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