There are many different virtualisation options available in order to successfully host virtual machines on a 1&1 Dedicated Server. Unfortunately, virtualisation is not possible for 1&1 Dedicated Server Managed, 1&1 Virtual Servers or 1&1 Dynamic Cloud Servers because they are already virtual environments themselves or because they do not offer administrative or root-level access.
When configuring your virtual environment on a 1&1 Dedicated Server, please ensure that the guest machines are configured to use NAT as the networking mode. This is necessary as no traffic is permitted across the 1&1 network from any unknown interface.
Using NAT ensures that the traffic is routed through the host's networking interface and permitted across the internal network. Using an alternate method such as bridged mode is likely to generate outgoing traffic using an unknown virtual interface, which will result in the networking port of the server to be disabled for security reasons.
It is possible to order up to 7 additional IP addresses for 1&1 Dedicated Servers which can then be configured on the host machine to forward traffic directly to the guest machines in combination with NAT. If configured correctly, this should result in providing a dedicated IP address for each virtual machine on the host so that it can be reached from external sources. Unfortunately, 1&1 can not offer assistance in such advanced configuration or troubleshooting.