Re: MPLS VPN Design and BGP SoO

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
>>
>>
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>
>
> --
> Thanks & Regards,
> Gaurav Thukral

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Received on Mon Oct 08 2012 - 01:54:13 ART