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The TCP/IP protocol standards that define how the Internet works are managed by the IETF. However, the IETF doesn’t impose standards. Instead, it simply oversees the process by which ideas are developed into agreed-upon standards.

An Internet standard is published in the Request for Comments (RFC) document. When a document is accepted for publication, it is assigned an RFC number by the IETF. The RFC is then published. After it’s published, an RFC is never changed. If a standard is enhanced, the enhancement is covered in a separate RFC.

Thousands of RFCs are available from the IETF website (www.ietf.org). The oldest RFC is RFC 0001, published in April 1969. It describes how the host computers communicated with each other in the original ARPANET. As of this writing, the most recent proposed standard is RFC 8892, entitled “Guidelines and Registration Procedures for Interface Types and Tunnel Types.”

Not all RFCs represent Internet standards. The following paragraphs summarize the various types of RFC documents:

 Internet Standards Track: This type of RFC represents an Internet standard. Standards Track RFCs have one of three maturity levels, as described in Table 2-1. An RFC enters circulation with Proposed Standard status but may be elevated to Draft Standard status — and, ultimately, to Internet Standard status.

 Experimental specifications: These are a result of research or development efforts. They’re not intended to be standards, but the information they contain may be of use to the Internet community.

 Informational specifications: These simply provide general information for the Internet community.

 Historic specifications: These RFCs have been superseded by a more recent RFC and are thus considered obsolete.

 Best Current Practice (BCP): RFCs are documents that summarize the consensus of the Internet community’s opinion on the best way to perform an operation or procedure. BCPs are guidelines, not standards.

TABLE 2-1 Maturity Levels for Internet Standards Track RFCs xxx

Maturity Level	Description
Proposed Standard	Generally stable, have resolved known design choices, are believed to be well understood, have received significant community review, and appear to enjoy enough community interest to be considered valuable.
Draft Standard	Well understood and known to be quite stable. At least two interoperable implementations must exist, developed independently from separate code bases. The specification is believed to be mature and useful.
Internet Standard	Have been fully accepted by the Internet community as highly mature and useful standards.

Table 2-2 summarizes the RFCs that apply to the key Internet standards described in this book.

TABLE 2-2 RFCs for Key Internet Standards

RFC	Date	Description
768	August 1980	User Datagram Protocol (UDP)
791	September 1981	Internet Protocol (IP)
792	September 1981	Internet Control Message Protocol (ICMP)
793	September 1981	Transmission Control Protocol (TCP)
826	November 1982	Ethernet Address Resolution Protocol (ARP)
950	August 1985	Internet Standard Subnetting Procedure
959	October 1985	File Transfer Protocol (FTP)
1034	November 1987	Domain Names — Concepts and Facilities (DNS)
1035	November 1987	Domain Names — Implementation and Specification (DNS)
1939	May 1996	Post Office Protocol Version 3 (POP3)
2131	March 1997	Dynamic Host Configuration Protocol (DHCP)
3376	November 1997	Internet Group Management Protocol (IGMP) (Updates RFC 2236 and 1112)
7230 through 7235	June 2014	Hypertext Transfer Protocol – HTTP/1.1
5321	October 2008	Simple Mail Transfer Protocol (SMTP)

My favorite RFC is 1149, an experimental specification for the “Transmission of IP datagrams on avian carriers.” The specification calls for IP datagrams to be written in hexadecimal on scrolls of paper and secured to “avian carriers” with duct tape. (Not surprisingly, it’s dated April 1, 1990. Similar RFCs are frequently submitted on April 1.)