an RFC
/ are-eff-see /
Every protocol that runs the Internet is written down somewhere precise enough that two strangers can build interoperating software from it. That somewhere is usually an RFC — Request for Comments — a numbered document in the series that defines Internet standards. The name is a charming relic of 1969, when the early documents really were invitations to comment; today an RFC can be anything from a firm standard to an experiment to an April Fools' joke, but the core ones are the rulebooks of the Internet.
RFCs are published by the IETF (Internet Engineering Task Force), the open, volunteer-driven body that standardizes the Internet's core protocols, working by 'rough consensus and running code' rather than by vote. Each RFC gets a permanent number that never changes (RFC 791 is IP, RFC 9293 is the current TCP, RFC 9110 defines HTTP semantics); when a protocol is revised, a new RFC is issued that obsoletes the old one rather than editing it in place. Not every RFC is a standard — they carry status labels like Standards Track, Informational, Experimental, or Historic — but together they are the authoritative, freely-readable record of how the Internet works.
Why this matters for a beginner: when you want the real, unambiguous answer to 'how does this protocol actually behave?', the RFC is the source of truth, free to read at the RFC Editor's site. The IETF handles the protocols that flow over the Internet (IP, TCP, HTTP, DNS); a different body, the IEEE, standardizes many local-network and physical technologies (Ethernet is IEEE 802.3, Wi-Fi is IEEE 802.11). Knowing which standards body owns which piece, and that RFCs are public, is a real superpower for learning the field accurately.
When engineers argue about exactly how TCP should behave on a corner case, they cite the RFC by number ('per RFC 9293...') — the document, not anyone's memory, is the final authority.
Numbered, permanent, public — the IETF's record of how Internet protocols work.
An RFC number is permanent but its content is frozen: protocols are updated by issuing a new RFC that obsoletes the old one, never by editing the original. And not every RFC is a standard — check its status label.