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

Wed Sep 9 08:51:38 UTC 2020

I don’t think, anyone has proposed to use ‘’reserved ASNs” as a BCP, example of “ab”use of ASN0 is a de-facto artifact (unfortunate one).
My goal would be to provide a viable source of information to someone who is setting up a new ISP and has a very little clue as where to start. Do’s and don’t’s wrt inter-domain communities use. 

I really enjoyed the difference RFC7938 (Use of BGP for Routing in Large-Scale Data Centers) made, literally 100s of companies have used it to educate themselves/ implemented their DC networking.

Cheers,
Jeff

>> On Sep 9, 2020, at 10:04, adam via NANOG <nanog at nanog.org> wrote:
> 
> I don’t agree with the use of reserved ASNs, let alone making it BCP, cause it defeats the whole purpose of the community structure.
> Community is basically sending a message to an AS. If I want your specific AS to interpret the message I set it in format YOUR_ASN:<community value>, your AS in the first part of the community means that your rules of how to interpret the community value apply.
> Turning AS#0 or any other reserved AS# into a “broadcast-AS#” in terms of communities (or any other attribute for that matter) just doesn’t sit right with me (what’s next? multicast-ASNs that we can subscribe to?).
> All the examples in Robert’s draft or wide community RFC, all of them use an example AS# the community is addressed to (not some special reserved AS#).
>  
> Also should something like this become standard it needs to be properly standardized and implemented as a well-known community by most vendors (like RFCs defining the wide communities or addition to standard communities like no_export/no_advertise/…). This would also eliminate the adoption friction from operators rightly claiming “my AS my rules”.   
>  
> adam
>  
>  
> From: NANOG <nanog-bounces+adamv0025=netconsultings.com at nanog.org> On Behalf Of Douglas Fischer via NANOG
> Sent: Tuesday, September 8, 2020 4:56 PM
> To: NANOG <nanog at nanog.org>
> Subject: BGP Community - AS0 is de-facto "no-export-to" marker - Any ASN reserved to "export-only-to"?'
>  
> 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.
>  
> --
> Douglas Fernando Fischer
> Engº de Controle e Automação
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