Re: MPLS VPN Design and BGP SoO

Hi Keller,

You are right on this..To make it plain & simple:
1)In regular scenarios where different ASN numbers are used for the
customers,BGP uses AS_PATH for loop prevention thus there is no point of
using BGP SOO or any form of community to do the ftilering as AS_PATH
automatically takes care of it.
2)When you are using the same ASN on customer sites, then BGP AS_PATH will
not be used for filtering. Thus, BGP SOO or any other community can be used
to tag/filter routes.

Thank You

On Mon, Oct 8, 2012 at 10:25 AM, Keller Giacomarro <keller.g_at_gmail.com>wrote:

> Hi Karim,
>
> That supports what I was thinking -- the only time you would ever need to
> use BGP SoO is when you have multiple sites using the same BGP ASN and some
> of them are multihomed. In that case, you would have to do either
> 'as-override' or 'allowas-in', but you wouldn't want to have routes enter
> via one PE and then get re-advertised via the other PE. So, we use SoO to
> prevent these looping updates from being re-accepted into the
> originally-advertising site.
>
> Is that about right?
>
> Keller Giacomarro
> keller.g_at_gmail.com
>
>
>
> On Mon, Oct 8, 2012 at 2:22 AM, Karim Jamali <karim.jamali_at_gmail.com>wrote:
>
>> Hi Keller,
>>
>> The only scenario I have came across is suppose you have two sites one is
>> dual homed to two PE routers and another site connected to a third PE
>> within an MPLS VPN using the same AS. When you use as-override for instance
>> routes can be propagated between sites. Thus we have a problem that a route
>> originated within site 1 can go to PE1 to PE2 which will do the as-override
>> and send it CE2 within the same site. Thus the BGP SOO or any community can
>> be used to filter this behavior.
>>
>> Thanks
>> On Oct 8, 2012 10:11 AM, "Gaurav Thukral" <pearlgaurav_at_gmail.com> wrote:
>>
>>> Hi Keller
>>>
>>> It's my fault. Let me go through the requirement.
>>>
>>> Thanks
>>> Gaurav
>>>
>>> On Mon, Oct 8, 2012 at 12:24 PM, Keller Giacomarro <keller.g_at_gmail.com
>>> >wrote:
>>>
>>> > Hi Gaurav,
>>> >
>>> > I have read through that doc, and it addresses EIGRP SoO only. My
>>> > questions are specifically about BGP SoO.
>>> >
>>> > Keller Giacomarro
>>> > keller.g_at_gmail.com
>>> >
>>> >
>>> >
>>> > On Mon, Oct 8, 2012 at 1:48 AM, Gaurav Thukral <pearlgaurav_at_gmail.com
>>> >wrote:
>>> >
>>> >> Hi
>>> >>
>>> >> Kindly go through the below doc.
>>> >>
>>> >>
>>> >>
>>> http://blog.ine.com/wp-content/uploads/2010/04/understanding-eigrp-soo-bgp-cost-community.pdf
>>> >>
>>> >> Thanks
>>> >> Gaurav
>>> >>
>>> >> On Mon, Oct 8, 2012 at 9:48 AM, Keller Giacomarro <keller.g_at_gmail.com
>>> >wrote:
>>> >>
>>> >>> I am having issues understanding when to use SoO where. These are
>>> the
>>> >>> scenarios I can think of where we'd be using BGP as the IGP and would
>>> >>> consider the use of some of these more advanced BGP multi-homing
>>> >>> features...
>>> >>>
>>> >>> Two sites, different ASNs, no backdoor link
>>> >>> - no special config needed
>>> >>>
>>> >>> Two sites, same ASN, no backdoor link
>>> >>> - use either allowas-in or as-override to allow the sites to accept
>>> >>> routes
>>> >>> from each other
>>> >>> - if any of the site are multi-homed, use SoO to keep the routes from
>>> >>> circling back into the same site via the other PE
>>> >>>
>>> >>> Two sites, different ASNs, with backdoor (backup-only) link
>>> >>> - peer the backdoor CE routers via eBGP and prepend to prefer the
>>> MPLS
>>> >>> link
>>> >>>
>>> >>> Two sites, same ASN, with backdoor (backup-only) link
>>> >>> - ???
>>> >>>
>>> >>> One site, one ASN, multiple MPLS exit points, with intra-site active
>>> >>> (non-backup) links
>>> >>> - no special config needed, but MPLS cannot be used if the internal
>>> site
>>> >>> becomes segmented (due to AS_PATH loop prevention)
>>> >>>
>>> >>> First, are the above designs correct?
>>> >>>
>>> >>> And second, what is the proper way to setup "Two sites, same ASN,
>>> with
>>> >>> backdoor (backup-only) link"? I put it into GNS3, and I can't get
>>> the
>>> >>> traffic to prefer the MPLS backbone instead of the backup (iBGP)
>>> link.
>>> >>> The
>>> >>> PE routers both prefer the eBGP link towards the internal network,
>>> and
>>> >>> neither will accept the (preferred) iBGP ad from their peer PE
>>> router.
>>> >>> It
>>> >>> works fine going the reverse -- backup link works great, and if the
>>> >>> backup
>>> >>> link goes down the MPLS core is used.
>>> >>>
>>> >>> The only way I can figure to get the desired "MPLS primary, backdoor
>>> link
>>> >>> is backup" behavior is to do some kludge between the CE routers so
>>> that
>>> >>> they only advertise the routes to each other if the MPLS network is
>>> down.
>>> >>>
>>> >>> Is the only time you want to use BGP SoO when all your sites are on
>>> the
>>> >>> same AS (forcing allowas-in or as-override), and some are multihomed?
>>> >>> Otherwise, won't BGP AS_PATH loop prevention prevent the looping?
>>> >>>
>>> >>> Very confused, appreciate your input!
>>> >>>
>>> >>> Keller Giacomarro
>>> >>> keller.g_at_gmail.com
>>> >>>
>>> >>>
>>> >>> Blogs and organic groups at http://www.ccie.net
>>> >>>
>>> >>>
>>> _______________________________________________________________________
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>>> >>>
>>> >>>
>>> >>>
>>> >>>
>>> >>>
>>> >>>
>>> >>>
>>> >>
>>> >>
>>> >> --
>>> >> Thanks & Regards,
>>> >> Gaurav Thukral
>>> >>
>>> >>
>>> >>
>>> >>
>>> >>
>>> >>
>>> >>
>>> >
>>>
>>>
>>> --
>>> Thanks & Regards,
>>> Gaurav Thukral
>>>
>>>
>>> Blogs and organic groups at http://www.ccie.net
>>>
>>> _______________________________________________________________________
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>>> http://www.groupstudy.com/list/CCIELab.html
>>>
>>>
>>>
>>>
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>>>
>>>
>

-- 
KJ
Blogs and organic groups at http://www.ccie.net