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

[Owen DeLong <owen () delong com>]

> On Sep 8, 2020, at 9:22 AM, Mark Tinka via NANOG <nanog () nanog org> wrote:
>
>
>
> 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.

To the extent that communities are standardized, they’re supposed to be ASN:Community, so 0:<TargetASN> seems like a 
bad convention to begin with.

Further, many of the things people claim they want from odd-ball techniques trying to cram things into 32-bit 
communities are actually standardized and easily implemented (without hackery) using either Extended Communities, or 
Large Communities, with the advantage that you can also accommodate 4-octet ASNs without stupid router tricks.

Please consider looking at existing standards before making up new ones.

Thanks,

Owen