Public vs. Private IP Addresses: What's the Difference?

Every device connected to a TCP/IP network, including the internet, needs a unique IP address to communicate. These addresses fall into two main categories: public and private. Understanding the difference is key to understanding how home and business networks function.

Public IP Addresses

A public IP address is an address that is assigned to you by your Internet Service Provider (ISP). This is the address that your home or business router uses to communicate with the rest of the internet. It's globally unique and routable on the public internet. Think of it as your home's mailing address—it's how the outside world finds you.

You can find your public IP address by searching "what is my IP" on Google or by visiting a site like whatismyipaddress.com.

Private IP Addresses

A private IP address is an address used within a local, private network (like your home Wi-Fi network). These addresses are not routable on the public internet. This is why you can't directly connect to your friend's laptop at their house using its private IP.

To solve the problem of a limited number of IPv4 addresses, the Internet Engineering Task Force (IETF) reserved specific ranges of IP addresses for private use, as defined in RFC 1918.

If you've ever looked at your computer's IP address and seen something like 192.168.1.10, you've seen a private IP address. Every device inside your house (laptops, phones, smart TVs) has a unique private IP on your local network.

How Do They Work Together? NAT

So if your devices have private IPs that can't access the internet, how do you browse the web? The magic is a process called Network Address Translation (NAT).

Your router sits at the edge of your local network. It has one foot in the private network (with a private IP like 192.168.1.1) and one foot in the public internet (with the public IP from your ISP).

When your laptop wants to visit a website, it sends the request to the router. The router "translates" the request, swapping your laptop's private source IP for its own public source IP, and sends it out to the internet. When the website replies, the router receives the response, looks at its internal NAT table to see which device made the original request, and forwards the traffic to your laptop's private IP. This allows many devices to share a single public IP address.