Re: MPLS VPN Design and BGP SoO

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

-- 
Thanks & Regards,
Gaurav Thukral
Blogs and organic groups at http://www.ccie.net