How to Check the Health of Your Active Directory

Active Directory (AD) is the backbone of most enterprise IT infrastructures, serving as the directory service for managing users, groups, computers, and permissions. Because of its central role, ensuring the health of your Active Directory is crucial to avoid service disruptions, security issues, and operational inefficiencies. A proactive approach to AD health checks can help identify problems before they cause significant issues.

In this article, we’ll walk through several steps to help you check the health of your Active Directory and keep it running smoothly.

1. Check Replication Health

One of the core functionalities of Active Directory is replication, where changes made on one Domain Controller (DC) are copied to other DCs to ensure consistency across the network. If replication fails, it can lead to outdated or inconsistent information across your AD environment, causing issues like login failures or inconsistent permissions.

Tools to Check Replication:

• Repadmin: This command-line tool is one of the most effective ways to check replication status.

  • To check the status of replication between domain controllers, run:This command will show the current replication status and highlight any failures or delays.

    repadmin /replsummary
    

• DCDiag: This tool is often used to test the health of Domain Controllers. You can use it to run various diagnostic tests, including replication checks.

  • Run the following to check the general health of your DCs:

    dcdiag /test:replications
    

Key things to look for:

• Replication delays or failures.
• Non-functioning or unreachable domain controllers.
• Warning or error messages related to replication issues.

2. Test DNS Functionality

Active Directory heavily relies on DNS for its operations. If DNS is not working correctly, AD might not function as expected, leading to login problems, service disruptions, or even domain-wide failures. It is vital to ensure your DNS settings are correct and that DNS servers are properly replicating.

Tools to Check DNS:

• Dcdiag: The DCDiag tool can also test DNS health.

  • To run a DNS test, use:

    dcdiag /test:DNS
    

• Nslookup: This tool can help check whether the domain controllers are resolving correctly.

  • To check the DNS records for your domain controllers, use:This should return the IP address and DNS records related to that DC.

    nslookup <domain controller name>
    

Key things to look for:

• DNS lookup failures or timeouts.
• Incorrect or missing DNS records for domain controllers.
• Misconfigured DNS zones or delegation.

3. Monitor Active Directory Services

Several key services must be running on your domain controllers for Active Directory to function properly. These include the Kerberos Key Distribution Center (KDC), Netlogon, Active Directory Domain Services (AD DS), and more.

Check Services on a DC:

• On the domain controller, run:and verify that all the necessary services are running. You should ensure that:

  services.msc
  

  • Active Directory Domain Services is running.
  • Kerberos Key Distribution Center is running.
  • Netlogon is running.
  • DNS Server is running (if the DC also serves as a DNS server).

Key things to look for:

• Stopped or paused services.
• Services that are frequently restarting or generating errors in event logs.

4. Event Log Monitoring:

Event logs can provide valuable insights into the health of Active Directory and reveal issues that might not be immediately apparent from a high-level check.

Useful Event Logs:

• Directory Service logs (Event Viewer > Applications and Services Logs > Directory Service) contain AD-related events such as replication errors, authentication issues, and more.
• DNS Server logs (Event Viewer > Applications and Services Logs > Microsoft > Windows > DNS-Server) are important to monitor for DNS-related issues.
• System logs (Event Viewer > Windows Logs > System) to look for critical system-related errors.

Key things to look for:

• Repeated error codes or critical warnings.
• Kerberos authentication failures or issues with user logons.
• Replication-related error events (e.g., event ID 1311).

• Regularly review event logs: Scrutinize security, application, and system logs on domain controllers. Look for critical errors, warnings, and suspicious activities.
• Utilize event log management tools: Tools like Microsoft's Event Viewer or third-party SIEM solutions can help filter, analyze, and alert on critical events.
• Focus on specific events: Pay close attention to events related to:
  • Account Lockouts: Frequent lockouts could indicate brute-force attacks.
  • Failed Logon Attempts: Monitor for unusual patterns in failed login attempts.
  • Group Policy Changes: Track modifications to critical Group Policy Objects (GPOs).
  • Replication Issues: Identify and resolve replication problems between domain controllers.

5. Test Authentication and Logon Procedures

Active Directory’s primary role is user authentication. Ensuring that users can authenticate properly and that group policies are applied correctly is crucial.

Testing Authentication:

• Use the Klist tool to check Kerberos ticket cache:

  klist
  

  This command will show the tickets that have been granted for the user or machine. If there are problems, the Kerberos tickets may not be issued correctly.

• Perform a manual test to ensure users can log in to the domain. Try logging into several workstations with different user accounts to verify that authentication is functioning correctly.

• Group Policy Results: Run the gpresult command to verify that group policies are applied correctly to users and computers:

  gpresult /r
  

Key things to look for:

• User login failures.
• Group policy application issues.
• Delays or errors in authentication.

