One of the main challenges in getting SmartLink to operate properly and passing the SmartLink network test to achieve a positive green circle indicator is due to multiple routers performing Network Address Translation (NAT), known as "double NATing" or "multiple NATing" or GC-NAT (Carrier Grade NAT).
SmartLink only works properly when your ISP router is the only device performing NAT, also known as "single NATing". If other routers in your ISP's network are performing network address translations, this situation is not compatible with SmartLink. If the FLEX-6000 or FLEX-8000 is assigned a public IP address or if the radio is in a "DMZ", making it publicly accessible, this configuration is also not supported by SmartLink.
What is Network Address Translation?
Network Address Translation (NAT) is a method used in computer networking to modify network address information in the IP header of packets while they are in transit. Its main purpose is to allow multiple devices on a private network, such as your home network, to share a single public IP address when accessing external networks, like the Internet. The network address translation occurs on your home router, which is connected to your ISP.
What is Carrier Grade Network Address Translation?
Carrier-Grade Network Address Translation (CGNAT or Large-Scale NAT) is an extension of NAT that Internet Service Providers (ISPs) use when they don’t have enough public IPv4 addresses to assign to every customer a unique one. Instead of assigning each customer a public IP, the ISP puts many customers behind a shared public IP address.
What type of diagnostic procedures can I use to determine if my ISP is using CG-NAT, or if my Internet connection has multiple network address translations?
Here are the most effective approaches you can try for detecting whether your ISP is putting your router behind Carrier-Grade NAT (CGNAT) or determining if your Internet connection is passing through multiple layers of NAT (double NAT, triple NAT):
Option 1: Check for Private or Shared Address Ranges
Check the WAN IP address assigned to your router from the ISP using the router's management interface. Check to see if it is one of the classes of IP addresses below.
-
Private IPv4 ranges (per RFC 1918):
- 10.0.0.0 – 10.255.255.255 (10.0.0.0/8)
- 172.16.0.0 – 172.31.255.255 (172.16.0.0/12)
- 192.168.0.0 – 192.168.255.255 (192.168.0.0/16)
-
Shared address range for CGNAT (RFC 6598):
- 100.64.0.0 – 100.127.255.255 (100.64.0.0/10)
👉 If your router’s WAN IP is in the RFC6598 shared range (100.64-127.x.x), your ISP is definitely using CGNAT
👉 If your router’s WAN IP is in the RFC1918 private ranges (10.x.x.x, 172.16–31.x.x, 192.168.x.x), then your router is definitely behind multiple NATs
Option 2. Compare Your Router’s WAN IP vs. Public IP
Check the WAN IP address assigned to your router from the ISP using the router's management interface.
- Compare it to the public IP shown at a site such as https://whatismyip.com.
👉 If they are different, there’s at least one extra NAT between you and the Internet, or your ISP is using CGNAT
Option 3. Run a Traceroute to a Known Public IP Address
- From a PC used to access the FLEX-6000 or FLEX-8000 on your local network, open Command Prompt and run a Traceroute to Google (8.8.8.8)
- Press the Windows Key on your Keyboard or click the Start Button
- Type CMD and press Enter
- In the Command Prompt window, type tracert -d 8.8.8.8
👉 If your TraceRoute test reveals more than one private IP address in RFC1918 private ranges (10.x.x.x), 172.16–31.x.x, 192.168.x.x) or RFC6598 shared range (100.64.0.0/10), then you are definitely behind multiple NATs.
Below is an output from a successful traceroute that is not multi-NATed
C:\Users\HomePC>tracert -d 8.8.8.8
Tracing route to 8.8.8.8 over a maximum of 30 hops
1 <1 ms <1 ms <1 ms 192.168.1.1 (this is your routers LAN interface IP address)
2 1 ms 1 ms <1 ms 61.198.164.1
3 <1 ms 1 ms 1 ms 61.198.165.146
4 11 ms 11 ms 12 ms 61.98.0.25
5 11 ms 11 ms 11 ms 206.126.236.21
6 11 ms 11 ms 10 ms 108.170.246.1
7 11 ms 11 ms 11 ms 216.239.54.205
8 11 ms 11 ms 11 ms 8.8.8.8
Trace complete.
C:\Users\HomePC>