Active Directory replication issues.

Active Directory (AD) replication issues can lead to inconsistencies and disruptions in your network. Addressing them promptly is crucial. Here are steps to help you resolve AD replication problems:

1. Check Event Viewer:
   • Review the Event Viewer logs on domain controllers for replication-related errors and warnings. This can provide valuable information about the nature of the issue.
2. Verify Network Connectivity:
   • Ensure that all domain controllers have reliable network connectivity. Use tools like ping, tracert, and nslookup to test connectivity.
3. Run Repadmin Tool:
   • Use the Repadmin tool to diagnose and repair replication problems. Common commands include repadmin /replsummary and repadmin /showrepl.
4. Check DNS Configuration:
   • Ensure that DNS is properly configured and that all domain controllers can resolve each other's names. Use nslookup to verify DNS resolution.
5. Verify Firewall Settings:
   • Ensure that firewalls are not blocking the necessary ports used for AD replication (e.g., TCP 135, TCP 389, TCP/UDP 53).
6. Check Time Synchronization:
   • Ensure that all domain controllers are synchronized with a reliable time source. Time discrepancies can lead to replication issues.
7. Check AD Sites and Services:
   • Verify that the correct sites, subnets, and site links are configured in Active Directory Sites and Services. This is crucial for replication routing.
8. Monitor Replication Traffic:
   • Use tools like Network Monitor or Wireshark to analyze network traffic between domain controllers to identify potential issues.
9. Force Replication:
   • Use tools like repadmin /syncall or AD Sites and Services to manually trigger replication between domain controllers.
10. Check Replication Topology:
    • Ensure that the replication topology is correct and that domain controllers are correctly identified as replication partners.
11. Review Replication Partners:
    • Verify that domain controllers are paired with the correct replication partners. Use the repadmin /showreps command to check the replication status.
12. Resolve Lingering Objects:
    • Lingering objects can cause replication problems. Use tools like repadmin /removelingeringobjects and dcdiag /cleanupmetadata to address this.
13. Check AD Database Integrity:
    • Use tools like ntdsutil to check and repair the integrity of the AD database.
14. Review Replication Schedule:
    • Verify that the replication schedule is configured appropriately to ensure timely replication between domain controllers.
15. Monitor the Health of DCs:
    • Regularly monitor the health of domain controllers, including hardware status, disk space, and system logs.
16. Document Changes and Solutions:
    • Keep detailed records of any changes made during troubleshooting, as well as the solutions applied. This helps in case of future issues.

If you continue to experience replication problems after following these steps, consider seeking assistance from Microsoft support or a professional IT consultant with expertise in Active Directory.