When can the double colon be used?

The double colon may appear only once in an address and only to replace a run of two or more zero groups, never a single zero group. On a tie between runs of equal length, the leftmost run is chosen.

What is an IPv4-mapped IPv6 address?

An IPv4-mapped address has the form ::ffff:a.b.c.d and embeds an IPv4 address in the low 32 bits. This tool detects and preserves that dotted tail.

IPv6 Compress / Expand

Validate any IPv6 address and convert it between the fully expanded form and the RFC 5952 compressed canonical form. The tool also reports the address scope and detects IPv4-mapped addresses. Everything runs in your browser.

IPv6 address

Global

Compressed (RFC 5952)

2001:db8::ff00:42:8329

Expanded

2001:0db8:0000:0000:0000:ff00:0042:8329

Full hexadecimal (128-bit)

20010db8000000000000ff0000428329

Frequently asked questions

What is IPv6 compression?

Per RFC 5952 leading zeros in each group are dropped, the largest run of zero groups becomes a double colon, and hex digits are lowercase: 2001:0db8:0000:0000:0000:ff00:0042:8329 becomes 2001:db8::ff00:42:8329.

When is the double colon allowed?

Only once per address, only for a run of two or more all-zero groups, and never for a single zero group. When two runs are equally long, the leftmost one is compressed.

What is an IPv4-mapped address?

An address such as ::ffff:192.168.1.1 embeds an IPv4 address in the low 32 bits. The tool flags it and keeps the dotted tail in the compressed form.

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