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

[adam via NANOG <nanog () nanog org>]

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 () nanog org> On Behalf Of Douglas Fischer via NANOG
Sent: Tuesday, September 8, 2020 4:56 PM
To: NANOG <nanog () 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