Last Updated on July 26, 2026
How NAT translates public IP addresses to private IP addresses
If you work in the field of IT (Information Technology) then you are most likely familiar with at least the basics of networking such as switches, routers, cabling, IP addresses and so on. But have you ever wondered how the information from the Internet knows how to get to the right computer on your internal network? Or how about at home if you have multiple computers sharing the same Internet connection?
Well it may seem like magic but it’s really not unless of course you consider the whole idea of networking as magic. How this works is by using a process called Network Address Translation or NAT for short. What this does is take the information coming into your network from its external IP address and translating it to the appropriate internal IP address of the computer it needs to go to.
If it wasn’t for NAT you would need to have a public IP address for every computer on your internal network and that would not be possible because we are pretty much out of public IPv4 addresses and they are not cheap to begin with if you want your own.
There are 2 main NAT configurations, static (or 1 to 1) or dynamic NAT. There are other more advanced types but we will stick with the 2 most commonly used versions here.
Understanding Static NAT Configurations
1. The Core Function of Static NAT
Static NAT uses a mapping table to map a single public IP address to a single internal private IP address. When data comes in for that public IP address, the router which stores the NAT table will know exactly which internal private IP address to send the data to. It acts as a permanent, fixed bridge between the outside world and your internal network.
2. When to Use Static NAT
This is used when you have more than one public IP address and want the mapping to stay consistent and not change. You would use a static NAT mapping for something like a web server or an email server. This ensures the public IP address of the website always points directly to the internal address of the web server without any confusion or dynamic shifting.
Understanding Dynamic NAT Configurations
1. The Core Function of Dynamic NAT
Dynamic NAT is used in situations where you only have one public IP address and you need Internet access for multiple inside computers. This is most likely the exact configuration your home Wi-Fi router is using for its Internet connection. It allows dozens of devices to share a single public-facing identity.
2. The Concept of IP Masquerading
This is also called IP masquerading or one-to-many NAT because one IP address is servicing multiple devices simultaneously. The outside internet only ever sees the single public IP address of your router. It never sees the private local IP addresses of your individual smartphones, laptops, or smart TVs.
3. How Port Address Translation (PAT) Works
Dynamic NAT uses Port Address Translation (PAT) where the router assigns the internal client a specific port number to be used with the IP address so the packets are sent to the right computer. This is needed because multiple internal computers are sharing the exact same external or public IP address at the same time. The port number acts like an apartment number in a large building, telling the router exactly which device requested the data.
4. The Invisible Process
If PAT wasn’t in use then packets would get lost or you would need to have a way to map the public IP address to each private IP address one at a time as needed which would not work too well. This whole process is completely transparent to the user. There is absolutely nothing for them to do or configure in order to make this connection work.
