What is Domain Controller?

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By Sameeksha Medewar

User authentication and authorization are essential functions that help in ensuring that only authorized and relevant individuals access and use a system. The authentication process is a key factor for ensuring that the data of your customer is preserved and also reduces the chances of data leakage.

For this, the Windows Server domain groups users and devices along with other objects in a network, and a domain controller authenticates the service requests for the domain’s resources. In addition, it also stores data regarding user accounts and secures it with policies. This blog provides detailed information about domain controllers and covers various aspects of domain controllers as well.

What is Domain Controller?

A domain controller or DC is a server that is responsible for security authentications and requests within a particular Windows server domain. It was first introduced by Microsoft and acts as the epicenter for Windows Active Directory services. Typically, it is used for authenticating users and storing their confidential details along with enforcing security policies for any Windows domain.

The basic idea behind a domain controller is to help IT, professionals, to manage user data securely within a domain. All the user requests are sent back to the domain controller for authentication and identification. Right after authenticating a user’s identity (with the help of credentials), a domain controller validates requests and provides access accordingly.

In simple words, right after an individual visits a domain, the domain controller performs authentication and validation of their credentials (by using the username, password, IP location, etc.) and allows or denies the access request accordingly. Following are some of the key highlights of a domain controller:

  • Offers centralized management of users and the identification process.
  • Allows sharing of resources for files/printers.
  • Makes use of FSMO and Federated configuration for redundancy.
  • Allows distribution and replication on large networks.
  • Encrypts user data.
  • Provides a strong firewall for improved security.

The Primary Function of Domain Controller

The major responsibility of DC is running the authentication and validation process for users accessing a network or domain. It checks the username, password, and other optional credentials for allowing or denying access. Along with a username and password for authentication, domains can also use biometric techniques or multifactor authentication (MFA) for providing more robust security. Also, DC checks whether the user is a normal user or a system administrator with extra privileges.

The Authentication Cycle

DC is generally part of the Microsoft environment and looks for all the authentication requests received by it. It takes the input and verifies whether the user is eligible to access the system or not. Further, it runs the login process and regulates permissions for allowing access to only specific parts of the network. In this way, a domain controller helps to eliminate the attempt to hack a system.

Types of Domain Controllers

Domain controllers are of two types are as follows:

1. Primary Domain Controller

As described by its name, it is the first-line domain controller used for handling all the user-authentication requests in the first place and there can only be one primary domain controller within a domain. To attain the best of security, it is suggested that the server on which the primary DC is placed shall be dedicated to domain services only. Therefore, the primary DC servers shouldn’t execute files, applications, etc. because it may reduce the speed and increase the risk of crashing.

2. Backup Domain Controller

The role of a backup domain controller is to tackle catastrophes such as the failure of the primary DC. A domain can have multiple backup DCs for enhanced security. It is suggested to employ a backup DC because it eliminates the risk of users being not able to gain access to the network in case the primary domain stops working. When someone sends a login request, it first goes to primary DC but if the primary DC fails, the request proceeds to backup DC. The backup DC will be treated as the primary controller if the primary DC has permanently stopped working.

Keep in mind that all the information regarding the authentication such as users, passwords, etc. can only be stored at primary DC first. Later, this information gets fetched by backup DC databases. You may consider it as a master-slave pattern where the primary DC is the master and all the backup DCs are the slaves.

Difference Between a Domain and a Domain Controller

A domain centralizes all the data regarding users, systems, applications, networks, database servers, etc. that are managed with a similar pattern. Therefore, if you’re into the domain, you’ll be trusted and easily get authenticated every time you try to access it. Moreover, it also allows users to log in from any device.

Whereas, a domain controller (typically Microsoft Active Directory) is a server that is situated within a Domain. It is used for managing networks and works as a gatekeeper for authenticating users who want to enter a particular domain.

What is Active Directory?

By definition, Active Directory is a framework that is an essential component required for managing various Windows Server domains. A domain controller is a component of an Active Directory. DC authenticates users on the basis of the data stored in the Active Directory.

An Active Directory is composed of information that further gets organized into forests, trees, and domains. A single Active Directory can have multiple domains, and a DC manages the trust among those domains for granting access to users from one domain to another. Following are the type of trust that exists between domains:

  • One-way trust: One-way access from one domain to another
  • Two-way trust: Two-way access from one domain to another
  • Transitive trust: Two-way trust build automatically between a parent and child domain
  • Explicit trust: Manually created trust directly by the administrator
  • Forest trust: Trust between two forests
  • External trust: Trust among two domain that belongs to different forest

Setting Up a Domain Controller

Following is a two-step guide for users to learn how to set up a domain controller. But before starting, ensure to align a static IP address to the Domain Controller for helping the Active Directory to locate the DC smoothly:

Step 1: Install Active Directory Domain Services

  • Use admin credentials for logging into the Active Directory. Now open the Server Manager, click on the Roles Summary and then click on add roles and features. Click “Next” on the “Before you begin” screen.
  • Start the installation by either selecting to deploy your DC in a VM or select the Remote Desktop Services installation.
  • Now select the location of installation after ensuring that your IP address is on the selected server.
  • Now confirm the installation selections and click on the “Restart the destination server automatically if required” button. Click on the “Install” button and exit the window after the installation process gets completed.

Step 2: Shift the Server into a Domain Controller

  • Right after the installation of Active Directory Domain Services, a notification flag will pop up adjacent to the Manage menu. Click on “Promote this server into a domain controller” and “Add a new forest” by entering the root domain name in the dedicated section. The same name will be assigned to the forest name as well.
  • Because it is the first DC, it will automatically be converted into the DNS server and Global Catalog (GC).
  • Give a unique and strong password to your Active Directory for successfully retrieving the data.
  • Enter the NetBIOS name for the domain. Keep it similar to the name of the root domain name.
  • Select the place for storing all the log files; choose SYSVOL or go with the default space assigned.
  • Review everything and hit the install button. Your device will reboot to implement the changes automatically. Run a health check-up by running the dcdiag /v command in the command line.


To reduce the malicious attacks and hacking risks, Windows has come up with the Domain Controller that is majorly used for authenticating users entering a domain. It validates users with credentials such as username and password and also uses IP or biometrics for enhanced security. The authentication process makes use of two types of domain controllers, i.e. primary domain controller and backup domain controller. The primary domain controller plays a major role as it handles all the system access requests. On the other hand, the backup controller is used in the case the primary domain controller fails to respond.

The blog also covered the difference between domain and domain controller along with Active Directory that is utilized by DC to get information about the users who are trying to access the system. Also, a step-by-step guide for setting up the domain controller is mentioned that will help you to get started.

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