1. Open your router status
Look for Internet, WAN or Connection status. Copy the IPv4 address shown there.
Free network tool
CGNAT test
Compare your router’s WAN address with your public IPv4 address to check for upstream NAT.
Your result
Checking
Finding your public address…
Next, enter the WAN IPv4 address shown on your router’s Internet status page.
Public IPv4Checking…
Turn off your VPN or proxy before comparing. A router address in 100.64.0.0–100.127.255.255 is a strong sign of shared carrier address space.
Find the right address to compare
Carrier-grade NAT (CGNAT) lets an internet provider share a public IPv4 address across several customers. This can prevent a port forwarding rule on your own router from making a home server reachable from the internet.
Use the WAN address on the ISP-facing router or modem, rather than your computer's local address. Once the WAN comparison is complete, use the open port checker to test whether your running service accepts an incoming TCP connection.
2. Compare the addresses
Matching public IPv4 addresses show no upstream IPv4 address translation on the observed path. A mismatch needs more context.
3. Understand private ranges
A WAN address starting with 10, 192.168 or 172.16–172.31 shows upstream NAT. It may be another router or your ISP.
4. Confirm with your ISP
Ask whether your connection uses CGNAT and whether a public IPv4 address is available. Use an outbound tunnel when router port forwarding is unavailable.
View comparison details
Run the test to see its detected details.
Common questions
Can the browser check CGNAT on its own?
Usually not. Your browser cannot read the router’s WAN address, so entering it provides the missing comparison.
Does a private WAN address prove CGNAT?
No. It proves private addressing upstream of that router. Another home router can cause the same result.
Why is my public IPv4 unavailable?
Your browser may be using an IPv6-only path, or the IPv4 probe may have failed. The tool needs a confirmed IPv4 path for an IPv4 WAN comparison.
Why does CGNAT affect port forwarding?
Your router cannot usually create inbound forwarding rules on an ISP’s shared router. Your ISP may offer a public IP, or you can use an outbound tunnel.
