What are FSMO Roles? List them
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Answer Posted / deepak dev
What are the FSMO Roles in Active Directory?
Windows 2000/2003 Multi-Master Model
A multi-master enabled database, such as the Active
Directory, provides the flexibility of allowing changes to
occur at any DC in the enterprise, but it also introduces
the possibility of conflicts that can potentially lead to
problems once the data is replicated to the rest of the
enterprise. One way Windows 2000/2003 deals with conflicting
updates is by having a conflict resolution algorithm handle
discrepancies in values by resolving to the DC to which
changes were written last (that is, "the last writer wins"),
while discarding the changes in all other DCs. Although this
resolution method may be acceptable in some cases, there are
times when conflicts are just too difficult to resolve using
the "last writer wins" approach. In such cases, it is best
to prevent the conflict from occurring rather than to try to
resolve it after the fact.
For certain types of changes, Windows 2000/2003 incorporates
methods to prevent conflicting Active Directory updates from
occurring.
Windows 2000/2003 Single-Master Model
To prevent conflicting updates in Windows 2000/2003, the
Active Directory performs updates to certain objects in a
single-master fashion.
In a single-master model, only one DC in the entire
directory is allowed to process updates. This is similar to
the role given to a primary domain controller (PDC) in
earlier versions of Windows (such as Microsoft Windows NT
4.0), in which the PDC is responsible for processing all
updates in a given domain.
In a forest, there are five FSMO roles that are assigned to
one or more domain controllers. The five FSMO roles are:
Schema Master:
The schema master domain controller controls all updates and
modifications to the schema. Once the Schema update is
complete, it is replicated from the schema master to all
other DCs in the directory. To update the schema of a
forest, you must have access to the schema master. There can
be only one schema master in the whole forest.
Domain naming master:
The domain naming master domain controller controls the
addition or removal of domains in the forest. This DC is the
only one that can add or remove a domain from the directory.
It can also add or remove cross references to domains in
external directories. There can be only one domain naming
master in the whole forest.
Infrastructure Master:
When an object in one domain is referenced by another object
in another domain, it represents the reference by the GUID,
the SID (for references to security principals), and the DN
of the object being referenced. The infrastructure FSMO role
holder is the DC responsible for updating an object's SID
and distinguished name in a cross-domain object reference.
At any one time, there can be only one domain controller
acting as the infrastructure master in each domain.
Note: The Infrastructure Master (IM) role should be held by
a domain controller that is not a Global Catalog server
(GC). If the Infrastructure Master runs on a Global Catalog
server it will stop updating object information because it
does not contain any references to objects that it does not
hold. This is because a Global Catalog server holds a
partial replica of every object in the forest. As a result,
cross-domain object references in that domain will not be
updated and a warning to that effect will be logged on that
DC's event log. If all the domain controllers in a domain
also host the global catalog, all the domain controllers
have the current data, and it is not important which domain
controller holds the infrastructure master role.
Relative ID (RID) Master:
The RID master is responsible for processing RID pool
requests from all domain controllers in a particular domain.
When a DC creates a security principal object such as a user
or group, it attaches a unique Security ID (SID) to the
object. This SID consists of a domain SID (the same for all
SIDs created in a domain), and a relative ID (RID) that is
unique for each security principal SID created in a domain.
Each DC in a domain is allocated a pool of RIDs that it is
allowed to assign to the security principals it creates.
When a DC's allocated RID pool falls below a threshold, that
DC issues a request for additional RIDs to the domain's RID
master. The domain RID master responds to the request by
retrieving RIDs from the domain's unallocated RID pool and
assigns them to the pool of the requesting DC. At any one
time, there can be only one domain controller acting as the
RID master in the domain.
PDC Emulator:
The PDC emulator is necessary to synchronize time in an
enterprise. Windows 2000/2003 includes the W32Time (Windows
Time) time service that is required by the Kerberos
authentication protocol. All Windows 2000/2003-based
computers within an enterprise use a common time. The
purpose of the time service is to ensure that the Windows
Time service uses a hierarchical relationship that controls
authority and does not permit loops to ensure appropriate
common time usage.
The PDC emulator of a domain is authoritative for the
domain. The PDC emulator at the root of the forest becomes
authoritative for the enterprise, and should be configured
to gather the time from an external source. All PDC FSMO
role holders follow the hierarchy of domains in the
selection of their in-bound time partner.
In a Windows 2000/2003 domain, the PDC emulator role holder
retains the following functions:
* Password changes performed by other DCs in the domain
are replicated preferentially to the PDC emulator.
* Authentication failures that occur at a given DC in a
domain because of an incorrect password are forwarded to the
PDC emulator before a bad password failure message is
reported to the user.
* Account lockout is processed on the PDC emulator.
* Editing or creation of Group Policy Objects (GPO) is
always done from the GPO copy found in the PDC Emulator's
SYSVOL share, unless configured not to do so by the
administrator.
* The PDC emulator performs all of the functionality
that a Microsoft Windows NT 4.0 Server-based PDC or earlier
PDC performs for Windows NT 4.0-based or earlier clients.
This part of the PDC emulator role becomes unnecessary when
all workstations, member servers, and domain controllers
that are running Windows NT 4.0 or earlier are all upgraded
to Windows 2000/2003. The PDC emulator still performs the
other functions as described in a Windows 2000/2003 environment.
At any one time, there can be only one domain controller
acting as the PDC emulator master in each domain in the forest.
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