Internet Core Protocols: The Definitive Guide

Requirement levels

Because there are so many different types of documents published, not all of which are suggested or required, RFC 2026 also defines a set of “requirement levels” that should be applied to each RFC that gets published. These requirement levels are listed in Table 1.1.

Table A.1. Requirement Levels Listed in RFC 2026

Level	Description
Required	The specification is required in order for an implementation to be considered as Internet-compliant. For example, RFC 791 and RFC 1122 are required to be followed in order for a vendor’s implementation of the IP protocol to be considered compliant.
Recommended	The specification is not required in order for the implementation to be considered as Internet-compliant, but experience shows that the system and/or network would benefit from the specification being implemented.
Elective	Neither the system nor the network will be helped or harmed by the specification being implemented.
Limited Use	The specification should be used only in extraordinary situations. This is commonly seen with experimental and historic RFCs that may cause some problems if implemented in production implementations.
Not Recommended	This is the same as “limited use,” except its usage is strongly discouraged. RFCs labelled as “not recommended” should only be used when they absolutely have to be.

STD 1 acts as a clearinghouse for the status of each RFC, and also provides the current requirement level status for each of them. Only standards-track documents will have requirement ...