Purpose: Port forwarding allows remote computers (for example, computers on the Internet) to connect to a specific computer or service within a private local-area network (LAN).

Port forwarding means that we specify a port in the address translation table for a particular device, and any traffic that comes in on this port is forwarding to the corresponding device. It’s essentially a very specialized form of routing using TCP and UDP port numbers instead of IP addresses to decide where to send packets. It is a way of making sure that device outside of the internal network can get to devices inside, so port mapping is  a bit like NAT in reverse.