The internal workings of the Internet are defined by a set of documents
called RFCs (Request for Comments). The general process for creating
an RFC is for someone wanting something formalized to write a document
describing the issue and mailing it to Jon Postel
The RFCs can be divided into five groups: required, suggested, directional, informational and obsolete. Required RFCs (e.g., RFC-791, The Internet Protocol) must be implemented on any host connected to the Internet.
Suggested RFCs are generally implemented by network hosts. Lack of them does not preclude access to the Internet, but may impact its usability. RFC-793, Transmission Control Protocol, is a must for those implementing TCP.
Directional RFCs were discussed and agreed to, but their application has never come into wide use. This may be due to the lack of wide need for the specific application (RFC-937, The Post Office Protocol) or that, although technically superior, ran against other pervasive approaches (RFC-891, Hello). It is suggested that, should the facility be required by a particular site, an implementation be done in accordance with the RFC. This ensures that, should the idea be one whose time has come, the implementation will be in accordance with some standard and will be generally usable.
Informational RFCs contain factual information about the Internet and its operation (RFC-990, Assigned Numbers).
There is also a subset of RFCs called FYIs (For Your Information). They are written in a language much more informal than that used in the other, standard RFCs. Topics range from answers to common questions for new and experienced users to a suggested bibliography.
Finally, as the Internet has grown and technology has changed, some RFCs become unnecessary. These obsolete RFCs cannot be ignored, however. Frequently when a change is made to some RFC that causes a new one to obsolete others, the new RFC only contains explanations and motivations for the change. Understanding the model on which the whole facility is based may involve reading the original and subsequent RFCs on the topic.
RFCs and FYIs are available via FTP from many sources, including:
They're also available through mail by writing to
"Knowledge is of two kinds. We know a subject ourselves, or we know where we can find information upon it." Samuel Johnson Letter to Lord Chesterfield February, 1755
Copyright © 1998, Software Engineering Laboratory
National Technical University of Athens