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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical RE: BGP Confederation config problem...
On Sat, 7 Mar 1998, Dave Van Allen wrote: dave> >Avi Freedman suggested using a +1 metric when leaving each member-AS. dave> (Thanks Avi!) But it doesn't seem to help - perhaps I didn't do it dave> right. dave> dave> Did our friend Avi also suggest that you need to add: dave> dave> ! dave> bgp always-compare-med dave> ! dave> dave> ?? dave> dave> Best regards, dave> dave> David Van Allen - FASTNET(tm) / You Tools Corporation Yep. And I have. Doesn't seem to help. -- Andy McConnell アンディ マッコネル Network Architect, NTT Multimedia Communications Laboratories I think myself that we have more machinery of government than is necessary, too many parasites living on the labor of the industrious. -- Thomas Jefferson, 1812 dave> [email protected] (888)321-FAST(3278) http://www.fast.net dave> FASTNET - Business and Personal Internet Solutions dave> dave> dave> -----Original Message----- dave> From: Andy McConnell [mailto:[email protected]] dave> Sent: Friday, March 06, 1998 1:02 PM dave> To: [email protected] dave> Subject: BGP Confederation config problem... dave> dave> dave> I have a problem I cannot solve. If anyone is running confederations dave> like dave> mine, I would appreciate some help :-) dave> dave> We have a 4-memberAS confederation, each with two IBGP peers. The dave> arrangement looks sort of like an octagon. the "r" is AS3 is an dave> internal dave> hop, not a BGP peer. dave> dave> _______ ______ dave> | R-----R---r | dave> | / | | | | dave> |AS2 R | |AS3 R | dave> ----|-- ----|- dave> | | dave> ____|__ ____|_ dave> |AS4 R | |AS1 R | dave> | \ | | / | dave> | R-------R | dave> ------- ------ dave> dave> The problem is this: How do you get BGP to choose the shortest "AS dave> PATH", dave> since internal AS paths are ignored in selecting BGP routes? Right now, dave> to top router in AS4 will always choose a route through (2 3 1) instead dave> of dave> (1), because it prefers "external" routes (even external confederation dave> routes) over internal routes. dave> dave> So, when given a choice, the router on the distant side of the AS will dave> ALWAYS prefer the three-AS-hop path, because it is external. Is there a dave> way around this?!? dave> dave> Avi Freedman suggested using a +1 metric when leaving each member-AS. dave> (Thanks Avi!) But it doesn't seem to help - perhaps I didn't do it dave> right. dave> In fact, it doesn't look like the metrics are adjusted more than 1. for dave> example, from AS2, the lower router sees every route outside of AS2 as dave> having only metric 1! The top router in AS3 does not add 1 to the dave> metrics dave> it readvertises to AS2. dave> dave> I've been stewing over this problem for some time... I believe there is dave> some clue that I've missed. Any help would be greatly appreciated! dave> dave> -Andy dave> dave> dave> -- dave> Andy McConnell fAf"fffB f}fbfRflf< dave> Network Architect, NTT Multimedia Communications Laboratories dave> dave> Writing about music is like dancing about architecture. dave>
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