Re: MPLS VPN Design and BGP SoO

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
> >>>
> >>>
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> >>>
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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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Received on Mon Oct 08 2012 - 10:22:10 ART