Carrier-Grade NAT (CGNAT) is when an ISP shares one public IPv4 address among many customers. Your router typically gets an address in 100.64.0.0 – 100.127.255.255 (RFC 6598), and the ISP NATs traffic before it reaches the internet.

What are the implications of CGNAT?

You generally cannot host inbound services, port forwarding fails, some peer-to-peer apps and games struggle, and your public IP is shared with other customers of your ISP.

How does this CGNAT check work?

The browser's WebRTC API collects ICE candidates that include local IP addresses. If any address falls within 100.64.0.0/10, CGNAT is confirmed.

Why was detection blocked?

A VPN or WebRTC-blocking extension can prevent local IP discovery. Disable the block or temporarily allow WebRTC, then re-run the check.

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CGNAT Check

Detects whether your ISP is using Carrier-Grade NAT (CGNAT) by probing your local network addresses via WebRTC.

What is CGNAT?

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.

Frequently Asked Questions

What is CGNAT?: Carrier-Grade NAT (CGNAT) is when an ISP shares one public IPv4 address among many customers. Your router typically gets an address in 100.64.0.0 – 100.127.255.255 (RFC 6598), and the ISP NATs traffic before it reaches the internet.
What are the implications of CGNAT?: You generally cannot host inbound services, port forwarding fails, some peer-to-peer apps and games struggle, and your public IP is shared with other customers of your ISP.
How does this CGNAT check work?: The browser's WebRTC API collects ICE candidates that include local IP addresses. If any address falls within 100.64.0.0/10, CGNAT is confirmed.
Why was detection blocked?: A VPN or WebRTC-blocking extension can prevent local IP discovery. Disable the block or temporarily allow WebRTC, then re-run the check.

Related Tools

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CGNAT Check

Detects whether your ISP is using Carrier-Grade NAT (CGNAT) by probing your local network addresses via WebRTC.

What is CGNAT?

Frequently Asked Questions

What is CGNAT?: Carrier-Grade NAT (CGNAT) is when an ISP shares one public IPv4 address among many customers. Your router typically gets an address in 100.64.0.0 – 100.127.255.255 (RFC 6598), and the ISP NATs traffic before it reaches the internet.
What are the implications of CGNAT?: You generally cannot host inbound services, port forwarding fails, some peer-to-peer apps and games struggle, and your public IP is shared with other customers of your ISP.
How does this CGNAT check work?: The browser's WebRTC API collects ICE candidates that include local IP addresses. If any address falls within 100.64.0.0/10, CGNAT is confirmed.
Why was detection blocked?: A VPN or WebRTC-blocking extension can prevent local IP discovery. Disable the block or temporarily allow WebRTC, then re-run the check.