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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