A method of operating an Internet protocol (IP) address allocates, creates, and processes an interface identifier (ID) of an IP address area. In the allocation, the IP address area includes a subnet prefix area and an Interface ID area, and certain bits of the Interface ID area are used as an index area of a subnet gateway. The allocation is implemented in order from the higher layer to the lower layer so that the Interface ID area is sequentially allocated from the higher bits for the index areas of the respective layers. The combination of the certain bits of the allocated Interface ID and the subnet prefix area of the IP address area is used as the subnet ID of the subnet layers. The lowest subnet gateway allocates the Interface ID to terminating equipment to access the IP network based on a format of the IP address.