What is port forwarding

Port forwarding is a functionality of the network router when a port or range of ports is mapped to a specific internet IP address (or an IP address range). This is done to enable connections from the remote computers to a computer within the network. Such connection is not possible directly because computers on the local network are firewalled from the internet by the router. Port forwarding is one of the proper ways to build a secure tunnel through a firewall and enable certain connections.

Port forwarding is a great tool when used properly. Let’s consider an example when you need to connect to your home computer remotely when you are outside of your home or even outside of your country. From your home network router is the only device visible to the outside world. ISP assigns an IP address to your modem (in most of the cases modem also functions as a router) which typically stays fixed or could be changed rarely. To make sure that IP address assigned to your router never changes you need to ask your ISP to assign a “static IP address” to your modem. Static IP address ensures that only are using the IP address assigned and it won’t be changed by ISP unless you request so. Having static IP also enables you to connect to your modem/router remotely using it as an address. So, if you need to establish a remote desktop connection to your computer you will need to use the static IP address of the router. But the problem is that your modem/router needs to know that you are connecting the specific computer. In order to communicate this information port forwarding is used. Instead of just connecting to a modem static IP address you connect to it using a specified port which is set to be forwarded to that computer.

Port forwarding is utilized by UPnP (Universal Plug and Play) network protocol. UPnP could be used by compliant devices to automatically establish port forwarding through a compatible router without additional setup by user. Most UPnP compatible routers allow turning UPnP off for additional security.