One question I often hear is what CAL types can be used with what OS versions of Remote Desktop Licensing Server and Remote Desktop host server. 

Background information: 


Windows Server 2016 RD Licensing article
Windows Server 2012 R2 licensing document
Windows Server 2008R2 How To Install CALs article
How to control issuance of RDS CALs

The following matrix shows which TS CAL’s and RDS CAL’s can be entered on different versions of the TS and RD Licensing Server:

   TS|RD Licensing Server OS Version
CAL type 2000 2003 2003R2 2008 2008R2 2012 2012R2 2016
2000
Yes
Yes
Yes
Yes
Yes
No
No
No
2003
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
2008(2)
No
No
No
Yes
Yes
Yes
Yes
Yes
2012
No
No
No
No
No
Yes
Yes
Yes
2016
No
No
No
No
No
No
No
Yes

The following matrix shows which TS CAL’s and RDS CAL’s can be used to allow a user to connect to an RDS host OS version (from official article):


   RD Session/Virtual Host OS version
CAL type 2000 2003 2003R2 2008 2008R2 2012 2012R2 2016
2000
Yes
No
No
No
No
No
No
No
2003
Yes
Yes
Yes
No
No
No
No
No
2008
Yes
Yes
Yes
Yes
Yes
No
No
No
2012
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
2016
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes

 
Notes:
(1) Per http://technet.microsoft.com/en-us/library/hh553159(v=ws.10).aspx to install RDS CAL’s on a Windows Server 2008 License Server, http://support.microsoft.com/kb/968074 required

(2) Despite the new name, the Windows Server 2008 TS CAL is functionally equivalent to the Windows Server 2008 R2 RDS CAL (per  http://technet.microsoft.com/en-us/library/hh553159 )        

(3) Can be RDSH (Session-based) or RDVH (Virtual machine-based).