Port forwarding

Port forwarding, also referred to as port mapping, is a method of forwarding a network port from one network node to another. This technique can allow an external user to reach a port on a private IP address (inside a LAN) from the outside using a NAT-enabled router.
Port forwarding allows remote computers (e.g. public machines on the Internet) to connect to a specific computer within a private LAN.
For example:
Port forwarding is not necessary with IPv6, because every IPv6-enabled device has a public IPv6 address.