![]() ![]() ![]() In this illustration, the detection of USN rollback occurs on VDC2 when a replication partner detects that VDC2 has sent an up-to-dateness USN value that was seen previously by the replication partner, which indicates that VDC2's database has rolled back in time improperly.Ī virtual machine (VM) makes it easy for hypervisor administrators to roll back a domain controller's USNs (its logical clock) by, for example, applying a snapshot outside of the domain controller's awareness. If a domain controller is rolled back in time outside of the domain controller's awareness and a USN is reused for an entirely different transaction, replication will not converge because other domain controllers will believe they have already received the updates associated with the re-used USN under the context of that InvocationID.įor example, the following illustration shows the sequence of events that occurs in Windows Server 2008 R2 and earlier operating systems when USN rollback is detected on VDC2, the destination domain controller that is running on a virtual machine. The InvocationID of a domain controller and its USN together serve as a unique identifier associated with every write-transaction performed on each domain controller and must be unique within the forest.ĪD DS replication uses InvocationID and USNs on each domain controller to determine what changes need to be replicated to other domain controllers. Each domain controller's database instance is also given an identity, known as an InvocationID. ![]() AD DS replication, for example, uses a monotonically increasing value (known as a USN or Update Sequence Number) assigned to transactions on each domain controller. Virtual environments present unique challenges to distributed workloads that depend upon a logical clock-based replication scheme. This article explains the role of USNs and InvocationIDs in Domain Controller replication and discusses some potential issues that can occur. ![]() Safely virtualizing Active Directory Domain Services (AD DS)Īpplies to: Windows Server 2022, Windows Server 2019, Windows Serverīeginning with Windows Server 2012, AD DS provides greater support for virtualizing domain controllers by introducing virtualization-safe capabilities. ![]()
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