Airport Extreme - double NAT error message
I have a wireless network with Airport Extreme as the main router and Airport Express as an extender. On the Airport Utility, I am getting a Double NAT warning with an orange light for the Airport Extreme on the graphic of the network. The Airport Express does not show up on the Airport Utility.
My ISP have recently fixed an issue with the internet connection, which is now working fine, as is the wireless network.
I have several MacBooks and iPhones connected to this network.
The internet and wireless network seem to working fine, but I would like to get rid of the error message and able to see the Airport Express on the network.
My main device has OS X Yosemite 10.10.3
Any suggestions?
MacBook Pro, OS X Yosemite (10.10.3)