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What is Active Directory (AD)?

Active Directory (AD) is Microsoft’s directory and identity management service for Windows domain networks. It was introduced in Windows 2000, is included with most MS Windows Server operating systems, and is used by a variety of Microsoft solutions like Exchange Server and SharePoint Server, as well as third-party applications and services.

AD is made up of a number of different directory services, including:

  • Active Directory Domain Services (AD DS) – the core Active Directory service used to manage users and resources.
  • Active Directory Lightweight Directory Services (AD LDS) – a low-overhead version of AD DS for directory-enabled applications.
  • Active Directory Certificate Services (AD CS) – for issuing and managing digital security certificates.
  • Active Directory Federation Services (AD FS) – for sharing identity and access management information across organizations and enterprises.
  • Active Directory Rights Management Services (AD RMS) – for information rights management (controlling access permissions to documents, workbooks, presentations, etc.)

Fundamental AD features and capabilities include:

  • A schema that defines the classes of objects and attributes contained in the directory.
  • A global catalog that contains detailed information about every object in the directory.
  • A query and index mechanism that allows users, administrators, and applications to efficiently find directory information.
  • A replication service that disseminates directory data across the network.

The Active Directory schema supports various types of objects like User, Group, Contact, Computer, Shared Folder, Printer, and Organizational Unit, along with a set of descriptive attributes for each object. For example, User Object attributes include information like the user’s name, address, and telephone number.

Active Directory makes use of other security and networking protocols including LDAP (Lightweight Directory Access Protocol), DNS (Domain Name System), and Microsoft’s version of the Kerberos authentication protocol.

AD Domain Services Overview

Active Directory Domain Services is the primary Active Directory service. It is used to authenticate users and to control access to network resources. A server running AD DS is called a domain controller. Most Windows domain networks have two or more domain controllers; a primary domain controller and one or more backup domain controllers for resiliency. During login, users authenticate to a domain controller and are granted access to particular resources based on administratively defined policies.

AD Data Structures

Active Directory stores information about network users (names, phone numbers, passwords, etc.) and resources (servers, storage volumes, printers, etc.) in a hierarchical structure consisting of domains, trees, and forests.

  • A domain is a collection of objects (e.g. users, devices) that share the same Active Directory database. A domain is identified by a DNS name like
  • A tree is a collection of one or more domains with a contiguous namespace (they have a common DNS root name like,, and
  • A forest is a collection of one or more trees that share a common schema, global catalog, and directory configuration—but aren’t part of a contiguous namespace. The forest typically serves as the security boundary for an enterprise network.

Objects within a domain can be grouped into organizational units (OUs) to simplify administration and policy management. Administrators can create arbitrary organizational units to mirror functional, geographical, or business structures, and then apply group policies to OUs to simplify administration. OUs also make it easier to delegate control over resources to various administrators.

AD Benefits

Active Directory provides a variety of functional and business benefits, including:

  • Security – Active Directory helps businesses improve security by controlling access to network resources.
  • Extensibility – companies can easily organize Active Directory data to align with their organizational structure and business needs.
  • Simplicity – administrators can centrally manage user identities and access privileges across the enterprise, helping businesses simplify management and reduce operations expenses.
  • Resiliency – Active Directory supports redundant components and data replication to enable high availability and business continuity.

Relationship to Azure Active Directory

Azure Active Directory is Microsoft’s next-generation, cloud-based identity management solution used to control access to SaaS solutions like Microsoft 365 (Office 365), internally developed cloud apps running on Azure, as well as traditional enterprise applications and other on-premises resources. It adds support for just-in-time access controls, multi-factor authentication and passwordless technologies, native mobile-device management, and identity federation standards like SAML and Oauth2, among other capabilities.

CyberArk Identity integrates with both Active Directory and Azure AD and enables you to provide Single Sign-On, Multi-Factor Authentication, and Lifecycle Management capabilities for users stored in these directories.