What does the :: in an IPv6 address mean?

The double colon represents one or more consecutive groups of all-zero hextets. It may appear only once in an address. This tool expands it back to the correct number of 0000 groups.

What is RFC 5952 compression?

RFC 5952 is the canonical text representation — lowercase hex, leading zeros dropped per group, and the longest run of two or more zero groups replaced by ::. The tool shows this canonical form alongside the full one.

How many groups does a full IPv6 address have?

A full IPv6 address has eight groups (hextets) of four hexadecimal digits each, separated by colons — 128 bits in total. The expander pads every group to four digits and restores any groups hidden by the double colon.

Why does my address fail validation?

Common reasons are using the double colon more than once (only one is permitted), a group longer than four hex digits, non-hex characters, or more than eight groups once expanded. The tool flags these so you can correct the input.

Can the double colon appear at the start or end?

Yes. A leading :: (as in ::1, the loopback) or trailing :: is valid and represents zero-groups at that position. The expander fills in the correct number of 0000 groups in each case.

Are addresses uploaded?

No. Parsing and formatting happen entirely in your browser.

IPv6 Expander — Gera Tools

Expand and canonicalise IPv6 addresses

Paste a compressed IPv6 address such as 2001:db8::1 and see its fully expanded eight-group form plus the canonical RFC 5952 compressed form. This is handy when configuring firewalls, ACLs or DNS records that need the full, unambiguous address, and for verifying two addresses are actually the same.

How it works

The tool first validates the input — only one :: is permitted, each hextet must be 1–4 hex digits, and the total must resolve to eight groups. To expand, it replaces the :: with enough 0000 groups to reach eight, then left-pads each group to four digits. To compress to RFC 5952 canonical form, it lowercases the hex, drops leading zeros in each group, and replaces the longest run of two or more zero groups with ::.

Example

Form	Address
Input (compressed)	`2001:db8::1`
Fully expanded	`2001:0db8:0000:0000:0000:0000:0000:0001`
Canonical (RFC 5952)	`2001:db8::1`

Everything runs locally in your browser; nothing is uploaded.