---
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
---

[All posts](/blog) [Networking](/blog/category/networking) Dec 26, 2025 · 3 min read · WatchFor Team

# What is an IP Address?

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).

[#networking](/blog/tag/networking)[#basics](/blog/tag/basics)

## Start monitoring your services today

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[Learn more](/docs/monitors)[Start free](/auth/sign-up)

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