I have a question regarding domain functionality. I have completed upgrading my domain from Server 2003 to 2012 R2. At the moment, the domain functional level is still 2003. MSPDC1 is server 2003 and MSPDC2 is server 2012 R2. In the coming months, I will be running DC promo on the 2003 domain controller. I will then reformat and install a fresh copy of server 2012R2 on MSPDC1 and this will be the additional domain controller running server 2012R2. At the moment, does it cause any issue having a 2003 domain controller and 2012 domain controller existing together? Everything is working and in Sync.