help with multiplayer

[Roumata]

how many of you are able to create an internet server ? i can't at all, it is always telling me i need an external IP adress, although i have one.
Although i read the multiplayer readme and did a lot of things that are written inside, i still can create any server. Any help ?
My friend has exactly the same probleme and therefore both of us we can't play multiplayer.
Version is 1.3.0

Thanks

Roum