Hi there,
I have set up the Microsoft MFA Server and RD Gateway per TechNet http://technet.microsoft.com/en-us/library/dn394287.aspx and having an issue with RADIUS. The RD Gateway sessions would not make it to triggering MFA and time out. I ran Wireshark on the MFA server to verify the RADIUS packets were making it OK to the system over UDP. When looking at the MFA server log for RADIUS I noticed:
Received invalid ACCESS_REQUEST packet. Dropping packet.