In this article, we’ll describe how to generate all Domain Controllers in the Active Directory Sites and Services tool.
Active Directory Sites and Services can be seen as an administrative tool used to manage sites and the related components on Microsoft Server systems.
It contains a list of all Domain Controllers (DCs) connected to the system, regardless of their number.
In some situations, admins can notice more than one DC listed under Windows NT Directory Services (NTDS) settings.
What are these other DCs, and how can they be generated automatically?
Those DCs are called KCCs (Knowledge Consistency Checkers). They are nominated bridgehead servers per site that handle replication tasks between specific sites.
A bridgehead server is responsible for replicating any changes to all remaining DCs in its site.
In simple words, KCCs take care of replication by generating DCs, which communicate with other DCs and KCCs—consequently, the auto-generated domain controllers take care of the replication.
How to create automatically generated Domain Controllers
There are instances, such as during server moves or adding new organizational Domain Controllers, when Active Directory is unable to create ‘Automatically Generated’ connections with the root Domain Controller.
In such a situation, the Domain Controller can be seen, but not on the “real” Domain Controller list.
There is more than one solution to this problem.
Let’s talk about two of the most used and tested solutions.
1. Manually forcing auto generation
This first method, although it can get in the quick “workaround” category, involves manually forcing auto-generation.
It can be done by right clicking on the NTDS Settings option and then choosing ‘All Tasks and Check Replication Topology’ in the end.
That should force trigger auto-generation of all Domain Controllers, and your Domain Controllers should now be visible on the list.
Repadmin is a command line tool used for diagnosing and repairing replication problems.
It can be used from an elevated command prompt by typing ntdsutil.
Then, entering this command:
repadmin / showrepl*
To create an output that replicates the state of all DCs in the system, enter this command:
As a result, force replication will be started. This command forces replication and generates all Domain Controllers on the Sites and Services list.
It is usually not necessary to create manual connections when the KCC is being used to generate automatic connections; if any conditions change, the KCC automatically reconfigures the connections.
Adding manual connections when the KCC is employed can potentially increase replication traffic and conflicts with optimal settings stipulated by KCC.
If a connection is not working due to a failed domain controller, the KCC automatically builds temporary connections to other replication sites (if the damage is not too big) to ensure that replication occurs.
If all the domain controllers in a site are unavailable, KCC automatically creates replication connections between domain controllers from another site.
It is not recommended to manually modify this, unless you have a very specific use case.
As long as these records are auto-generated, they can survive a Domain Controller failure, as the KCC/ISTG will automatically create a new connection.
However, if you manually create a connection or specify a bridgehead server, and that server goes offline, KCC will not create a new connection and replication between the affected sites will stall.