An IPv6-only stack supports IPv6 interfaces, but it does not support IPv4 interfaces. These TCP/IP stacks support AF_INET6 sockets and applications that use them, as long as the IP addresses that are used are not IPv4-mapped IPv6 addresses. They do not support AF_INET sockets. Applications can send and receive IPv6 packets by way of an IPv6-only stack, but they cannot send and receive IPv4 packets.