router billion port forward

Hi! im new here, well im trying to set up a web server with my billion 5200 adsl router, i test with no-ip.com and dyndns.com with (this comes with the router) and in two cases the domain answer the ping command, but wen i try to see by web mydomain.dyndns.com my router answer (popup the login page for setup the router) and is the same if y try with telnet command; i make the rules for port forward (start at 80 port, end 80 port) but in all cases answer the router (my iis works ok in localhost), how i can do for the router only answer for the internal network?.
Thanks in advance

mmm UPnP? i´ll try .. but in some forums talk about ACL rules..last night i move some there and i cant conect to my router from the LAN, well still it doesn´t work.