BGP Community - AS0 is de-facto "no-export-to" marker - Any ASN reserved to "export-only-to"?'

Tue Sep 8 16:22:16 UTC 2020

On 8/Sep/20 17:55, Douglas Fischer via NANOG wrote:

> Most of us have already used some BGP community policy to no-export
> some routes to some where.
>
> On the majority of IXPs, and most of the Transit Providers, the very
> common community tell to route-servers and routers "Please do
> no-export these routes to that ASN" is:
>
>  -> 0:<TargetASN>
>
> So we could say that this is a de-facto standard.
>
>
> But the Policy equivalent to "Please, export these routes only to that
> ASN" is very varied on all the IXPs or Transit Providers.
>
>
> With that said, now comes some questions:
>
> 1 - Beyond being a de-facto standard, there is any RFC, Public Policy,
> or something like that, that would define 0:<TargetASN> as
> "no-export-to" standard?
>
> 2 - What about reserving some 16-bits ASN to use
> <ExpOnlyTo>:<TargetASN> as "export-only-to" standard?
> 2.1 - Is important to be 16 bits, because with (RT) extended
> communities, any ASN on the planet could be the target of that policy.
> 2.2 - Would be interesting some mnemonic number like 1000 / 10000 or so.

The standard already exists... "NO_EXPORT". Provided ISP's or exchange
points can publish their own local values to match that within their
network, I believe they can do whatever they want, since it's
locally-significant.

I'm not sure we want to go down the trail of standardizing a "de facto"
usage. Just like QoS, it may be doomed as different operators define
what it means for them.

Mark.
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