Re: BGP Local Preference

As long as Cogent and Savvis know what that community value happens to
be, and as long as it's their policy to set local pref based on it, then
yes it'll work fine!

The community values are interpreted based on receiving group's
policies. Other than the well-known ones defined by RFC.

By the way, don't forget to send-community to your neighbor! :)

HTH,

*Scott Morris*, CCIE/x4/ (R&S/ISP-Dial/Security/Service Provider) #4713,

JNCIE-M #153, JNCIS-ER, CISSP, et al.

JNCI-M, JNCI-ER

evil_at_ine.com

Internetwork Expert, Inc.

http://www.InternetworkExpert.com

Toll Free: 877-224-8987

Outside US: 775-826-4344

Knowledge is power.

Power corrupts.

Study hard and be Eeeeviiiil......

groupstudy 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

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Received on Wed Sep 02 2009 - 14:06:22 ART