How to fix Error 9642 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: Error 9642 – Service Broker/Database Mirroring Transport Connection Endpoint Error

Why This Error Happens

Error 9642 typically occurs when the TCP transport layer used by Service Broker or Database Mirroring encounters a disruption while establishing or maintaining a connection endpoint. This is commonly caused by a blocked or conflicting port in the Windows Firewall, an expired or mismatched SSL/TLS certificate used for endpoint authentication, or network instability between the mirroring/broker partners. In some cases, the issue stems from incorrect endpoint configuration (wrong state, protocol, or authentication mode) on one of the SQL Server instances.

Step-by-Step Resolution Guide

Step 1: Verify Endpoint Configuration and State

  • Run SELECT * FROM sys.database_mirroring_endpoints; or SELECT * FROM sys.service_broker_endpoints; on both instances to confirm the endpoint exists and is in a STARTED state.
  • If the state shows STOPPED or DISABLED, run ALTER ENDPOINT [EndpointName] STATE = STARTED;.
  • Confirm the correct port (default 5022) is assigned using SELECT port FROM sys.tcp_endpoints;.

Step 2: Check Windows Firewall and Network Connectivity

  • Open Windows Defender Firewall with Advanced Security on Windows Server 2025 / Windows 11.
  • Create or verify an Inbound Rule allowing TCP traffic on port 5022 (or your custom mirroring/broker port).
  • Test connectivity between partner servers using Test-NetConnection -ComputerName <PartnerServer> -Port 5022 in PowerShell.
  • Ensure no intermediate network firewalls or NSGs (if on Azure VMs) are blocking the connection.

Step 3: Validate SSL/TLS Certificates Used for Authentication

  • Check certificate expiration dates using SELECT name, expiry_date FROM sys.certificates;.
  • If a certificate has expired or is mismatched between partners, regenerate and re-exchange certificates using CREATE CERTIFICATE and BACKUP CERTIFICATE.
  • Re-import the updated certificate on the partner server and recreate the endpoint authentication using:
    ALTER ENDPOINT [EndpointName] FOR DATABASE_MIRRORING (AUTHENTICATION = CERTIFICATE [CertName]);

Step 4: Review SQL Server Error Logs and Extended Events

  • Open SQL Server Management Studio (SSMS) and navigate to Management > SQL Server Logs.
  • Look for related entries near Error 9642, such as network timeout messages or certificate validation failures.
  • Enable an Extended Events session targeting the broker_login or mirroring_state_change events for deeper diagnostics.

Step 5: Restart the Endpoint and SQL Server Service

  • Run ALTER ENDPOINT [EndpointName] STATE = STOPPED; followed by ALTER ENDPOINT [EndpointName] STATE = STARTED; to reset the connection.
  • If the issue persists, restart the SQL Server (MSSQLSERVER) service via Services.msc or Restart-Service MSSQLSERVER in PowerShell.

Alternative or Verification Steps

  • Verify the fix by checking sys.dm_broker_connections and sys.database_mirroring DMVs to confirm active, healthy connections without error states.
  • If the issue persists after certificate and firewall checks, consider recreating the Mirroring/Broker endpoints entirely using DROP ENDPOINT followed by a fresh CREATE ENDPOINT statement with validated authentication settings.