socket.connect throw exception

I want to learn socket programming in C#, and related settings. I've download a demo from a site. when i set Remote Host IP address to my local address it connect to server (my pc) and send receive works.

however when i set Remote Host IP address to my router external IP, i doesn't connect and throw exception: "No co开发者_如何学Pythonnnection could be made because the target machine actively refused it 91.99.166.161:300"

i set port forwarding in my router. what's wrong? Thanks in advance.

Either your port forwarding configuration is incorrect, there's a firewall in the way, or the host you're forwarding to is not listening on the destination port.