Every device that connects to the internet is given an IP address, or Internet Protocol address. They are assigned by your ISP (Internet Service Provider). That includes computers, tablets, phones, game consoles, smart devices, routers, you name it. Your IP is a unique identifier. Although you are not usually assigned a static IP — an address that stays the same — it’s still possible for interested parties to identify you using this number.

It’s unfortunate that many people browse and use their devices without understanding even the basics of how this protocol works. For example, downloading illegal content, or someone using your local internet to do so, can land you in hot water. That’s usually tracked through your IP address. Your IP can also be used to discern your general location, and monitor your activity — like what websites you visit or web applications you use.

IP addresses are always numeric and assigned in a range starting with 0.0.0.0 and ending with 255.255.255.255. They exist simply to facilitate the effective connection between two devices or machines, allowing them to talk to one another over a network. This “talking” is nothing more than a data exchange shared back and forth.

How does an IP address actually work?

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When you connect to the internet, your ISP assigns your core device an IP — that core device is usually your modem. The modem is what connects to the internet. Meanwhile, your router essentially acts as a switch, splitting the signal to other devices.

Your modem, and by proxy your router, are assigned a public IP. This is externally facing, meaning it’s what’s actually used while browsing the internet. All devices on your home network, no matter what they are, connecting to the internet through that router use the same public IP. On your home network, each device is also assigned an IP, but this is a private IP address. I realize that may sound confusing. To put it in simpler terms, a public IP is internet-facing, a private IP is home network facing. A corporate or business network works pretty much the same way, for the most part.

Believe it or not, public IP addresses are not randomly assigned. IP address usage follows a mathematical process and is handled by the Internet Assigned Numbers Authority (IANA). These identifiers are created, coordinated and allocated by said authority. But wait, earlier we established that your ISP assigns your public IP? Which is it?

Technically, it’s both. But when you connect to your ISP, your modem — or router if it’s also a modem — requests an IP address from the ISP’s DHCP server. Your ISP then assigns your device an available address from a pool of addresses they manage, which were originally allocated by IANA. So, essentially, IANA gives a bunch to the ISPs, then they give one to you from their pool.

Now, here’s where things get a little more confusing. Most ISPs assign what’s called a dynamic IP address to you.

Dynamic versus static IP addresses

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Because of how IP addresses work, you will never have the same one throughout your lifetime of use on the internet. If you switch to a new ISP, your public IP address will change. That’s because it’s being assigned from a completely different pool. But even if you stay with the same ISP for years, your IP is still changing from time to time. ISPs use DHCP leases to rotate IP assignments, so their active pool changes as well.

A dynamic IP address is one that changes periodically versus a static IP address that stays the same — hence the term “static” there.

Let’s use a real-world example. You connect to the internet through your modem, activating access for your home network. Your ISP assigns you an IP address. Everything in your home now uses that externally facing IP. That IP stays with you for as long as that connection remains active. But let’s say there’s a power surge in your neighborhood, or your modem freezes up and it resets. There’s a pretty good chance that when it reboots and connects, you’ll have a new public IP. That’s not always the case, but it still happens enough to make a difference.

IP logs are a real thing

The thing is that public IPs, although assigned temporarily, stay associated with your devices long enough that interested third-parties can track you and your family. More importantly, there is a backend system of logs used to track and report what people are doing. Law enforcement can, say, look up what an IP address was doing at a particular period and then technically associate that to you. If you visit illegal websites without the appropriate blocking tools, they can still see that months or years later. It depends on how long those logs are preserved.

That is precisely why VPNs talk about and advertise a “no-logs policy.”

Interesting, so what does any of this have to do with me?

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It is extremely important that you understand how this process and how IP addresses work. That’s true even if you’re not doing anything technically advanced. To add to that, it’s also important regardless of what you’re doing when you browse, even if you’re not doing anything wrong or illegal. It’s a fallacy that most people fall into the trap of believing: You should only care about any of this if you’re doing something wrong or have something to hide.

IP addresses are fundamental to how the internet works. Not only is it important to understand how they’re used to track and identify you, and your devices, but also how they affect your experiences while online. Your IP can be used for technical troubleshooting, geotargeting, online communications, and much, much more. In some cases, you could even be assigned an IP temporarily that has been flagged by another nefarious user — specific public IPs get blocked by services all the time for various behaviors. IP blacklisting, for example, is a method that blacklists a certain IP or a range, which could sometimes be a kneejerk approach locking out legitimate users.

If I block a hacker using a specific IP, and then it’s reassigned to someone else, that block usually stands. But IP addresses are also used legally in courts, though circumstantial. They can be used to track and log your habits, or your family’s, and to doxx you — publicly identifying you or your family.