What is my IP address?

What it is for

• Allow-listing: many servers, firewalls and hosting panels only accept connections from certain addresses. That is where you enter the address shown above.
• Checking a VPN: with a VPN switched on, the address above is that of the VPN server, not of your own connection. If you still see your own, traffic is bypassing the VPN.
• Setting up remote access: to reach your home network from outside, you need to know whether your connection has a public address of its own at all (see carrier-grade NAT further down).
• Troubleshooting: when support asks for your IP, they mean this public address – not the one in your computer’s network settings.

IPv4 or IPv6?

There are two kinds of IP address. IPv4 is 32 bits long and written as four numbers separated by dots, such as 203.0.113.7. IPv6 is 128 bits long and written as hexadecimal blocks separated by colons, such as 2001:db8::7. Both examples come from ranges reserved for documentation only.

Many connections have both today. Which of the two your browser uses for a connection is up to the browser: it tries IPv6 and IPv4 in quick succession and keeps whichever connects first (“Happy Eyeballs”). That is why the tool shows exactly one address – the one this page was just loaded over. If you see IPv6, your connection may still have an IPv4 address as well, and vice versa.

Why the address in your network settings looks different

On your home network your computer has a private address, usually from one of these ranges: 192.168.0.0/16, 10.0.0.0/8 or 172.16.0.0/12. These addresses are reserved for internal networks and cannot be reached from the internet. On the way out, the router translates them into the single public IPv4 address of your connection (NAT). So every device on your Wi-Fi appears with the same IPv4 address. How big your home network is and which addresses in it are free for devices is what the Subnet Calculator works out.

IPv6 is different: each device normally gets its own globally valid address. So that you cannot be recognised by the same address for weeks, most operating systems also create temporary addresses for outgoing connections and change them regularly. Do not be surprised if your IPv6 address looks different tomorrow.

When the address shown is not your own

• Carrier-grade NAT (CGNAT) and DS-Lite: some connections – depending on the provider and plan, and very common on mobile networks – do not get a public IPv4 address of their own. The provider shares one IPv4 address among many customers. You then see the address of your provider’s equipment above, and an IPv4 port forward on your own router leads nowhere. In that case you can only be reached over IPv6.
• VPN, proxy, Tor or “Private Relay”: the connection reaches xmoo.app from the server you route it through. That is exactly what these services are for.
• Company network: behind a corporate firewall you see the address your company uses to go online – shared with all your colleagues.

Does my IP address change?

On home connections it usually does. Many providers assign the public address afresh each time the router reconnects, so it can change after a restart or an outage. If you want to reach your connection from outside under a fixed name, a dynamic DNS service helps; many routers have one built in. Fixed addresses usually come only with business plans.

Limits of this tool

• It shows only the one address this page was loaded over – not both at once.
• It does not look up a location or a provider. Such details come from databases that often know only the provider’s city and are regularly wrong for mobile connections.
• It cannot check whether your connection can be reached from outside.

Privacy: to show the address, your browser asks my server which address your request arrives from. The address is only displayed, not stored; my server keeps no access log (privacy policy, section 3).

Sources

• IPv4, 32-bit addresses: RFC 791
• IPv6, 128-bit addresses: RFC 8200, text representation: RFC 5952
• Private IPv4 ranges: RFC 1918
• Shared address space for carrier-grade NAT: RFC 6598, DS-Lite: RFC 6333
• Happy Eyeballs: RFC 8305
• Temporary IPv6 addresses: RFC 8981
• Documentation addresses: RFC 5737 (IPv4), RFC 3849 (IPv6)