Windows 11 25H2 SQL Server Linked Server Distributed Transaction Failure Diagnosis

Symptoms

• Distributed transactions between linked SQL Server instances fail with timeout or rollback errors.
• Event Viewer logs showing MSDTC errors or warnings under the System or Application logs.
• SQL Server error messages referencing distributed transaction coordinator or linked server communication issues.
• Inability to commit transactions spanning multiple linked servers.

Likely causes

• MSDTC service misconfiguration or failure to start on Windows 11 25H2.
• Network firewall or Windows Defender blocking RPC or MSDTC ports required for distributed transactions.
• Changes in Windows 11 25H2 security policies affecting DCOM or RPC communication for MSDTC.
• Incorrect linked server setup or SQL Server service account permission issues.

What FixWin checks

• Verify that the Distributed Transaction Coordinator (MSDTC) service is running and set to automatic.
• Check Windows Firewall inbound and outbound rules for MSDTC (TCP ports 135 and dynamic RPC range).
• Review DCOM configuration settings via dcomcnfg to ensure MSDTC has proper permissions.
• Inspect Event Viewer logs under System and Application for MSDTC-related errors.
• Confirm linked server security settings and SQL Server service account permissions.

AI diagnostic workflow

• Open Services.msc and confirm MSDTC service status and startup type.
• Use Event Viewer to identify specific MSDTC or RPC errors during transaction attempts.
• Run 'dtcping' tool between linked server hosts to test MSDTC connectivity.
• Check Windows Defender Firewall settings for blocked RPC or MSDTC communications.
• Validate linked server configuration in SQL Server Management Studio focusing on security context and distributed transaction support.

Related Windows entities

• Distributed Transaction Coordinator (MSDTC) service
  Coordinates distributed transactions across multiple resource managers like SQL Server linked servers.
• Windows Defender Firewall component
  May block necessary RPC and MSDTC ports required for distributed transaction communication.
• Event Viewer - System and Application Logs log
  Contains critical error and warning entries related to MSDTC and SQL Server linked server failures.
• dcomcnfg.exe tool
  Used to configure DCOM permissions essential for MSDTC operation and communication.
• SQL Server Management Studio (SSMS) tool
  Used to configure linked servers and review distributed transaction settings.

Repair logic

Since distributed transaction failures on Windows 11 25H2 often stem from MSDTC service issues, firewall blocks, or permission changes, the repair approach focuses on verifying and correcting MSDTC service status and settings, ensuring network ports are open for RPC/MSDTC traffic, adjusting DCOM permissions, and validating linked server configurations to restore transaction functionality.

FAQ

Why do distributed transactions fail after upgrading to Windows 11 25H2?

Windows 11 25H2 introduces security and network policy changes that can affect MSDTC communication, including stricter firewall rules and DCOM permission alterations, leading to distributed transaction failures.

How can I verify if MSDTC is working correctly?

Check that the MSDTC service is running, use the 'dtcping' utility to test connectivity between servers, and review Event Viewer logs for MSDTC-related errors.

What ports need to be open for SQL Server distributed transactions to work?

MSDTC requires TCP port 135 and a range of dynamic RPC ports to be open on Windows Defender Firewall and any network firewalls to allow distributed transaction communication.

Related Windows problems

• Diagnosing SQL Server Service Broker Queue Activation Issues on Windows 11 25H2
• Windows 11 25H2 Microsoft Graph PowerShell Authentication Popup Not Appearing