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@xxxxxxx> wrote: > > > --On Monday, June 24, 2013 16:28 -0400 Alia Atlas > <akatlas@xxxxxxxxx> 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 > >