IPv4 Addresses Embedded in IPv6 Addresses

Stateful NAT64 and XLAT464 embed IPv4 addresses in IPv6 addresses by using an IPv6 prefix that you specify. The prefix length you use determines how the IPv4 address is embedded.

IPv6 addresses with embedded IPv4 addresses are composed of a variable-length prefix, the embedded IPv4 address, and a variable-length suffix. Bits 64 to 71 are reserved and must be set to 0. The suffix follows the last bit of the embedded IPv4 address, and the suffix bits are ignored and should be set to 0.

The format for the IPv4-embedded IPv6 address depends on the prefix length, as shown in Table 1.

Table 1: IPv6 Address With Embedded IPv4 Address
Prefix length	Prefix bits	IPv4 address bits	Reserved bits (must be set to 0)	Suffix bits
32	0-31	32 to 63	64 to 71	72 to 127
40	0 to 39	40 to 63 and 72 to 79	64 to 71	80 to 127
48	0 to 47	48 to 63 and 72 to 87	64 to 71	88 to 127
56	0 to 55	56 to 63 and 72 to 95	64 to 71	96 to 127
64	0 to 63	72 to 103	64 to 71	104 to 127
96	0 to 95	96 to 127	64 to 71	No suffix bits

The following table shows an example of an IPv4 address embedded in an IPv6 address for various prefix lengths.

IPv6 Prefix	IPv4 Address	IPv4 Address Embedded in IPv6 Address
2001:db8::/32	192.0.2.33	2001:db8:c000:221::
2001:db8:100::/40	192.0.2.33	2001:db8:1c0:2:21::
2001:db8:122::/48	192.0.2.33	2001:db8:122:c000:2:2100::
2001:db8:122:300::/56	192.0.2.33	2001:db8:122:3c0:0:221::
2001:db8:122:344::/64	192.0.2.33	2001:db8:122:344:c0:2:2100::
2001:db8:122:344::/96	192.0.2.33	2001:db8:122:344::192.0.2.33