What Is an IP Address? A Complete Plain-English Guide

Updated: 2026-05-31

An IP address is the "postal address" of a device on a network. Every packet of data on the Internet carries a source and a destination IP address, and routers use the destination to forward the packet, hop by hop, until it reaches the right machine. Without IP addresses there is no way to say where data should go.

"IP" stands for Internet Protocol, defined back in 1981 by RFC 791. Two versions are in use today: IPv4 (still the most common) and IPv6 (designed to replace it). This guide focuses on IPv4 and points to deeper articles where useful.

The structure of an IPv4 address

An IPv4 address is 32 bits long. To make it human-readable, those 32 bits are split into four 8-bit groups called octets, each written in decimal and separated by dots — dotted-decimal notation.

        192    .    168    .     0     .     1
     11000000   10101000   00000000   00000001
     └─8 bits┘  └─8 bits┘  └─8 bits┘  └─8 bits┘   = 32 bits total

Each octet ranges from 0 to 255 (the values an 8-bit number can hold), so the whole space is 2³² ≈ 4.3 billion addresses. That sounds like a lot, but it ran out years ago — which is exactly why IPv6 exists and why CGNAT and NAT are now everywhere.

From dotted-decimal to bits

It helps to see how a decimal octet maps to 8 bits:

You can convert any address between decimal, binary, hexadecimal and a 32-bit integer with the IP converter.

Network portion and host portion

A single address actually encodes two things: which network the device is on, and which host it is within that network. The boundary between them is set by the subnet mask or, equivalently, by CIDR notation such as /24.

This split is the foundation of routing and subnetting. The full mechanics — masks, broadcast, host counts and how to divide a block — are covered in subnetting and CIDR basics, and you can compute any of it instantly with the subnet calculator.

Public, private, static and dynamic

Not all IP addresses are equal:

• Public addresses are globally unique and routable on the Internet. Private addresses (like 192.168.x.x) are reused inside millions of home and office networks and are translated by NAT — see public vs private IP.
• Static addresses are fixed; dynamic addresses are leased by DHCP and can change over time — see static vs dynamic IP.
• Some addresses are special-purpose, such as the loopback 127.0.0.1 (your own machine) — see special addresses and localhost and 127.0.0.1.

IPv4 vs IPv6 in one paragraph

IPv6 uses 128-bit addresses written in hexadecimal (e.g. 2001:db8::1), giving an effectively unlimited supply and removing the need for NAT. It is not backward-compatible with IPv4, so the two run side by side ("dual stack") during the long migration. Start with what is IPv6 and IPv6 vs IPv4.

How to find your own IP address

There are two different answers: your local (private) IP, set on your device, and your public IP, which the world sees.

Your public IP is shown instantly at the top of this site's home page, along with reverse DNS, country and network. From a terminal you can also ask an echo service:

curl https://show-ip-addr.com/api/myip

Your local IP, per operating system:

# Linux
ip -4 addr show          # or: ip a
# macOS (Wi-Fi)
ipconfig getifaddr en0

# Windows (PowerShell)
Get-NetIPAddress -AddressFamily IPv4
# or the classic:
ipconfig

The two usually differ — your PC might show 192.168.0.10 while the world sees 203.0.113.5. That gap is NAT at work, explained in public vs private IP.

Investigate any address

To look up who owns an address and which network it belongs to, use the IP Lookup tool (registration data via RDAP) and the ASN lookup (the routing/AS view). To see what an address can reveal about a person, read what your IP can reveal.

Note: The IP your computer shows internally and the IP the world sees are usually different. Internal IPs are private and reused everywhere; only your public IP is unique on the Internet — and even that is often shared with neighbours under CGNAT.