182.57.xx.xx

mine modem ip address is 10.20.30.40 but mine isp ip address is 182.57.xx.xx how to get modem ip address identity on network i mean when some one sees mine ip address it should come 10.20.30.40 not 182.57.xx.xx is there any software which can change ip address to 10.20.30.xx i want to change...