RFC 1123

networking, standard The RFC "Requirements for Internet

Hosts Application and Support" which clarifies or changes the

specification of protocols given in earlier RFCs.

RFC 1123 defines the terms "MUST", "SHOULD", "MAY",

"unconditionally compliant", "conditionally compliant".

Capitals are used to emphasise that the official definition of

the word is being used.

MUST or REQUIRED means an absolute requirement for

conformance.

SHOULD or RECOMMENDED means the item can be ignored under

certain circumstances, although the full implications should

be understood.

MAY or OPTIONAL means the implementor can choose, usually

depending on whether it is needed or not.

Something "unconditionally compliant" meets all the MUST and

SHOULD requirements, "conditionally compliant" meets all the

MUST requirements and "not compliant" - does not meet some

MUST requirement.

For example, RFC 1123 amends RFC952 to say software MUST

handle either a letter or a digit as the first character of a

hostname.

(rfc:1123).

(1996-01-13)