Give your xbox a static ip. Make sure you enter the correct info at the Gateway and subnet part, to find out what you fill in here open CMD on your computer thats in the same network and write ipconfig /all, write the info down.After you've setup the static IP, go to your routers page which is probably something like 192.168.1.1 and forward the ports you've set within FSD to the xbox's static IP.
It can't be easier, if done correctly you won't have any problems. Me and all my friends, who conveniently also are from the netherlands, can find and play with eachother just fine on every game.