Troubleshooting SQL Server Connectivity Issues

When you failed to connect to your SQL Server, the issue could be:

•  Network issue
• SQL Server configuration issue
• Firewall issue
• Client driver issue
• Application configuration issue
• Authentication and logon issue

Please go throught the below link on how to resolve these issues,

https://blogs.msdn.microsoft.com/sql_protocols/2008/04/30/steps-to-troubleshoot-sql-connectivity-issues/

Best Practices

Server Side:

- Check that TCP/IP protocol is enabled in SQL Server Network Configuration section in SQL Server Configuration manager

- Check that SQL Server Service is Running.

- SQL Browser service status is “Running”. (if you have got an instance that is not by default with port 1433)

- Check that Firewall is configured to allow acces to SQL Server by opening the desired port.

https://docs.microsoft.com/en-us/sql/sql-server/install/configure-the-windows-firewall-to-allow-sql-server-access

https://support.microsoft.com/en-us/help/968872/how-to-open-the-firewall-port-for-sql-server-on-windows-server-2008

- Verify whether Remote Connections are accepted by the server or not.

Client Side:

- Verify that the Connection string is correct and pointing to the right server. Be sure on the instance name.

- Check whether the Server is reachable from client machine or not.(use Ping)

- Also try connecting to Server machine out of your application.(use SQLCMD)