You don't need to do all that if you just wanna play simple Games like Diablo with a few friends
Just install a third party program like
Hamachi or
Evolve to set up a LAN connection between you and your friends.
With that made, you all should be able to connect to each other easily!
Those Online games have built-in options for Multiplayer, you'll be the one hosting the "server" as soon as you choose to do so in-game.
All you need to do is:
1) Install the program
2) Create a Network and ask your friends to join it
3) After they've joined, run Diablo, set up the Multiplayer world
4) Send them your IP adress shown in the program
5) They'll use it to connect through TCP/IP inside the Diablo
6) Done
It's easier than you think, i've done that quite a few times already never had a problem
Hope it works for you too!