Double NAT can cause issues with your connection. It occurs when two or more routers on a network are performing Network Address Translation (NAT). Generally it does not affect computer use or web browsing but can cause issues with P2P connection.

You can check if you are using a double NAT by performing a trace route. Once the trace route is complete, check the first two IP addresses listed. If they are both private IP addresses, you are using a double NAT. Private IP addresses usually appear in these number ranges:

​10.0.0.0 to 10.255.255.255

172.16.0.0 to 172.31.255.255

192.168.0.0 to 192.168.255.255

In a double NAT set up, the connection will travel through two private networks, which can cause or add to other connectivity issues. It's commonly seen in large networks, such as student accommodation, schools and offices. Forwarding ports can help resolve some of the issues you may be experiencing. For more information on resolving double NAT issues, please contact your internet service provider (ISP) or your router manufacturer.