P2P from behind of routers

Question

I want to make an application for transferring data P2P. Is there a way to dynamically unlock data port in router to make connection (if it's not set manually)? Is there protocol to do it? How can I use it in cpp?

Answer 1

You can try UPnP, it has the ability to forward ports if the router supports it.

If you're looking for a free library, there's a few, like GUPnP: https://live.gnome.org/GUPnP/ or libupnp: http://pupnp.sourceforge.net/