GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:bcp:bcp14

[Note that this file is a concatenation of more than one RFC.]

Network Working Group S. Bradner Request for Comments: 2119 Harvard University BCP: 14 March 1997 Category: Best Current Practice

      Key words for use in RFCs to Indicate Requirement Levels

Status of this Memo

 This document specifies an Internet Best Current Practices for the
 Internet Community, and requests discussion and suggestions for
 improvements.  Distribution of this memo is 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 terms "REQUIRED" or "SHALL", mean that the

 definition is an absolute requirement of the specification.

2. MUST NOT This phrase, or the phrase "SHALL NOT", mean that the

 definition is an absolute prohibition of the specification.

3. SHOULD This word, or the adjective "RECOMMENDED", 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 "NOT RECOMMENDED" mean that

 there may exist valid reasons in particular circumstances when the
 particular behavior is acceptable 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", 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, of course, for the feature the
 option 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 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.

7. Security Considerations

 These terms are frequently used to specify behavior with security
 implications.  The effects on security of not implementing a MUST or
 SHOULD, or doing something the specification says MUST NOT or SHOULD
 NOT be done may be very subtle. Document authors should take the time
 to elaborate the security implications of not following
 recommendations or requirements as most implementors will not have
 had the benefit of 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.

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 Best Current Practice [Page 3]

Internet Engineering Task Force (IETF) B. Leiba Request for Comments: 8174 Huawei Technologies BCP: 14 May 2017 Updates: 2119 Category: Best Current Practice ISSN: 2070-1721

     Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words

Abstract

 RFC 2119 specifies common key words that may be used in protocol
 specifications.  This document aims to reduce the ambiguity by
 clarifying that only UPPERCASE usage of the key words have the
 defined special meanings.

Status of This Memo

 This memo documents an Internet Best Current Practice.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 BCPs is available in Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc8174.

Leiba Best Current Practice [Page 1] RFC 8174 RFC 2119 Clarification May 2017

Copyright Notice

 Copyright (c) 2017 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
 2.  Clarifying Capitalization of Key Words  . . . . . . . . . . .   3
 3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
 4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
 5.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
 Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   4

1. Introduction

 RFC 2119 specifies common key words, such as "MUST", "SHOULD", and
 "MAY", that may be used in protocol specifications.  It says that the
 key words "are often capitalized," which has caused confusion about
 how to interpret non-capitalized words such as "must" and "should".
 This document updates RFC 2119 by clarifying that only UPPERCASE
 usage of the key words have the defined special meanings.  This
 document is part of BCP 14.

Leiba Best Current Practice [Page 2] RFC 8174 RFC 2119 Clarification May 2017

2. Clarifying Capitalization of Key Words

 The following change is made to [RFC2119]:
 === OLD ===
 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.
 === NEW ===
 In many IETF documents, several words, when they are in all capitals
 as shown below, are used to signify the requirements in the
 specification.  These capitalized words can bring significant clarity
 and consistency to documents because their meanings are well defined.
 This document defines how those words are interpreted in IETF
 documents when the words are in all capitals.
 o  These words can be used as defined here, but using them is not
    required.  Specifically, normative text does not require the use
    of these key words.  They are used for clarity and consistency
    when that is what's wanted, but a lot of normative text does not
    use them and is still normative.
 o  The words have the meanings specified herein only when they are in
    all capitals.
 o  When these words are not capitalized, they have their normal
    English meanings and are not affected by this document.
 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", "NOT RECOMMENDED",
    "MAY", and "OPTIONAL" in this document are to be interpreted as
    described in BCP 14 [RFC2119] [RFC8174] when, and only when, they
    appear in all capitals, as shown here.
 === END ===

Leiba Best Current Practice [Page 3] RFC 8174 RFC 2119 Clarification May 2017

3. IANA Considerations

 This document does not require any IANA actions.

4. Security Considerations

 This document is purely procedural; there are no related security
 considerations.

5. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119,
            DOI 10.17487/RFC2119, March 1997,
            <http://www.rfc-editor.org/info/rfc2119>.

Author's Address

 Barry Leiba
 Huawei Technologies
 Phone: +1 646 827 0648
 Email: barryleiba@computer.org
 URI:   http://internetmessagingtechnology.org/

Leiba Best Current Practice [Page 4]

/data/webs/external/dokuwiki/data/pages/rfc/bcp/bcp14.txt · Last modified: 2017/05/19 21:11 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki