Flexible Single Master Operation (FSMO) Roles

Are roles that determine special functions in AD that only one Domain Controller (DC) can perform at a time.

These are made to avoid conflicts when multiple DCs are running.

Only one DC holds each role at a time, but the role can be moved to another if needed.

Roles

Domain Local

• Schema Master: Control changes to the Active Directory Schema
• Domain Naming Master: Handles creation/deletion of Domains in the forest.

Forest Wide

• Relative ID (RID) Master: Allocates blocks of unique RID values to DCs for Object SID creation.
• PDC Emulator: Handles password changes, time sync, authentication requests, and manages Group Policy Objects (GPOs). It also provides backward-compatibility for legacy Windows clients.
• Infrastructure Master: Updates cross-domain Object references (e.g. GUID or SID) when objects move between Domains.