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This article will explain in detail how to solve the problem of SQLServer2008 data engine connection. The content of the article is of high quality, so the editor will share it for you as a reference. I hope you will have some understanding of the relevant knowledge after reading this article.

A timeout error usually occurs when the instance of the SQL Server database engine is not running, the server name is typed incorrectly, or there are network problems or firewalls.

Error text

In SQL Server Management Studio, this error is displayed as:

"unable to connect to."

"the timeout has expired. The timeout has expired or the server is not responding before the operation is completed. (Microsoft SQL Server, error:-2)"

Timeout errors that may occur in sqlcmd include:

"SQL network interface: error locating specified server / instance"

"Sqlcmd: error: Microsoft SQL Server NativeClient: the client cannot establish a connection."

"Sqlcmd: error: Microsoft SQL Server NativeClient: login timeout has expired."

"unable to establish a connection with SQL Server"

"an error occurred while establishing a connection to the server. When connecting to SQL Server, this failure may be caused by the fact that SQL Server does not allow remote connections by default."

Common causes of this error

Reason

Solution method

The server name you typed is incorrect.

Use the correct server name and try again.

The SQL Server service in the server is not running.

Start the instance of the SQL Server database engine.

The TCP/IP port of the database engine instance is blocked by a firewall.

Configure the firewall to allow access to the database engine.

The database engine does not listen on port 1433 because it has been changed or is not the default instance, and the SQL Server Browser service is not running.

Either start the SQL Server Browser service or specify the TCP/IP port number to connect.

The SQL Server Browser service is running, but UDP port 1434 is blocked by a firewall.

Configure the firewall to allow access to UDP port 1434 on the server, or the connection specifies the TCP/IP port number.

The client and server are not configured to use the same network protocol.

Using SQL Server configuration Manager, verify that the server and client computers have at least one common enabling protocol.

The network cannot resolve the server name to an IP address. This can be tested using the PING program.

Fix computer name resolution problems on the network, or connect using the IP address of the server. This is not a SQL Server problem. For assistance, refer to the Windows documentation or contact your network administrator.

Cannot connect to the network using an IP address. This can be tested using the PING program.

Fix TCP/IP problems on the network. This is not a SQL Server problem. For assistance, refer to the Windows documentation or contact your network administrator.

Uncommon mistakes

Multiple server IP addresses

Clients on Windows Vista or Windows Server 2008 may receive this error when connecting to a SQL Server named instance installed on a cluster or on a non-clustered computer with multiple IP addresses. This problem can occur in all SQL Server versions.

Reason

When connecting to a named instance on a remote computer, the client uses user Datagram Protocol (UDP) to connect to the SQL Server Browser service on the SQL Server computer or cluster to obtain the connection endpoint (TCP port number or named pipe).

Firewalls on WindowsVista or Windows Server 2008 clients do not allow loose source mapping of UDP. That is, the response must be returned from the same IP address that was queried. If the response is not returned from the IP address that was originally targeted, the client firewall deletes the packet. This problem can occur when trying to connect to a clustered server or a non-clustered server computer with multiple IP addresses.

The following table describes the operating system combinations that can cause UDP packets to be deleted. This blocks a named instance of SQL Server or a default instance of SQL Server that is not listening on TCP port 1433.

Client operating system

Operating system running SQL Server

SQL Server 2008 result

SQL Server 2005 result

Windows XP or Windows Server 2003

Windows XP or Windows Server 2003

The UDP packet was not deleted.

The UDP packet was not deleted.

Windows XP or Windows Server 2003

Windows Vista or Windows Server 2003

The UDP packet was not deleted.

The UDP packet was not deleted.

Windows Vista or Windows Server 2008

Windows XP or Windows Server 2003

The UDP packet is deleted. Unable to connect.

The UDP packet is deleted. Unable to connect.

Windows Vista or Windows Server 2008

Windows Vista or Windows Server 2008 (x86, IA64)

The UDP packet was not deleted.

