Re: New Version Notification for draft-leiba-rfc2119-update-00.txt

Mark Andrews <marka@isc.org> Tue, 09 August 2016 23:59 UTC

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To: "John Levine" <johnl@taugh.com>
From: Mark Andrews <marka@isc.org>
References: <20160809232819.1291.qmail@ary.lan>
Subject: Re: New Version Notification for draft-leiba-rfc2119-update-00.txt
In-reply-to: Your message of "09 Aug 2016 23:28:19 +0000." <20160809232819.1291.qmail@ary.lan>
Date: Wed, 10 Aug 2016 09:58:53 +1000
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In message <20160809232819.1291.qmail@ary.lan>an>, "John Levine" writes:
> >Obviously, taste and correctness matter.
> >It still won't be a good idea to say "The reserved bit must be zero on
> >send and must be ignored on receive," arguing "Well, we don't want to
> >use MUST because some implementations don't do that so it can't be
> >normative."
> 
> I'd write "The reserved bit is set to zero on send and is ignored on
> receive" and save the command terms for things where one might think
> that there was a reason to do something else.

RFC2671/RFC6891 has

   Z
      Set to zero by senders and ignored by receivers, unless modified
      in a subsequent specification.

which resulted in 2% of deployed nameservers just copying reserved
bits to the reply or 3% of nameservers not answering because a
reserved bit is set.

https://ednscomp.isc.org/compliance/ts/alexa.flagsfail.html

A bit more emphasis may have changed the result.

At least the TLD servers no longer copy the reserved bits.  The
last server doing that was just upgraded a week or so ago.

https://ednscomp.isc.org/compliance/ts/tld.flagsfail.html

Mark

> >The point of lower case keywords shouldn't be to allow people to be
> >sloppy and to avoid normative text to make a false consensus easier.
> >This SHOULD be about writing clearer RFCs and not having to contort
> >language when should and must are perfectly good non-normative things to
> >say.
> 
> Yup.
> 
> R's,
> John
> 
-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka@isc.org