Summary of SQL Server connection failure error resolution

server| Error | Resolving the problem with SQL Server is that the most common problems users encounter are the failure of the connection. Generally, there are two ways to connect to SQL Server:
One is to take advantage of SQL Server's own client tools, such as Enterprise Manager, Query Analyzer, transaction Profiler, and so on.
The second is to use the user's own development of client programs, such as ASP scripts, VB programs, and so on, the client program is to use ODBC or OLE DB and other connected SQL Server. Next, we'll talk about how to solve the problem of connection failure in terms of these two ways of connecting.

One, client tool connection failed
When you connect to SQL Server with SQL Server's own client tools (for example, in Enterprise Manager), the most common errors are as follows:

1. SQL Server does not exist or access is denied
ConnectionOpen (Connect ())
2, user ' sa ' login failed. Reason: not associated with a trusted SQL Server connection
3, timeout has expired
Here's how to solve the three most common connection errors in turn.

The first error "SQL Server does not exist or access is denied" is usually the most complex, the cause of the error is more, there is more to be examined. Generally speaking, there are several possibilities:

1, the SQL Server name or IP address spelling error;

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
　
Or

Ping Server name >

If the ping server IP address failed, indicating that there is a problem with physical connectivity, this time to check hardware devices, such as network cards, HUB, routers and so on. Another possibility is that the firewall software is installed between the client and the server, such as ISA server.

Firewall software may block the response to Ping, Telnet, and so on, so when checking connectivity problems, we have to temporarily shut down the firewall software or open all the blocked ports.

If the ping server IP address is successful and ping the server name fails, there is a problem with name resolution, so 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 may use the Hosts file for name resolution, the specific method is:

1, use Notepad to open the Hosts file (usually located in C:\WINNT\system32\drivers\etc).

2, add an IP address and server name of the corresponding records, such as:

172.168.10.24 MyServer

It can also be configured in SQL Server's client Network Utility, which is described 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 properly and listening for TCP/IP connections on port 1433, and that the server side does not start SQL if the command returns an error message "Cannot open connection" Server service, either 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.

Next, we check the server-side network configuration on the server, check whether named Pipes are enabled, whether the TCP/IP protocol is enabled, and so on. We can use SQL Server's own server network using tools to check.

Click: Program-> Microsoft SQL Server-> Server network usage tool.

From here we can see what protocols are enabled by the server. Generally speaking, we enable named Pipes and TCP/IP protocols.

Point in the TCP/IP protocol, select "Properties", we can check the SQK Server service default port settings

Generally, we use SQL Server's default 1433 port. If "Hide Server" is selected, it means that the client cannot see the server by enumerating the servers, and it has a protective effect, but does not affect the connection.

After checking the server-side network configuration, we will then go to the client to check the client's network configuration. We can also take advantage of the use of SQL Server's own client network tools to check, but this time it is on the client to run the tool.

Click: Program-> Microsoft SQL Server-> Client Network usage tool

From here we can see what protocols are enabled by the client. In general, we also need to enable named Pipes and TCP/IP protocols.

Click the TCP/IP protocol and select Properties to check the client default connection port settings, which must be consistent with the server.

You can also configure aliases for the server by clicking the Alias tab. The server alias is the name used for the connection, and the server in the connection parameter is the true server name, which can be the same or different. We can use MyServer instead of the real server name sql2kcn-02 and use the network library Named pipes. The alias settings are similar to those used in the Hosts file.

Through the above several aspects of the examination, error 1 The cause of the occurrence can basically be excluded. Let's describe in detail how to troubleshoot error 2.

The error message shown in Figure 2 is often encountered when a user attempts to connect to SQL Server using SA in Query Analyzer, or when using SA to create a new SQL Server registration in Enterprise Manager.

This error occurs because SQL Server uses Windows only authentication, so users cannot connect using SQL Server's logon account, such as SA. The workaround looks like this:

1. Use Enterprise Manager on the server side and select "Use Windows Authentication" to connect to SQL Server;

2, expand the "SQL Server group", the right mouse click on the name of the SQL Server server, select Properties, and then select the Security tab;

3. Under Authentication, select SQL Server and Windows;

4. Restart the SQL Server service.

In the above workaround, if using Windows Authentication to connect to SQL Server fails in step 1th, then we are faced with a dilemma: First, the server allows only Windows authentication, and second, it still fails to connect even with Windows authentication On the server.

This situation is vividly referred to as "locking yourself out of the door" because, in any way, the user cannot use the connection. In fact, we can change the authentication mode to SQL Server and Windows mixed authentication by modifying a registry key, as shown in the following steps:

1, click "Start"-"Run", input regedit, enter the Registry Editor;

2, expand the registry keys in turn, and browse to the following registry key:

[HKEY_LOCAL_MACHINE\Software\Microsoft\MSSqlserver\MSSqlServer]

3, on the right side of the screen to find the name "LoginMode", double-click Edit Double byte value;

4, change the original value from 1 to 2, click "OK";

5, close Registry Editor;

6. Restart the SQL Server service.

At this point, users can successfully use SA to create new SQL Server registrations in Enterprise Manager, but still cannot use Windows Authentication mode to connect to SQL Server. This is because there are two default login accounts in SQL Server: BUILTIN\Administrators and the machine name >\administrator are deleted. To recover both accounts, you can use the following methods:

1, open Enterprise Manager, expand the server group, and then expand the server;

2, expand Security, right-click Login, and click New Login;

3, in the "Name" box, input BUILTIN\Administrators;

4. In the Server Roles tab, select System Administrators;

5, click "OK" exit;

6, use the same method to add the machine name >\administrator login.

