Re: [netmod] Deviations and augmentations

Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de> Tue, 13 November 2018 17:06 UTC

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Date: Tue, 13 Nov 2018 18:06:52 +0100
From: Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de>
To: Robert Wilton <rwilton@cisco.com>
CC: Andy Bierman <andy@yumaworks.com>, "netmod@ietf.org" <netmod@ietf.org>
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Subject: Re: [netmod] Deviations and augmentations
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On Tue, Nov 13, 2018 at 03:54:11PM +0000, Robert Wilton wrote:

> Today, just using the status element alone to mark removed nodes means that
> a client would have to check for all changes in the module between two
> revisions to determine whether or not the new module revision is backwards
> compatible with the old one.

A client needs to know whether it is _affected_ by changes. This
requires to match what is used by a client against what has been
changed (including any changed deviations). A three digit number
simply does not tell you that.

<soap>
Corner cases:

- An implementation claims to support the latest semver but then
  deviates things back to an earlier version.

- An implementation claims to support an earlier semver but then
  deviates things forward to a more recent version.

Of course, nobody would do that...
</soap>

My point is that semver is _at best_ a hint whether there is a version
mismatch potentially affecting a client. It is not sufficient to
determine whether there is indeed a problem.

In other words, robust automation requires to match what is used by a
client against what has been updated (taking deviations into account
during the comparison).

/js

-- 
Juergen Schoenwaelder           Jacobs University Bremen gGmbH
Phone: +49 421 200 3587         Campus Ring 1 | 28759 Bremen | Germany
Fax:   +49 421 200 3103         <https://www.jacobs-university.de/>