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Must-read RFCs

Below is a practical, high impact list of RFCs that most software engineers should at least understand at a conceptual level. They are grouped by area and prioritised for real world relevance.

Core Internet Fundamentals

  • RFC 791 - Internet Protocol (IPv4) Foundation of packet routing and addressing.

  • RFC 8200 - Internet Protocol Version 6 (IPv6) Modern IP standard.

  • RFC 792 - Internet Control Message Protocol (ICMP) Used for ping and network diagnostics.

  • RFC 768 - User Datagram Protocol (UDP) Connectionless transport.

  • RFC 9293 - Transmission Control Protocol (TCP consolidation"] Reliable transport layer behaviour.

Why it matters: Understanding packet flow, latency, retries, and connection behaviour is essential for debugging distributed systems.

HTTP and Web

  • RFC 9110 - HTTP Semantics Methods, status codes, headers, caching rules.

  • RFC 9112 - HTTP/1.1 Persistent connections, chunked encoding.

  • RFC 7540 - HTTP/2 Multiplexing, streams, header compression.

  • RFC 6455 - WebSocket Protocol Full duplex communication over HTTP.

Why it matters: Every backend, API, or web platform engineer relies on correct HTTP semantics.

DNS

  • RFC 1034 - Domain Names - Concepts and Facilities
  • RFC 1035 - Domain Names - Implementation and Specification

Why it matters: DNS misconfiguration is a frequent cause of outages.

Security and Cryptography

  • RFC 8446 - Transport Layer Security 1.3 Modern TLS handshake and encryption model.

  • RFC 6749 - OAuth 2.0 Authorization Framework Delegated authorisation.

  • RFC 7519 - JSON Web Token Token structure and claims.

  • RFC 7617 - Basic HTTP Authentication

Why it matters: Authentication and encryption mistakes are high impact.

Email (Often Overlooked)

  • RFC 5321 - Simple Mail Transfer Protocol
  • RFC 5322 - Internet Message Format

Useful if your product sends email at scale.

Data Formats and APIs

  • RFC 8259 - JavaScript Object Notation (JSON)
  • RFC 3986 - Uniform Resource Identifier

Why it matters: URI encoding and JSON edge cases cause subtle bugs.

Real Time and Networking Extras

  • RFC 5905 - Network Time Protocol Version 4 Clock synchronisation for distributed systems.

  • RFC 9000 - QUIC Transport Protocol Basis of HTTP/3.

If You Build Distributed Systems

  • RFC 1122 - Host Requirements Defines host behaviour in TCP/IP stacks.

  • RFC 7234 (Historic but influential) - HTTP caching model Now replaced by RFC 9111, but worth understanding historically.

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