Re: BGP Local Preference

Precisely!!! (Doc Brown voice and bugged out eyes)

On Wed, Sep 2, 2009 at 1:10 PM, Narbik Kocharians <narbikk_at_gmail.com> wrote:

> 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
>

-- 
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