Fixing SQL Server Error 35206 in Always On Availability Groups with SQLOPS 

Nigel Menezes
Fixing SQL Server Error 35206 in Always On Availability Groups with SQLOPS

Maintaining a seamless operational flow within SQL Server Always On Availability Groups is crucial for ensuring data availability and system reliability. Error 35206 presents a significant challenge in this context, signaling a disruption in the connection to the primary replica. SQLOPS’s expert guide is designed to navigate you through the troubleshooting process for this error, aimed at restoring connectivity and ensuring the stability of your SQL Server environment. 

Pinpointing Error 35206 in SQL Server 

When Error 35206 surfaces, it indicates that the secondary replicas are unable to communicate with the primary replica. This breakdown in connectivity can stall data synchronization processes, impacting the overall functionality of the Availability Group. 

Primary Causes: 

  • Network connectivity issues between replicas. 
  • Configuration discrepancies in the SQL Server environment. 
  • Firewall or network security configurations blocking communication. 

Resolving Error 35206 

Assess Network Connectivity 

Objective: Confirm unimpeded network communication between the primary and secondary replicas. 

Conduct Basic Connectivity Tests: 

Employ ping and telnet to ensure the primary and secondary replicas can reach each other, focusing on the ports designated for SQL Server and the Always On endpoints. 

Review SQL Server Configuration 

Discrepancies in SQL Server or Always On configurations can inadvertently lead to connectivity issues. 

Check Listener Configuration: 

Ensure the SQL Server Always On listener is correctly configured and operational. The listener facilitates connectivity to the primary replica and should resolve to the correct IP address. 

SELECT [dns_name], [port], [ip_configuration_string] FROM sys.availability_group_listeners 

Examine Firewall Settings 

Firewalls can often block necessary communication between replicas if not correctly configured. 

Configure Firewall Exceptions: 

Verify that the firewall on both the primary and secondary replicas allows traffic on the SQL Server port (default 1433) and the endpoint port used by the Always On Availability Group (default 5022). 

Validate Always On Availability Group Configuration 

Misconfigurations within the Availability Group can disrupt connectivity. It’s essential to review and rectify any issues. 

Check Availability Group Health: 

Utilize the following T-SQL command to assess the health status of the Availability Group, focusing on any anomalies that could indicate connectivity issues. 

SELECT [name], [synchronization_health_desc] FROM sys.availability_groups 

Test and Re-Establish Connection 

After addressing potential causes, attempt to re-establish the connection between the primary and secondary replicas, monitoring the status of the Availability Group. 

Resume Data Movement: 

If synchronization has been suspended, resume data movement in the Availability Group by using SQL Server Management Studio (SSMS) or the following T-SQL command: 


Error 35206 can pose a significant threat to the integrity and availability of your SQL Server environment. However, with diligent troubleshooting and careful attention to connectivity, configuration, and security settings, this challenge can be effectively managed. SQLOPS’s detailed guide empowers SQL Server administrators to restore and maintain optimal operations within Always On Availability Groups. 

Struggling with SQL Server Always On Availability Groups or other database challenges? SQLOPS offers a range of specialized services to support your database needs, from troubleshooting and optimization to comprehensive management solutions. Explore how we can enhance your SQL Server deployment at SQLOPS. 

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