Event ID 8456 in Active Directory replication fail

Event ID 8456 in Active Directory replication indicates that the source server is currently rejecting replication requests

1. Verify DNS Configuration:

Ensure that all domain controllers are correctly configured to use the appropriate DNS servers.

Use the nslookup command to verify DNS resolution for all domain controllers.

2. Check Network Connectivity:

Confirm that all domain controllers can communicate with each other over the network. Use the ping command to test connectivity.

3. Run Repadmin Tool Use the repadmin tool to diagnose and fix replication issues. Commands like repadmin /showrepl and repadmin /replsummary can help identify the problem areas1.

4. Check for Offline or Stale Domain Controllers:

If the error refers to a domain controller that is currently offline but still valid, make it operational.

If the error refers to an inactive domain controller, remove the stale metadata for that DC from the destination DCs’ copy of Active Directory.

5. Review Event Logs:

Look at the Directory Service event logs for any related errors that might provide more context about the replication failure.

6. Run DCDIAG Tool:

Use the dcdiag tool to perform a comprehensive health check of your domain controllers. This tool can identify issues that might be affecting replication.

7.Check Time Synchronization:

Ensure that the time is synchronized across all domain controllers. Time discrepancies can cause replication issues. Use the w32tm /query /status command to check the time configuration.