Re: BGP "Allowas-in" -- scenarios to use this?

Hi David -

Typically you would have a need to use this knob if you have multiple
remote-sites connected to a providers MPLS VPN network and each of the
remote-sites are configured with non-unique BGP ASN's.

Using this knob would allow your remote-sites to accept updates that have
the same ASN in the as-path, otherwise eBGPs loop prevention mechanism would
drop the update and although your announcements from each remote-site would
be propagated throughout the VPN you would not have site-to-site
connectivity from the perspective of your CE devices.

Typically, the service-provider (at least the one I work for) will have
as-override configured to allow for this type of design whereby all of your
remote-sites have non-unique ASN's and will replace the non-unique ASN with
the provider's own ASN outbound towards the CE
On Tue, Aug 18, 2009 at 7:25 AM, David Swafford <david_at_davidswafford.com>wrote:

> Hi Groupstudy List--
>
> While learning the ins and outs of BGP I've come across something I'm
> a bit fuzzy on--
>
> In BGP we have this configuration option under the neighbor
> configuration of "allowas-in" which defeats BGP's loop prevention
> mechanism and allows the programmed router to accept routes that
> already contain it's own AS in the AS PATH list. Does anyone actually
> implement this in their production environment? I'm interested to
> know what kind of scenarios would require this.
>
> Thanks,
> David Swafford.
>
>
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Received on Wed Aug 19 2009 - 20:03:27 ART