IP Address

When you open a website on your phone or message a friend, invisible chunks of data travel across the internet. In networking, these chunks are called "packets." Just as a shipping box has the sender's and receiver's addresses on it, each packet carries the IP address of where it started and where it is headed.

Without IP addresses, there would be no way to know which of the billions of connected devices should get the data. Your router and other relay devices read the IP address on each packet and, like mail carriers, find the fastest route to the destination. That is how one click from your room can bring you information from a server on the other side of the planet, delivered to your phone screen with no mix-ups.

A string of numbers like `192.168.0.1` is an IP address. It joins four numbers from 0 to 255 with dots, and that pins down exactly where a device sits on the network.

A home has a building address, and each unit inside has its own number. IP addresses split in a similar way into public IPs and private IPs. The IP your internet provider gives your home is a "public IP," and it is one of a kind across the whole world. Think of it as the street address of the whole apartment building. The addresses your home router hands out to your phone, laptop, and smart TV are called "private IPs."

When your router talks to the outside internet, it uses the one public IP as the front door. Inside the house, each device gets its own private IP so data never gets mixed up. This setup lets many phones and laptops get online at once while saving a limited supply of addresses.

You may also have noticed your IP address changing when you connect to Wi-Fi at a cafe or at home. Most homes use a "dynamic IP," which is an address you borrow each time you connect. So if you restart your router or reconnect to the network, your address may change.

The four-number format with dots that most of us still use is called Internet Protocol version 4, or "IPv4." It can make only about 4.3 billion different addresses. When the internet was first built, 4.3 billion seemed more than enough for all of humanity. But the internet spread fast, and by the early 1990s people were already predicting a shortage.

So engineers around the world designed a new format in the mid-1990s called "IPv6," which can make a nearly endless supply of addresses. In 2011, the last new IPv4 addresses were handed out, and as smartwatches and even refrigerators joined the Internet of Things, moving to IPv6 became even more important. IPv6 writes addresses in hexadecimal with colons (:), and it offers a mind-bogglingly huge pool of addresses, enough to give one to every grain of sand on Earth and still have plenty left.

Many people think website names (domains) and IP addresses are separate things. But when you type a name like `google.com` into the address bar, your computer quietly looks up the site's real numeric IP address using "DNS," which works like a phone book. Computers can find another device only by its numeric IP address, not by words.