Reference

Lookup tables and cheat sheets for status codes, ports, record types, and more.

The 128 US-ASCII code points with decimal, hex, octal, and binary values, control names, and C escape sequences.

Quick-reference table of every IPv4 prefix length: subnet mask, wildcard mask, address count, and usable hosts.

Quick reference for IPv6 prefix lengths — address counts, /64 subnet counts, typical use — plus the common special-purpose prefixes.

Cheat sheet for Unix file permissions: the rwx bits, octal digits, setuid/setgid/sticky, common modes, and umask.

The seven OSI layers side by side with the four-layer TCP/IP model — protocol data units, functions, and example protocols.