THE FIELD NOTES / IPV6

A longer address. A shorter explanation.

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.