IPv6 Subnet Calculator

IPv6 addresses are 128 bits, written as eight groups of hex digits (e.g. 2001:0db8:0000:0000:0000:0000:0000:0001), usually compressed by dropping leading zeros in each group and collapsing the longest run of all-zero groups to :: (giving 2001:db8::1).

Common ranges you'll run into: fe80::/10 link-local, fc00::/7 unique local (private), 2001:db8::/32 reserved for documentation, and 2000::/3 global unicast (the publicly routable space). Full list on the CIDR Cheat Sheet page.