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Re: BGP Confederation config problem...

  • From: Andy McConnell
  • Date: Mon Mar 09 12:10:27 1998

But it isn't considered IBGP within the confederation.  The router makes a
distinction between routes learned from an IBGP peer (internal) and a
confederation EBGP peer (confederation-external) and will ALWAYS pick the
external route, all other items above it in the selection list being
equal.

I've eliminated trying to increase the AS path, since it's ignored within
the confederation.

Setting the MED is the crux of the problem - I can set it "statically",
but the idea is to make the whole confederation dynamic.  I want the
confederation to work like a true "internet".  (Yes, I'm asking for the
world...)

-Andy

--
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 

On Sat, 7 Mar 1998, Rich Sena wrote:

ras> 
ras> Hey Andy if it is a Confederation the BGP is treated like IBGP even if it
ras> is EBGP so you can set a MED value to favor a specific route, you can also 
ras> manipulate the AS_PATH attribute - appending the AS number 2 or more times
ras> to the announcement for the least favored route applied to the appropriate
ras> interface.
ras> 
ras> Since it's all considerred IBGP simply set the MED to 50 on the least
ras> favored and 20 on the favored - or what ever incriments you deem
ras> appropriate.
ras> 
ras> You may have to set "bgp always-compare-med" for it to be considered on
ras> multiple AS numbers within a confederation though.
ras> 
ras> On Fri, 6 Mar 1998, Andy McConnell wrote:
ras> 
ras> > At each member AS, either IGRP or OSPF.  They do not interact.  By
ras> > design... two of the AS's are across the Pacific from the other two :-)
ras> > 
ras> > -Andy
ras> > 
ras> > --
ras> > Andy McConnell       アンディ マッコネル
ras> > Network Architect, NTT Multimedia Communications Laboratories
ras> > 
ras> > Slogan of 105.9, the classic rock radio station in Chicago: "Of
ras> > all the radio stations in Chicago ... we're one of them."
ras> > 
ras> > On Fri, 6 Mar 1998, Blake Willis wrote:
ras> > 
ras> > blakew> Andy,
ras> > blakew> 
ras> > blakew> 	What IGP are you running on this network?
ras> > blakew> 
ras> > blakew> 	-Blake Willis
ras> > blakew> 	CAIS Engineering
ras> > blakew> 
ras> > blakew> ---------------------------------------------------------------------------
ras> > blakew> Blake Willis           					703-448-4470x483
ras> > blakew> Network Engineer, New Customers				blakew@cais.net
ras> > blakew> CAIS Internet, a CGX Communications Company
ras> > blakew> ---------------------------------------------------------------------------
ras> > blakew> 
ras> > blakew> On Fri, 6 Mar 1998, Andy McConnell wrote:
ras> > blakew> 
ras> > blakew> > I have a problem I cannot solve.  If anyone is running confederations like
ras> > blakew> > mine, I would appreciate some help :-)
ras> > blakew> > 
ras> > blakew> > We have a 4-memberAS confederation, each with two IBGP peers.  The
ras> > blakew> > arrangement looks sort of like an octagon.  the "r" is AS3 is an internal 
ras> > blakew> > hop, not a BGP peer.  
ras> > blakew> > 
ras> > blakew> >    _______     ______
ras> > blakew> >   |      R-----R---r |
ras> > blakew> >   |     / |   |    | |
ras> > blakew> >   |AS2 R  |   |AS3 R |
ras> > blakew> >    ----|--     ----|-
ras> > blakew> >        |           |
ras> > blakew> >    ____|__     ____|_
ras> > blakew> >   |AS4 R  |   |AS1 R |
ras> > blakew> >   |     \ |   |   /  |
ras> > blakew> >   |      R-------R   |
ras> > blakew> >    -------     ------
ras> > blakew> > 
ras> > blakew> > The problem is this:  How do you get BGP to choose the shortest "AS PATH",
ras> > blakew> > since internal AS paths are ignored in selecting BGP routes?  Right now,
ras> > blakew> > to top router in AS4 will always choose a route through (2 3 1) instead of
ras> > blakew> > (1), because it prefers "external" routes (even external confederation
ras> > blakew> > routes) over internal routes.
ras> > blakew> > 
ras> > blakew> > So, when given a choice, the router on the distant side of the AS will
ras> > blakew> > ALWAYS prefer the three-AS-hop path, because it is external.  Is there a
ras> > blakew> > way around this?!?
ras> > blakew> > 
ras> > blakew> > Avi Freedman suggested using a +1 metric when leaving each member-AS. 
ras> > blakew> > (Thanks Avi!) But it doesn't seem to help - perhaps I didn't do it right. 
ras> > blakew> > In fact, it doesn't look like the metrics are adjusted more than 1.  for
ras> > blakew> > example, from AS2, the lower router sees every route outside of AS2 as
ras> > blakew> > having only metric 1!  The top router in AS3 does not add 1 to the metrics
ras> > blakew> > it readvertises to AS2.
ras> > blakew> > 
ras> > blakew> > I've been stewing over this problem for some time... I believe there is
ras> > blakew> > some clue that I've missed.  Any help would be greatly appreciated!
ras> > blakew> > 
ras> > blakew> > -Andy
ras> > blakew> > 
ras> > blakew> > 
ras> > blakew> > --
ras> > blakew> > Andy McConnell       アンディ マッコネル
ras> > blakew> > Network Architect, NTT Multimedia Communications Laboratories
ras> > blakew> > 
ras> > blakew> > Writing about music is like dancing about architecture.
ras> > blakew> > 
ras> > blakew> 
ras> > 
ras> 
ras> --
ras> I am nothing if not net-Q! - ras@poppa.clubrich.tiac.net
ras>