Subnet Calculator Guide: CIDR, VLSM & IPv4/IPv6 Math

A 192.168.1.0/24 network gives 254 usable hosts; a /23 gives 510; a /22 gives 1,022. The math behind CIDR notation, subnet masks, VLSM planning, RFC 1918 private ranges and IPv6 prefixes is the foundation of every network engineer's daily work. This guide walks through subnet math from first principles with worked examples for /8 to /30, plus the magic number shortcut and the most common subnet calculation mistakes.