
Active Directory supports multi-master updates of the directory between all of the domain controllers in a domain. However, some changes are impractical to perform in multi-master fashion because of replication traffic and the potential for conflicts in essential operations. For these reasons, special roles, such as global catalog server and operations masters, are assigned only to specific domain controllers. An understanding of these roles is important because if a domain controller that holds one of these roles is not available, the specific functions of that role in Active Directory will not be available.