IPv4-compatible IPv6 addresses constitute a special class of IPv6 addresses. Such an IPv6 address has its first 96 bits set to zero, while its last 32 bits represents an IPv4 address.

IPv6#Transition_mechanisms no longer use IPv4-compatible addresses. The only remaining use of these addresses is to represent an IPv4 address in a table with fixed size members that must also be able to store an IPv6 address.

It should be noted that the undefined IPv6 address :: and the loopback IPv6 address ::1 are not really IPv4-compatible addresses, even if they are included in the IPv6 address space ::/96.

=See also=