Accessing SQL Server in Failover Cluster

Question

Hi All, I am seeking your expert advice regarding a connectivity issue we have encountered with our SQL Server setup. Previously, we were able to access SQL Server 2012 on Windows 2012 R2 seamlessly from our third-party client application. However, after performing an in-place upgrade to Windows 2016 Standard, we are now facing challenges connecting to the SQL Server from the client machine. SQL server is running as Always On High Availability in windows failover cluster. The issue is to connect to availability group listener. The firewall on the windows server side is disabled, while the client machine has its firewall enabled. Strangely, we can only establish a connection to the SQL Server when the Windows firewall on the client machine is disabled. This issue didn't exist before the upgrade, and users were able to access the SQL Server with the firewall enabled. As a temporary workaround, we have either disabled the Windows firewall on the client machine or created incoming rules to allow all ports. However, this is an unexpected deviation from our previous setup. I am seeking your expert advice to identify the root cause of this issue. Your insights into why the Windows firewall on the client end is impacting SQL Server access post the Windows upgrade would be highly appreciated. Thank you and looking forward to your assistance. Sarwar

Answer 1

• Have you tried to run netstat -an command to check the session established on which ports ?
• Check Windows Event Logs if you see any event logs that gives any clue.
• Also Ensure that the SQL Server ODBC or .NET drivers on the client machine are up-to-date. Sometimes, using outdated drivers can lead to compatibility issues.

Good luck !!