I worked for a company developing a custom P2P video streaming protocol. It was amazingly hard to get working properly and testing all the quirks in different r

I worked for a company developing a custom P2P video streaming protocol. It was amazingly hard to get working properly and testing all the quirks in different routers from different manufacturers. The combination of all the NAT strategies (I think there were 5 main ones) created quite a matrix of possible ways that things can work, and you had to implement and test them all before there was any kind of standard way to do it. We built a mock internet with dozens of consumer routers, as many as we could get our hands on. We eventually got it to work and that company exists to this day, but I think they switched to WebRTC long ago.