SQL Connectivity Issues:
You might have observed or attempted to resolve SQL connectivity difficulties as a DBA. So, I decided to post some tips here on how to fix SQL Server connectivity issues. Based on my experience, I’ve provided the essential actions to do below. The following are the things I look for while trying to connect to SQL Server but failing:
- SQL Server configuration Issue
- Firewall Issue
- Network Issue
- Logon Issue
- Configuration Issue in Application
SQL Server configuration Issue:
- Verify that the machine hosting SQL Server is up and listening on protocols.
- In SQL Server Configuration Manager, protocols can be verified and enabled.
- Named Pipes and TCP protocols are needed for SQL Server to connect remotely, ensure sure they are enabled.
- In SQL Server Errorlog, we can check to see if the server is listening on the appropriate protocols or not.
- Additionally, if the SQL instance is a named instance, check sure SQL Server Browser is operating on the machine.
Firewall Issue:
- SQL connectivity requests between the client and server may be prevented by a firewall.
- Although disabling the firewall can temporarily solve the problem, we can disable it permanently in real time.
- Adding SQL Server and SQL Browser to the Firewall Exception list will permanently cure issue.
- Provide the port number in which SQL is listening while adding the exception for the SQL Server DB Engine.
- When adding a SQL Browser exception, make sure to include UDP port 1434.
Network Issue:
- The Ping response from your Source Server to Target Server is the first thing to check for SQL connectivity.
- Additionally, you can use Telnet to connect to a SQL Server computer from a client machine and test UDL.
- Run a nslookup to see if an incorrect DNS entry is the root of the SQL connectivity problem.
Logon Issue to SQL Server:
- This is distinct from the aforementioned instances. Based on the error message we receive from the application team, this has to be troubleshot.
- As it is a problem with the login connection to SQL, we must look at each situation separately.
- If a login attempt is made to a SQL server and is unsuccessful, the errors can be seen in the server’s event viewer and SQL error logs.
- We can examine the logs and resolve the problem.
Configuration Issue in Application:
- An incorrect configuration in the application can also cause a problem with SQL connectivity.
- In the application configuration file, look for the connection string parameters.
- Additionally, verify the login account application being used to connect to SQL.
- Check the SQL instance properties to see if the authentication mode is enabled if the account is a SQL account.
- Check the account’s permissions level as well.