What is an IP address?

An IP address is a number that identifies a device on a network so that other devices know where to send data. Every phone, laptop, router, and server that talks over the internet uses one. When you load a web page, your request carries your IP address as the return address, and the reply comes back to it.

“IP” stands for Internet Protocol, the set of rules that describes how data is addressed and moved between networks. You can see the address your connection is using right now on the WebIPTool home page.

What an IP address looks like

There are two versions in use today, and they look different.

An IPv4 address is four numbers from 0 to 255, separated by dots:

203.0.113.42

An IPv6 address is eight groups of letters and numbers, separated by colons. One run of zeros can be shortened with a double colon:

2001:db8:85a3::8a2e:370:7334

Both do the same job. IPv6 exists because the world ran short of IPv4 addresses. The two versions run side by side on many networks, and you may have one of each. Our guide to IPv4 vs IPv6 covers the differences.

How an address gets your data where it is going

Data on the internet travels in small pieces called packets. Each packet is labeled with two addresses: where it came from and where it is going. Routers along the way read the destination address and pass the packet one step closer, a little like sorting offices reading a postal code.

Every packet carries a 'from' and a 'to' address. The reply follows the 'from' address home.

No single device knows the whole route. Each router only knows which neighbor is the best next step for a given range of addresses. That is why addresses are handed out in blocks: a router can keep one entry for a whole block instead of one entry per device.

The website you reach uses the “from” address on your packets to send its reply. Without it, the response would have nowhere to go. This is also why every site you visit can see your IP address. It is not a leak. It is how the conversation works.

Who assigns your IP address

Addresses are handed down in layers:

The Internet Assigned Numbers Authority (IANA) manages the global pool.
IANA allocates large blocks to five regional registries, one for each part of the world.
The registries allocate smaller blocks to internet providers, hosting companies, and large organizations.
Your internet provider assigns one address from its block to your connection.

So the address you see on the home page belongs to your provider, not to you. You are borrowing it for as long as the provider lets you keep it.

Inside your home or office there is a second layer. Your router gives each device its own private address, usually starting with 192.168. or 10., using a system called DHCP. Those addresses only mean something inside your network. See public vs private IP addresses for how the two layers fit together.

Why your IP address changes

Most home and mobile connections get a dynamic address. The provider lends it to you for a period and may give you a different one later. Common triggers:

Your router restarts or loses power.
The provider’s lease on the address expires and is not renewed with the same one.
The provider reorganizes its network.
You move between Wi-Fi and mobile data, which are two separate networks with separate addresses.

A static address stays the same until you or the provider change it. Businesses pay for static addresses when they host something that other people need to find reliably, such as a mail server, a VPN endpoint, or a site-to-site link between offices. For everyday browsing, a dynamic address works exactly as well.

On a phone, the address changes when you switch between Wi-Fi and mobile data, and it can change again when the mobile connection reconnects. That is normal.

Public and private at a glance

	Public address	Private address
Assigned by	Your internet provider	Your router
Visible to	Every site and service you connect to	Only devices on your own network
Unique	Across the whole internet	Only inside your network
Example	`203.0.113.42`	`192.168.1.20`

The private ranges are reserved in RFC 1918 so that millions of separate networks can reuse the same numbers without clashing.

What an IP address is not

A few misunderstandings come up often.

It is not a permanent ID. A dynamic address can pass from one customer to another. The address you have today may have belonged to someone else last month.

It does not identify a person. An address identifies a connection. Everyone on your home Wi-Fi shares the same public address, and on some mobile networks thousands of customers share one. Our guide to CGNAT explains how that sharing works.

It does not show your exact location. An address can usually be tied to a provider and a rough area, often a city and sometimes only a country. It does not reveal a street address. What your IP address reveals goes through what can and cannot be learned.

How to check yours

Your public address is on the home page, along with the provider and approximate location that go with it.
To look up any other address, use the IP Lookup tool.
To see how many addresses fit in a block such as 192.168.1.0/24, try the Subnet Calculator.

Key points

An IP address is a return address for network traffic. Every site you visit sees the one your connection uses.
IPv4 addresses are short and scarce. IPv6 addresses are long and plentiful. Many connections have both.
Your provider assigns your public address. Your router assigns private addresses to your devices.
Most addresses are dynamic and can change without warning.