A routing device is provided, the routing device includes a first network interface unit, a second network interface unit and a processing unit. The first network interface unit connects the routing device to a local private network. The second network interface unit connects the routing device to the Internet. The processing unit assigns a virtual subnet to a remote routing device for a remote host in a remote private network to obtain a virtual Internet protocol (IP) address according to the virtual subnet. The processing unit receives a network packet from a local host in the local private network through the first network interface unit, and encapsulates the network packet according to a public IP address of the remote routing device to generate an alternative packet. Then, the processing unit delivers the alternative packet to the Internet through the second network interface unit.