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What is a Domain Controller? Definitions, Functions, Benefits & Limitations, and More

by Chris Brook on Thursday October 20, 2022

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What is a domain controller (DC) and why is it critical to the security of your network? Learn all about the functions of a domain controller, including how make them more secure in this blog.

When it comes to the security of your network, one of the most critical components is the domain controller (DC). A compromised domain controller can leave your network wide open to attack and cause irreparable damage to both your network and your reputation. With that in mind, let’s review its key functions and what action you should take to maintain its integrity.

What is a Domain Controller?

A domain controller (DC) is a type of server that’s essential for centralizing user data and protecting network security. The most important function of a domain controller is ensuring that only relevant and trustworthy users can access network resources by processing authentication requests and verifying users.

It’s like a gatekeeper that allows access to domain resources and enforces security protocols, and, as such, it stores users’ account information and runs Active Directory Domain Services (ADDS). Organizations generally have several DCs, and each of them uses a copy of Active Directory.

A domain controller can be a single system, but they’re often installed in clusters to enhance availability and reliability. When domain controllers run with Windows Active Directory (AD), every cluster will have a primary domain controller (PDC). It should also have backup domain controllers (BDC), while domain controllers running on a Linux environment have a replica domain controller that copies the authentication database from the PDC.

Functions of a Domain Controller

A domain controller authenticates users before letting them access network resources. For example, the domain controller in a Windows AD domain would draw authentication details from Active Directory. Here’s a closer look at its most important functions:

Validation and Authentication

The domain controller first authenticates users to see if they are eligible to access the network. The user’s identity is validated by checking their account information, such as their username and password, by comparing it with the information stored in Active Directory.

Permission and Access Regulation

The domain controller manages the organizational hierarchy of the users. It uses Active Directory to determine if a user is allowed to access domain resources and then identifies their entitlements to check what resources they should have access to.

Group Policy Implementation

The domain controller is responsible for implementing security protocols and rules. Some examples of these rules are:

  • Requirements for entering complex passwords Requirements for the frequency of password updates
  • Granting resource access to specific users
  • Configuring the devices in a domain to enter a locked status after a specific period of inactivity

The Importance of a Domain Controller

Domain controllers are responsible for domain access management and the prevention of unwanted access to domain networks. Since they control network access, they can be the primary target of a hacker trying to disrupt your network.

Here are the main reasons why a domain controller can be helpful for an organization:

  • It simplifies the administrative workload.
  • It maximizes the security of the company network.
  • It centralizes the control over user settings.
  • It increases collaborative potential within a domain.

Limitations of a Domain Controller

Domain controllers shouldn’t be relied on exclusively to prevent unwanted network access. They have a few limitations, such as:

  • Domain controllers need additional security mechanisms and infrastructure.
  • Since the domain controller is responsible for user authentication, its failure will cause network damage.
  • The failure of a DC can also cause network damage, which makes it a common target for cyber attackers.
  • Networks are dependent on domain controllers. Therefore, to reduce downtime risk, it’s best to deploy them in clusters.

How to Make Domain Controllers More Secure

Since domain controllers are high risk, it’s important to keep them secure. Here are some steps companies should take to safeguard their DCs:

  • Review and take action on threat intelligence.
  • Monitor and audit the domain controller.
  • Limit the remote and physical access to the domain controller.
  • All virtual domain controllers should be run on dedicated physical hosts.
  • Grant domain admin access to only a few users.
  • Implement strong security protocols and strict authentication processes such as multi-factor authentication.
  • Do not have internet connectivity on the domain controller server.
  • Domain controllers should run on the most up-to-date version of the operating system.
  • Implement user activity monitoring to gain visibility into all user behaviors across the network. A user activity monitoring solution like Digital Guardian alerts your team to suspicious user behavior and collects and preserves chain-of-custody forensic evidence to prove malicious intent.

How to Set Up Domain Controllers in Active Directory

Servers that run Active Directory can handle authentication requests, but as discussed earlier, it’s best not to depend on a single domain controller – even if you have a small company. It’s a good idea to have a primary domain controller and one or multiple backup domain controllers. This will reduce the risk of network downtime.

Every domain controller should be deployed on a dedicated physical server. If you have a virtual domain controller, it should run on a dedicated virtual machine that runs on a secure physical host.

Here are the two main steps to set up domain controllers:

Domain assessment: Assess the domain in which you want to set up the domain controller. Find out the type of domain controllers you need and where they will be located. Also, determine their interoperability with the existing system.

Maintain security: The domain controllers will need to be secured from not just external but also internal attacks. The architecture of the DC should be secured from disruptions such as loss of power, loss of connectivity, and system failure.

Do You Need a Domain Controller?

A domain controller is a good addition to any business or organization. It protects customer data on the network and thus improves security. Before setting up a DC, you must ask yourself, “where is my customer data located and who is allowed to access it?” This will help you accurately determine your requirements.

Conclusion

While a domain controller isn’t the only component of your network security, it certainly plays an important part. Besides helping to maintain the security of your network, it also

  • Restricts access to sensitive data
  • Stores user account information
  • Maintains password security
  • Locks inactive devices
  • Reduces the administrative workload

Domain controllers are critical to the security of your network and, ultimately, to the success of your company. Taking the time to establish and maintain your domain controller can save you a lot of trouble further down the road.

Tags:  Cybersecurity Networking Authentication

Chris Brook

Chris Brook

Chris Brook is the editor of Digital Guardian’s Data Insider blog. He is a cybersecurity writer with nearly 15 years of experience reporting and writing about information security, attending infosec conferences like Black Hat and RSA, and interviewing hackers and security researchers. Prior to joining Digital Guardian–acquired by Fortra in 2021–he helped launch Threatpost, an independent news site that was a leading source of information about IT and business security for hundreds of thousands of professionals worldwide.

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