Short summary: It slows down your internet speed
Double NAT issue fixed (BONUS: no IP address conflicts!)
Anyone who has ever played a game online knows what a NAT type is – and they usually don’t have good implications, as NAT errors prevent people from playing together. The problem is only exacerbated when you have a double NAT.
Double NAT is not necessarily bad. You may not even notice it, but it can cause some unforeseen problems with some applications and hardware. Some of these are related to services that require UPnP (Universal Plug-and-Play) support or manual port forwarding.
But what exactly is a Double NAT and how can you solve the problems that can arise? Let's answer both questions here.