03 / IPv6 · 4 MIN READ

Read and write IPv6 with confidence

IPv6 looks less mysterious once you know what the colons and zeros are doing.

Eight groups of hexadecimal

An IPv6 address has eight 16-bit groups. Each is written with up to four hexadecimal digits. 2001:0db8:0000:0000:0000:0000:0000:0001 is a complete, expanded address.

Shorten zeros, keep the meaning

Leading zeros within a group can be removed. A run of zero groups can be replaced once with ::. The address above becomes 2001:db8::1. A canonical representation compresses the longest run, choosing the first run when tied.

Common scopes

::1 means loopback. fe80::/10 is link-local. fc00::/7 is unique-local. ff00::/8 is multicast. Documentation uses 2001:db8::/32. These prefixes have different purposes; they are not interchangeable public internet addresses.

Square brackets belong to URLs

A literal IPv6 address in a URL is surrounded by brackets, such as https://[2001:db8::1]/. Our address tools accept the address itself, without brackets, a port, or a local interface zone identifier.

Reference: RFC 5952 — IPv6 text representation.