Re: BGP Local Preference

Thanks Fellas!

I got it now.

S

On Wed, Sep 2, 2009 at 1:13 PM, Joe Astorino <jastorino_at_ipexpert.com> wrote:

> 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
Received on Wed Sep 02 2009 - 13:21:03 ART