A summary of the four most common error resolution scenarios for SQL Server connections is as follows:
One. " SQL Server does not exist or access is denied "
This is the most complex, the cause of the error is more, need to check the aspect also more.
Generally speaking, there are several possibilities:
1,sql server name or IP address is spelled incorrectly
2, server-side network configuration is incorrect
3, the client network configuration is incorrect
To solve this problem, we generally follow the steps below to find out the cause of the error step by step.
============= First, check the network physical connection =============
Ping < server IP address/server name >
If ping < server IP address > is unsuccessful, indicating that there is a problem with the physical connection, check hardware devices such as NIC, HUB, router, etc.
Another possibility is that the firewall software is installed between the client and the server, such as ISA server. Firewall software may mask responses to ping,telnet, etc.
So when checking connectivity problems, we have to temporarily shut down the firewall software, or open all the blocked ports.
Ping < server name > failed if ping < server IP address > success
If there is a problem with name resolution, check to see if the DNS service is normal.
Sometimes the client and the server are not in the same LAN, it is very likely that the server name can not be used directly to identify the server, at this time we could use the Hosts file for name resolution,
The specific methods are:
1. Use Notepad to open the Hosts file (usually located in C:\WINNT\system32\drivers\etc).
Add a corresponding record for the IP address and server name, such as:
172.168.10.24 MyServer
2. Or configure in SQL Server's client Network Utility, which is explained in detail later.
============= second, use the Telnet command to check the working status of the SQL Server server =============
Telnet < server IP address > 1433
If the command succeeds, you can see the cursor flashing in the upper-left corner after the screen flashes, indicating that the SQL Server server is working and listening for TCP/IP connections on port 1433
If the command returns an error message "Cannot open connection", the server side does not start the SQL Server service.
It is also possible that the TCP/IP protocol is not enabled on the server side, or the server side is not listening on SQL Server's default port 1433.
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