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Key words for use in RFCs to Indicate Requirement Levels (RFC2119)

IP.com Disclosure Number: IPCOM000002672D
Original Publication Date: 1997-Mar-01
Included in the Prior Art Database: 2000-Sep-13
Document File: 2 page(s) / 4K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

S. Bradner: AUTHOR

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:

This text was extracted from a ASCII Text document.
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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.

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 ...