10 Decommission Child Domain Best Practices

Decommissioning a child domain is a complex process that requires careful planning and execution. It involves migrating resources, users, and data from the child domain to the parent domain. It also involves ensuring that the child domain is completely removed from the network and that all security policies are updated accordingly.

In this article, we will discuss 10 best practices to follow when decommissioning a child domain. Following these best practices will help ensure that the process is successful and that the security of the parent domain is not compromised.

1. Ensure that all user accounts have been migrated to the parent domain

Migrating user accounts to the parent domain ensures that users can still access their data and applications. This is important because it eliminates any disruption in service for users, which could lead to a decrease in productivity or even lost data.

The process of migrating user accounts involves creating new user accounts on the parent domain with the same username and password as the old account. The user’s profile and settings are then transferred from the child domain to the parent domain. This ensures that all of the user’s data and settings remain intact after the migration.

Once the user accounts have been migrated, the next step is to decommission the child domain. This involves disabling the domain controller, removing the DNS records associated with the domain, and deleting the domain from Active Directory. By ensuring that all user accounts have been migrated before decommissioning the child domain, you can ensure that no data is lost during the process.

2. Remove any trusts between the child and parent domains

Trusts are used to allow users in one domain access resources in another. When a child domain is decommissioned, the trust relationship between it and its parent domain should be removed so that users in the parent domain can no longer access resources in the child domain. This ensures that any sensitive data stored in the child domain remains secure and inaccessible.

Removing trusts also helps prevent security issues such as privilege escalation attacks. If an attacker were able to gain access to the parent domain, they could use the trust relationship to gain access to the child domain and potentially escalate their privileges. By removing the trust, this type of attack vector is eliminated.

The process for removing trusts depends on the type of trust being used. For example, if a forest trust exists between two forests, then the trust must be deleted from both sides. On the other hand, if a shortcut trust exists between two domains within the same forest, then only one side needs to delete the trust. In either case, the steps involved include deleting the trust object from Active Directory, disabling the trust authentication protocol, and verifying that the trust has been successfully removed.

3. Disable DNS forwarding for the child domain

When a child domain is decommissioned, it’s important to ensure that any DNS requests for the child domain are not forwarded to other domains. This prevents users from inadvertently accessing resources in the child domain after it has been decommissioned.

To disable DNS forwarding for the child domain, administrators must first remove all of the resource records associated with the child domain from the parent domain’s DNS server. This includes removing any A, CNAME, MX, and SRV records associated with the child domain. Once this is done, the administrator can then configure the DNS server to no longer forward requests for the child domain to other domains.

It is also important to note that disabling DNS forwarding for the child domain does not prevent users from manually entering the IP address of the child domain into their web browser. To prevent this, administrators should also block access to the child domain at the firewall level.

4. Uninstall the Active Directory Domain Services role from the child domain controller

The Active Directory Domain Services role is responsible for managing the domain, including user accounts, group policies, and other settings. When decommissioning a child domain, it’s important to remove this role from the controller in order to ensure that no changes are made to the domain while it is being decommissioned.

To uninstall the Active Directory Domain Services role, open Server Manager on the child domain controller and select “Remove Roles and Features” from the Manage menu. Select the server you want to remove the role from, then select the Active Directory Domain Services role and click Next. On the Confirmation page, check the box next to “Restart the destination server automatically if required” and click Uninstall. The server will restart and the role will be removed.

Once the role has been uninstalled, the child domain can be safely decommissioned without any risk of changes being made to the domain. This ensures that all data associated with the domain remains intact and secure during the decommission process.

5. Remove the child domain from the forest

Removing the child domain from the forest helps to reduce complexity and improve security. It eliminates any potential for users in the parent domain to access resources in the decommissioned child domain, as well as reducing the attack surface of the entire forest.

The process of removing a child domain is relatively straightforward. The first step is to move all user accounts, computer accounts, and other objects from the child domain into the parent domain. This can be done using Active Directory Migration Tool (ADMT) or by manually moving each object one at a time. Once all objects have been moved, the next step is to remove the trust relationship between the two domains. This can be done through the Active Directory Domains and Trusts snap-in. After that, the final step is to delete the child domain from the forest. This can be done through the Active Directory Domains and Trusts snap-in as well.

