Remote Access/Port Forwarding Theory

Port Forwarding Theory

The Basics To really explain port forwarding, you first need to understand a little more about what your router does. Your internet service provider assigns one IP address to your internet connection. All computers on the internet need a unique IP address, but you have multiple computers in your house and only one address. So how does this work?

NAT - What is it? Why do we use it? Your home router has a function called Network Address Translation, or NAT, built in. Inside your network, computers have addresses like 192.168.1.100. All addresses in the 192.168.* range (or in the 10.*) range are "private" or "reserved" addresses. These addresses are officially assigned by IANA to be used inside of private networks. Your router automatically assigns such an address to each computer connected via DHCP. These addresses are how computers in your network communicate with the router and with each other.

Your router has a separate network interface that connects it to the internet. This interface has a very different address which is assigned by your ISP. This is the one address that I mentioned before, and your router uses it to communicate with other computers on the internet. Computers inside of your network have non-routable private IP addresses, meaning that if they send packets directly to the internet the packets will automatically be dropped (packets with private addresses are not allowed to traverse the internet for stability reasons). But your router has a routable address. Network Address Translation, as its name suggests, translates between these two kinds of addresses, allowing the multiple computers inside of your network to appear to the internet as one computer with one address.