A list of all Operations Master roles and their uses.
What are Operations Master roles?
Operations Masters are unique server roles within a domain or forest that ensure the overall operation of AD. Although DCs are peers in replication, each Operations Master role is held by only one server, usually the first server in the domain or forest. There are five Operations Master roles: two unique to the entire forest (usually held by its first DC) and three unique to each domain (usually held by the first DC in each domain). This is because normal replication is multimaster, with all DCs equal and holding a writable directory copy, so some values cannot be handled this way and instead use a singlemastermodel, where one DC is the master and changes are made there. These roles are called Operations masters roles. Changes to the same value in multiple locations are checked for collisions using the attribute's version number.
Schema master – a forest-wide role
Schema master maintains and manages the entire AD schema. If you request a schema upgrade on any DC, that DC contacts the schema master, which performs the upgrade. The modified AD database schema is then distributed to all DCs according to the configured replication. A schema change cannot be undone!!!
Domain naming master – a forest-wide role
Domain naming master is responsible for checking and managing all names within domains and forests. When adding or removing a domain, this role is contacted to determine whether the action is possible.
RID master – a domain-wide role
Relative Identifier (RID) Master allocates blocks of RIDnumbers to controllers for creating SID (security identifiers – unique identifiers for every object in AD). After exhausting its allocation, each DC contacts the RID master for another block of RID.
PDC emulator – a domain-wide role
Primary domain controller (PDC) emulator handles time synchronisation between DCs and down to clients, and maintains the most current list of password hashes for all users. If a DC cannot authenticate a user (invalid password), it contacts the PDC emulator to check whether it has more current password hash data.
Infrastructure master – a domain-wide role
Infrastructure Master maintains links between objects in different domains and uses the global catalog.
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