North American Network Operators Group|
Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical
BGP Confederation config problem...
I have a problem I cannot solve. If anyone is running confederations like (Bmine, I would appreciate some help :-) (B (BWe have a 4-memberAS confederation, each with two IBGP peers. The (Barrangement looks sort of like an octagon. the "r" is AS3 is an internal (Bhop, not a BGP peer. (B (B _______ ______ (B | R-----R---r | (B | / | | | | (B |AS2 R | |AS3 R | (B ----|-- ----|- (B | | (B ____|__ ____|_ (B |AS4 R | |AS1 R | (B | \ | | / | (B | R-------R | (B ------- ------ (B (BThe problem is this: How do you get BGP to choose the shortest "AS PATH", (Bsince internal AS paths are ignored in selecting BGP routes? Right now, (Bto top router in AS4 will always choose a route through (2 3 1) instead of (B(1), because it prefers "external" routes (even external confederation (Broutes) over internal routes. (B (BSo, when given a choice, the router on the distant side of the AS will (BALWAYS prefer the three-AS-hop path, because it is external. Is there a (Bway around this?!? (B (BAvi Freedman suggested using a +1 metric when leaving each member-AS. (B(Thanks Avi!) But it doesn't seem to help - perhaps I didn't do it right. (BIn fact, it doesn't look like the metrics are adjusted more than 1. for (Bexample, from AS2, the lower router sees every route outside of AS2 as (Bhaving only metric 1! The top router in AS3 does not add 1 to the metrics (Bit readvertises to AS2. (B (BI've been stewing over this problem for some time... I believe there is (Bsome clue that I've missed. Any help would be greatly appreciated! (B (B-Andy (B (B (B-- (BAndy McConnell $B%"%s%G%#(B $B%^%C%3%M%k(B (BNetwork Architect, NTT Multimedia Communications Laboratories (B (BWriting about music is like dancing about architecture.