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IPv4 to IPv6

Write an IPv4 address in its IPv6 forms: IPv4-mapped, 6to4, NAT64 and ISATAP. Or paste an IPv6 address to find the IPv4 address hidden inside it.

A network-specific NAT64 prefix is /32, /40, /48, /56, /64 or /96. Leave it empty to use only the well-known 64:ff9b::/96.

Try:

IPv6 forms

198.51.100.20

Example: type your own address above.

IPv4-mapped::ffff:198.51.100.20as server logs show it
NAT64 (well-known prefix)64:ff9b::198.51.100.20through the well-known NAT64 prefix

6to4 prefix: 6to4 needs a public IPv4 address. This one isn't, so the prefix wouldn't work.

NAT64 (well-known prefix): RFC 6052 forbids the well-known prefix for non-public IPv4 addresses. Use a network-specific prefix instead.

Every form

IPv4-mapped
::ffff:198.51.100.20
IPv4-mapped (hex)
::ffff:c633:6414
IPv4-compatible, deprecated
::198.51.100.20
IPv4-compatible (hex), deprecated
::c633:6414
6to4 prefix
2002:c633:6414::/48
NAT64 (well-known prefix)
64:ff9b::198.51.100.20
NAT64 (hex)
64:ff9b::c633:6414
ISATAP interface ID
::5efe:198.51.100.20
ISATAP link-local
fe80::5efe:198.51.100.20

Standards: IPv4-mapped and IPv4-compatible RFC 4291, 6to4 RFC 3056, NAT64 RFC 6052, ISATAP RFC 5214. The ISATAP ID uses 5efe because this IPv4 address isn't public.

Under other NAT64 prefixes

RFC 6052

The same address under RFC 6052's example prefix at each allowed length:

PrefixIPv6 address
2001:db8::/322001:db8:c633:6414::
2001:db8:100::/402001:db8:1c6:3364:14::
2001:db8:122::/482001:db8:122:c633:64:1400::
2001:db8:122:300::/562001:db8:122:3c6:33:6414::
2001:db8:122:344::/642001:db8:122:344:c6:3364:1400:0
2001:db8:122:344::/962001:db8:122:344::198.51.100.20
  • Prefix
    2001:db8::/32
    IPv6 address
    2001:db8:c633:6414::
  • Prefix
    2001:db8:100::/40
    IPv6 address
    2001:db8:1c6:3364:14::
  • Prefix
    2001:db8:122::/48
    IPv6 address
    2001:db8:122:c633:64:1400::
  • Prefix
    2001:db8:122:300::/56
    IPv6 address
    2001:db8:122:3c6:33:6414::
  • Prefix
    2001:db8:122:344::/64
    IPv6 address
    2001:db8:122:344:c6:3364:1400:0
  • Prefix
    2001:db8:122:344::/96
    IPv6 address
    2001:db8:122:344::198.51.100.20

How it works

IPv6 has several ways to carry an IPv4 address inside its 128 bits. They exist because the two protocols have to live side by side while networks move to IPv6. Each one puts the 32-bit IPv4 address in a fixed place, so you can always get it back out.

IPv4-mapped addresses (::ffff:192.0.2.1) are how software holds an IPv4 address in an IPv6 socket; you see them in server logs. NAT64 addresses (64:ff9b::192.0.2.1) let IPv6-only phones and servers reach IPv4 sites through a translator. RFC 6052 also lets a network use its own prefix, skipping bits 64 to 71. 6to4 (2002::/16), Teredo (2001::/32) and ISATAP are older tunnels, now mostly switched off. The IPv4-compatible form ::192.0.2.1 was deprecated in 2006.

Teredo hides its numbers: the client's port and IPv4 address are stored inverted (XOR with all ones), so NATs don't rewrite them. This page undoes that. To see what kind of address you have, use the IP type checker. For the address in other notations, try IPv6 to decimal or IPv6 expand and compress.