What is my IP address, why does it keep changing, and which one does my router have?

Every site that shows "your IP" gives me a different number from the one in my router settings, and it changes every few days. I want to host a small game server for friends. What am I looking at?

Two different addresses, both correct:

• Private IP: what your router hands your devices at home, typically 192.168.x.x or 10.x.x.x. Only meaningful inside your network. This is the one in your router's device list.
• Public IP: the address the whole internet sees, assigned to your router by the ISP. This is what "what is my IP" sites show. Your router's admin page shows it as the WAN address.

Why it changes: most ISPs give home customers a dynamic public IP with a lease that gets renewed, so a reboot or a routine renewal can change it. A static IP is usually a paid extra, mostly aimed at businesses.

One more possibility: if your router's WAN address starts with 100.64 to 100.127, you are behind CGNAT, meaning you share a public IP with other customers and you cannot accept incoming connections at all. For hosting you would have to ask the ISP for a real public IP (often a small fee) or use a tunnel service.

For a game server: use a dynamic DNS name so your friends connect to a name that follows your changing IP, forward the game's port on the router, and give the server PC a reserved private IP (by its MAC address) so the forward does not break. IPv6, if your ISP provides it, sidesteps most of this.

Quick commands: ipconfig on Windows and ip a on Linux or Mac (ifconfig on older Macs) show the private address. For the public one, curl ifconfig.me from a terminal, or just ask a search engine "what is my IP".