From: Mike Kraus \(mikraus\) (mikraus@cisco.com)
Date: Tue Jul 10 2007 - 16:09:44 ART
John,
This is a good doc for BGP path selection:
http://www.cisco.com/warp/public/459/25.shtml
The important excerpt is: "The AS_CONFED_SEQUENCE and AS_CONFED_SET
are not included in the AS_PATH length."
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
John Gibson
Sent: Tuesday, July 10, 2007 1:41 PM
To: Jason Guy (jguy)
Cc: ccielab@groupstudy.com
Subject: RE: BGP path selection process, confederation peer's AS numbers
doesn't count toward AS path lengh right?
We are not talking about the same thing.
Yes, (65502) is stripped when going out of the big AS (the typically
registered).
But within the big AS, when a different confed receives "(65502)" , this
"(65502)" does not count toward "AS path length". My key emphasis is
"length" here.
My experiment has Path of "(65502) 200 i" and "100 i" of 2 routes
arriving at the router.
And I use always compare med.
When I change med (set metric) from outside the big AS, it effects path
selection. MED is lower ranked than AS path length. This means "(65502)
200 i" and "100 i" are considered of the same "As path length".
Mike Kraus says I am correct.
John
--- "Jason Guy (jguy)" <jguy@cisco.com> wrote:
> John,
>
> The AS-Path counts within the confederation. As soon as the prefix is
> advertised outside (to the real world) the confederation AS-path is
> stripped, and the global AS is prepended. Within the confederation,
> most of the same eBGP rules apply.
>
> The MED value can be set regardless of where the prefix is advertised
> (confed peer or other peer).
>
> Jason
>
>
> > -----Original Message-----
> > From: nobody@groupstudy.com
> [mailto:nobody@groupstudy.com] On Behalf Of
> > johngibson1541@yahoo.com
> > Sent: Tuesday, July 10, 2007 2:18 PM
> > To: ccielab@groupstudy.com
> > Subject: BGP path selection process, confederation
> peer's AS numbers
> > doesn't count toward AS path lengh right?
> >
> > I have tried to use MED to influence 2 routes
> >
> > one with "(65502)" confederation peer AS
> >
> > another without the confederation peer AS
> >
> > MED takes effect.
> >
> >
> > John
> >
> >
>
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