1. Check your SQL Server Error log to make sure that it enables TCP/IP protocol and establish the listening on a specific TCP port.Normally, if SQL Server is configured to enable TCP/IP protocol, when it starts it will log a message similar to the following error log: 2010-01-04 12:30:40.47 Server Server is listening on [ ‘any’ <ipv4> 1433].
This means that the SQL Server instance is using TCP/IP protocol and listening on the TCP port 1433.
2. Enable TCP/IP protocol if you could not find the message in the Error Log.
You can enable protocols via SQL Server Configuration Manager. Under SQL Server Network Configuration->Protocols for <instance name>, enable TCP/IP protocol.
3. Check Network issue after TCP/IP enabled.
To check if your network is healthy, you can use ping and telnet orders to check.
· Run “ping -t” for 1-2 minutes to check if there any timeout response
ping -t <the remote server IP address>
If there are timeout responses, contact your network administrator to check the network issue.
· Run “telnet” command directly to the TCP port on the server to check if you can access the TCP port.
Telnet <servername> <listening tcp port>
4. Check firewall if you cannot telnet to the specific TCP port.
Ensure that the TCP port on which SQL Server is listening has been put into the exceptions of your firewall. If you connect to a named instance, it is also recommended that you put the UDP port 1434 for SQL Server Browser service into your firewall exception.
The connection issues may be due to other causes like client drivers, application configuration, authentication and ect.