Double NAT Test
Check whether another private NAT layer sits between your router and the public internet.
Double NAT check
Enter the WAN IPv4 shown by the router closest to your devices. Connection Vitals compares it with the public IPv4.
The public IP shown here is detected from this browser request. External probes are restricted to that same public IP.
Look for another private router or gateway upstream
If the router closest to your devices receives a WAN IPv4 in 10/8, 172.16/12 or 192.168/16, another device is translating traffic before it reaches the public internet. In a home network that is commonly a second router or an ISP gateway, but the address alone cannot identify which device owns the upstream layer.
What to do with that finding
- Identify which upstream device owns the next routing layer.
- If appropriate for your network, put one layer in bridge/AP mode or configure the required inbound mapping at both routing layers.
- Retest after changing one layer so the result remains interpretable.
Do not label 100.64.0.0/10 as ordinary double NAT
That block is Shared Address Space reserved for carrier-grade NAT use. If it appears as the WAN address, continue with the CGNAT Test rather than troubleshooting a second household router.
For a port that still fails after the address path is understood, follow the port-forwarding troubleshooting order.