Some programs such as BitTorrent clients, video games, and servers may require you to have certain ports open; that is, your computer should be able to accept remote requests on those ports. Often, a firewall (which may be software-based such as Windows Firewall or Netfilter, or hardware-based like a router with NAT enabled) will hinder this activity and close unused ports, preventing incoming connections. This simple script will determine whether your computer can receive connections on a specified port.
Launch the application1 that requires a port (or several ports) to be open and enter the number of a port to check.