Introduction

Many companies have multiple versions of Remote Desktop Session Host servers (formerly known as terminal servers), such as Windows 2000 Server, Windows Server 2003, Windows Server 2008, and Windows Server 2008 R2, in their environment. A remote desktop connection to any of these host servers requires a client access license (CAL) of the same or higher version. The CALs are installed on and managed by a Remote Desktop license server by using Remote Desktop Licensing Manager (RD Licensing Manager). Here you can find how to install and manage different version CALs on a single Remote Desktop license server.
What CALs can a specified license server manage?

Any license server can manage all lower version CALs along with the current version. For example, a license server that is running Windows Server 2008 R2 can manage all lower version CALs including Windows 2000 Server, Windows Server 2003, Windows Server 2008, as well as Windows Server 2008 R2 CALs. These CALs can be installed and managed by the Licensing Administrator on the license server by using RD Licensing Manager in Windows Server 2008 R2.

The license server running Windows Server 2008 R2 will also be able to cater to requests from all lower version terminal servers appropriately, allowing the customer business to continue seamlessly.

Note: Beginning with Windows Server 2008 R2, terminal servers are now called Remote Desktop Session Host servers. All earlier versions are still referred to as terminal servers.

A new feature introduced in Windows Server 2008 R2 allows you to migrate user CALs from one server to another. With this capability, you can migrate your existing Windows Server 2003 CALs from a license server running Windows Server 2003 to a license server running Windows Server 2008 R2 and manage them from the latest server. The attached compatibility matrix shows which CALs can be managed by which license servers.

http://www.danieletosatto.com/wp-content/uploads/2010/03/license_matrix.pdf

 FAQ

1. When a lower version CAL is migrated or installed on a higher version license server, do the rights of the CAL change?

No. For example, if you install a Windows Server 2003 Terminal Services client access license (TS CAL) on a license server running Windows Server 2008 R2, that CAL will only allow the user to access a terminal server running Windows Server 2003 or lower; you cannot use it to access an RD Session Host server running Windows Server 2008 R2.

2. Can a license server manage higher version CALs?

No, a license server can only manage CALs of the same version or lower. For example, a license server running Windows Server 2003 can manage Windows Server 2003 TS CALs and Windows 2000 Server TS CALs, but not Windows Server 2008 or Windows Server 2008 R2 CALs. Note that Windows Server 2008 R2 CALs are compatible with Windows Server 2008 CALs, so both can be managed by Windows Server 2008 (as well as by Windows Server 2008 R2). For more information, see Windows Server 2008 R2 RDS and Windows Server 2008 TS CAL Compatibility.