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.
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Douglas Fernando Fischer
Engº de Controle e Automação