Free Subnet Calculator - IPv4/IPv6 subnets, VLSM and binary view. Free, private

Most subnet calculators only show the basics. This one gives you everything from one IP and mask: network, broadcast, host range, usable hosts, wildcard mask, class, IP type, reverse DNS, and a binary breakdown of network vs host bits. It also includes a Subnet Divider, a VLSM Planner, an IP-in-subnet checker and an IPv6 prefix calculator. Use the slider or quick presets, and copy all results in one click. Everything runs in your browser and nothing is uploaded. No signup.