Requirement to be met before promoting an additional domain controller in our domain. We must prepare our active directory using the ADPREP utility that we will have on the Windows Server CD/DVD 2008 R2 to prepare each domain, The forest, Group Policies and if we are interested in having RODC (Read Only Domain Controller).

From the domain controller with the Schema Master FSMO function we will run ADPREP. We will have this utility in the directory “SupportADPrep” if our DC is 32bits we can run adprep32.exe, if it is 64-bit directly adprep.exe. First we will execute “adprep32 /domainprep” to prepare the local domain or “adprep /domainprep”. We could take advantage of the command and run Group Policy preparation using '/gpprep'.

We wait for all our domain controllers to have the new replicated information and run “ADPREP32 /ForestPrep” to prepare the forest or “adprep /forestprep”.

If we haven't previously updated the Group Policy object (GPO) we can update it by “adprep32 /domainprep /gpprep” to update GPOs or “adprep /domainprep /gpprep”.

And if we need to have a read-only domain controller (RODC Read Only Domain Controller), we must expand this information by “ADPREP32 /RODPREP” or “adprep /rodprep”.