[15549] in North American Network Operators' Group
RE: BGP Confederation config problem...
daemon@ATHENA.MIT.EDU (Andy McConnell)
Mon Mar 9 12:13:46 1998
Date: Mon, 9 Mar 1998 08:52:57 -0800 (PST)
From: Andy McConnell <andym@nttlabs.com>
To: Dave Van Allen <dave@fast.net>
cc: nanog@merit.edu, "'freedman@netaxs.com'" <freedman@netaxs.com>
In-Reply-To: <4DB4BFFE4768D011954E0000C0815AEDBC6FAA@fnbdc1.youtools.com>
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 $B%"%s%G%#(B $B%^%C%3%M%k(B
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>
