A network system adopting a first IP protocol is provided. The network system includes an address allocating server and a communication terminal supporting both the first IP protocol and a second IP protocol, wherein the address allocating server dynamically allocates an address of the second IP protocol to the communication terminal. The communication terminal includes a dynamic address manager for acquiring the dynamically allocated address of the second IP protocol of the communication terminal from the address allocating server and a second IP protocol address of the destination of a second IP protocol packet from a second IP protocol application, and an address adapter for encapsulating the second IP protocol packet from the second IP protocol application into a first IP protocol packet, wherein the second IP protocol address of the communication terminal in the header of the second IP protocol packet and the second IP protocol address of the destination are encapsulated into the first IP protocol packet.