Section: Volume B
Explanation/Reference:
Explanation:
Adprep.exe performs operations that must be completed on the domain controllers that run in an existing Active Directory environment before you can add a domain controller that runs that version of Windows Server.
Preparing to run adprep /domainprep (see step 2 below).
To help ensure that the adprep /domainprep command runs successfully, complete these steps before you run the command on the infrastructure operations master role holder in each domain:
Make sure that the schema updates that adprep /forestprep performs replicated throughout the forest

or that they at least replicated to the infrastructure master for the domain where you plan to run adprep /domainprep.
Make sure that you can log on to the infrastructure master with an account that is a member of the

Domain Admins group.
Verify that the domain functional level is appropriate.

References: Running Adprep.exe
https://technet.microsoft.com/en-us/library/dd464018(v=ws.10).aspx