What is an IPv4-mapped IPv6 address?

An address of the form ::ffff:203.0.113.7 defined in RFC 4291. It lets software that works with IPv6 sockets represent an IPv4 peer inside the IPv6 format. It is a notation, not a tunnel: packets still travel as plain IPv4.

What is a 6to4 address?

6to4 (RFC 3056) derives the prefix 2002:V4HEX::/48 from a public IPv4 address, giving a whole IPv6 network to a site that only has IPv4 connectivity. The mechanism is largely deprecated today, but the addresses are still seen in logs and routing tables.

Can every IPv6 address be converted back to IPv4?

No. Only IPv6 addresses that embed an IPv4 address can, mainly the IPv4-mapped ::ffff:a.b.c.d form, 6to4 2002:: addresses and NAT64 64:ff9b:: addresses. A native IPv6 address has no IPv4 equivalent.

IPv4 to IPv6 Converter

IPv4 address, or an IPv6 address with embedded IPv4

Examples:

What this converter does

There is no single "IPv6 version" of an IPv4 address; the two protocols use separate address spaces. What does exist are standard notations that embed an IPv4 address inside an IPv6 one, and this tool produces all of them at once. Type an IPv4 address and you get the IPv4-mapped form (::ffff:203.0.113.7, RFC 4291) in both dotted and pure hex spelling, its fully expanded 8-group notation, the 6to4 prefix (2002:cb00:7107::/48, RFC 3056), the NAT64 well-known-prefix form (64:ff9b::203.0.113.7, RFC 6052), plus the raw 32-bit value in hex and decimal.

It also works in reverse: paste an IPv6 address that carries an embedded IPv4 (mapped, 6to4 or NAT64) and the original IPv4 address is extracted and linked to its full IP lookup report. Everything runs in your browser; nothing is sent to a server.

Where you meet these forms

IPv4-mapped addresses show up constantly in server logs of dual-stack software (nginx, Node.js, Java) that listens on an IPv6 socket: an IPv4 client is logged as ::ffff:198.51.100.9. 6to4 addresses appear in old routing tables and traceroutes, and NAT64 forms are what mobile carriers with IPv6-only networks use to reach the IPv4 internet. Recognising which IPv4 host hides inside is often the first step of an abuse investigation.