Every device that talks on a network has one: an IP address. It's the most fundamental piece of internet plumbing, the thing that lets your request actually find a server among billions of machines. Yet most people never think about what it is. Let's change that.
What an IP address is
An IP address is a unique number that identifies a device on a network. When data travels the internet, it needs a destination — and the IP address is that destination, like a postal address for packets.
You usually type a name (example.com), and DNS translates it into an IP address behind the scenes. The name is for humans; the IP is what the network actually uses to route your data.
Two versions: IPv4 and IPv6
There are two formats of IP address in use today:
| IPv4 | IPv6 | |
|---|---|---|
| Looks like | 192.0.2.10 | 2001:db8::1 |
| Size | 32-bit (~4.3 billion) | 128-bit (effectively endless) |
| Status | Exhausted; workarounds in use | The long-term future |
IPv4's ~4.3 billion addresses ran out years ago, which is why IPv6 exists — with a practically unlimited supply. Both run side by side today. (Full story in IPv4 vs IPv6.)
Public vs private addresses
Not every IP is reachable from the internet. There are two kinds:
| Type | Where it works | Example |
|---|---|---|
| Public | Reachable across the internet | Your home router's external IP |
| Private | Only inside a local network | 192.168.x.x, 10.x.x.x |
Your laptop and phone at home have private addresses on your local network; your router has one public address that the whole house shares — which is possible thanks to NAT.
IP + port = a specific service
An IP address gets you to the right machine, but a machine runs many services. The port number picks the right one. So 192.0.2.10:443 means "this machine, on the HTTPS service." IP = building, port = room.
Why IP addresses matter day to day
You'll bump into them more than you'd expect:
- DNS records (A/AAAA) map your domain to its IP.
- Firewalls allow or block by IP.
- Monitoring checks reach your services by resolving names to IPs — and you may need to allowlist a monitor's IPs.
- Geolocation estimates a visitor's rough location from their IP.
Want to see your own? Your public IP is what the world sees you as — the address your requests appear to come from. (You can look it up instantly with a What's My IP tool.)
The bottom line
| In one line | |
|---|---|
| What | A unique number identifying a device — a postal address for data. |
| Versions | IPv4 (192.0.2.10) and IPv6 (2001:db8::1). |
| Public vs private | Internet-reachable vs local-network-only. |
| With a port | IP = the machine, port = the specific service. |
The IP address is the unglamorous foundation everything else rides on: DNS, firewalls, monitoring, routing. Names are for people; IP addresses are how the internet actually delivers your data to the right place.
Related: IPv4 vs IPv6, how DNS works, what is NAT?; see your own with What's My IP.