Port forwarding in C#/software possible? Isn't it only managed by the router?

Isn't port forwarding managed by the router? Like, I've googled up some software applications that seem to port forward with great success, but it technically seems to be impossible. The packet must first go to the router. The router must forward it to the correct computer based on port forwarding rules. So how can a software application manage port forwarding if the packet must GO to the computer running this software application in the first place, meaning that port forwarding already is s开发者_开发百科uccessful in the first place?

You're seeing UPNP, which allows a program running on a local network to forward a port on the router.