Dedicated Servers come with one IP address. It is possible to order additional IP addresses through the 1&1 Control Panel. When ordering additional IP addresses, 1&1 ensures that the IP is set to route correctly to your individual server however it is still necessary to add this IP address to the operating system to ensure the server knows which additional IPs are available to use.
When the Remote Desktop session begins responding again, it is advised to restart the server. The IPs should be added already and responding at this time, but please reboot and double-check that there are no problems.