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draft-bradner-key-words-02.txt --> rfc2119.txt
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Network Working Group                                         S. Bradner
Internet-Draft
Request for Comments: 2119                            Harvard University
                                                             August 1996
BCP: 14                                                       March 1997
Category: Best Current Practice


        Key words for use in RFCs to Indicate Requirement Levels


                    <draft-bradner-key-words-02.txt>

Status of this Memo

   This document is specifies an Internet-Draft. Internet-Drafts are working
   documents of Internet Best Current Practices for the
   Internet Engineering Task Force (IETF), its areas, Community, and its Working Groups. Note that other groups may also distribute
   working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid requests discussion and suggestions for a maximum
   improvements.  Distribution of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time. It this memo is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as ``work in progress.''

   To learn the current status of any Internet-Draft, please check the
   1id-abstracts.txt listing contained in the Internet-Drafts Shadow
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   ftp.isi.edu (US West Coast). unlimited.

Abstract

   In many standards track documents several words are used to signify
   the requirements in the specification.  These words are often
   capitalized.  This document defines these words as they should be
   interpreted in IETF documents.  Authors who follow these guidelines
   should incorporate this phrase near the beginning of their document:

      The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
      NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and
      "OPTIONAL" in this document are to be interpreted as described in
      RFC 2119.

   Note that the force of these words is modified by the requirement
   level of the document in which they are used.

1. MUST   This word, or the adjectives terms "REQUIRED" or "SHALL", means mean that the
   definition is an absolute requirement of the specification.

2. MUST NOT   This phrase, or the phrase "SHALL NOT", means mean that the
   definition is an absolute prohibition of the specification.

3. SHOULD   This word, or the adjective "RECOMMENDED", means mean that there
   may exist valid reasons in particular circumstances to ignore a
   particular item, but the full implications must be understood and
   carefully weighed before choosing a different course.

4. SHOULD NOT   This phrase, or the phrase means "NOT RECOMMENDED" mean that
   there may exist valid reasons in particular circumstances when the
   particular behavior is acceptable



Bradner                                                         [Page 1]

Internet-Draft                RFC Key Words                  August 1996 or even useful, but the full
   implications should be understood and the case carefully weighed
   before implementing any behavior described with this label.





Bradner                  Best Current Practice                  [Page 1]

RFC 2119                     RFC Key Words                    March 1997


5. MAY   This word, or the adjective "OPTIONAL", means mean that an item is
   truly optional.  One vendor may choose to include the item because a
   particular marketplace requires it or because the vendor feels that
   it enhances the product while another vendor may omit the same item.
   An implementation which does not include a particular option MUST be
   prepared to interoperate with another implementation which does
   include the option, though perhaps with reduced functionality. In the
   same vein an implementation which does include a particular option
   MUST be prepared to interoperate with another implementation which
   does not include the option.(except, option (except, of course, for the feature the
   option provides) provides.)

6. Guidance in the use of these Imperatives

   Imperatives of the type defined in this memo must be used with care
   and sparingly.  In particular, they must MUST only be used where it is
   actually required for interoperation or to limit behavior which has
   potential for causing harm (e.g., limiting retransmisssions)  For
   example, they must not be used to try to impose a particular method
   on implementors where the method is not required for
   interoperability.

6.

7. Security Considerations

   These terms are frequently used to specify options or behavior in a
   way that can effect with security risks.  Careful consideration should
   implications.  The effects on security of not implementing a MUST or
   SHOULD, or doing something the specification says MUST NOT or SHOULD
   NOT be
   taken done may be very subtle. Document authors should take the time
   to understand elaborate the security implications of any use not following
   recommendations or requirements as most implementors will not have
   had the benefit of these
   imperatives.

7. the experience and discussion that produced the
   specification.

8. Acknowledgments

   The definitions of these terms are an amalgam of definitions taken
   from a number of RFCs.  In addition, suggestions have been
   incorporated from a number of people including Robert Ullmann, Thomas
   Narten, Neal McBurnett, and Robert Elz.

   8.












Bradner                  Best Current Practice                  [Page 2]

RFC 2119                     RFC Key Words                    March 1997


9. Author's Address

      Scott Bradner
      Harvard University
      1350 Mass. Ave.
      Cambridge, MA 02138

      phone - +1 617 495 3864

      email - sob@harvard.edu









































Bradner                                                         [Page 2]

Internet-Draft                RFC Key Words                  August 1996





















































Bradner                  Best Current Practice                  [Page 3]

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