In a communication network (200) having an IPv6 communication backbone (210), each multi-protocol subnet (215 and 220) comprises: a mixture of IPv4 (215B and 220B), IPv6 (215D and 220D), and dual-stack (215C and 220C) hosts; and a communication protocol interface (215E and 220E). A corresponding gateway subnet (225) for communication beyond the communication network (200), includes a gateway communication protocol interface (225C). The communication protocol interfaces (215E and 220E) transport IPv4 data packets across the IPv6 communication backbone (210) within IPv6 data packets, allowing IPv4 hosts operating in any of the subnets to communicate with each other. The gateway communication protocol interface (225C) operates with the communication protocol interfaces (215E and 220E) to extend communication between IPv4 hosts in any of the subnets, to communication with IPv4 (108) hosts on the Internet 107.