The following registry key

Hkey_local_machine\software\microsoft\mssqlserver\mssqlserver\loginmode

Value determines what authentication mode SQL Server will take. The value is 1, which means that the Windows Authentication mode is used; The value is 2, which means mixed mode (Windows authentication and SQL Server authentication).

After watching how to solve the first two errors, let's take a look at the third error.

If you encounter a third error, it is generally stated that the client has found the server and can connect, but that an error occurs because the connection time is greater than the allowed time. This situation typically occurs when a user runs Enterprise Manager on the Internet to register another server that is also on the Internet, and is a slow connection, which may cause the above timeout error. In some cases, this error can also be caused by network problems in the LAN.

To resolve such an error, you can modify the client's connection timeout setting. By default, the timeout setting for registering another SQL Server through Enterprise Manager is 4 seconds, and the Query Analyzer is 15 seconds (which is why there is a greater likelihood of errors occurring in Enterprise Manager). The specific steps are:

1, in Enterprise Manager, select the "Tools" on the menu, and then select "Options";

2, in the pop-up SQL Server Enterprise Manager Properties window, click on the "Advanced" tab;

3. Enter a larger number, such as 20, in the box to the right of login timeout (seconds) under Connection settings.

It can also be set in the same location in the Query Analyzer.

Second, application connection failed

All three of the above error messages occur in SQL Server's own client tools, and similar error messages are encountered in the application, such as:

Microsoft OLE DB Provider for SQL Server (0x80004005)
[DBNETLIB] [ConnectionOpen (Connect ()).] Specified SQL Server not found.

Microsoft OLE DB Provider for SQL Server (0x80004005)
User ' sa ' login failed. Reason: not associated with a trusted SQL Server connection.

Microsoft OLE DB Provider for ODBC Drivers error ' 80004005 '.
[Microsoft] The [ODBC SQL Server Driver] timeout has expired.

First, let's take a look at the diagram below to see what is different about using ODBC and using OLE DB to connect to SQL Server.

In practice, the application creates and uses various ADO objects, and the ADO object framework invokes the OLE DB provider that is enjoyed.

To access a SQL Server database, OLE DB provides two different methods: The OLE DB Provider for SQL Server and the OLE DB Provider for ODBC. These two different methods correspond to two different connection strings, and the standard connection string is written as follows:

1. Use OLE DB providers for SQL Server:

Using SQL Server authentication:

oConn.Open "Provider=sqloledb" & _
"Data source=myservername;" & _
"Initial catalog=mydatabasename;" & _
"User id=myusername;" & _
"Password=mypassword"

To use Windows authentication (trusted connection):

oConn.Open "Provider=sqloledb" & _
"Data source=myservername;" & _
"Initial catalog=mydatabasename;" & _
"Integrated SECURITY=SSPI"

2. Use an OLE DB provider for ODBC (without using an ODBC data source):

Using SQL Server authentication:

oConn.Open "Driver={sql Server};" & _
"Server=myservername;" & _
"Database=mydatabasename;" & _
"Uid=myusername;" & _
"Pwd=mypassword"

To use Windows authentication (trusted connection):

oConn.Open "Driver={sql Server};" & _
"Server=myservername;" & _
"Database=mydatabasename;" & _
"Trusted_connection=yes"

3. Use an OLE DB provider for ODBC (using an ODBC data source):

oConn.Open "Dsn=mysystemdsn" & _
"Uid=myusername;" & _
"Pwd=mypassword"

If you encounter a failure of the connection, we simply follow the method shown in one, combining the connection string in the program to check, basically can be solved. In addition, there are several places to note:

1, when configuring an ODBC data source, click on the "Client" configuration option allows us to specify the network library, port number and other properties used by the connection.

2. If you encounter a connection timeout error, we can modify the timeout setting of the Connection object in the program, and then open the connection. For example:

<%set Conn = Server.CreateObject
("ADODB.") Connection ") dsntest=" Driver={sql
Server}; Server=servername; Uid=user;
Pwd=password;database=mydatabase "Conn.
Properties ("Connect Timeout") = 15 '
Conn.Open dsntest%> in seconds
3. If you encounter a query timeout error, we can modify the Recordset object time-out settings in the program, and then open the result set. For example:

Dim cn as New ADODB. ConnectionDim rs as ADODB. Recordset ...
CMD1 = Txtquery.textset rs = New ADODB. Recordsetrs.properties
("Command Time Out") = 300 '
Also in seconds, if set to 0 indicates unrestricted
Rs. Open CMD1, CNRS. MoveFirst ...

Third, summary
This article focuses on how to troubleshoot and troubleshoot connection failures in both cases of using SQL Server client tools and user-developed applications for the common failure of connections that most users use during SQL Server. After reading this article, I believe that every reader will have a more comprehensive and in-depth connection to how SQL Server works, how to authenticate, and how to develop applications.

All of the tests or samples in this article are passed on Windows Advanced server + SQL Server 2000 Enterprise Edition.