The Window 2012 R2 server is located in a data center behind a Sophos UTM 9 firewall, and the firewall is running NAT from public IP address to the private subnet. I could see on the server the remote IP when using netstat on the correct port number coming through the Sophos firewall. However, when testing from a Windows 7 VM or remotely from the client’s office using a Windows 10 Thin client, it would look like it’s connecting the server, show certificate warning and then fail during the login process.

I also installed an RDP client on my iPhone and it too connected. I wasn’t able to connect from my OSX laptop using Microsoft Remote Desktop v8.x for Mac, but after upgrading I could connect using Microsoft Remote Desktop 10.x no problem. Network Address Translation (NAT) Remote Desktop Connection error Microsoft Windows Server 2012 R2 Standard The client is running Windows Server 2012 R2 Standard with Terminal Services, and they’re having a problem where Remote Desktop Connection is getting an error. Windows 2012 R2 Terminal Services Remote Desktop connection internal error