Active Directory

Active Directory (AD) is Microsoft's directory service for Windows networks. It is a central database that stores information about users, computers, groups and other objects and provides authentication (verifying identity) and authorization (determining access rights) across your environment.

Core Concepts:

• Domain - A security boundary; all objects within share the same AD database and trust each other.

• Forest - The top-level container; one or more domain trees that share a common schema but don't automatically trust each other.

• Tree - A hierarchical set of domains sharing a contiguous DNS namespace (e.g., corp.example.com).

• Organizational Unit (OU) - A container within a domain for grouping users/computers to apply Group Policy or delegate admin rights.

• Domain Controller (DC) - A server running Active Directory Domain Services that holds a copy of the directory and handles authentication (Kerberos).

• Global Catalog - A domain controller that holds a partial, forest-wide index of every object — enables cross-domain searches and logon.

• Group Policy (GPO) - Centralized configuration rules pushed to users and computers (password policies, software deployment, security settings, etc.)

• FSMO Roles - Five special roles (Schema Master, Domain Naming Master, RID Master, Infrastructure Master, PDC Emulator) held by one DC each to handle specific write operations.

How It Works:

• A user logs in the Domain Controller authenticates them via Kerberos (or NTLM as fallback).

• AD checks the user's group memberships to determine what they can access.

• Group Policy is applied at logon to enforce security and configuration.

• Change (new user, password reset) are replicated to all domain controllers in the domain.

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