A gateway device includes a local area network (LAN) interface including a plurality of LAN ports, and a processor connected to the LAN interface. The gateway device communicates with an Internet Protocol Version 4 (IPv4) network and at least two Internet Protocol Version 6 (IPv6) networks. All the plurality of LAN ports are classified into a plurality of port groups corresponding to the at least two IPv6 networks. When an IPv6 user device is connected to any one of the plurality of LAN ports, the processor identifies the LAN port connected to the IPv6 user device, and enables the IPv6 user device to communicate with the IPv6 network corresponding to the port group which includes the LAN port connected to the IPv6 user device.