An address for every connection
For two devices to exchange data, each needs to be identifiable. On the internet and on home networks, that identifier is an IP address, a number assigned to a device or connection so that data sent across a network knows where to go and where to come back to. It works much like a postal address: without one, a reply would have nowhere to be delivered.
What an address looks like
The older and still most common format, IPv4, writes the address as four numbers between 0 and 255 separated by dots, such as 192.168.1.20. Because it is built from 32 bits, it allows a little over 4.29 billion possible addresses (2 to the power of 32 is 4,294,967,296). That sounded like plenty when it was designed, but the number of connected devices worldwide has far outgrown it.
The newer format, IPv6, uses 128 bits and is written in longer groups of letters and numbers separated by colons. It provides vastly more addresses, enough that shortage is no longer a concern. Many providers and websites support both formats, and your devices usually switch between them without you doing anything.
Public and private addresses
There are two layers of addressing in a typical home.
The public address is the one the wider internet sees. Your provider assigns it to your connection, and websites you visit see requests as coming from it. All devices in the house usually share this single address.
Private addresses are used only inside your home. Certain ranges are reserved for this purpose and are never used directly on the public internet. The commonly used ranges are those starting with 10., those from 172.16. to 172.31., and those starting with 192.168.. That is why many home networks look so similar: your laptop at 192.168.1.20 and a stranger’s laptop at 192.168.1.20 do not clash, because the two networks never meet directly.
The router translates between the two worlds. When your phone requests a page, the router sends the request out under the public address and, when the reply returns, passes it on to the phone’s private address. The essential point is that private addresses make one public address go a long way.
How devices get their address
When a device joins the network, the router normally assigns it a private address automatically through a service called DHCP. The address is loaned for a period and may be renewed or replaced later. You can see yours in the network settings of a phone or computer, usually under the Wi-Fi details.
If you need a device, such as a printer or a media server, to be found reliably, you can ask the router to reserve the same address for it each time, or set one manually, taking care not to duplicate an address already in use.
Why the public address can change
Most providers give home customers a dynamic public address, which can change when the router restarts, or after a period of time. Some offer a fixed (static) address, often at extra cost. For ordinary browsing and streaming this makes no difference.
Some providers also share one public address among several customers, a practice often called carrier-grade NAT. This can cause trouble when you try to reach a device in your home from outside, such as hosting a game or accessing a camera directly. If that applies, checking with the provider is the usual route.
What an address does and does not reveal
A public address generally gives a rough location, often the city or region of your provider’s equipment, not your street address. Websites and advertising systems can use it as one clue among many for location tracking, and combined with other information it can contribute to what is known about you. It does not by itself identify you as a person: only your provider can link it to your account, and they usually keep that private unless legally required to share it.
If you are concerned about online privacy, remember that the address is only one piece. Cookies and accounts reveal far more. A virtual private network replaces the address that sites see with the service’s own, which can reduce one kind of exposure, though it shifts trust to the VPN company.
Gadgets and addresses
Every device on your network counts, not just phones and laptops. Cameras, speakers, TVs and the many gadgets in the internet of things each take a private address. If you open your router’s list of connected devices, you may be surprised by how many there are, and unfamiliar entries are worth investigating.
Looking up your own addresses
- Private address: check the network or Wi-Fi details on your device.
- Router’s address: often printed on the router, and commonly something like
192.168.1.1; it is the number you type into a browser to reach its settings. - Public address: search for “what is my IP” on a search engine, or look in the router’s status page. The two sometimes differ, which can reveal that your provider shares addresses.
Treat the public address as mildly sensitive rather than secret. There is no need to hide it, but there is little reason to publish it either.