Domain Controllers (DCs) are critical to protecting network security, centralising user data, and rolling out standard system security protocols. In this article we take you through DCs main functions, why they’re so important, and when MSPs need them.

What is a domain controller?

A domain controller is a server that runs Active Directory Domain Services (AD DS). The DC is responsible for authentication requests within a certain domain. Organizations typically have a number of DCs, each of which has a copy of the Active Directory (AD).

What is Domain Controller InfoGraphic

All login credentials from across the network are consolidated and held in the DC’s active directory service. For this reason, the DC is critical in helping manage the network’s security and maintain user identity security.

The most common examples of Active Directory (of which your DC is a part of) are Microsoft Active Directory (on-premises) , Microsoft AzureAD (cloud-based) for Windows, and Samba for Linux.

What does a domain controller do?

Think of a domain controller as a gatekeeper that handles user authentication, entitlements, authorizes users, and security protocols within your domain. It does this using an active directory.

Authentication and validation

The DC is responsible for authenticating a user’s right to access your network when they attempt to log in. It will usually validate a user’s identity by cross-referencing the account information, like a username and password, against the logged information in its active directory. Based on this, it will either permit or deny entry into your network.

Regulates permissions and access

The DC facilitates a hierarchical organization of your users based on different levels of entitlement. The DC oversees a user’s access rights within your domain. Using its active directory, it first determines whether a user is permitted to access domain resources and then identifies a user’s entitlements and what they should be able to see or access within your network.

Implement group policies

Using the DC, you can also implement network-wide rules and security protocols. For example:

  • Set requirements for unique or complex passwords
  • Set minimum length or other requirements for passwords
  • Set requirements for how often passwords need to be changed
  • Configure your network so that user settings follow them wherever they log in
  • Grant access to specific services across the network to certain users
  • Configure all computers in your domain to lock their screens after a certain period of inactivity

In addition, some MSPs implement AD groups. This eases administrative workload, since permissions don’t need to be assigned individually. Instead, if a user is placed in a specific AD group, they gain access to the relevant resources automatically.

Why are domain controllers important?

MSPs should not overlook the importance of domain controllers. As the gatekeepers to your client’s networks and computer networks, your DCs determine who can gain access and to what.
What is an AD?

Active Directory (AD) is essentially a database that holds all the information about your network’s users and devices. Think of it as a log book that contains critical network information such as user accounts, groups, contacts, and computer data.

The DC is the server that runs the AD. The AD facilitates the DC’s operations, enabling it to carry out its authentication, validation, and to grant access to resources within the network.

An AD has 3 sections: domains, trees, and forests.

A domain refers to a group of users, computers, and other objects that are related. A domain is a section of a network where all comprised objects can be managed together.

A tree is where numerous domains are combined.

A forest is a collection of trees (or groups of domains). It also constitutes a restricted security area, because inter-forest objects cannot interact unless a ‘trust’ is created.

When do MSPs need a domain controller?

As MSPs, one of your key roles is running and managing your clients’ networks. Here’s when and why MSPs need a DC:

  • Simplifies your administrative workload
  • Centralizes your control over user settings and entitlements
  • Ensures and maximizes the security of your clients’ network and data
  • Provides a centralised database of user credentials
  • Increased collaborative possibilities within the domain

Why can domain controllers be a risk?

Given that DCs are a critical gatekeeper to your domain, they’re also a prime target for cyber attacks. Their crucial role in authenticating users and granting access to your networks make them highly liable to being preyed on.

A successful breach of your DC can lead to serious damage to your AD DS database, security leaks, and compromised user credentials and data. Should your AD forest be compromised, you’ll be unable to use it again unless you have a good and reliable backup.

That’s why MSPs should ensure that they implement sturdy cybersecurity measures to protect their domain controllers.

Another issue to consider is just how dependent your networks are on your DC’s uptime. For this reason, it’s advisable that your DCs are dedicated solely to domain services. This is because running any other services risks slowing down or crashing the system.

How MSPs should ensure security of their DCs

Given the high-value and high-risk of the DCs and therefore the AD, it’s absolutely critical that you take the necessary steps to protect it. Here are a couple of strategies you can use:

  • Limit physical and remote access to your DCs
  • For virtual domain controllers, run them on dedicated physical hosts
  • Continually monitor and audit your DC
  • Implement robust security protocols, including stringent authentication processes like multi-factor authentication (MFA) and unique or complex password requirements
  • Minimize the vulnerability of your DCs and AD by granting domain admin status to only a select few users
  • Ensure your DCs always have empty disk space and limit the other services that your DC is running
  • Block internet access on your DCs
  • Run all DCs on the most up-to-date OS

Sounds difficult? It doesn’t have to be, as Atera’s Network Discovery makes it easy to proactively maintain and audit your clients’ networks by scanning your customers’ workgroups and DC networks. Try it for free with our free trial.

What is a primary domain controller?

Given the importance of the DC, it’s always advisable to have at least two domain controllers. This is a backup mechanism for occasions when one DC goes down.

In this context, you may hear the terms ‘Primary Domain Controller (PDC)’ as well as ‘Backup Domain Controllers (BDCs)’ being used. In fact, since 2008, the hierarchical arrangement between PDCs and BDCs has been redundant. Instead, all DCs are now considered to be ‘equal’, with the active directory synchronised across all of them.

Final thoughts

MSPs will know both the value and the vulnerability of DCs. Though DCs help to make your life easier, and give you the peace of mind that comes with a secure network, they’re also the first port of call for potential attackers. As with anything, it’s always better to be safe than sorry.

Always ensure to implement robust security measures for your DC so that you can reap all the benefits without the risk.

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