How do I get Nat Type 2 (Open Nat) for the PS3?

I did everything; I tried DMZ mode, I tried port forwarding, I even tried enabling UPNP, but still nothing. Is it my router or is it my modem that is giving me problems? If anybody needs to know what my router is, my router is D-Link DIR-655, and my modem is Windstream Gigaset 4300. Any help would be great, thanks everybody!