How to Add a Domain Controller to an Existing Domain

When you add a domain controller (DC) to an existing domain, you’re not just enhancing Active Directory availability, you are also balancing authentication requests and ensuring that your system is fault-tolerant.

This article provides a detailed, step-by-step guide on how to add a domain controller to your current domain.

Benefits of Adding a Domain Controller to an Existing Domain

1. Increased Availability: Having multiple domain controllers means there's less chance of downtime.
2. Load Balancing: Authentication and directory services are shared among the DCs, making everything run smoother.
3. Disaster Recovery: With redundancy in place, Active Directory stays up and running even during failures.
4. Geographical Coverage: Placing a DC in a distant location can boost authentication speeds for users nearby.

Pre-Requisites

1. Access Rights: Please make sure you have either Domain Admin or Enterprise Admin privileges.
2. Server Configuration: Please install the Windows Server operating system on the new domain controller.
3. Network Configuration: Assign a static IP address to the new server and set up DNS to point to the existing domain controller.
4. Connectivity: Confirm that the server can communicate with the current domain controller.
5. Time Synchronization: Please check that the server's time is aligned with the existing domain controller.

Steps to add a Domain Controller

1. Install the Active Directory Domain Services Role

1. Open Server Manager on the new server.
2. Click Add roles and features and follow the wizard.
3. Select Active Directory Domain Services under Server Roles.
4. Upon completion of the installation, reboot the server if prompted.

2. Promote the Server to a Domain Controller

1. Open Server Manager and click the notification flag.
2. Select Promote this server to a domain controller.
3. In the Deployment Configuration window:
   • Choose Add a domain controller to an existing domain.
   • Specify the existing domain name and provide administrator credentials.
4. Configure domain controller options:
   • Domain Name System: Please enable this option to install DNS on the new DC.
   • Global Catalog: Ensure this is checked for directory-wide searches.
   • Read-Only Domain Controller: Leave unchecked unless needed.
5. Set a Directory Services Restore Mode  password.

3. Verify and Install

1. The wizard will check prerequisites for the new domain controller.
2. If there are no errors, click Install to promote the server to a DC.
3. The server will restart automatically after installation.

4. Replicate Active Directory

1. Open Active Directory Sites and Services on the new DC.
2. Verify replication by expanding the site and checking the NTDS Settings for the new DC.
3. Force replication if needed: Right-click on NTDS Settings and select Replicate Now.

Post-Configuration Checks

1. Validate Replication: Run the repadmin /replsummary command on the new DC to ensure replication is successful.
2. Test Authentication: Please log in using domain credentials to test authentication.
3. DNS Configuration Check: Please ensure DNS records for the new DC are updated and functioning.
4. Backup: Finally, create a backup of the new DC for recovery purposes.