In message <20160809232819.1291.qmail@xxxxxxx>, "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@xxxxxxx