Network
IPv6 Address Tools
Expand a shorthand IPv6 address, compress a long one, or work out the range for an IPv6 CIDR block.
Runs entirely client-side, works offline. Nothing sent anywhere.
Related: the MAC address analyzer, since IPv6 addresses can be derived from a MAC via EUI-64.
Runs entirely in your browser. Nothing you enter is sent anywhere.
Learn about IPv6 addressing
Why IPv6 addresses need shorthand at all
An IPv6 address is 128 bits, written as eight groups of four hex digits separated by colons, four times longer than an IPv4 address. Two shorthand rules keep that readable: leading zeros within a group can be dropped, and exactly one run of consecutive all-zero groups can be collapsed to ::. That second rule can only apply once per address. If it applied twice, there'd be no way to tell how many zero groups each :: was standing in for.
A few addresses worth recognizing
::1 is the IPv6 loopback (equivalent to IPv4's 127.0.0.1). fe80::/10 is the link-local range, auto-assigned on every interface and only routable on the local network segment. fc00::/7 is unique local address space, roughly IPv6's counterpart to IPv4's private ranges. 2001:db8::/32 is reserved specifically for documentation and examples, so it's always safe to use in configs and writeups without it being a real, routable address.
Common questions
Is IPv6 CIDR math the same as IPv4's? Yes, the same prefix-bits-vs-host-bits concept applies, just across 128 bits instead of 32. The main practical difference is scale: rather than carving out small blocks like a /24, IPv6 typically hands out a /64 as the standard size for a single subnet, with much larger allocations for whole networks.
Why does my address look different every time I check it? Many operating systems use IPv6 privacy extensions, which periodically generate a new temporary address for outbound connections specifically to make long-term tracking harder. That's expected behavior, not a misconfiguration.