Q. What's Remote Desktop Services IP Virtualization and why would I want it?

A. With RDS, multiple users have their own sessions on a single OS server instance. Because these sessions are on the same server OS instance, they all share the IP address of the server. The sharing of an IP address for multiple sessions sometimes causes problems in an environment. For example:

• Certain applications, such as a softphone (VoiP with RDP 7 bi-directional audio support introduced in Windows 7 and Windows Server 2008 R2) require a unique IP address that can't be the same as any other instance of the application. Some management applications work based on the clients' IP addresses.
• Tracking of traffic by IP address (all users on the same RDS server would have the same IP address and are therefore difficult to track).
• Filtering or charging traffic based on IP address.

Windows Server 2008 R2 Remote Desktop Services Session Host (RDSH) introduces a new feature, IP virtualization, that allows each session to have its own virtual IP address. Each user session gets a unique IP address for its network communication. The IP virtualization has two modes: per-session, where the entire user session uses the virtual IP address, or per-program, where only certain programs run by the user run with a virtual IP address (such as the problematic softphone application).

IP Virtualization uses a DHCP server that's configured for the same subnet as the RDSH server, so make sure the DHCP scope has enough addresses to cater for all the new IP addresses that will be used by the RDS users. To enable it, use the RD Session Host Configuration snap-in and select the Properties of the server. Under RD IP Virtualization, check Enable IP virtualization and select the adapter on the RDSH server and IP virtualization mode. If you use Per program, you need to select the programs that should use IP virtualization.

New users logging on will now get a virtual IP address that will be used for their communication.