What Is an IP Address?

Every device that talks on a network has an IP address — but what is it, exactly, and why does your laptop have a different one at home than the one websites see? This guide covers the essentials.

What is an IP address?

An IP (Internet Protocol) address is a numeric label that identifies a device on a network and lets data find its way to it. It plays two roles at once: identification (which device) and location (where to route traffic). Without IP addresses, packets wouldn't know where to go.

IPv4 and IPv6

There are two versions in use. IPv4 addresses are 32-bit, written like 192.168.1.10 — about 4.3 billion possible. IPv6 addresses are 128-bit, written like 2001:db8::1, providing a practically unlimited supply to replace the exhausted IPv4 space. Most networks run both side by side ("dual-stack"). We compare them in IPv4 vs IPv6.

Public vs private addresses

This is the part that confuses people. Certain ranges are private (RFC 1918) — 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 — and are reused on every home and office network behind a router. They're never routed on the public internet. Your laptop's 192.168.1.10 is private; the single public address websites see belongs to your router.

How NAT lets devices share one address

Because IPv4 ran short, most networks use Network Address Translation (NAT). Your router has one public IP, and every device behind it shares that address. The router keeps track of which internal device asked for what, and translates between the private and public sides. That's why every device in your home can browse the web through a single public address.

Static vs dynamic addresses

• Dynamic — assigned automatically by DHCP and may change over time. This is the default for most home devices.
• Static — manually fixed and unchanging. Useful for servers, printers and anything other devices need to find at a known address.

Subnets: grouping addresses

IP addresses are organised into subnets using a prefix like /24. Subnetting splits an address into a network part and a host part, which is how networks are segmented for organisation, performance and security. Our subnet guide explains this in depth.

Is an IP address personal data?

Under privacy laws like GDPR, an IP address can be considered personal data because it may identify an individual. That's worth knowing if you log or process them — see our GDPR overview.

Try it

Explore how addresses divide into networks with our IPv4 subnet calculator and IPv6 subnet calculator, and translate blocks and ranges with the CIDR ↔ IP range converter.