Microsoft KB Archive/230123

= How Conflicts Are Resolved in Active Directory Replication =

PSS ID Number: 230123

Article Last Modified on 10/9/2002

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The information in this article applies to:


 * Microsoft Windows 2000 Server

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This article was previously published under Q230123



SUMMARY
Active Directory in Windows 2000 uses a replication model called "multi-master loose consistency with convergence." All computers that provide multi-master updates must deal with potential conflicts that may arise when concurrent updates originating on two separate master replicas are inconsistent. This article provides a basic overview of how Active Directory deals with these conflicts.



MORE INFORMATION
Because of the semantics of the Lightweight Directory Access Protocol (LDAP), there are three potential types of conflicts created by multi-master updates of normal Active Directory objects:
 * Attribute value: An object's attribute is set concurrently to one value at one master, and another value at a second master.
 * Add/move under a deleted container object or the deletion of a non-leaf object: Essentially, this conflict is a situation in which one master records the deletion of a container object, while another master records the placement of another object subordinate to that deleted object.
 * Sibling name conflict: This conflict occurs when one replica attempts to move an object into a container in which another replica has concurrently moved another object with the same relative display name (RDN).

The basic approach taken by Active Directory to deal with these conflicts is to order all update operations (add, modify, move, or delete) by assigning a globally unique stamp to the originating update. If there is a conflict, the ordering of stamps allows a consistent resolution. This approach is used in the following ways:
 * Attribute value: The value whose update operation has the larger stamp wins.
 * Add/move under a deleted container object or the deletion of a non-leaf object: After resolution at all replicas, the container object is deleted, and the leaf object is made a child of the folder's special Lost&Found container. Stamps are not involved in this resolution.
 * Sibling name conflict: The object with the larger stamp keeps the RDN. The sibling object is assigned a unique RDN by the computer. This does not conflict with any client-assigned value [using a reserved character (the asterisk), the RDN, and the object's GUID].

Keywords: kbenv kbinfo KB230123

Technology: kbwin2000Search kbwin2000Serv kbwin2000ServSearch

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