Port forwarding is the literal act of forwarding a network port from one single network to another. This networking technique is used to allow external users to reach ports on private IP addresses from the outside via a router. An example of port forwarding would be to allow remote computers, such as public machines on the internet, to connect to a specific computer inside a private LAN.
In typical home networking setups, internet access is through a DSL or Cable modem and these modems are commonly connected to a router. The router is then connected to several networked computers by WiFi or Ethernet. When communicating online, the router is the only device that can be seen on the internet as it holds a public IP address, but all computers behind the router will be invisible. Port forwarding is necessary for the router, as it will need to distinguish which direction to send information received from both the internet and the networked computers.
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