Three of the most common errors in SQL Server connections

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:winntsystem32driversetc).

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