Re: BGP Local Preference

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

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Received on Wed Sep 02 2009 - 12:50:19 ART