Proper way to handle Master Server and NAT

Hi! I have a networked game that works pretty well even tho its very early in its network adoption, just a few bugs here and there. My main concern tho is the proper way to handle the master server and the NAT-punch through. This feature is absolutely vital to my game to I would like to get the full understanding of how things work. There seems to have been bugs in the Unity code that might still be present since i notice a higher connection success rate after forcing NAT mode to both my servers and clients. So, any known bugs, examples of how you guys made all your games perfect so that everyone can connect etc. If anyone requests it I can post my current connection script featuring a quickmatch function that will search and join/host all by itself. //Patrik