Port forwarding
Port forwarding is the process of redirecting a connection arriving on a specific port over a computer network to another computer. Since the corresponding network service is not provided by the forwarding computer itself, the term "virtual server" is misleading.
Incoming data packets are masked using Destination NAT, and outgoing packets are masked using Source NAT (which replaces the destination and source addresses) to forward the request to the actual server and its response to the original client. This creates the appearance to both the server and the client that the incoming packets originate from the computer performing the port forwarding.
Port forwarding is often used to run FTP, web servers, or other server-based applications behind a NAT gateway.