Our AD domain functional level is still on 2003. Our current Domain Controllers are on either 2003 or 2008R2. We recently have purchased some more new MS server licenses which come with 2016. Question to you, considering our current functional level is still on 2003, can we add 2016 server to be our domain controller and hope it will work well with other 2003/2008 domain controllers? Is there any compatibility issue for doing that?