Active Directory has five special roles which are vital for its smooth running as a multimaster system. Some functions of AD require there is an authoritative master to which all Domain Controllers can refer to. These roles are installed automatically and there is normally very little reason to move them, however if you demoting a DC and DCPROMO fails to run correctly or have a catastrophic failure of a DC or you are Installing a new DC that is a lot more powerful than your old DC, you will need to know about these roles to recover or transfer them to another DC.
The Five FSMO roles are divided in two Categories as shown in Image below
There are five FSMO roles, two per forest, and three in every Domain.
Forest Wide Roles:
- Schema Master
The schema is shared between every Tree and Domain in a forest and must be consistent between all objects. The schema master controls all updates and modifications to the schema.
- Domain Naming
When a new Domain is added to a forest the name must be unique within the forest. The Domain naming master must be available when adding or removing a Domain in a forest.
Domain Wide Roles:
- Relative ID (RID) Master
Allocates RIDs to DCs within a Domain. When an object such as a user, group or computer is created in AD it is given a SID. The SID consists of a Domain SID (which is the same for all SIDs created in the domain) and a RID which is unique to the Domain.
When moving objects between domains you must start the move on the DC which is the RID master of the domain that currently holds the object.
- PDC Emulator
The PDC emulator acts as a Windows NT PDC for backwards compatibility, it can process updates to a BDC.
It is also responsible for time synchronizing within a domain.
It is also the password master (for want of a better term) for a domain. Any password change is replicated to the PDC emulator as soon as is practical. If a logon request fails due to a bad password the logon request is passed to the PDC emulator to check the password before rejecting the login request.
- Infrastructure Master
The infrastructure master is responsible for updating references from objects in its domain to objects in other domains. The global catalogue is used to compare data as it receives regular updates for all objects in all domains.
Any change to user-group references are updated by the infrastructure master. For example if you rename or move a group member and the member is in a different domain from the group the group will temporarily appear not to contain that member.
Unless there is only one domain in Forest Infrastructure role should not be on the DC that is hosting the global catalogue. If they are on the same server the infrastructure master will not function, it will never find data that is out of date and so will never replicate changes to other DCs in a domain.
If all DCs in a domain also host a global catalogue then it does not matter which DC has the infrastructure master role as all DCs will be up to date due to the global catalogue.
How to Check which server have the FSMO Roles-
Open the Command Prompt and Type- “netdom query fsmo” and press enter.
This Command will tell you the server which have the FSMO Roles.
Transfer FSMO roles-
There are 2 ways to Transfer FSMO roles-
First one is using GUI and second is using the Command line Interface.
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