How the CGNAT Test Works
This tool compares the WAN IPv4 shown by your router with the public IPv4 that 17NAS observes from your current web request. It does not connect to or probe the address you enter.
Network Diagnostics
CGNAT Checker & Test
Compare the WAN IPv4 shown by your router with the public IPv4 seen by 17NAS to identify signs of CGNAT, double NAT, or upstream NAT.
No port scan. The WAN address you enter is never probed.
CGNAT Checker & Test
Step 1
Your public IPv4
216.73.216.48This is the public IPv4 that 17NAS observed from your current web request.
Where to find your router WAN IPv4
Look for one of these fields on your router Internet / WAN / status page: WAN IP, Internet IP, IPv4 Address, or External IP
Do not enter your router's LAN address or default gateway.
Ready to check
Comparison evidence
Router WAN IPv4
Public IPv4
Address classification
Comparison
This is an address-observation diagnostic, not proof of CGNAT. Even a matching address does not guarantee inbound connectivity or successful port forwarding.
Next steps
Use these tools to continue checking inbound connectivity and network configuration after comparing the addresses.
How to Read Your Result
- An address in 100.64.0.0/10 belongs to the RFC6598 shared address space and is a strong CGNAT signal.
- An RFC1918 address indicates private NAT upstream of your router, which may be another router, double NAT, or carrier equipment.
- When the two public addresses match, a public IPv4 is likely available on the current connection, but firewall and port reachability still need separate checks.
- When two valid public addresses differ, upstream NAT is likely; one address comparison cannot prove CGNAT by itself.
Why CGNAT Can Affect Port Forwarding
Upstream NAT can prevent a home router from directly controlling internet-side inbound mappings, which may affect remote NAS access, home servers, game servers, or P2P connections. Relay, VPN, or IPv6 alternatives may still work.
What to Do If You Are Behind CGNAT
First confirm the WAN and public addresses, then check the open port and local port-forwarding setup. If you need inbound access, ask your ISP about a public IPv4 or consider IPv6, a VPN, or a reverse tunnel.