When discussing IP addresses, you've probably heard the terms "public" and "private" used. These descriptors are confusing if you're not familiar, but they're important to know so you can better understand how IP addresses work.
Let's compare public and private IP addresses to learn how they work together on the modern internet.
What Is an IP Address?
Before we examine public and private IP addresses, we should review what an IP address actually is. IP address is short for "Internet Protocol address," and like the name suggests, they are numbers used to identify computers and other devices on a network.
While your computer might have a name that you identify it by, like Sam's Laptop, computers work better with numbers. Thus, when a computer needs to talk to another device on your network or the internet, it sends information to that IP address. Today, we still generally use IPv4 addresses, which use a format like 192.168.10.1.
Just like you would send a letter to a street address, an IP address lets a computer address data for another machine. When you visit a website, your computer connects to the server's IP address in order to load content from it.
See our introduction to IP addresses for more background info.
What Are Public IP Addresses?
A public IP address refers to the address that represents your home network to the rest of the internet. Because most personal networks use a router to connect to the internet, your router is assigned this public address.
Then, because all the devices in your home get online through your router, they each use this public IP address when going online. No matter which device you're using—a desktop, phone, smart home device, or similar—other devices online will see your public IP when they interact with them. Any computer can also use your public IP to reach your router.
Unless you've paid to get a static IP address, which most people don't need, your public IP is dynamic. This means that your internet service provider (ISP) changes your IP address every so often. The reasons for this are mostly historical—in the early days of the internet, most people were only connected to the internet for short periods of time. It wouldn't make sense to assign a static IP address to every user when they weren't connected often enough to use them.
Public IP addresses are also called global or external IPs; these all refer to the same term.
What Are Private IP Addresses?
A private IP address is an address that's only used for devices inside your home network. These addresses aren't reachable by other devices on the internet that are outside your home. Instead, they're used for devices to talk to each other, and so your router knows where to send incoming information.
The private IP addresses used in one home network are also used on thousands of other networks. For example, your phone might have the IP address 192.168.100.17 on your home network. That address is not unique—there are likely people in your neighborhood with the same private IP address for one of their devices.
But these don't clash, because they are on separate networks. If you ever do have two of the same IP addresses on one private network, you'll end up with an IP conflict.
You may also hear private IP addresses called local IPs or internal IPs. These all have the same meaning.
How Public and Private IP Addresses Work Together
For an analogy on how public and private IP addresses work, think about a college campus with student mailboxes. If you lived on campus and wanted to send a letter to the owner of box 561, you could simply write "Box 561" on the envelope and drop it into the campus mailbox. The mail staff would deliver it easily.
However, if you lived off-campus and wanted to send a letter to box 561's owner, you couldn't just write "Box 561" on an envelope and drop it off in a standard mailbox. The mail delivery wouldn't know which building to bring the letter to, since there are many box 561 locations in the country.
Instead, you would have to address the letter to the college building's address, plus "Box 561." If you didn't include the box number, then the mail staff wouldn't know which box should get the letter. In this case, the campus address is akin to the public IP address, while the box number is like the private IP address.
NAT and the Evolution of Internet Protocol
NAT, which stands for network address translation, is an important home networking term that ties public and private IP addresses together. NAT allows your router to share your one public IP across many private IP addresses.
Using this, your router keeps track of the incoming traffic it receives, then sends it to the right device on your network. This is why you can play an online game on one device while streaming music on another device, and have both work properly.
NAT is important because the world has run out of available IP addresses under IPv4, the current version of the Internet Protocol. There are a little over four billion possible IP addresses, which we've exhausted thanks to the huge number of internet-connected devices across the world.
The solution is IPv6, the next iteration of the protocol. This has room for 340 undecillion IP addresses, which is a number so massive that it's not possible to comprehend. Under IPv6, we won't run out of addresses for a long, long time. An IPv6 address looks like this: 2001:db8:8a2e:370:7334.
How to Find Your Public and Private IP Address
It's not difficult to find either type of IP address for your devices. You shouldn't need to worry about them most of the time, but there are situations where it's important to know.
To check your home network's public IP address, you can simply search Google for "what is my IP?" This will show a box with your public IP. Remember that this might change, so don't be surprised if it's different when you check again a month later.
Finding your private IP address depends on what platform you're using. For phones, see how to find your IP address on Android and iPhone. On desktop, we've covered how to find your IP address on Windows 10 and how to find your Mac's IP address.
Private and Public IPS Make the Internet Work
Understanding how both types of IP addresses work helps you appreciate the internet we use every day. Public IPs allow every local network to be identified on the internet at large, while private IPs cut down on IPv4 address usage and let your router handle traffic for all your home devices.
They're both important, and in most cases, work without much input from you. But if you're interested, there's more to learn about home network technologies.