6. Delete the child domain object in the Active Directory Users and Computers console

When a child domain is no longer needed, it should be removed from the Active Directory forest. This process involves deleting the child domain object in the Active Directory Users and Computers console. Doing so will remove all references to the child domain from the parent domain, including any trusts that were established between them.

Deleting the child domain object also ensures that users and computers associated with the child domain are not able to authenticate against the parent domain. This prevents any potential security risks or unauthorized access to resources on the parent domain. Additionally, it helps reduce clutter in the Active Directory structure by removing unnecessary objects.

The process of deleting the child domain object is relatively straightforward. In the Active Directory Users and Computers console, right-click the child domain object and select Delete. Confirm the deletion when prompted. Once the child domain object has been deleted, the child domain can no longer be used for authentication or authorization purposes.

7. Verify that the child domain is removed from the forest

When decommissioning a child domain, it is important to ensure that all objects and resources associated with the domain are removed from the forest. This includes user accounts, computer accounts, group policies, DNS records, etc. If any of these objects or resources remain in the forest after the child domain has been decommissioned, they can cause conflicts and security issues.

To verify that the child domain has been completely removed from the forest, administrators should use Active Directory tools such as ADSI Edit, LDP, and PowerShell cmdlets. These tools allow administrators to view and delete objects and resources associated with the child domain. Additionally, administrators should also check the event logs for errors related to the child domain.

Verifying that the child domain is removed from the forest is an essential step when decommissioning a child domain. It ensures that all objects and resources associated with the domain have been properly removed, preventing potential conflicts and security issues.

8. Update the DNS records of the child domain to point to the parent domain

When decommissioning a child domain, it is important to ensure that all users and services are able to access the resources they need. By updating the DNS records of the child domain to point to the parent domain, you can ensure that any requests for resources in the child domain will be redirected to the parent domain. This ensures that users and services do not experience any disruption when the child domain is decommissioned.

The process of updating the DNS records of the child domain to point to the parent domain involves creating a new zone delegation record in the parent domain’s DNS server. This record should include the name of the child domain as well as the IP address of the parent domain’s DNS server. Once this record has been created, all requests for resources in the child domain will be directed to the parent domain’s DNS server, which will then redirect them to the appropriate resource.

It is also important to update the DNS records of any other domains that may have previously pointed to the child domain. This ensures that any requests for resources in those domains will still be routed correctly even after the child domain has been decommissioned.

9. Back up the system state data of the child domain

The system state data of a child domain contains information about the Active Directory database, including user accounts, group policies, and other important settings. This data is essential for restoring the child domain in case of an emergency or if it needs to be re-created at a later date.

Backing up this data can be done using Windows Server Backup, which is included with Windows Server operating systems. The backup should include all system state data from the child domain, as well as any additional files that may be needed for restoration. It’s also important to store the backup in a secure location, such as an offsite storage facility or cloud service.

Once the backup has been completed, the next step is to decommission the child domain. This involves removing the domain controller from the network, uninstalling the server software, and deleting the domain from Active Directory. After the decommissioning process is complete, the backed up system state data can be used to restore the child domain if necessary.

10. Re-add the child domain as a new domain in the forest

Re-adding the child domain as a new domain in the forest allows for an easier transition of resources and users from the old domain to the new one. This is because all of the existing objects, such as user accounts, groups, computers, printers, etc., can be migrated over to the new domain without having to recreate them manually. Additionally, any security policies or settings that were configured on the old domain will also be preserved when re-adding it as a new domain.

The process of re-adding the child domain as a new domain in the forest involves creating a new Active Directory Domain Services (AD DS) instance in the same forest as the original domain. Once this has been done, the administrator can then use the AD DS Migration Tool to migrate all of the objects from the old domain to the new one. The tool will also take care of updating any references to the old domain name with the new one. After the migration is complete, the old domain can then be decommissioned.