Windows 2000 Active Directory FSMO Roles

ID: Q197132

The information in this article applies to:

Microsoft Windows Datacenter Server
Microsoft Windows Advanced Server
Microsoft Windows Server

SUMMARY

The Microsoft Windows 2000 Active Directory is the central repository in which all objects in an enterprise and their respective attributes are stored. It is a hierarchical, multi-master enabled database, capable of storing millions of objects. Because it is multi-master, changes to the database can be processed at any given domain controller (DC) in the enterprise regardless of whether the DC is connected or disconnected from the network.

MORE INFORMATION

Windows 2000 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 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 incorporates methods to prevent conflicting Active Directory updates from occurring.

Windows 2000 Single-Master Model

To prevent conflicting updates in Windows 2000, 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 3.51 and 4.0), in which the PDC is responsible for processing all updates in a given domain.

The Windows 2000 Active Directory extends the single-master model found in earlier versions of Windows to include multiple roles, and the ability to transfer roles to any domain controller (DC) in the enterprise. Because an Active Directory role is not bound to a single DC, it is referred to as a Flexible Single Master Operation (FSMO) role. Currently in Windows 2000 there are five FSMO roles:

Schema master

Domain naming master

RID master

PDC emulator

Infrastructure daemon

Schema Master FSMO Role

The schema master FSMO role holder is the DC responsible for performing updates to the directory schema (that is, the schema naming context or LDAP://cn=schema,cn=configuration,dc=<domain>). This DC is the only one that can process updates to the directory schema. Once the Schema update is complete, it is replicated from the schema master to all other DCs in the directory. There is only one schema master per directory.

Domain Naming Master FSMO Role

The domain naming master FSMO role holder is the DC responsible for making changes to the forest-wide domain name space of the directory (that is, the Partitions\Configuration naming context or LDAP://CN=Partitions, CN=Configuration, DC=<domain>). 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.

RID Master FSMO Role

The RID master FSMO role holder is the single DC responsible for processing RID Pool requests from all DCs within a given domain. It is also responsible for removing an object from its domain and putting it in another domain during an object move.

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 Windows 2000 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. There is one RID master per domain in a directory.

PDC Emulator FSMO Role

The PDC emulator FSMO role holder is a Windows 2000 DC that advertises itself as the primary domain controller (PDC) to down-level workstations, member servers, and domain controllers. For down-level workstations requiring directory writes (such as password changes), only the PDC emulator can service such requests. Backup domain controllers (BDCs) in down-level domains (such as Windows NT 3.51 or 4.0 domains) replicate domain changes from the PDC emulator. In networks running the Windows NT Browser service, the PDC emulator plays the role of domain master browser. In addition, any NetBIOS program that issues a NetGetDCName() API call must talk to the PDC emulator.

In a Windows 2000 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.

Note that the PDC emulator role becomes unnecessary as down-level workstations, member servers, and domain controllers are all upgraded to Windows 2000, in which case the following information applies:

Windows 2000 clients (workstations and member servers) and down-level clients that have installed the distributed services client package do not perform directory writes (such as password changes) preferentially at the DC that has advertised itself as the PDC; they use any DC for the domain.

Once backup domain controllers (BDCs) in down-level domains are upgraded to Windows 2000, the PDC emulator receives no down-level replica requests.

Windows 2000 clients (workstations and member servers) and down-level clients that have installed the distributed services client package use the Active Directory to locate network resources. They do not require the Windows NT Browser service.

Infrastructure FSMO Role

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.

NOTE: The infrastructure role should be held by a DC that is not a global catalog (GC). If this role is hosted on a GC server, cross-domain object references in that domain are not updated, and a warning to that effect is entered in that DC's event log.

Keywords : ntdomain
Version : WINDOWS:
Platform : WINDOWS
Issue type : kbinfo