Re: MPLS VPN Design and BGP SoO

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