Active Directory Replication is more or less the center of all sorts of problems. It is a crucial service and it becomes more complicated when dealing with more than one domain controller. Issues relating to replication can vary from authentication issues and problems arising when trying to access resources over the network.
All objects in the Active Directory are replicated between domain controllers so that all partitions are synchronized. A large company with multiple sites means that replication takes place at the local site as well as the other sites to keep all partitions synchronized. This article aims to show you how to troubleshoot Active Directory replication issues.
Active Directory replication problems come from different sources, some of which are Domain Name System failures, network problems, or security issues.
Resources Needed to Troubleshoot Active Directory Replication
Failures coming in and out the active directories due to replication issues lead to many inconsistencies between domain controllers. Such failures lead to systemic failures or inconsistent output. Identifying the main cause of replication failure helps system administrators identify the possible cause and hence elimination of the problem. One of the commonly used interfaces based replication-monitoring tool is the Active Directory Replication Status Tool.
Understanding Recommendations from the tool solution
The red and yellow warning events in the system logs will always point out to the specific cause of replication failure and give the source and destination in the Active Directory. Any steps that are suggested by the warnings should be tried as explained. Other tools such as the Repadmin tool can give more information to help resolve replication issues.
- Eliminating Disruptions or Hardware Failures
Before troubleshooting replication failures, it is important to rule out any issues related to software updates or upgrades, intentional disruptions, software configurations, and hardware failures.
- Intentional Disruptions
Disruptions caused by unavailability (offline state) of a remote domain controller can be corrected by adding the computer as a member server using the Install From Media (IFM) method to configure the Active Directory Domain Services. The Ntdsutil command-line tool can be used to create installation media.
- Software Upgrades and Hardware Failures
Hardware failures can come from failing motherboards or hard drives. Once a hardware problem is identified, system administrators should take immediate action to replace the failing components. Active Directory Replication failures can take place after a planned upgrade. The best way to handle this is through an effective communication plan that prepares people in advance.
- Software Configurations
Some software settings such as the typical windows firewall have port 135 open alongside other advanced security settings. Some firewalls can be configured to allow for replication.
Responding to Failures Reported on Windows 2000 Server
Active Directory configured on Windows 2000 Server that has failed beyond the tombstone lifetime should be resolved by:
- Moving the server from a corporate to a private network
- Removing the Active Directory or Reinstalling the Operating System
- Removing its metadata from the Active Directory to hide its objects
Removing the server metadata ensures that any attempt by the server to revive objects settings after 14 days is impossible. This also helps avert further error logs due to replication attempts with a missing Domain Controller.
What are the Root Causes of Replication?
Apart from the already discussed causes leading to replication failures, here are some other reasons.
Network Connectivity: caused by unavailable network or wrong configurations
Name Resolutions: Wrong DNS configurations
Authentication and Authorizations: Aces denied errors every time a domain controller tries to connect for replication
Directory Database: A slow data store not being able to handle fast transactions that take place within replication timeouts.
Replication Engine: when replication schedules are short, it will lead to longer queues and large processing which may not be possible within the outbound replication schedule.
Replication Topology: All domain controllers need to have links linking them to other sites within the Active Directory. The links should map wide area networks or the virtual private network connections. All objects should be supported by the same site topology within the network to avoid replication failures.
How do We Fix Replication Problems
Any of the following approaches can be used to fix Active Directory Replication Issues:
- Daily monitoring of the state of replication using the Repadmin.exe to extract daily status updates
- Resolving reported replication failures as soon as possible, using steps provided in the event logs. Replication failures resulting from software configurations require un-installation of the software before attempting any other solutions.
- If all attempts to resolve replication issues do not work, remove the Active Directory Directory Services from the server and reinstall.
When an attempt to remove AD DS fails when the server is online, any of the following methods can resolve the issue.
- Force the removal of the AD DS from the Directory Restore Mode (DSRM) by cleaning up the server metadata and reinstall the AD DS.
- Reinstall Operating system and reconfigure the Domain Controller
Retrieving Replication Status Using Repadmin
When everything in the Active Directory is working as intended and produces no errors, then it means the following services are working correctly:
- Remote Procedure Call (RPC)
- Network Connectivity
- Window Time Service (W32time)
- Kerberos Authentication Protocol
The Repadmin tool is used to study the daily replication activities. The tool is able to access all the replication status of all domain controllers in the forest. The report is relayed in a .CSV format that can be accessed using any spreadsheet reader.
Generating Repadmin for Domain Controllers in a Spreadsheet.
Using the command prompt as an administrator type the following:
Repadmin /showrepl * /csv > showrepl.csv
- Open Microsoft Excel, navigate to the showrepl.csv, and click open
- Hide or delete column A and the Transport Type Column
- Select the row below the column heading and click freeze panes by clicking on Freeze Top Row
- Select the whole spreadsheet and click filter from the data tab
- Click on the down arrow below the source DC column, point to text filters, and select the custom filter.
- In the custom AutoFilter box, below show rows where click on does not contain. On the box next to it, type Del to eliminate results from deleted domain controllers.
- Repeat the previous step for the Last Failure Known Column and use does not equal and type 0
- Resolve replication issues.
Replication going on smoothly throughout the Active Directory is critical. Poor replication means all manner of problems from authentication to inconsistent results. The article is supposed to help you check on your system’s replication status and learn how to resolve the common replication errors.
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