniel 12:10
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