There are several categories of RFCs identified by their status. The category is listed in the RFC heading, along with the RFC number, RFC authors, the date, and whether this RFC obsoletes or updates another RFC, as shown in the figure. The categories of RFCs are:
- Internet Standard - Internet standard RFCs are documents defining a mature, useful, and validated protocol or technology. These are also known as normative documents. Internet standards have undergone a thorough process from an (I-D), to a proposed standard and, if approved, to an Internet standard. An example of an Internet standard RFC is RFC 2460, Internet Protocol, Version 6 (IPv6) Specification.
- Best Current Practice (BCP) - Best current practice RFCs describe official rules or methodologies. The difference between an Internet standard and a BCP is sometimes unclear. Like an Internet standard RFC, a BCP usually goes through the same process as Internet standards. RFC 1918, which defines the use of private IPv4 addresses, is an example of a BCP RFC.
- Informational - Information RFCs can be almost anything from describing a DNS Structure and Delegation, RFC 1591, to jokes, such as Hypertext Coffee Pot Control Protocol (HTCPCP/1.0), described in RFC 2324. Another example of an informational RFC is RFC 1983, Internet Users Glossary that provides definitions for basic Internet terms and acronyms.
- Experimental - Experimental RFCs are documents that are not on the Internet standards approval track. This includes documents that have been submitted by an individual and have not yet been approved as an I-D. It may be that it is not certain that the proposal works as stated, or it is unclear if the proposal can gain wide acceptance. An experimental RFC may be promoted to the Internet standards track if it eventually meets those requirements.
- Historic - Historic status is given to an RFC when it has been made obsolete by a newer RFC. RFC numbers are never reused. Any RFC that updates an existing RFC receives a unique number and the RFC it updates is moved to Historic status. For example, RFC 1883, IPv6, became a standard in 1995. Several changes were made to IPv6 and in 1998, RFC 2460, with the same name, made RFC 1883 obsolete. The header of RFC 2460 includes “Obsoletes: 1883.”
Some RFCs are not entirely new technologies or protocols, but instead are an update or extension of an existing RFC. In these cases, the RFC indicates in the header that it is an update and which RFC it is updating.
After an RFC has become an Internet standard, occasionally mistakes or errors are found. In these cases, an errata is created and the RFC includes “Errata Exist” in its header. Errata can be found in the RFC editor site, http://www.rfc-editor.org/errata.php.