---
title: What is an IP Address?
description: An IP address is how one machine on the internet finds another — the postal address of the digital world. Here's what it is, the difference between public and private, and the two versions in use.
canonical: https://watchfor.io/blog/what-is-an-ip-address
---

# What is an IP Address?

2025-12-26 · WatchFor Team · Networking · networking, basics

An IP address is how one machine on the internet finds another — the postal address of the digital world. Here's what it is, the difference between public and private, and the two versions in use.

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](/blog/how-dns-works) 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](/blog/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](/blog/nat-explained).

## IP + port = a specific service

An IP address gets you to the right *machine*, but a machine runs many services. The **[port](/blog/what-is-a-network-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](/blog/dns-record-types-explained)** (A/AAAA) map your domain to its IP.
- **[Firewalls](/blog/what-is-a-firewall)** 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](/docs/reference/probe-locations).
- **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](/whats-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](/blog/ipv4-vs-ipv6), [how DNS works](/blog/how-dns-works), [what is NAT?](/blog/nat-explained); see your own with [What's My IP](/whats-my-ip).

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Canonical page: https://watchfor.io/blog/what-is-an-ip-address · All articles: https://watchfor.io/blog/all.md · Site guide: https://watchfor.io/llms.txt