Some users have a router that doesn't allow port forwarding or forces restricted NAT on all devices, which can give them connection problems when playing the game such as players not being able to join their servers or not being able to join certain servers themselves.
By following this guide you will be able to connect to your connection directly from Windows, bypassing your router.
Note: Only do this as a last resort if you're sure that your router doesn't allow port forwarding or similar. Remember that you will have all ports open while using the connection we're going to setup.

This guide was made using Windows 8.1 with English (United Kingdom) as display language. Steps may vary slighlty depending on your windows version and language, but they should be the same overall.

Open the Network and Sharing Center by right clicking the connection icon in the right of your taskbar and selecting "Open Network and Sharing Center".


Click "Setup a new connection or network"


Click "Connect to the Internet"


If this screen appears, click "Set up a new connection anyway". Don't worry, your old connection won't be deleted.


Choose "Broadband (PPPoE)"


Now in "Username" and "Password" insert respectively the username and password your ISP (Internet Service Provider) gave you. Some ISPs use the same username/password for everyone, while others give individual ones for each user.
For the "Connection name" you can use any name you want, use one that will let you easily recognize this connection.


Now wait while Windows is configuring and testing the connection. The screen will look like this:


If everything went correctly you should be greeted with a message stating that the connection was configured succesfully.
If you open the connection list (by left clicking the connection icon in your task bar) you will see two connections: the regular one you've been using and the new one we just setup (you can recognize them by their name). You can connect to either of those.
If you connect to the old one you will pass though your router like before.
If you connect to the new one your router will be bypassed and you will have all ports open and open nat.
Note: By default your PC will connect to the old connection. Make sure you manually connect to the new one when you want to play/have open ports and NAT.

To verify that your connection works properly, open OGAT and go to the settings. Under the "Network Settings" section it will show a message displaying the state of your NAT.
If the message says "Public IP", then the connection is working properly and you should be able to join and host without any problem.