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Re: BGP Confederation config problem...
More info: (B (BPer Avi's suggestion, I implemented this route map for all outbound (Badvertisements: (B (B route-map addone permit 10 (B set metric +1 (B (B(assumes match all) (B (BI'm running IOS 11.2 or 11.1(11) on the routers. The Command reference (Bfor 11.1 and 11.2 does not mention the ability to use +1 to increment, but (Bthe online command "help" shows: (B (BEnter configuration commands, one per line. End with CNTL/Z. (Brouter(config)#route-map addone (Brouter(config-rou)#set metric ? (B +/-<metric> Add or subtract metric (B <0-4294967295> Metric value or IGRP bandwidth in Kbits per second (B <cr> (B (BDoes this really mean "Add one", or "Reset to Positive 1"? (B (B-Andy (B (B-- (BAndy McConnell $B%"%s%G%#(B $B%^%C%3%M%k(B (BNetwork Architect, NTT Multimedia Communications Laboratories (B (BSlogan of 105.9, the classic rock radio station in Chicago: "Of (Ball the radio stations in Chicago ... we're one of them." (B (BOn Fri, 6 Mar 1998, Andy McConnell wrote: (B (Bandym> I have a problem I cannot solve. If anyone is running confederations like (Bandym> mine, I would appreciate some help :-) (Bandym> (Bandym> We have a 4-memberAS confederation, each with two IBGP peers. The (Bandym> arrangement looks sort of like an octagon. the "r" is AS3 is an internal (Bandym> hop, not a BGP peer. (Bandym> (Bandym> _______ ______ (Bandym> | R-----R---r | (Bandym> | / | | | | (Bandym> |AS2 R | |AS3 R | (Bandym> ----|-- ----|- (Bandym> | | (Bandym> ____|__ ____|_ (Bandym> |AS4 R | |AS1 R | (Bandym> | \ | | / | (Bandym> | R-------R | (Bandym> ------- ------ (Bandym> (Bandym> The problem is this: How do you get BGP to choose the shortest "AS PATH", (Bandym> since internal AS paths are ignored in selecting BGP routes? Right now, (Bandym> to top router in AS4 will always choose a route through (2 3 1) instead of (Bandym> (1), because it prefers "external" routes (even external confederation (Bandym> routes) over internal routes. (Bandym> (Bandym> So, when given a choice, the router on the distant side of the AS will (Bandym> ALWAYS prefer the three-AS-hop path, because it is external. Is there a (Bandym> way around this?!? (Bandym> (Bandym> Avi Freedman suggested using a +1 metric when leaving each member-AS. (Bandym> (Thanks Avi!) But it doesn't seem to help - perhaps I didn't do it right. (Bandym> In fact, it doesn't look like the metrics are adjusted more than 1. for (Bandym> example, from AS2, the lower router sees every route outside of AS2 as (Bandym> having only metric 1! The top router in AS3 does not add 1 to the metrics (Bandym> it readvertises to AS2. (Bandym> (Bandym> I've been stewing over this problem for some time... I believe there is (Bandym> some clue that I've missed. Any help would be greatly appreciated! (Bandym> (Bandym> -Andy (Bandym> (Bandym> (Bandym> -- (Bandym> Andy McConnell $B%"%s%G%#(B $B%^%C%3%M%k(B (Bandym> Network Architect, NTT Multimedia Communications Laboratories (Bandym> (Bandym> Writing about music is like dancing about architecture. (Bandym>