Adding a new domain to an existing forest

Adding a new domain to an existing forest is a process called "domain joining" or "domain creation". Here's a step-by-step guide to help you through the process:

Prerequisites:

1. You have an existing Active Directory forest with a functional domain controller.
2. You have a new domain name that you want to add to the existing forest.
3. You have a domain controller with the necessary permissions and resources to create a new domain.

Step 1: Prepare the new domain

1. Choose a domain name that is not already in use in the existing forest.
2. Create a new DNS zone for the new domain in the existing forest's DNS server.
3. Create a new domain controller for the new domain.

Step 2: Create the new domain

1. Open the Active Directory Domain Services console on the domain controller that will host the new domain.
2. Right-click on the "Domains" container and select "New Domain..."
3. Enter the name of the new domain and the domain functional level (e.g., Windows Server 2019).
4. Choose the domain controller that will host the new domain.
5. Click "Next" and then "Create" to create the new domain.

Step 3: Promote the new domain controller

1. Open the Active Directory Domain Services console on the new domain controller.
2. Right-click on the "Domain Controllers" container and select "New Domain Controller..."
3. Enter the name of the new domain controller and the domain functional level (e.g., Windows Server 2019).
4. Choose the domain controller that will host the new domain.
5. Click "Next" and then "Create" to promote the new domain controller.

Step 4: Add the new domain to the forest

1. Open the Active Directory Domains and Trusts console on the domain controller that hosts the existing forest.
2. Right-click on the "Domains" container and select "New Domain..."
3. Enter the name of the new domain and the domain functional level (e.g., Windows Server 2019).
4. Choose the domain controller that hosts the new domain.
5. Click "Next" and then "Create" to add the new domain to the forest.

Step 5: Configure DNS and replication

1. Update the DNS server with the new domain's DNS records.
2. Configure replication between the new domain controller and the existing domain controllers in the forest.

Step 6: Verify the new domain

1. Verify that the new domain is visible in the Active Directory Domains and Trusts console.
2. Verify that users and computers can join the new domain.
3. Verify that the new domain is replicating correctly with the existing domain controllers.

Additional considerations:

• Make sure to plan for DNS and replication infrastructure to support the new domain.
• Consider implementing a new domain controller for the new domain to ensure high availability and redundancy.
• Make sure to update any existing applications and services that rely on the existing domain to support the new domain.

By following these steps, you should be able to successfully add a new domain to an existing forest.