Having already looked at what the operations masters roles are responsible for in previous articles, in this section we take a look at the actual management of the 5 roles, which includes the transfer or seizing of the roles. Just to quickly recap, the operations masters roles are special role held by certain domain controllers on a per domain/ per forest basis. The 5 roles are:
- Schema Master – controls originating updates to the Schema. One domain controller per forest holds this role.
- Domain Naming Master – controls the addition / deletion of domains from the forest. This system must also be a Global Catalog Server. One domain controller per forest holds this role.
- PDC Emulator – acts as the PDC for BDCs when the domain is in mixed mode, manages password changes for downlevel (pre-win2k) clients, is the focus for group policy changes, and is immediately forwarded all password changes. One domain controller per domain holds this role.
- RID Master – allocates the pool of relative identifiers (RIDs, which are the unique part of SIDs) to each domain controller in the domain. One domain controller per domain holds this role. Note that you can view the RID pool allocation using a utility called dcdiag, the domain controller diagnostic utility.
- Infrastructure Master – is responsible for updating user-to-group references between domains. This role should not be held on a domain controller which is also acting as a global catalog server – the infrastructure master will not function in this scenario because it holds a copy of all objects, and therefore has no external references. One domain controller per domain holds this role.
The ability to transfer roles is important, since a domain controller may need to be taken offline for maintenance. In this scenario, we simply transfer the role as will be described shortly. However, in the event that a DC holding an operations master role should crash, we might need to transfer the role by seizing it, a more drastic action. If you are taking a domain controller offline for a significant period of time, be sure to transfer the roles that the domain controller holds. Note that since changes to the schema and adding and removing domains are both rare, it may not be necessary to transfer these roles, even if a domain controller needed to be taken offline for a longer period of time.