Network Working Group P. Hoffman Internet-Draft VPN Consortium Updates: 2119 (if approved) January 15, 2008 Expires: July 18, 2008 Additional Key words to Indicate Requirement Levels draft-hoffman-additional-key-words-00.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on July 18, 2008. Copyright Notice Copyright (C) The IETF Trust (2008). Abstract Some document authors want to express requirement levels using the traditional definitions of "MUST" and "SHOULD" from RFC 2119, but also want to express that there is an expectation that later versions of the document may change those requirements. For example, they may want to express "this SHOULD be implemented now, but we expect that this will become a MUST requirement in a future update to this standard". Hoffman Expires July 18, 2008 [Page 1]
Internet-Draft Additional Key Words January 2008 This document defines three new keywords, "MUST-", "SHOULD+", and "SHOULD-" to facilitate such definitions. 1. Introduction RFC 2119 [RFC2119] defines keywords that are used in the RFC series. Using those definitions allows a document writer to specify the requirements level in a generally-understood manner. However, in some protocols, the authors want to convey that the requirements levels are expected to change in the future. There are three requirements level changes that can be easily envisioned: o A MUST requirement that is expected to be demoted to SHOULD in the future. o A SHOULD requirement that is expected to be elevated to MUST in the future. o A SHOULD requirement that is expected to be demoted to MAY in the future. RFC 4307 [RFC4307] defined new terms for these three states. The purpose of defining new terms in RFC 4307 was to alert implementers that there was a widespread expectation that some of the cryptographic algorithms that were listed as SHOULD-level in the document were expected to become MUST-level in a few years; similarly, there was a widespread expectation that some of the MUST- level algorithms would be demoted to SHOULD-level in a few years. Since then, other RFCs and Internet Drafts have re-used those definitions. This document provides stand-alone definitions based on RFC 4307, and explicitly updates RFC 2119. It is important to note that this document does not change any of the definitions in RFC 2119; it only adds new ones. 2. Definitions of MUST-, SHOULD+, and SHOULD- Three new terms are defined: Hoffman Expires July 18, 2008 [Page 2]
Internet-Draft Additional Key Words January 2008 MUST- This term means the same as MUST. However, the authors expect that this requirement will no longer be a MUST in a future revision of this document. Although its status will be determined at a later time, it is reasonable to expect that if a future update this document alters the status of a MUST- requirement, it will remain at least a SHOULD or a SHOULD-. SHOULD+ This term means the same as SHOULD. However, the authors expect that a requirement marked as SHOULD+ will be promoted at some future time to be a MUST. SHOULD- This term means the same as SHOULD. However, the authors expect a requirement marked as SHOULD- will be demoted to a MAY in a future version of this document. 3. Acknowledgements The definitions here are based on those in RFC 4107, which was authored by Jeff Schiller. The genesis for the idea of requirements language that includes foreshadowing of changes came from Russ Housley during the discussion of RFC 4107. 4. Security Considerations There are no security considerations specific to the new definitions. 5. References 5.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 5.2. Informative References [RFC4307] Schiller, J., "Cryptographic Algorithms for Use in the Internet Key Exchange Version 2 (IKEv2)", RFC 4307, December 2005. Appendix A. Change History [[ This entire section is to be removed upon publication. ]] Hoffman Expires July 18, 2008 [Page 3]
Internet-Draft Additional Key Words January 2008 This is the first version of the document. Author's Address Paul Hoffman VPN Consortium 127 Segre Place Santa Cruz, CA 95060 US Phone: 1-831-426-9827 Email: paul.hoffman@vpnc.org Hoffman Expires July 18, 2008 [Page 4]
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