Re: [Idr] BGP Attribute for Large communities (Attribute 30) was squatted on - Let's get a new attribute number (1 week WG call (10/18 to 10/25)

Nick Hilliard <nick@foobar.org> Tue, 18 October 2016 16:05 UTC

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Date: Tue, 18 Oct 2016 17:05:35 +0100
From: Nick Hilliard <nick@foobar.org>
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Cc: 'IETF IDR WG' <idr@ietf.org>, 'Kristian Larsson' <kll@dev.terastrm.net>
Subject: Re: [Idr] BGP Attribute for Large communities (Attribute 30) was squatted on - Let's get a new attribute number (1 week WG call (10/18 to 10/25)
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Susan Hares wrote:
> IDR should recommend that the following attribute numbers be deprecated:  
> 
> BGP Attribute 30
> BGP attribute 129

unless this is a temporary deprecation, I'm not sure if this is a good
idea, as it could be interpreted as sending a message to vendors that
squatting path attribute code points will result in being told, "that's
very naughty and we're going to punish you by ensuring that no-one else
gets these numbers, so don't do it again!"

There is an objective problem here, namely that there is no
vendor-specific range for path attributes.  Given the nature of path
attribute interpretation, it could be argued that this might be a good
thing because different vendors will interpret TLVs in different ways,
which is a potential source of bgp session instability.  On the other
hand, it means that if vendors need to go off and do something new,
there are no options other than squatting.  A vendor-specific range will
at least contain this problem, so that IANA won't run into the same
problem in future.

On a related issue, it would probably be a good idea to run beacon tests
with other path attributes to see how they affect reachability, i.e.
have any other vendors squatted any other path attribute values, and if
large-communities is moved to 31 or 32, will it suffer the same problem?

Nick