What is an IP address?

The simple explanation

Computers need an address to send data to each other. Every time you open a website, your request carries your IP address so the website knows where to send the page back. Without it, the reply would never reach you.

IP stands for Internet Protocol, the set of rules that decides how data is addressed and routed across networks. You never have to type an IP address yourself, because your device and the domain name system handle it for you.

Public and private IP addresses

Most people use two kinds of address at the same time. A public address is the one the wider internet sees. It belongs to your router or to your mobile carrier's network. A private address is used inside your home or office network to tell your phone, laptop and television apart.

Private addresses come from reserved ranges such as 192.168.x.x, 10.x.x.x and 172.16.x.x to 172.31.x.x. They cannot be reached from the internet, so millions of households can use the same ones without any conflict.

Who assigns IP addresses

Five regional internet registries, ARIN, RIPE NCC, APNIC, LACNIC and AFRINIC, hand out large blocks of addresses to internet providers and big organisations. Providers then assign addresses from those blocks to their customers.

Because each block is registered to a particular organisation in a particular region, location databases can estimate where an address is used. That is how an IP lookup can show a country, a city and a provider name.

Static and dynamic addresses

Most home and mobile connections use dynamic addresses, which can change when your router restarts or your provider reassigns it. Static addresses stay the same and are common for servers and businesses.

On many mobile networks, hundreds of customers share a small pool of public addresses. This is one reason two people on the same carrier can show the same public IP address.

What an IP address can show

Using a public IP address, a lookup tool can usually show:

• The approximate country, region or city where the address is used.
• The internet provider or organisation that operates the address.
• The network number (ASN) that routes the traffic.
• Sometimes, whether the address belongs to a data centre rather than a home connection.

What an IP address cannot show

An IP address does not reveal your name, your home address, your phone number, your passwords or the other websites you visit. Only your internet provider can connect an address to a customer account, and that information is not public.

Location results are estimates, not exact positions. Our guide on why an IP address can show the wrong location explains the most common reasons.