Active Directory Domain Services
Explained: Core Components & Key Functions
In the realm of enterprise
IT, Active Directory Domain Services (AD DS) stands as a
foundational pillar for managing identities, resources, and security across
networks. Whether you’re an IT professional or just curious about how large
organizations keep their digital environments organized, understanding AD DS is
a must.
🧱 Core Components
of AD DS
AD DS is built on a set of
interrelated components that work together to provide structure, scalability,
and control:
- Domain: The fundamental unit of organization
in AD DS. A domain contains users, computers, and other objects, all
governed by common policies and security boundaries.
- Forest: A collection of one or more domains
that share a common schema, configuration, and global catalog. Forests
enable trust relationships and resource sharing across domains.
- Organizational Units (OUs): Logical
containers within a domain used to group objects like users and computers.
OUs simplify administration by allowing targeted application of policies
and delegation of control.
- Domain Controllers (DCs): Servers that store
the AD DS database and handle authentication and directory queries.
Multiple DCs ensure redundancy and load balancing.
- Global Catalog: A distributed data
repository that contains a searchable index of all objects in the forest.
It speeds up queries and enables cross-domain lookups.
🔐 Key Functions of AD DS
AD DS isn’t just a directory—it’s
a powerful system that governs access, enforces policies, and maintains
consistency across the network:
- Authentication: Validates user identities
using secure protocols like Kerberos. This ensures that only authorized
individuals can access the network.
- Authorization: Determines what resources a
user or device can access based on permissions and group memberships.
- Policy Enforcement: Uses Group Policy to
apply security settings, software installations, and configuration rules
across users and computers.
- Replication: Keeps data synchronized across
all domain controllers to ensure consistency and reliability.
- Scalability: Designed to support millions of
objects and multiple domains, making it suitable for organizations of any
size and geographic spread.
Active Directory Domain Services
Explained:
1. What is Active Directory and
what are its main components?
Active Directory is a directory
service developed by Microsoft that provides centralized authentication and
authorization for Windows-based computers. Active Directory (AD) is a Microsoft
directory service used to manage users, computers, and resources on a network.
Main components:
- Domain – Logical grouping of objects.
- Organizational Units (OUs) – Containers for
organizing users/computers.
- Domain Controllers – Servers hosting AD data and
handling authentication.
- Global Catalog – Partial replica of all objects in
the forest.
- Group Policy – Centralized management of OS,
applications, and user settings.
2. How does Active Directory
authentication work?
AD primarily uses the Kerberos
protocol:
- User logs in → credentials sent to KDC (Key
Distribution Center).
- KDC issues a Ticket Granting Ticket (TGT).
- TGT is used to get service tickets for access.
- NTLM may be used for legacy systems.
3. What is the difference
between a domain and a forest?
- Domain – Logical unit with its own policies and
database.
- Forest – A collection of one or more domains
sharing a common schema and trust relationships.
4. What are Group Policy
Objects (GPOs) and how are they used?
GPOs allow centralized management
of settings like:
- Security policies
- Desktop configurations
- Software installations
They are applied to sites,
domains, or OUs.
5. How do you troubleshoot
replication issues in Active Directory?
- Use repadmin /replsummary
- Check DNS configuration
- Use Event Viewer and dcdiag
- Ensure network connectivity is stable
6. What is the role of FSMO
roles?
FSMO (Flexible Single Master
Operations) Roles:
- Schema Master
- Domain Naming Master
- RID Master
- PDC Emulator
- Infrastructure Master
These prevent conflicts and ensure
consistency.
7. How do you secure Active Directory?
- Enforce strong passwords and MFA
- Audit accounts and permissions
- Use Group Policies for security
- Regular patching and updates
- Implement firewalls and IDS/IPS
8. Difference between a
security group and a distribution group?
- Security Group – Used for permissions and GPOs.
- Distribution Group – Used for email distribution
only.
9. How do you perform an AD
health check?
- Use dcdiag and repadmin
- Check event logs
- Review GPO application with gpresult
- Verify site and services configuration
10. What is Kerberos
authentication?
A secure protocol using tickets
and symmetric keys:
- Prevents plaintext credentials
- Protects against replay attacks
11. How do you restore a
deleted AD object?
If Recycle Bin is enabled:
Use AD Administrative Center or
PowerShell (Restore-ADObject)
Otherwise: Restore from system state backup
12. What is the Global Catalog
and its purpose?
Partial replica of all objects in
the forest
Enables fast object searches and cross-domain logon
13. How do you migrate users between
domains?
Use ADMT (Active Directory Migration Tool)
- Establish trust relationships
- Migrate users, groups, and passwords
- Test post-migration access
14. What are AD Sites and how
do they affect replication?
- Represent geographical locations/subnets
- Optimize replication traffic
- Help clients find nearest domain controller
15. How do you monitor AD
performance?
- Use Performance Monitor (PerfMon)
- Analyze Event Viewer logs
- Use System Center Operations Manager (SCOM) or
3rd-party tools
- Check replication and GPO health
16. Trust vs Federation
- Trust – For resource sharing between domains.
- Federation – For identity sharing across
organizations (uses SAML/OAuth, supports SSO).
17. How do you implement Least
Privilege in AD?
- Assign minimum necessary permissions
- Use security groups and RBAC
- Regularly review group memberships
- Monitor and adjust based on role changes
18. What is the purpose of the
AD Recycle Bin?
Allows recovery of deleted objects
(with attributes and memberships)
Reduces downtime due to accidental deletion
19. How do you troubleshoot DNS
issues in AD?
- Check SRV and CNAME records
- Use nslookup, ping
- Review DNS logs
- Ensure correct DNS server settings
20. Native Mode vs Mixed Mode
- Native Mode – Only Windows 2000+ DCs, full feature
support
- Mixed Mode – Supports legacy NT4 DCs, limited
features
21. How do you manage Group
Policy Preferences?
- Use Group Policy Management Console (GPMC)
- Configure Drive Maps, Printers, Environment
Variables
- Use Item-Level Targeting for granular control
22. What is the role of the AD
Schema?
- Defines object classes and attributes
- Controls how data is created, modified, and deleted
- Extensible, but changes should be planned carefully
23. How do you audit changes in
AD?
- Enable audit policies via GPO
- Use Event Viewer to track:
- Event ID 5136 – Object modifications
- Event ID 5138 – Group membership changes
- Use SIEM or third-party tools for alerts
24. Best practices for AD
Backup and Recovery
- Backup System State regularly
- Use Windows Server Backup or third-party tools
- Test restores in non-production
- Document procedures and train staff
- Have redundant DCs
25. How do you handle a
compromised AD account?
- Disable the account immediately
- Investigate the breach
- Check logs for activity
- Reset passwords, enable MFA
- Educate users and update security policies
