Re: [Anima] [saag] towards using of MUST-/SHOULD+/SHOULD- in draft-ietf-autonomic-control-plane-24

Nico Williams <> Sat, 27 June 2020 03:06 UTC

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Date: Fri, 26 Jun 2020 22:06:24 -0500
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From: Nico Williams <>
To: Michael Richardson <>
Cc: Russ Housley <>, Toerless Eckert <>,, Ben Kaduk <>,
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Subject: Re: [Anima] [saag] towards using of MUST-/SHOULD+/SHOULD- in draft-ietf-autonomic-control-plane-24
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On Fri, Jun 26, 2020 at 09:15:19PM -0400, Michael Richardson wrote:
> 1) So, BCPs can point to multiple documents.
>    BCP14 actually is RFC2119 and RFC8174 now, so we can add a third document if
>    desired. That is, it's cheaper to not spin 2119.

Sure.  Plus, RFC2119 is iconic, and used far and wide outside the IETF.

> 2) I'm not claiming others won't use it, I just don't know if they will.
>    Crypto progresses... what other things do that in the same way?

Any time we have a migration from one [sub]protocol to a newer one and
need to retain support for the old one for a while, we will need
something like SHOULD-.  I agree this comes up most often in the context
of cryptographic algorithms.