Public and private IP addresses

The address websites see and the address your phone shows in its Wi-Fi settings are two different numbers. One is public, the other is private.

Two addresses, two jobs

A public IP address is unique on the whole internet. Your internet provider gives one to your router (or shares one between several customers). Every website you visit sees this address.

A private IP address is unique only inside your own home or office network. Your router hands one to each device that joins the Wi-Fi. It never travels on the internet, which is why the same private addresses can be used in millions of homes without any clash.

The private ranges

Three blocks of IPv4 addresses are set aside for private use. Any address inside them is private.

Two more ranges are worth knowing. 100.64.0.0 to 100.127.255.255 is used by internet providers for carrier-grade NAT. 169.254.x.x is an address a device gives itself when the router did not answer; if you see it, the connection is not working.

Type any address into our address checker to see which kind it is.

How one public address serves a whole house: NAT

Your router does a job called NAT (network address translation). When your laptop at 192.168.1.7 asks for a web page, the router rewrites the request so that it appears to come from the public address, remembers which device asked, and passes the reply back to it. From outside, the whole house looks like one device.

This has a useful side effect. A stranger on the internet cannot start a connection to your laptop, because the router has no note telling it which device an unasked-for packet is meant for, so it drops the packet. That is not a full firewall, but it stops a great deal.

How to tell which one you are looking at

• The address on the home page of this site is your public address.
• The address in your phone's or computer's Wi-Fi settings is your private address. Steps: Windows, Android and iPhone, Mac and Linux.
• The "gateway" or "router" address in those settings, often 192.168.1.1 or 192.168.0.1, is the private address of the router itself. See logging in to your router.

When the difference matters

• Setting up a printer, camera or game server at home: you use private addresses.
• Port forwarding or reaching a home camera from outside: you need your public address, and it must really be yours alone, not shared by the provider.
• A support person asks "what is your IP?": ask which one. For "the site has blocked me" they need the public one. For "my printer is not found" they need the private one.