RFC Explained

RFC 5321: The protocol that actually delivers your email.

2026-07-08T00:00:00Z

RFC 5321 is SMTP, the protocol that moves email between servers. It defines the envelope (MAIL FROM, RCPT TO) and the delivery conversation, separate from the message itself.

RFC 3164: The syslog format that was never really a standard.

2026-07-08T00:00:00Z

RFC 3164 documented the old BSD syslog format: the number, a year-less timestamp, free-text message. Informational, obsoleted by RFC 5424, still everywhere.

RFC 2822: The email format's in-between edition.

2026-07-08T00:00:00Z

RFC 2822 was the 2001 revision of the email message format, between RFC 822 and RFC 5322. It fixed the two-digit year and tidied the syntax. Now obsolete.

RFC 1123: The RFC that let hostnames start with a digit.

2026-07-08T00:00:00Z

RFC 1123 corrects email, DNS, FTP and Telnet for real hosts. It legalised hostnames starting with a digit and defined the date format HTTP still calls rfc1123-date.

RFC 1122: Ten years of TCP/IP bug reports, written down.

2026-07-08T00:00:00Z

RFC 1122 tells hosts what they MUST do with IP, TCP and UDP. Half of STD 3, home of the Robustness Principle, and the reason independent TCP stacks interoperate.

RFC 822: The shape of every email, defined in 1982.

2026-07-08T00:00:00Z

RFC 822 defined the email message format in 1982: header fields, a blank line, then the body. Obsoleted by RFC 2822 and 5322, but its structure survives everywhere.

RFC 768: UDP, the protocol that promises nothing.

2026-07-08T00:00:00Z

RFC 768 defines UDP: an eight-byte header, no handshake, no retransmission, no ordering. Why DNS, video and HTTP/3 all choose the protocol that guarantees nothing.

RFC 9110: What HTTP means, no matter how it travels.

2026-07-05T00:00:00Z

RFC 9110 defines HTTP semantics: methods, status codes and headers, independent of version. The 2022 Internet Standard (STD 97) that reorganized 25 years of HTTP.

RFC 6749: How apps get access without getting your password.

2026-07-05T00:00:00Z

RFC 6749 defines OAuth 2.0: how apps get scoped, revocable access tokens to act on your behalf without handling your password. The framework behind every 'Sign in with' button.

RFC 6598: The fourth private range nobody voted for.

2026-07-05T00:00:00Z

RFC 6598 reserves 100.64.0.0/10 as Shared Address Space for carrier-grade NAT. Why your ISP hands you a 100.x address, and how to tell you are behind CGN.

RFC 5424: Syslog, with a real timestamp at last.

2026-07-05T00:00:00Z

RFC 5424 defines the modern syslog message format: precise timestamps, structured data and clear fields. It replaced the loose BSD syslog of RFC 3164.

RFC 5322: The anatomy of an email, and why the From line can lie.

2026-07-05T00:00:00Z

RFC 5322 defines the email message format: headers, body and valid address syntax. Why the From line can lie, and how it differs from SMTP (RFC 5321).

RFC 3339: The timestamp format you google ten times a week.

2026-07-05T00:00:00Z

RFC 3339 is the internet timestamp format, like 2026-07-05T14:30:00Z. A strict profile of ISO 8601 with a required offset, used across JSON APIs, logs and databases.

RFC 2544: The MOT test for network boxes, explained.

2026-07-05T00:00:00Z

RFC 2544 is the standard bench test for switches and routers: throughput, latency, frame loss and back-to-back, run across fixed frame sizes so a datasheet claim can be verified.

RFC 2119: MUST, SHOULD and MAY, defined once and for all.

2026-07-05T00:00:00Z

RFC 2119 defines what MUST, SHOULD, MAY and their negatives mean in a spec. The keyword dictionary behind almost every RFC, updated by RFC 8174.

RFC 1918: Private IP addresses, explained like you're new here.

2026-07-05T00:00:00Z

RFC 1918 reserves 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 for private networks. What that means and why your router is 192.168.0.1, in plain English.

RFC 793: TCP, the protocol that turns postcards into a phone call.

2026-07-05T00:00:00Z

RFC 793 defines TCP: the three-way handshake, sequence numbers and retransmission that make delivery reliable and ordered. The 1981 spec was replaced by RFC 9293 in 2022. Same protocol on the wire.

RFC 791: IPv4, the envelope every packet travels in.

2026-07-05T00:00:00Z

RFC 791 defines IPv4: the 32-bit addresses, the packet header and how routers forward and fragment datagrams. The 1981 spec still runs most of the internet.