Issue: when adding a new database copy to an Exchange 2013 DAG you receive the following error:
error WMI exception occurred on server ‘EXCH02.enterpriseit.co’: The RPC server is unavailable. (Exception from HRESULT: 0x800706BA)
Cause: As stated this error is caused by RPC communication issues between the Exchange DAG members. Likely ports in the 6001-6032 range are being blocked.
Resolution: You will need to proceed to troubleshooting RPC unavailable 0x800706BA on Windows Server. The preceding link will guide you through diagnosing and troubleshoot RPC communication problems on the network.