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.

RFCTitle & StatusDetails & Relevance
RFC 791
Internet Protocol (IPv4)
Core Internet FundamentalsStandard
Foundation of packet routing and addressing.
Strategic Relevance: Understanding packet flow, latency, retries, and connection behaviour is essential for debugging distributed systems.
RFC 8200
Internet Protocol Version 6 (IPv6)
Core Internet FundamentalsStandard
Modern IP standard resolving IPv4 address exhaustion.
Strategic Relevance: Understanding packet flow, latency, retries, and connection behaviour is essential for debugging distributed systems.
RFC 792
Internet Control Message Protocol (ICMP)
Core Internet FundamentalsStandard
Used for ping, traceroute, and network diagnostics.
Strategic Relevance: Understanding packet flow, latency, retries, and connection behaviour is essential for debugging distributed systems.
RFC 768
User Datagram Protocol (UDP)
Core Internet FundamentalsStandard
Simple, connectionless, and low-overhead transport layer.
Strategic Relevance: Understanding packet flow, latency, retries, and connection behaviour is essential for debugging distributed systems.
RFC 9293
Transmission Control Protocol (TCP)
Core Internet FundamentalsStandard
Consolidated standard for reliable, connection-oriented transport layer behaviour.
Strategic Relevance: Understanding packet flow, latency, retries, and connection behaviour is essential for debugging distributed systems.
RFC 9110
HTTP Semantics
HTTP & WebStandard
Core HTTP architecture, methods (GET, POST, etc.), status codes, headers, and caching rules.
Strategic Relevance: Every backend, API, or web platform engineer relies on correct HTTP semantics.
RFC 9112
HTTP/1.1
HTTP & WebStandard
HTTP/1.1 syntax, persistent connections, and chunked transfer encoding.
Strategic Relevance: Every backend, API, or web platform engineer relies on correct HTTP semantics.
RFC 7540
HTTP/2
HTTP & WebProposed Standard
Multiplexing, streams, header compression (HPACK), and server push.
Strategic Relevance: Every backend, API, or web platform engineer relies on correct HTTP semantics.
RFC 6455
WebSocket Protocol
HTTP & WebProposed Standard
Full-duplex communication over a single TCP connection.
Strategic Relevance: Every backend, API, or web platform engineer relies on correct HTTP semantics.
RFC 10008
The HTTP QUERY Method
HTTP & WebProposed Standard
Defines the QUERY method for safe, idempotent, and cacheable read-only requests with a request body.
Strategic Relevance: Solves the limitation of using GET for complex search queries with payloads, avoiding the need for POST.
RFC 1034
Domain Names - Concepts and Facilities
DNSStandard
High-level concepts, architecture, and query structure of the Domain Name System.
Strategic Relevance: DNS misconfiguration is a frequent cause of outages.
RFC 1035
Domain Names - Implementation and Specification
DNSStandard
Technical details of DNS transmission formats, record types, and resolution algorithms.
Strategic Relevance: DNS misconfiguration is a frequent cause of outages.
RFC 8446
Transport Layer Security 1.3
Security & CryptographyProposed Standard
Modern TLS handshake, cipher suites, and encryption model.
Strategic Relevance: Authentication and encryption mistakes are high impact.
RFC 6749
OAuth 2.0 Authorization Framework
Security & CryptographyProposed Standard
Industry-standard protocol for delegated authorisation.
Strategic Relevance: Authentication and encryption mistakes are high impact.
RFC 7519
JSON Web Token (JWT)
Security & CryptographyProposed Standard
Compact, URL-safe container for transferring claims between parties.
Strategic Relevance: Authentication and encryption mistakes are high impact.
RFC 7617
Basic HTTP Authentication
Security & CryptographyProposed Standard
Standard mechanism for basic web authentication using username/password.
Strategic Relevance: Authentication and encryption mistakes are high impact.
RFC 5321
Simple Mail Transfer Protocol (SMTP)
EmailProposed Standard
Core protocol for transmitting electronic mail between servers.
Strategic Relevance: Useful if your product sends email at scale.
RFC 5322
Internet Message Format (IMF)
EmailProposed Standard
Defines the standard textual structure of email headers and bodies.
Strategic Relevance: Useful if your product sends email at scale.
RFC 8259
JavaScript Object Notation (JSON)
Data Formats & APIsStandard
The ubiquitous, text-based data interchange format.
Strategic Relevance: URI encoding and JSON edge cases cause subtle bugs.
RFC 3986
Uniform Resource Identifier (URI)
Data Formats & APIsStandard
Syntax definitions and resolving rules for URIs/URLs.
Strategic Relevance: URI encoding and JSON edge cases cause subtle bugs.
RFC 5905
Network Time Protocol Version 4 (NTPv4)
Real-Time & NetworkingProposed Standard
Clock synchronisation specification for distributed systems.
Strategic Relevance: Time skew can cause subtle errors in consensus systems, security, and logging.
RFC 9000
QUIC Transport Protocol
Real-Time & NetworkingProposed Standard
UDP-based multiplexed transport protocol serving as the basis of HTTP/3.
Strategic Relevance: Provides faster connection establishment, improved congestion control, and connection migration.
RFC 1122
Host Requirements
Distributed SystemsStandard
Defines host behaviour and requirements in TCP/IP stacks.
Strategic Relevance: Specifies how computers must behave as network hosts.
RFC 7234
HTTP Caching Model (Historic)
Distributed SystemsHistoric
Historically influential caching guidelines (mostly replaced by RFC 9111, but historically significant).
Strategic Relevance: Important to understand the historical evolution of caching strategies.
Created: July 2, 2026Last modified: July 2, 2026