6. Check Domain Controller Health with DCDiag

The DCDiag tool is a comprehensive diagnostic utility that checks the overall health of your domain controllers. It performs tests on the key components of AD, including DNS, replication, and more.

To run a complete test of a domain controller, execute:

dcdiag

This will run several health checks and output the results, pointing out any issues with a specific domain controller.

Key things to look for:

• Failing tests or errors in any of the checks.
• Warnings that indicate potential issues, such as replication problems or DNS misconfigurations.

7. Check SYSVOL and Group Policy Replication

The SYSVOL folder contains important files related to Group Policy, scripts, and other domain-wide configuration settings. If replication fails between domain controllers, Group Policy might not be applied correctly.

Tools to Check SYSVOL Health:

• Net Share: Run the following command on each domain controller to ensure that SYSVOL is shared:

  net share
  

• DFSR (Distributed File System Replication): Check the health of SYSVOL replication by using DFSR diagnostics:

  dfsrdiag pollad
  

• Event Logs: Check for SYSVOL replication issues in the DFS Replication logs (Event Viewer > Applications and Services Logs > DFS Replication).

Key things to look for:

• SYSVOL not shared or not replicated correctly.
• Group Policy not being applied due to replication issues.

8. Ensure Security Updates Are Applied

Active Directory’s security is essential, and ensuring that your domain controllers are up to date with the latest security patches is critical to prevent vulnerabilities.

Key things to check:

• Make sure all domain controllers have the latest security updates installed.
• Verify that your AD infrastructure is protected by adequate firewall and security policies.

Best Practices for Active Directory Health

Maintaining the health of your Active Directory (AD) environment is essential to ensure smooth operations, security, and performance. Below are some key best practices to help keep your AD infrastructure in optimal condition:

1. Group Policy Object (GPO) Management

• Regularly review GPOs: Periodically audit and verify that Group Policy Objects (GPOs) are applied correctly and consistently across all domain controllers.
• Test GPO changes in a lab environment: Before deploying any changes to production, always test them in a controlled, isolated lab environment to identify potential issues.
• Utilize Group Policy Management Console (GPMC): Leverage the GPMC to manage, troubleshoot, and document GPOs effectively. It provides a centralized platform for all your Group Policy-related tasks.
• Monitor for unexpected changes: Implement change tracking and auditing mechanisms to monitor GPO modifications. Investigate any unauthorized or unexpected changes promptly to ensure policy integrity.

2. Domain Controller Health Checks

• Monitor server performance: Keep track of the performance of domain controllers by monitoring CPU usage, memory utilization, disk space, and network traffic. This helps identify resource bottlenecks before they affect AD services.
• Check for disk space issues: Ensure sufficient free space on system drives, especially for the system partition and the volume storing the AD database (NTDS.DIT) and logs.
• Monitor replication status: Regularly verify that replication is occurring successfully between all domain controllers. Use tools like repadmin to identify any replication issues or delays.
• Perform regular backups: Implement a comprehensive backup strategy to ensure that all domain controllers are backed up regularly, including system state backups. Verify the integrity of backups periodically to ensure they can be restored in case of failure.

3. User Account Management

• Review user accounts: Regularly audit user accounts, especially those with elevated privileges. Disable or delete inactive accounts and ensure that user account information is accurate.
• Implement strong password policies: Enforce password policies that require strong, complex passwords with specific length and composition rules. Also, ensure regular password changes to mitigate security risks.
• Utilize multi-factor authentication (MFA): Implement MFA for all administrative accounts and other sensitive user accounts to enhance security and reduce the risk of unauthorized access.

4. Security Audits

• Conduct regular security audits: Perform periodic security assessments of your AD environment to identify and address potential vulnerabilities. Regular audits help ensure that security policies are being enforced properly.
• Utilize security tools: Use security scanning tools like Microsoft Baseline Security Analyzer (MBSA) or third-party vulnerability scanners to assess your AD infrastructure for known vulnerabilities and configuration weaknesses.
• Address identified vulnerabilities: Promptly address any security vulnerabilities discovered during audits. Ensure that all systems are up-to-date with the latest patches and security updates.

5. Regular Maintenance

• Apply security updates: Ensure that all critical security updates and patches for Windows Server and AD-related components are installed in a timely manner to protect your environment from known threats.
• Perform regular maintenance tasks: Regularly defragment AD database files, clean up temporary files, and optimize system performance to avoid performance degradation over time.
• Stay informed: Stay updated with the latest security advisories, best practices, and feature updates from Microsoft. This will help you stay ahead of emerging threats and optimize your AD infrastructure.

Regularly checking the health of your Active Directory is essential for maintaining a stable, secure, and efficient IT environment. By using a combination of tools like Repadmin, DCDiag, and Event Viewer, you can identify issues early, avoid service disruptions, and ensure that AD services are running smoothly. Remember, proactive monitoring and maintenance are key to keeping your AD infrastructure in top shape.