From: Brian McGahan (brian@cyscoexpert.com)
Date: Sun Nov 17 2002 - 23:22:45 GMT-3
David,
Administrative distance doesn't have anything to do with the BGP
best path selection process. The BGP best path selection determines
which prefix will be candidate to be installed in the IP routing table,
and will be propagated to other BGP neighbors. Administrative distance
determines which prefix is actually installed in the routing table if
you have multiple longest matches from multiple protocols.
The reason your router is not picking the iBGP learned prefix
over the EBGP learned prefix is most likely synchronization. Your iBGP
learned paths are not synchronized, and the synchronization rule does
not apply to EBGP neighbors. Next-hop reachability could also be the
issue, but I'm assuming you already have this due to IGP. Turn
synchronization off and see what happens.
AFAIK, there is no way to change the EBGP over iBGP selection
other than changing that actual peering session. For more information
on the selection process:
http://www.cisco.com/en/US/tech/tk648/tk365/technologies_tech_note09186a
0080094431.shtml
On a side note, Jennifer, distance can be changed using the
routing process command 'distance'. For more info on the distance
command:
http://www.groupstudy.com/archives/ccielab/200208/msg00909.html
HTH
Brian McGahan, CCIE #8593
Director of Design and Implementation
brian@cyscoexpert.com
CyscoExpert Corporation
Internetwork Consulting & Training
Voice: 847.674.3392
Fax: 847.674.2625
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> Jennifer Bellucci
> Sent: Sunday, November 17, 2002 6:58 PM
> To: Giveortake@aol.com; ccielab@groupstudy.com
> Subject: Re: BGP path selection
>
> I read somewhere that it is now possible to change the AD for a given
> route
> by using route-maps or some other filtering tech
>
> Someone correct me
> ----- Original Message -----
> From: <Giveortake@aol.com>
> To: <ccielab@groupstudy.com>
> Sent: Monday, November 18, 2002 12:23 AM
> Subject: BGP path selection
>
>
> > I am trying to make my router select a path from an IBGP peer over
the
> same
> > path from an EBGP peer. In my demo scenerio, I can not use "no
synch"
> I
> > have tried adjusting the meds, local pref, and weights, but
apparently
> the
> > Admin distance of 20 will always take precidence. Any suggestions?
> Please
> > only answer if certain!
> >
> > output from router is as follows
> >
> > 200.0.0.2/32 150.50.17.2 0 0 100 ?
> > * i 150.50.78.7 75 100 0 100 ?
> > *> 200.0.0.4/32 150.50.17.2 65 0 100 ?
> > * i 150.50.78.7 139 100 0 100 ?
> > *> 200.0.0.5/32 150.50.17.2 65 0 100 ?
> > * i 150.50.78.7 11 100 200 100 ?
> > *> 200.0.0.6/32 150.50.17.2 65 0 100 ?
> > * i 150.50.78.7 11 100 0 100 ?
> > *> 200.0.0.7/32 150.50.17.2 75 0 100 ?
> > * i 150.50.78.7 0 100 200 100 ?
> >
> > Thank You,
> >
> > David
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