Detects whether your ISP is using Carrier-Grade NAT (CGNAT) by probing your local network addresses via WebRTC.
Carrier-Grade NAT (CGNAT) is a technique used by ISPs to share a single public IPv4 address among many customers simultaneously. Instead of assigning you a public IP, your ISP assigns your router an address in the 100.64.0.0 – 100.127.255.255 range (RFC 6598), then NATs your traffic at their infrastructure before it reaches the internet.
Implications of CGNAT: You cannot host servers or services reachable from the internet, port forwarding will not work, some peer-to-peer applications and games may have issues, and your public IP is shared with other customers of your ISP.
How this check works: The browser's WebRTC API is used to collect ICE candidates, which contain your device's real local IP addresses. If any of those addresses fall within 100.64.0.0/10, CGNAT is confirmed. WebRTC-blocking extensions or VPNs can prevent detection.