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Re: SHOULD and RECOMMENDED

"Bradner, Scott" <sob@harvard.edu> Mon, 24 June 2013 21:03 UTC

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From: "Bradner, Scott" <sob@harvard.edu>
To: IETF Discussion Mailing List <ietf@ietf.org>
Subject: Re: SHOULD and RECOMMENDED
Thread-Topic: SHOULD and RECOMMENDED
Thread-Index: AQHOcR4ucoJQiU61AE60u3/tDt4UZQ==
Date: Mon, 24 Jun 2013 21:02:48 +0000
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while I like to take credit for the good things in RFC 2119 (and disclaim the bad things) - the
term RECOMMENDED (good or bad)  comes from RFC 1122 

basically I copied the definition section from RFC 1122 for the 1st version of what became RFC 2119.
(see http://www.sobco.com/ids/draft-bradner-key-words-00.txt) 

based on mailing list discussion I produced two revisions of the ID (mostly to add guidance on usage)
http://www.sobco.com/ids/draft-bradner-key-words-01.txt
and
http://www.sobco.com/ids/draft-bradner-key-words-02.txt

the 02 version is what was approved by the IESG as RFC 2119

all of the above is to say that I can not help in this discussion about the difference between SHOULD & 
RECOMMENDED other than the fact they represent  different parts of speech

maybe Bob Braden has an idea since I do find  not a usage of RECOMMENDED in the RFC series before RFC 1122

Scott

On Jun 24, 2013, at 4:38 PM, John C Klensin <john-ietf@jck.com> wrote:

> 
> 
> --On Monday, June 24, 2013 16:28 -0400 Alia Atlas
> <akatlas@gmail.com> wrote:
> 
>> I read SHOULD and RECOMMENDED as different.
>> 
>> SHOULD is how a implementation ought to behave unless there
>> are special circumstances (deployment, additional
>> functionality, better idea).  MUST says that there are no
>> circumstances special enough to change the behavior.
>> 
>> RECOMMENDED is closer to a Best Current Practice (BCP); so I
>> might write "It is RECOMMENDED that the network-converged
>> timer have a minimum value of 2 seconds."  but in 10 years,
>> maybe it'll only take 2 microseconds - so that'll become a bad
>> recommendation!
> 
> And that, again, is close to the distinction that a reasonable
> person might read into 2026.  But not into 2119 which appears
> (at least to me) to make them fully-substitutable alternatives.
> 
> The distinction doesn't make the comments made by Peter, Dave,
> or others any less valid.  If we told ourselves that readers
> should (lower case) infer conformance statements from SHOULD and
> applicability ones from RECOMMENDED... well, we would be pretty
> delusional.
> 
>   john
> 
>

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