Re: BGP Local Preference

Remember that you tag your prefixes with a given community and send it to
the other AS, now you did not send Local-Pref to the other AS, just the tag.
The router in the other AS, matches on the community tag and sets the local
pref. Like these guys are saying, Local-Pref is within your AS and can not
be given to another router in another AS.

On Wed, Sep 2, 2009 at 9:50 AM, groupstudy <groupstudy_at_gmail.com> wrote:

> That's what I thought about local preferences. I am being told now about
> the communities to set the local preference:
>
> set community 174:70 3356:70 additive
>
> What do you guys think about this?
>
> Thanks,
> danny
>
> On Wed, Sep 2, 2009 at 12:09 PM, Ryan West <rwest_at_zyedge.com> wrote:
>
> > Local pref on a upstream peer can be set via communities. This is a
> pretty
> > typical configuration as well. Local preference is only considered
> within
> > your own AS or confederation, but never sent to external BGP peers.
> >
> > Here is an example page for UUNET, I mean Worldcom, I mean Verizon :)
> >
> > http://www.onesc.net/communities/as701/
> >
> > -ryan
> >
> > -----Original Message-----
> > From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of
> > Joe Astorino
> > Sent: Wednesday, September 02, 2009 11:58 AM
> > To: groupstudy
> > Cc: ccielab_at_groupstudy.com
> > Subject: Re: BGP Local Preference
> >
> > Yes, you could do that. Now weather the other end cares about it is
> > another
> > story :P Some ISPs will allow you to set local preference on things to
> > influence routing, some will not.
> >
> > On Wed, Sep 2, 2009 at 11:54 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
> > >>
> > >
> > >
> >
> >
> > --
> > 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
>
>
> 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