After reading all of your comments, i spent the whole day on it and finally managed to port forward, i tried UPnP, DMZ, firewall settings but nothing helped, at last i figured out the external ip, server ip, ports, application name and all that stuff and add a total 7-8 port rules for modern warfare and finally got OPEN nat type. THANK YOU everyone who spent their time replying to the post and helped me figure out the problem
really appreciated