"IP address" is a term most of us have heard, but what does it actually mean, and where did it come from? In this post I'll go through the history of IP addresses, from the early days of ARPANET to IPv6, and explain the bits that matter for your own home network.
The birth of the internet
The story starts with ARPANET, a research network funded by the US Department of Defense that first connected computers in 1969. It let researchers share data and computing power between universities.
As more networks joined in, they needed one common way to identify every machine and pass data between them. That's where the Internet Protocol (IP) came in. An IP address is a bit like a postal address for a device. Without one, data would have no idea where to go, a bit like trying to deliver post in a city with no street names.
The arrival of IPv4
IPv4 was published as a standard in 1981 (RFC 791), and ARPANET switched over to it on 1 January 1983. That date is often called the birthday of the internet.
IPv4 addresses are 32 bits long, which allows about 4.3 billion unique addresses. At the time, ARPANET connected only a few hundred computers, so that looked like more than anyone would ever need.
An IPv4 address is written as four numbers from 0 to 255, separated by dots, for example 192.168.1.1. Each of the four numbers is 8 bits, which is why they can't go above 255.
Running out of addresses
Then the World Wide Web arrived in the 1990s, followed by broadband, smartphones and smart everything. 4.3 billion addresses wasn't going to be enough.
Two things bought us time:
- Private addresses and NAT. Certain ranges are reserved for private networks:
10.0.0.0/8,172.16.0.0/12and192.168.0.0/16. Your home devices all use addresses like these, and your router uses NAT (Network Address Translation) to share one public address between all of them. - Careful sharing out. Addresses are handed out by IANA to five regional registries, and they pass them on to internet providers. In the UK and Europe, that's RIPE NCC.
It still wasn't enough. IANA gave out its last big blocks of IPv4 addresses in 2011, and RIPE NCC ran out of its general pool in 2019. Today IPv4 addresses are bought and sold second-hand.
The rise of IPv6
IPv6 was designed to fix the shortage for good. It was first specified in 1995 and became a full internet standard in 2017 (RFC 8200).
IPv6 addresses are 128 bits long, which gives about 340 undecillion addresses. That's 340 followed by 36 zeros, enough to give every grain of sand on Earth its own address many times over.
They're written in hexadecimal, in eight groups separated by colons, for example:
2001:0db8:85a3:0000:0000:8a2e:0370:7334
Groups of zeros can be shortened, so that same address can also be written 2001:db8:85a3::8a2e:370:7334. Most UK broadband providers now give homes IPv6 as well as IPv4, and your devices use whichever works best without you noticing.
Public and private addresses
- Public address: the one your router uses on the internet, given to you by your broadband provider. Websites see this one.
- Private address: the ones inside your home, like
192.168.1.37, handed out by your router. They're only meaningful inside your own network, which is why millions of homes can all use192.168.1.1at the same time without a problem.
Static and dynamic addresses
- Dynamic addresses are handed out automatically by a DHCP server (at home, that's your router) and can change over time. This is the normal setup for phones, laptops and most home broadband connections.
- Static addresses are fixed. Servers, printers and things like a Pi-hole need one so other devices can always find them. On a home network, the easiest way is a DHCP reservation on your router, or you can set one by hand, as in my static IP guide for Windows.
How IP addresses and DNS work together
People are good at names and computers are good at numbers. When you type a web address into your browser, the Domain Name System (DNS) looks up the name and returns the IP address of the server. Your device then sends its request to that address, and the reply comes back to your public IP, where your router passes it to the right device. All of that happens in a fraction of a second.
The future
IPv4 and IPv6 will be running side by side for years to come, but more and more of the internet's traffic now uses IPv6, and smart home gadgets and the Internet of Things will only speed that up. The basic idea hasn't changed since the 1980s, though: every device needs an address, and every packet needs to know where it's going.
Next time you type a web address or troubleshoot a connection, spare a thought for the humble IP address. It's one of the unsung heroes of the internet.
