Re: BGP Local Preference

As long as its within your AS, you can do in or out bound.

On Wed, Sep 2, 2009 at 8:54 AM, groupstudy <groupstudy_at_gmail.com> wrote:

> Thanks Joe. I thought Local Preference was not exportable.
>
> I suppose you would just configure the same type of route setting the local
> preference and apply outbound to the peer?
>
> Thanks
>
>
>
> On Wed, Sep 2, 2009 at 11:23 AM, Joe Astorino <jastorino_at_ipexpert.com
> >wrote:
>
> > Hello there!
> >
> > Looks like you have the right idea here for the most part. You are right
> > -- Local Preference influences decisions in your own AS with the highest
> LP
> > winning the battle. AS Prepending is a good way to influence how traffic
> > comes BACK to you. However, highest LP beats shortest AS-Path so if the
> > remote-AS has a higher LP for a particular route it will select that path
> > first.
> >
> > The one thing I did want to clear up is that you can send
> local-preference
> > to an eBGP neighbor if you want to.
> >
> > On Wed, Sep 2, 2009 at 10:37 AM, groupstudy <groupstudy_at_gmail.com>
> wrote:
> >
> >> Hi,
> >>
> >> I have a question on local preference I'm sure someone in this group can
> >> clear up for me.
> >>
> >> My understanding of Local Preference and how I've always used it is that
> >> is
> >> used to influence path selection within a particular AS
> >>
> >> I have a situation where I am trying to influence the way traffic comes
> >> back
> >> to my network that I am advertising out to two different ASs. At the
> same
> >> time I am using Local Preference to influence path selection within my
> own
> >> AS (the higher the local preference the more preferred). For path 1
> (ASN
> >> 2)
> >> I am advertising my network without any manipulation and for routes
> >> learned
> >> via Path 1, I have set the local preference to 200. For Path 2 (ASN 3),
> I
> >> am advertising my network with my local AS (ASN 1) prepended 3 times and
> >> for
> >> routes learned from Path 2 I have set the local preference to 150. This
> >> results in traffic leaving and arriving via Path 1.
> >>
> >> Again, This is the way I have always understood it and done it and I
> >> believe
> >> this to be correct.
> >>
> >> Just for completeness, ASN 2 and ASN 3 have a peering to another AS, ASN
> >> 5.
> >> A router within ASN 3 learns of my network from AS 5 as well as from ASN
> >> 1.
> >> If a site attached to this router needs to get to my location, would it
> >> select the path through AS5 becasue the path is shorter (AS5 learns my
> >> network from AS 2 which i am advertising to it without any
> manipulation),
> >> or
> >> would it select the path through its own AS3 if the Local Preference is
> >> higher within its own AS3?
> >>
> >> I am being told AS prepending may not always work because the local
> >> preference within ASN 3 would override the path length if it was higher.
> >>
> >> My understanding is that Local Preference only matters within one AS
> (not
> >> exported).
> >>
> >> Any help in clearing this up would be greatly appreciated.
> >>
> >> Thanks!
> >> S
> >>
> >>
> >> Blogs and organic groups at http://www.ccie.net
> >>
> >> _______________________________________________________________________
> >> Subscription information may be found at:
> >> http://www.groupstudy.com/list/CCIELab.html
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >
> >
> > --
> > Regards,
> >
> > Joe Astorino - CCIE #24347 R&S
> > Technical Instructor - IPexpert, Inc.
> > Cell: +1.586.212.6107
> > Fax: +1.810.454.0130
> > Mailto: jastorino_at_ipexpert.com
>
>
> Blogs and organic groups at http://www.ccie.net
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
>
>
>
>
>
>
>
>

-- 
Narbik Kocharians
CCSI#30832, CCIE# 12410 (R&S, SP, Security)
www.MicronicsTraining.com
Sr. Technical Instructor
Blogs and organic groups at http://www.ccie.net