From: Joe Higgins (netsat@optonline.net)
Date: Sun Sep 22 2002 - 16:38:00 GMT-3
AS10 can do AS prepends but AS20 can change the default of AS path
length controlling route selection thereby negating AS 10s action. In
the final word the guy that is sending the route can always overrule the
guy that is receiving the routes as far as path selection is concerned.
Asim Khan wrote:
> thats fine, but the question here is AS20 wants to
> send its traffic through Link 2 and AS10 wants all
> traffic from AS20 comes through Link 1.
>
> --- "Steven A. Ridder" <saridder@attbi.com> wrote:
> > Incoming and outgoing traffic are treated
> > separately.
> >
> > -----Original Message-----
> > From: nobody@groupstudy.com
> > [mailto:nobody@groupstudy.com] On Behalf Of
> > Asim Khan
> > Sent: Sunday, September 22, 2002 11:59 AM
> > To: ccielab@groupstudy.com
> > Subject: Basic BGP decision process
> >
> >
> > Hi all,
> >
> > Suppose we have 4 routers Ra, Rb, Rc and Rd. Ra is
> > in
> > AS10 and Rb, Rc and Rd are in AS20 as shown below:
> >
> > AS10
> > | loopback 1.1.1.1/32
> > |
> > Ra
> > / \
> > Link 1 / \Link 2
> > -------------------------------
> > / \
> > Rc Rb
> > AS20 \ /
> > \ /
> > \ /
> > \ /
> > Rd
> > Now suppose the Administrator of AS20 wants all
> > outgoing traffic to take Link 2, so he set the local
> > preferance on Rb for incoming routes (1.1.1.1) from
> > Ra
> > as 200 and on Rc as 100(default). Rb,Rc and Rd are
> > in
> > full meshed. It means to reach 1.1.1.1 router Rd
> > will
> > take the path of Link 2. Now the administrator of
> > AS10
> > wants to influence the incoming traffic from AS20
> > and
> > force them to use Link 1. So he set the MED 5 for
> > all
> > the outgoing routes via Link 1 and the MED 10 for
> > all
> > the outgoing routes via Link 2.
> >
> > I know in BGP decision process local preference
> > comes
> > first then MED and in general BGP policies establish
> > after mutual consultation of both the Administrator.
> >
> >
> > But in this particular case, when both the
> > administrator are in complete disagreement, which
> > link
> > will be used for traffic going from AS20 to AS10.
> >
> > If Link 2 is used then is there any way for
> > Administrator of AS10 to force AS20 to use Link 1.
> >
> > Regards.
> >
> > Asim Khan
> >
> >
> >
> > __________________________________________________
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>
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