Forkort og udvid IPv6

An IPv6 address has 128 bits, written as eight groups of four hexadecimal digits. Almost nobody writes all 32 digits: leading zeros in a group may be dropped, and one run of all-zero groups may be replaced by ::.

Because several short forms are possible, RFC 5952 defines one canonical form that every tool should output: lower-case hex, no leading zeros, :: used for the longest run of two or more zero groups (the first one if there is a tie), and never for a single zero group. 2001:0db8:0000:0000:0000:ff00:0042:8329 becomes 2001:db8::ff00:42:8329.

The expanded form, with all eight groups and every leading zero, is what you need for sorting text, for some configuration files and for building reverse DNS names (ip6.arpa).