CGNAT Check

Checker

Best-effort CGNAT checker

This online, best-effort CGNAT test compares the WAN IPv4 shown by your router with the public IPv4 visible from the web. It can highlight strong signs of upstream NAT, but it cannot conclusively prove ISP policy.

CGNAT checker

Check your public IP against your router WAN IP

We can see the public IP used for this request. Enter the WAN IPv4 from your router's status page so the checker can compare them.

Your public IP

Checking...

This is the address visible to this site, not the address copied from your router.

Where do I find my router WAN IP?

Default Gateway / Router address is not the WAN IP

The gateway only helps you reach the router admin page. The checker needs a separate field labelled WAN IP, Internet IPv4, Broadband IPv4, Cellular IPv4, External IPv4, or similar.

Open your router or gateway

Choose the device you are using:

Windows

  1. Run ipconfig in Command Prompt.
  2. Find Default Gateway on the active connection.
  3. Open that gateway address in your browser.
  4. Sign in and find the separately labelled WAN or Internet IPv4.

Using a phone hotspot?

Your phone may not expose the carrier-side WAN IPv4. The Default Gateway on your computer is usually only the local link to the phone. If no WAN IPv4 is available, do not guess.

See the full WAN-IP guide

Router page won't open?

Try HTTPS or check whether the router uses an ISP or manufacturer app. On phone hotspots, workplace Wi-Fi, hotel Wi-Fi, or other managed networks, the upstream WAN address may not be available.

Do not enter your device's own local IP. The checker needs the WAN or Internet IPv4 shown by the router or gateway.

IP comparison

Public IP seen here
Checking...
Router WAN IP
Not entered
Comparison
Waiting for WAN IP

Result

Enter your router WAN IP

The checker needs the WAN or internet IPv4 shown by your router before it can compare anything useful.

Best-effort result. Browser-based checks are best-effort only. They can suggest CGNAT, but they cannot conclusively prove every ISP policy, network topology, or firewall condition.

What to do next

  1. 1.Open your router status page and find the WAN, internet, or external IPv4 address.
  2. 2.Enter the WAN IP exactly as shown by the router.
  3. 3.If the router only shows IPv6, treat this check as informational and confirm connectivity with your ISP or router vendor guidance.

How to use the result

  1. 1. Find the WAN IP

    Open your router status page and look for the internet or WAN IPv4 address. If you are not sure which value matters, use the WAN IP guide.

  2. 2. Run the CGNAT test

    Enter the WAN IP exactly as shown and compare it with the detected public IP online.

  3. 3. Verify the result

    If the result suggests CGNAT, confirm it with your ISP and check for double NAT at home.

Keep troubleshooting

Related toolkit pages

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Port Checker

Test whether a TCP port appears reachable from the public internet.

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NAT Type Check

Understand open, moderate, and strict NAT in plain English.

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Guide

What is CGNAT?

Learn why shared IPv4 can block hosting, peer connections, and inbound access.

Read more

Guide

Why port forwarding fails

Work through the most common causes of closed inbound connections.

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Guide

How to find your router WAN IP

Make sure you compare the checker against the actual internet-facing IPv4.

Read more

Guide

Solutions

Compare free and paid ways to work around CGNAT or other inbound issues.

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Methodology

How CGNATCheck works

Read the comparison methodology, example results, and technical limits.

Read more