CGNAT

At home, your router uses NAT to share one public IP address among all your devices. CGNAT (carrier-grade NAT) adds a second layer of the same trick inside your internet provider. Your router no longer gets a public address; it gets a private one from the provider, and the provider's big NAT boxes share each public IPv4 address among many customers at once.

Providers do it because IPv4 addresses ran out and buying more is expensive, while the number of customers, especially on mobile networks, keeps growing. A special range, 100.64.0.0/10, was reserved in 2012 (RFC 6598) for the addresses between the customer and the carrier NAT, so they do not clash with the 192.168.x.x addresses inside homes. If your router's WAN address starts with 100.64 to 100.127, you are almost certainly behind CGNAT.

For browsing and streaming you will not notice. The problems appear when someone outside needs to reach you: you cannot open ports to host a game server, a security camera or remote access, and some peer-to-peer apps and online games struggle. Because many people share one address, a block or ban aimed at one abusive user can hit all of them. Common ways out are asking the provider for a public IP (sometimes for a fee), using IPv6, or a tunnel or VPN service.