multimaster replication

Definition of multimaster replication in The Network Encyclopedia.

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What is Multimaster Replication (in computer networking)?

The method by which information stored in Active Directory in Microsoft Windows 2000 is replicated between domain controllers. Windows 2000 uses multimaster replication for replicating updates made to Active Directory on one domain controller to all other domain controllers in a domain.

Multimaster means that all domain controllers are “master” domain controllers - in other words, they are all peers as far as the replication process is concerned. This is different from the master/slave replication of the Security Account Manager (SAM) database between domain controllers on a Windows NT–based network, in which only the primary domain controller (PDC) has a writable copy of the SAM database, while the backup domain controllers (BDCs) have read-only copies of the database.

In Windows 2000, the Active Directory directory service on every domain controller is writable, and you can make changes to Active Directory at any domain controller on the network. Once you make these changes, multimaster replication ensures that Active Directory on all other domain controllers is updated accordingly.

The advantages of the multimaster replication method supported by Windows 2000 over the PDC/BDC master/slave replication method of Windows NT include the following:

  • You can make updates to Active Directory as long as any domain controller is functioning on the network.
  • When domain controllers are distributed at all sites, you can make updates to Active Directory anywhere on the network with a local domain controller, even when wide area network (WAN) links to other sites are down.

If an object in Active Directory has the same attribute modified almost simultaneously on two different domain controllers, a collision is said to have occurred. Collisions are resolved using timestamps as a tie-breaking mechanism.