From: Song Mu (songmu@yahoo.com)
Date: Mon Sep 23 2002 - 17:05:37 GMT-3
I tried to use different ways to accomplish this, but none of them
seems working. These including change the local pref, metric, change
ibgp to ebgp, and distance. For some reasons, I have confused myself
because I can not get the best path from R2 even I shoutdown the
connection between R1 and R3.
Any ideas?
Song
--- Hongbing Qin <hqin@houston.sns.slb.com> wrote:
> Brian,
>
> When I reviewed this thread again, I find I still cannot figure out
> the
> solution if we exactly follow the original requirement.
>
> 1, Weight is not an option, because it should be configured on R3,
> not on R2.
>
> 2. Local preference is not an option, because you are not allowed to
> touch
> R3, and it's not possible to send Local Preference out.
>
> 3. AS-Path is not an option, because it should be configured on R1's
> neighbor to R3.
>
> 4. Origin code is not an option, because the route is already there.
>
> 5. MED is no an option because R3 get the route from R1 without
> Metric
> (NULL), so it's impossible for R2 to send lower metric to R3.
>
> 6. Obviously, R3 ebgp with R1, and ibgp with R2.
>
> Am I right here? Please correct me if I am wrong. Any help? Thanks.
>
> Best Regards,
>
> Hongbing Qin
>
> At 11:32 AM 8/25/2002 -0700, you wrote:
> >Thai,
> >
> > The BGP decision process is:
> >
> >Weight
> >Local-Preference/locally originated
> >AS-Path
> >Origin code
> >MED
> >EBGP over iBGP
> >Shortest internal path
> >Router-ID (lowest)
> >
> > Based on this decision process, the reason R3 is routing
> towards
> >R1 is the AS-PATH. Distance doesn't come into play until you try to
> >install the route in the routing table. BGP best-path selection
> >determines which path is best in the BGP table, not which appears in
> the
> >IP routing table.
> >
> > Based on this, it should be fairly obvious which attribute
> you
> >need to modify (I hope). If not, review Halabi's book or Doyle vol
> 2 to
> >see how these attributes function.
> >
> > For more info on BGP bestpath:
> >
> >http://www.cisco.com/warp/public/459/25.shtml
> >
> >
> >HTH
> >
> >Brian McGahan, CCIE #8593
> >Director of Design and Implementation
> >brian@cyscoexpert.com
> >
> >CyscoExpert Corporation
> >Internetwork Consulting & Training
> >http://www.cyscoexpert.com
> >Voice: 847.674.3392
> >Fax: 847.674.2625
> >
> >
> > > -----Original Message-----
> > > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On
> Behalf
> >Of
> > > Nguyen, Thai
> > > Sent: Tuesday, August 20, 2002 6:40 PM
> > > To: 'ccielab@groupstudy.com'
> > > Subject: BGP Challenge
> > >
> > > Hi all,
> > >
> > > I've been working on this little problem for few days but have
> not
> >been
> > > able
> > > to crack it.
> > > Can anyone shed light into this please?
> > >
> > >
> > >
> > > R1============R2
> > > = =
> > > = =
> > > = =
> > > = =
> > > ========R3
> > >
> > >
> > > R1 is in AS 1
> > > R2 and R3 is in AS2
> > >
> > >
> > > R1 is advertsing a subnet eg 1.1.1.0/24. Normally R3 will have to
> path
> >to
> > > the network, first via R1 directly and second via R2.
> > > And the preferred path is via R1 because the administrative
> distance
> >of
> > > the
> > > route learning from R1 is 20 while the route learned via R2 is
> 200.
> > >
> > > The challenge of the excercise is to configure R2 so that R3
> would
> > > prefered
> > > the route it learned from R2 without additional configuration on
> R3.
> > >
> > > regards
> > >
> > >
> > > Regards,
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > Australia Post is committed to providing our customers with
> excellent
> > > service. If we can assist you in any way please either telephone
> 13 13
> >18
> > > or visit our website www.auspost.com.au.
> > >
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> Hongbing Qin
> Consultant
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