Issue: When installing Exchange 2013 or a 2013 Cumulative Update you receive the following error: “Setup can’t use the domain controller because it belongs to Active Directory site SITENAME. Setup must use a domain controller in the same site as this computer COMPUTERNAME”
Cause: The setup process is attempting to perform a /prepareschema or /preparead in order to update AD schema for the version of Exchange or CU being installed. Further, forstprep and domainprep must be ran on a machine in the same site as the Schema master (or on the schema master itself).
1) Copy the Exchange 2013 media or Cumulative Update to a machine in the same site as the Schema Master, or to the Schema Master itself.
2) Run Exchange 2013 setup /prepareschema and setup /preparead from the machine in step one, which is in the same site as the Schema Master (or from the Schema Master). Use the link for the complete procedure.