There are some ports necessary to communicate between the RED device and the RPS (TCP 3400) as well as between the RED device and the ASG (Port 3400 TCP / UDP), and if those ports are blocked, you are lost. The ports are hardcoded and cannot be changed, so the only chance to get the RED device working is switching to an ISP that does not filter these.
What do you mean exactly by RED does not register? Do you already have problems while adding your RED device on your ASG or does the RED device signal an error?
and I can telnet to red.astaro.com port 3400, and I have learned that TELE Greenland does not block udp/tcp port 3400 and the speedstream 5100 is configured to use port NAT.