How to Check for Double NAT
Learn how to detect double NAT by comparing your public IPv4 address, router WAN IP, private address ranges, and home network topology.
Double NAT happens when traffic passes through two separate NAT routers before reaching the public internet. The common home setup is an ISP gateway doing routing, plus a second Wi-Fi router also doing routing.
Double NAT can make port forwarding, game hosting, remote access, and some peer-to-peer connections confusing because opening a port on only one device may not expose the service to the internet.
Quick Answer
To check for double NAT, compare the public IPv4 address seen by an outside checker with the WAN or Internet IP shown in your router. If your router WAN IP is private, and that private upstream device is another router in your home, you likely have double NAT. If the WAN IP is 100.64.0.0/10 or an ISP-controlled private address, check for CGNAT too.
What Is Double NAT?
A single home router normally translates between private LAN addresses and one public internet address. Double NAT adds another translating device upstream, so the second router receives a private WAN address instead of a public one.
This is different from CGNAT. With double NAT at home, you often control both devices and can bridge one router or use access point mode. With CGNAT, the extra NAT layer is usually inside the ISP network.
How to Check if You Have Double NAT
1Find your public IPv4 address
Run the NAT checker or any public IP checker from a device on the same network. This is the IPv4 address outside services see.
2Find your router WAN or Internet IP
Log in to your router and look for WAN IP, Internet IP, IPv4 address, or status. Do not use your device's local address such as 192.168.1.25.
3Check whether the WAN IP is private or shared
Private ranges are 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. Shared address space is 100.64.0.0/10. A router WAN IP in one of these ranges means another NAT layer exists upstream.
4Identify the upstream device
Look at your wiring and admin pages. If your router plugs into an ISP modem/router that also has Wi-Fi, LAN DHCP, or firewall settings enabled, both devices may be routing.
5Confirm by changing topology or checking the first gateway
If you can log in to the upstream gateway, check whether it holds the public IPv4 address. If it does, the issue is local double NAT rather than ISP CGNAT.
How to Read the Result
| Signal | Meaning | Next step |
|---|---|---|
| Router WAN IP matches public IPv4 | Your router likely has a normal public IPv4 address. | Focus on firewall, UPnP, port forwarding, or app settings. |
| Router WAN IP is 10/8, 172.16/12, or 192.168/16 and the upstream box is in your home | Likely local double NAT. | Bridge the ISP gateway or set the second router to access point mode. |
| Router WAN IP is 100.64.0.0/10 | Strong CGNAT signal. | Read the CGNAT guide and ask the ISP about public IPv4. |
| Router WAN IP is public but different from public checker result | There may be upstream translation, VPN/proxy behavior, or multiple WAN paths. | Disable VPN/proxy and compare from the same network again. |
How to Fix Double NAT
Put the ISP gateway in bridge mode
Bridge mode lets your own router receive the public address and handle routing, Wi-Fi, firewall, and port forwarding.
Use access point mode on the second router
If you want the ISP gateway to stay as the main router, set the second router to AP mode so it stops doing NAT.
Remove one routing layer
Use only one router when possible. Fewer NAT layers make port forwarding and device discovery easier.
Do not treat ISP CGNAT as local double NAT
If the upstream NAT is inside the ISP network, router bridge mode at home will not remove it. You may need public IPv4, IPv6, a relay, or a tunnel.
Double NAT vs CGNAT
Double NAT and CGNAT can both make port forwarding fail, but the fix is different. Double NAT is usually local equipment you can reconfigure. CGNAT is upstream address sharing controlled by the ISP.
Check for CGNATStart With Your Current NAT Result
Run the NAT checker first, then compare the public IPv4 with your router WAN IP. That gives you the shortest path to the right fix.
Check NAT Type Now →FAQ
What does double NAT detected mean?
It means the device or app believes your connection passes through more than one NAT layer. Confirm by comparing public IPv4, router WAN IP, and the upstream gateway.
Does double NAT affect speed?
It usually does not reduce raw download speed by itself, but it can break hosting, port forwarding, device discovery, and some P2P connections.
How do I fix double NAT without bridge mode?
Set your own router to access point mode, remove the second router, or put the gaming device behind the main router only. DMZ can help in some setups, but it is usually not the cleanest first choice.
Does double NAT cause strict NAT in games?
It can. If only one router has forwarding rules, the other router may still block the inbound path, so games may report Strict or Moderate NAT.