Network Working Group T. Hansen Internet-Draft AT&T Laboratories Intended status: Informational D. Crocker Expires: August 29, 2016 Brandenburg InternetWorking February 26, 2016 Non-Normative Synonyms in RFCs draft-hansen-nonkeywords-non2119-04 Abstract Specifications in RFCs contain normative keywords, as defined in RFC 2119, to signify requirements, permission or prohibitions. These include MUST, SHOULD and MAY, which are commonly recorded in all CAPITALS (but need not be). The RFC 2119 words are sometimes also used with non-normative meaning; this non-normative usage can be confusing and it is better to restrict the RFC 2119 words to be used solely as normative directives. Happily, natural languages permit variation in phrasing, so that meaning can be retained without use of this otherwise-normative vocabulary. For such situations, this document provides some alternatives to the normative vocabulary of RFC 2119. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on August 29, 2016. Copyright Notice Copyright (c) 2016 IETF Trust and the persons identified as the document authors. All rights reserved. Hansen & Crocker Expires August 29, 2016 [Page 1] Internet-Draft RFC Non-Keywords February 2016 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. 1. Words That Do Double Duty To indicate a degree of requirement, permission or prohibition for an aspect of a specification, words such as MUST, SHOULD and MAY are defined as normative vocabulary in the formal aspects of the RFC series [RFC2119]. However it is also natural to use them non- normatively, in a narrative fashion. Even when this carries no obvious potential confusion, such as within RFCs that do not invoke the conventions of RFC 2119, non-normative use of these words in RFCs invites confusion for the reader; their normative meaning is too deeply ingrained in the culture of the RFC series. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are meant to reference their occurrence in [RFC2119]. The words are not used normatively here. Fortunately, there are other words readily available, in lieu of the RFC 2119 words, when a non-normative meaning is intended. These alternatives, or their equivalents, can be used instead of the normatively-encumbered vocabulary. Hansen & Crocker Expires August 29, 2016 [Page 2] Internet-Draft RFC Non-Keywords February 2016 +-------------+----------------------------------+------------------+ | RFC 2119 | When Used With This Meaning | Some Alternative | | Word | | Word(s) | +-------------+----------------------------------+------------------+ | MUST, | indicates that something is | needs to, | | REQUIRED, | essential | necessary | | SHALL | | | | | | | | SHOULD, | indicates that something is | ought to, | | RECOMMENDED | strongly urged | encouraged, | | | | suggested | | | | | | MAY, | indicates the possibility or | can, might | | OPTIONAL | capability of performing an | | | | action | | | | | | | | indicates permission to perform | is allowed to, | | | an action | is permitted to | +-------------+----------------------------------+------------------+ Because the word "NOT" (or "not") only takes on a special meaning when it is combined with one of the RFC 2119 normative words, the word "not" can be freely used with any of the above suggestions and not be taken to have any separate RFC 2119 connotation. For example, "ought not" is non-normative, while "should not" and "SHOULD NOT" might be normative in the RFC 2119 sense. By using these alternative wordings, authors of RFCs and internet drafts can avoid the possibility of vocabulary (that is sometimes used normatively) being misinterpreted. Note that the above list of synonyms is not meant to be exhaustive; other non-RFC-2119-normative words can, of course, also be used at the author's discretion. Authors who follow these guidelines might want to incorporate a declaration about usage at the beginning of their document. [Note to RFC Editor: please remove this paragraph before publication.] This document can be discussed on the ietf@ietf.org mailing list. 2. Acknowledgements The comments from Ran Atkinson are gratefully acknowledged. Hansen & Crocker Expires August 29, 2016 [Page 3] Internet-Draft RFC Non-Keywords February 2016 3. IANA Considerations This document has no IANA considerations. 4. Security Considerations The RFC 2119 terms are frequently used to specify behavior with security implications. The effects on security of changing something from a "MUST" to a "needs to", or vice versa, can be very subtle, as one can have normative meaning and the other does not. Document authors need to take the time to consider the effects of using non- normative verbiage as specified in this document instead of the normative verbiage from RFC 2119. 5. Informative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . Authors' Addresses Tony Hansen AT&T Laboratories 200 Laurel Ave South Middletown, NJ 07748 USA Phone: +1.732.420.8934 Email: tony@att.com D. Crocker Brandenburg InternetWorking 675 Spruce Dr. Sunnyvale USA Phone: +1.408.246.8253 Email: dcrocker@bbiw.net URI: http://bbiw.net Hansen & Crocker Expires August 29, 2016 [Page 4]