The UDP packet is deleted. Unable to connect.

Windows Vista or Windows Server 2008

Windows Vista or Windows Server 2008 (x64)

The UDP packet is deleted. Unable to connect.

The UDP packet is deleted. Unable to connect.

Solution method

To resolve this issue, do one of the following:

In the connection string, specify the TCP port number or named pipe name as part of the server name.

Create an exception in the Windows firewall with advanced security features on the client computer.

Note:

Creating an exception in a firewall may make your computer or network more vulnerable to malicious users or malicious software, such as viruses. It is recommended that you do not use this solution, and the purpose of this information is that if there is no practical alternative, you can decide for yourself whether or not to adopt this solution.

The exception can be any of the following:

Add exception rules for applications that connect to SQL Server.

Add an inbound rule to allow communication from all possible IP addresses of SQL Server computers or clusters.

Forcibly closed connection

This error may occur when connecting to SQL Server using TCP/IP.

Error text

The error may have the following format when it occurs:

TCP_PROV: the existing connection is forcibly closed by the remote host.

Access interface number: 7, error: 10054, error message: "TCP access interface: the existing connection has been forcibly closed by the remote host …"

Unhandled exception: a transport-level error occurred while sending a request to the server. (provider: TCP provider, error: 0-the existing connection has been forcibly closed by the remote host.)

Common causes of this error

The following table lists the common causes and solutions for this error.

Reason

Solution method

The client is connected to an unsupported version of SQL Server Native Client.

Update the client computer to the server version of SQL Server Native Client.

The failed network hardware is removing some TCP traffic.

Use a network monitor to analyze TCP SYN, ACK, and FIN messages.

The SynAttackProtect setting may be deleting the connection.

See the "connection may be forcibly closed when running on Windows Server 2003 SP1" section below.

When running on Windows Server2003 SP1, the connection may be forcibly closed

When trying to test scalability using a large number of client connections to SQL Server Database engine instances running on Windows Server 2003 ServicePack 1, Windows may delete those connections if the request arrives faster than the connection speed provided by SQL Server. This is a security feature of Windows Server 2003 Service Pack 1 that enables a limited queue of incoming TCP connection requests.

To resolve this problem, use the regedit.exe utility to add the following registry key:

Item

Types

Name

Value

HKEY_LOCAL_MACHINE\ SYSTEM\ CurrentControlSet\ Services\ Tcpip\ Parameters\

DWORD

SynAttackProtect

00000000

Security instructions:

Setting this registry key may expose the server to SYN flooding and denial of service attacks. You can add this registry value only if necessary and if you are aware of these security risks. After completing the test, delete this registry value

There is no process at the other end of the pipe

Clients connected to SQL Server may encounter this named pipe error if they connect to the server when named pipe support is not enabled on SQL Server, even if other protocols, such as TCP/IP, can be used.

If named pipes are not enabled on the server, the client is denied attempts to connect using named pipes. This error occurs in the following two situations:

The client attempts to connect using only named pipes, and the named pipe protocol is not enabled on the server.

The client attempts to connect using any available protocol, but in the client protocol order, named pipes is listed before TCP.

Error text

Named pipes provider: there are no processes at the other end of the pipe.

Microsoft SQL Server Native Client: communication link failed.

Microsoft SQL Server NativeClient: an error occurred while establishing a connection to the server. When connecting to SQL Server, this failure may be caused by the fact that SQL Server does not allow remote connections by default.

Common causes of this error

Reason

Solution method

The client attempts to connect using named pipes, but the server is not configured to allow remote connections using named pipes.

Connect using TCP/IP, or use SQL Server configuration Manager to connect remotely through named pipes.

The client protocol order is an attempt to connect using the named pipes protocol before attempting the TCP protocol, and named pipes is not enabled on the server.

Use the SQL Server configuration Manager on the client computer to move TCP before Named Pipes in the protocol order list.

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