Non-Normative Synonyms in RFCs

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Last updated 2016-08-29 (latest revision 2016-02-26)
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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.


Tony Hansen (
Dave Crocker (

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