Subject: Re: [Idr] draft-ietf-idr-reserved-extended-communities

From: Jeffrey Haas <[email-masked]>
Date: Sun, 11 Mar 2012 15:22:30 -0400

Bruno,

On Wed, Feb 22, 2012 at 11:05:59AM +0000, [email-masked] wrote:
> As a reminder, draft-ietf-idr-reserved-extended-communities currently proposes to use the AS number O to get a global space of "generic four-octet AS specific" extended community (as defined in draft-ietf-idr-as4octet-extcomm-generic-subtype) in order to be able to get IANA assigned extended communities values from. (i.e. the equivalent of formerly "well known" RFC 1997 communities).
> 
> Following some discussion on draft-ietf-idr-as0, another option is to use AS number 0x0000FFFF instead of AS 0. This seems also more in line with RFC 1997 which use the same AS number (0xFFFF) for the same purpose (IANA assigned communities).

I think using AS 0.65535 (as-dot notation) is probably reasonable given the
semantics you are looking for.

After spending some additional time thinking about your draft, I believe
that the primary desired behavior is to add the ability to create
non-transitive well-known communities.  Since transitive well-known
communities are easiest (and most backward-compatible at the moment) to
express as RFC 1997 4-byte communities I would make the following
suggestion:

- Recommend that IANA set aside the 0.65535 4-byte AS name space using
  draft-ietf-idr-as4octet-extcomm-generic-subtype.
- Recommend that only non-transitive types are registered in the above
  registry.
- Recommend that when a transitive well-known community is registered in the
  IANA RFC 1997 community that, when appropriate, a non-transitive version
  of the community be made similarly available in the new registry.

The above captures the spirit of backward compatibility in
draft-ietf-idr-as4octet-extcomm-generic-subtype:

:   Therefore, for backward compatibility with existing deployments and
:   to avoid inconsistencies between standard communities and 4-octet
:   extended communities, Autonomous Systems that use 2-octet Autonomous
:   System numbers SHOULD use standard 2-octet communities as defined in
:   RFC1997 rather than the 4-octet AS specific extended community as
:   defined in this document.

-- Jeff (not officially speaking for the other as4octet authors, but
probably capturing the spirit of our discussion)