TT_TT_TT_TT: Okay i'll try to answer your questions as best as possible and hopefully without getting too technical.
Regarding figuring out if your internet connection is actually realized as a "DS-Lite" connection or not - depending on how "accessible" your router is it should be stated there on the status page of your internet connection or else-wise it may be helpful if you state which ISP you are using and then may a fellow Italian knows if your ISP is actually using DS-Lite or not - i sadly myself don't have that kind of knowledge for italian ISP's only know it for German ones.
But regardless if you are actually using DS-Lite or just having issues with port forwarding using a VPN most likely can solve both.
An basic explanation of VPN services in general: You'll have to download a vpn client which is a small programm which on launch will establish a connection (more specifically an encrypted tunnel) to a server of your choice (e.g. a server in the United States). While being connected to this server the server assigns a new public ip adress to you (this is how the rest of the internet will see you/the ip your friend will have to connect to). So basically all data from the internet gets sent to this "new temporary IP" and then gets forwarded to your computer/original IP-Adress via the Tunnel. Using the VPN you wont have to worry about DS-Lite or portforwarding anymore as your new public IP address will be a reachable IP4 adress and the "VPN-Connection/tunnel" will just forward the data for you. I hope that explaination makes it kinda clear. Just be sure you would be getting the correct one - the homepage of Cyberghost is:
http://www.cyberghostvpn.com/en_us (just saw some shady google advertisements forwarding to other pages..)
Thank you so much, you were very clear,I'm a programmer but never did anything that need an high insight with my router and connection, anyway I talked to a friend of mine and he said he was able to connect, via gog and direct connection, to the game of a friend in steam, I tryed to connect via direct connection to the game of this friend using the game on gog but I had the same issue "connection failed" using the game ID, so I have this kind of problem, probably because I'm using a private IP (changed from a public one after several problems of lag spikes) and probably this is why I can't connect to my friends of gog and steam too, well if you said that this Cyberghost give me a new public IP to be used as my "main" IP address I have to give it a shot and maybe I will fix this annoying problem ^^
Thank you so much for your patience and your help
Anyway if could help my ISP is Fastweb.