Unlocking the Power of Microsoft KMS: An Overview of Deployment and Usage

This article delves into the essentials of setting up and activating a Windows KMS Server (Key Management Service), a crucial component for managing the volume activation of Windows operating systems and Microsoft Office products in on-premises (Active Directory) enterprise environments.

Introduction – What is Windows KMS Server?

The Key Management Service in Windows Server is a helpful component in Microsoft’s volume activation strategy. The simple-to-install service offers organizations a light administration solution for activating Windows and volume editions of Microsoft Office products on the local network.

By using KMS, enterprises can activate and manage hundreds and thousands of Windows-based client machines without needing to touch them at all.

How does KMS work?

A KMS host is installed on a server or client within the network. A host key is used to activate the service with Microsoft. Then there are several steps for activating Windows or Office:

1. The KMS host then publishes a special DNS record that allows KMS clients to locate it on the network.
2. KMS clients query the DNS namespace to locate the KMS host.
3. The KMS client then sends an activation request to the KMS host. The request includes the client machine ID and the product key information (Windows 11 Enterprise, Office 2024 LTSC, etc.).
4. The KMS host validates the activation request, sends a successful validation, and enables the client’s activation status.
5. KMS clients then periodically check in with one or more KMS hosts at least once every 180 days.

The KMS service has a minimum threshold of 25 endpoint devices before it starts to activate client machines. Microsoft built this minimum into the service primarily to prevent abuse. By requiring a large number of clients, Microsoft discourages individuals from setting up a KMS server to activate a small number of machines against licensing agreements/compliance agreements.

Important deployment considerations

Deploying an effective Key Management Service in your environment requires careful consideration and planning. Several factors should be considered to ensure a smooth design and rollout. Let’s go through the most important aspects.

Prerequisites / system requirements

• Ensure the KMS host server meets basic hardware and software prerequisites.
  • The KMS service itself adds a relatively minor load on top of Windows Server.
• The KMS host must be running on a supported version of Windows Server (today, this includes Windows Server 2016 up to and including Windows Server 2025) or a Windows 10/11 client device.
• Due to its minimal resource requirements, the KMS service does not necessitate a dedicated server. Instead, the KMS host service can be installed on an existing server that is already fulfilling other roles.

Licensing

You need to obtain a valid KMS host key from Microsoft. Typically, after you’ve purchased a volume license agreement from Microsoft, you’ll obtain a KMS host key. This is distinctly shown on the Microsoft 365 Admin Center website where Volume License Keys are now shown (they used to be on a dedicated Volume License Service Center (VLSC) website).

You will need limited outbound Internet access or a phone on your KMS host to activate the KMS server, similar to using a Volume License Key (VLK) to activate Windows or Office.

Best practices for KMS deployment

Although deploying a KMS server is on the lighter side of needs and resources from an IT Pro perspective, you still want to perform due diligence to make sure you have a smooth deployment. Follow these guidelines to offer your enterprise a pain-free and quick service.

• Network Configuration:
  • Ensure that firewall rules permit traffic on TCP port 1688, which is the default port used by KMS for activation requests.
  • Properly configure DNS to support KMS auto-discovery. The KMS host should automatically create a _vlmcs DNS record in the domain for clients to locate the KMS host.
    
• Security Measures:
  • Secure the KMS host by applying the latest security updates and patches. Be sure to run the Microsoft Security Baseline advisor for compliance needs.
  • Implement access controls to restrict who can modify the KMS configuration and manage the KMS host.
    
• Activation Thresholds:
  • Be aware of the activation thresholds that must be met before KMS starts activating clients: at least 25 clients for Windows client operating systems and 5 clients for Windows Server operating systems. Be sure you take into account the minimum number of computers you’ll need for KMS to work.
    
• High Availability:
  • Instead of using a single KMS host, consider setting up multiple KMS hosts to ensure high availability and redundancy.
    • If you have more than 50 clients, Microsoft recommends that you have at least two KMS hosts in case one of your KMS hosts becomes unavailable. Most organizations can operate with as few as two KMS hosts for their entire infrastructure.
      
• Monitoring and Maintenance:
  • Regularly monitor the KMS host for activation statistics and any potential issues using Event Viewer and/or other syslog-type monitoring tools and services.
    • Consider adding the KMS host service specifically to your monitoring tools.
  • Verify your KMS server(s) are patched regularly.
    
• Client Configuration:
  • Configure KMS clients to ensure they can locate and communicate with the KMS host.
  • Be aware of what client versions of Windows are supported.

Common troubleshooting tactics

Based on my experience with installing and managing a KMS environment, the hardest pain point is implementation. Adding the service via ‘Roles and Features’ in the Windows Server ‘Server Management’ console is relatively painless, but determining the correct KMS activation key, searching the various Microsoft Licensing websites for the correct account to gather the key, and dealing with the legacy and almost archaic GUI interfaces to manage KMS can be frustrating.

Plus, you’ll probably be irritated if you don’t like the command line – it is certainly the most efficient method to implement and troubleshoot KMS.

Once it’s up and running for a few months, it’s essentially a well-oiled machine. However, as I said, it can be a pain to install. You’ll certainly be using the command prompt to assist in diagnosing the service.

Let me go through the most basic issues you’ll run into and how to resolve them.

• Verify KMS Host Configuration:
  • Ensure the KMS host key is correctly installed and activated.
  • Confirm that the KMS service is running on the host server.
  • Check that the DNS _vlmcs record is correctly created and accessible by clients.
    
• Check Network Connectivity:
  • Ensure that TCP port 1688 is open and not blocked by firewalls or network security settings.
  • Use tools like ping and telnet to test connectivity between clients and the KMS host.
    
• Review Activation Count:
  • Ensure that the activation threshold is met (e.g., at least 25 clients for Windows client operating systems or 5 clients for Windows Server operating systems).
  • Use the slmgr.vbs /dli and slmgr.vbs /dlv commands on the KMS host to view the current activation count and status.
    
• Monitor Event Logs:
  • Check the Event Viewer on the KMS host for any error messages or warnings related to KMS.
  • Look for events in the “Key Management Service” log under Applications and Services Logs > Microsoft > Windows > Key Management Service.
    
• Verify Client Configuration:
  • Ensure that KMS clients are properly configured to use the KMS host for activation.
  • Use the slmgr.vbs /ato command on clients to force an immediate activation attempt and check for errors.
  • Check the client’s registry settings under HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\SoftwareProtectionPlatform to ensure they point to the correct KMS host.
    
• Resolve Activation Errors:
  • Common activation errors can often be resolved by checking the error code returned by the slmgr.vbs /ato command. You can also manually add a product key by using the slmgr.vbs /ipk command.
  • Refer to Microsoft’s documentation for specific error codes and recommended solutions.

Thank you for reading my article on Microsoft’s Key Management Service (KMS). Feel free to leave me a comment or question below. Thank you for reading!