What Is an IP Address?

When you send a letter, the envelope needs an address so the post office knows where to deliver it. Devices on a network work the same way. Every phone, laptop, printer and server that takes part in a network needs an address so that data can reach the right place. That address is called an IP address. "IP" stands for Internet Protocol, the set of rules that describes how data is addressed and sent across networks.

This entry explains what an IP address looks like, why there are two versions, the difference between public and private addresses, and how to see your own. You do not need any earlier knowledge.

What an IP address does

An IP address does two jobs. It identifies a device on a network, and it tells the network where to deliver data. When you open a web page, your device sends a request that contains two addresses: the address of the server you want to reach and your own address, so that the server knows where to send the answer.

An IP address is not a name and it is not permanent for every device. Think of it as the current "street number" of a device on the network it is connected to. When you move your laptop from home Wi-Fi to a coffee shop, it receives a different address.

IPv4 and IPv6: two formats

IPv4: the familiar format

The older and still widely used version is IPv4. An IPv4 address is made of four numbers from 0 to 255, separated by dots. This style is called dotted decimal.

For example, 192.0.2.45 is an IPv4 address. Each of the four numbers is one octet, which is 8 bits. Four octets make 32 bits in total. With 32 bits there are 4,294,967,296 possible combinations, about 4.3 billion. That sounded huge when the internet was small. Today there are far more connected devices than that, which is why a second version was needed.

Addresses such as 192.0.2.45 are reserved in a standard for use in examples and documentation. That is why this page uses them: they will never belong to a real device.

IPv6: the newer format

IPv6 uses 128 bits instead of 32. It is written as groups of hexadecimal characters (digits 0 to 9 and letters a to f) separated by colons. An example from the range reserved for documentation is 2001:db8::1. The double colon is a shortcut that replaces a run of groups that are all zeros.

The number of possible IPv6 addresses is so large that running out is not a practical concern. IPv6 was designed to replace IPv4 over time, but both run side by side today. Many networks give devices both kinds of address.

Public and private addresses

Not every address is visible to the whole internet. Standards set aside blocks of IPv4 addresses for private use inside homes, schools and offices:

Devices inside your home usually have private addresses such as 192.168.1.20. These addresses are only meaningful inside your own network. Two different homes can both use 192.168.1.20 without any conflict, because the addresses never travel across the internet as they are.

Your internet provider usually gives your router one public address. Some providers share one public address among many customers, but the idea is the same. When your devices talk to the internet, the router swaps their private addresses for the shared public one and keeps track of which reply belongs to which device. This technique is called network address translation, or NAT. It is one of the main reasons IPv4 has lasted as long as it has.

How devices get an address, and the special ones

Most devices do not have an address typed in by hand. When they join a network they ask for one, and a service called DHCP (Dynamic Host Configuration Protocol) hands one out automatically. In a home, the router normally runs this service (see Home Network Basics). It chooses a free address from its range and lends it to the device for a limited time.

Sometimes an address is set by hand and does not change. This is a static address. It is useful for things that must always be found at the same place, such as a printer or a server. The opposite, an address that can change over time, is called dynamic.

Special addresses worth knowing

Some addresses have a fixed meaning:

• 127.0.0.1 is the loopback address, also called localhost. It always means "this very device". Developers use it to test a program on their own computer.
• 0.0.0.0 often means "all addresses on this device" or "no address yet", depending on where you see it.
• Addresses starting with 169.254 are assigned by a device to itself when it asks for an address and gets no answer. If you see one, the device probably could not reach a DHCP service.

Finding your IP address

On your own device, the steps depend on the system:

1. Windows: open Command Prompt and type ipconfig. Look for "IPv4 Address".
2. macOS or Linux: open a terminal and type ifconfig or ip addr, depending on what your system includes (macOS uses ifconfig). Look for the line that starts with inet.
3. Phone: open the Wi-Fi settings and tap the network you are connected to. The address is shown in its details.

These show your private address. Your public address is the one websites see. You can find it by searching for "what is my IP" in a search engine, which asks a website to report the address your request came from.

What your address does and does not reveal

An IP address is sometimes described as a precise location, but that is misleading. Databases can estimate the area or the provider an address belongs to, usually at the level of a region or city, and the guess can be wrong. An address does not reveal your name or your street. It is also not the same as your device's physical hardware identifier, which is called a MAC address and works on the local network only.

Common mistakes

• Thinking the address stays the same. Most home addresses change when you change networks, and some public addresses change when your router restarts.
• Mixing up public and private addresses. If a guide tells you to use 192.168.1.1 from outside your home, it will not work, because that address only exists inside your network.
• Typing a number above 255. Each of the four parts of an IPv4 address stops at 255. 192.168.1.300 is not valid.
• Assuming IPv6 means a faster connection. The address version is about naming and reaching devices, not about speed.
• Sharing too casually. Your public address is not a secret, since every website you visit sees it, but there is no reason to post it publicly.

FAQ

Is my IP address the same as my Wi-Fi password?

No. The IP address says where your device is on the network. The Wi-Fi password only controls who is allowed to join the network.

Can two devices have the same IP address?

Not on the same network at the same time. That would cause a conflict, and data could go to the wrong place. DHCP exists partly to prevent this by handing out each address once.

Why do websites use names instead of IP addresses?

People remember names better than numbers. A separate system, called DNS, translates names into addresses behind the scenes. What Is DNS and Why Does It Matter? explains how, and How the Internet Works shows where addresses fit in the bigger picture. The rest is in the Computing and Networks area.

Does a VPN change my IP address?

A VPN sends your traffic through another server, so websites see that server's address instead of yours. It does not make you invisible, and it only helps in certain situations.

Do I need to understand IP addresses for an IT career?

They come up constantly in support, networking, cloud work and security. Knowing the basics, especially public versus private and IPv4 versus IPv6, makes many other topics easier.