Network Working Group T. Hansen
Internet-Draft AT&T Laboratories
Intended status: Informational D. Crocker
Brandenburg InternetWorking

Non-Normative Synonyms in RFCs


Specifications can contain normative keywords, as defined in RFC 2119, to signify requirements, permission or prohibitions. They include MUST, SHOULD and MAY, which are commonly spelled in all CAPITALS (but need not be). These words can also be used for non-normative purposes. However when used within an RFC this is confusing, given their typical use as normative vocabulary, even when they do not formally have normative import.

Several words and phrases are specified in this document for non-normative purposes as alternatives to the normative vocabulary of RFC 2119. Authors who follow these guidelines do NOT need to incorporate any declaration at the beginning of their document.

Status of This Memo

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1. A List of Synonyms

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 culture of RFCs.[RFC2119]. However it is also natural to use them non-normatively, in a narrative fashion. Even when this is permitted, such as RFCs that do not invoke the conventions of RFC 2119, non-normative use of these words can be confusing; their normative meaning is too deeply ingrained for RFCs.

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 [RFC2119].

Fortunately, there are other words readily available, in lieu of the RFC 2119 words.

This document may be discussed on the mailing list.

2. Acknowledgements


3. IANA Considerations

This document has no IANA considerations.

4. Security Considerations

The 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 has normative meaning and the other does not. Document authors should take the time to consider the effects of using non-normative verbiage as specified in this document instead of the normative verbiage from 2119.

5. References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.

Authors' Addresses

Tony Hansen AT&T Laboratories 200 Laurel Ave South Middletown, NJ 07748 USA Phone: +1.732.420.8934 EMail:
D. Crocker Brandenburg InternetWorking 675 Spruce Dr. Sunnyvale, USA Phone: +1.408.246.8253 EMail: URI:

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