Re: SHOULD and RECOMMENDED

On 6/24/2013 8:39 AM, John C Klensin wrote:
> --On Monday, June 24, 2013 07:52 -0400 Phillip Hallam-Baker
> <hallam(_at_)gmail(_dot_)com> wrote:
>
> > They are not synonyms
> >
> > Lets go back to 1980:
> >
> > Implementations SHOULD support DES
> > vs
> > RECOMMENDED encryption algorithms: DES, IDEA
> Actually, that is the point.  The usage above, although much
> earlier, reflects the Protocol Specification/ Applicability
> Statement split rather well.
>
> But 2119's language makes the two terms substitutable for and
> equivalent to each other, which is about as close a definition
> of "synonyms" as one can find.  What I said is that making them
> equivalent was probably a mistake and that treating them that
> was should be discouraged. Others expressed agreement with that
> assessment.
>
> Personally, I don't think the problem is severe enough to reopen
> 2119.  If others disagree and believe that 2119 is generating
> enough problems to be worth an update, I await a draft.
>
> So, other than quibbling about the "synonym" issue -- not
> generally, which no one has claimed, but in context with 2119--
> are you disagreeing and, if so, about what?
>
>     john
In my view, a SHOULD is just a highly RECOMMENDED mode of operation, the 
preferred mode, the mode that SHOULD be enabled out of the box.
The conflicts I see is whether the usage of a SHOULD means it really is 
a MUST be implemented as described and the exception is when there is no 
other alternative available. A common reference is use EHLO first, 
fallback to HELO.
What is often forgotten is the ON/OFF configuration aspect. So even if 
there is a MUST implement SHOULD thinking, the question is whether there 
is an allowance to disable or turn off the feature, i.e. can an SMTP 
server disable EHLO and operate in pure RFC821 (STD10) mode?  The answer 
to the question is yes, its possible, and therefore all implementations 
MUST be ready in operate in SMTP (821) mode FIRST, ESMTP mode second.
I think the dilemma is that we have new integration needs and in some 
cases, one protocol or set of integrated protocols simple works better 
when a traditional optional technology i.e. SMTP extension, is used. So 
there is a mindset, it seems, a SHOULD is really a MUST and only under 
extreme situations,  the alternative can be used, if presented.
--
HLS