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How to Troubleshoot SQL Server Connection Problems

In this blog we shall take a look at the steps to troubleshoot connection problems in SQL Sever. We need to keep in mind, there are lot of things that might be part of such an issue and also we need to consider which user or what application is reporting this connection problems. The exact cause of the connection failure can only be troubleshooted by testing and trying multiple remedial steps, eliminate that step and keep moving forward.

  • Is SQL Server currently running or SQL Server accepting new connections?
    • Make sure that SQL Server on that machine is currently running, before making any other attempts / trials. SQL Server status should be checked that it is not stopped  or paused ( of course the error message indicates if the SQL Server is not accepting any new connections). Either way see that SQL Server is running currently. Start SQL Server if needed from Configuration Manager or Services etc.
  • Are the required Protocols Enabled?
    • Ensure that all required protocols are enabled on the SQL Server. There is nothing wrong with enabling all protocols, but a word of caution about the VIA protocol, it should be disabled on most of the systems (depends on Server Hardware) and should be enabled only upon verifying with the Hardware Vendor.
  • Check the SQL Server Authentication Mode.
    • This step is also important, any connection coming to SQL Server either has to be a Windows User or a SQL Server user. If you are trying to connect using a SQL Server login, make sure the authentication mode on the SQL is Mixed Mode, else the login attemps will fail and you will not be able to connect to SQL Server.
  • Is the User / Login status active or enabled?
    • Make sure you are connecting to the SQL Server using an account which is not disabled. If a different user complains about connection issues (different credentials), make sure that account is not disabled in SQL Server (if SQL Login) or the Windows Active Directory account is not expired / locked.
  • Check the Firewall settings.
    • Make sure that the firewall is not blocking the port on which SQL Server listens. 
  • Check the SQL connection information.
    •  You need to check if the SQL Server being referred in the connection string is a default instance or a named instance. If the instance is a named instance, you will need to ensure that the connection string includes the instance information also, i.e, it has to be something like the IP Address,Port # such as 192.168.10.123,3456 or the Servername\Instance such as PhysicalServer\InstanceName.