A network-related or instance-specific error occurred while establishing a connection to SQL Server

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"A network-related or instance-specific error occurred while establishing a connection to SQL Server. Verify that the instance name is correct and that SQL Server is configured to allow remote connections"






  • provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server (Microsoft SQL Server, Error: 53)

A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections.

provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server (Microsoft SQL Server, Error: 53)

provider: TCP Provider, error: 0 - No such host is known. (Microsoft SQL Server, Error: 11001)



  • provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified

A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections.

provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified


  • [Microsoft][SQL Server Native Client 11.0]TCP Provider: No connection could be made because the target machine actively refused it

SQL Server Native Client Data Link Error

[Microsoft][SQL Server Native Client 11.0]TCP Provider: No connection could be made because the target machine actively refused it.

[Microsoft][SQL Server Native Client 11.0]Login timeout expired.

[Microsoft][SQL Server Native Client 11.0]A network-related or instance-specific error has occurred while establishing a connection to SQL Server. Server is not found or not accessible. Check if instance name is correct and if SQL Server is configured to allow remote connections. For more information see SQL Server Books Online.









"SQL Server does not exist or access denied"


Typically, this error indicates that the client is unable to locate the SQL Server instance. When at least one of the following issues present, this problem occurs:


  1. The name of the computer hosting SQL Server is incorrect.
  2. The instance doesn't resolve the correct IP.
  3. The TCP port number isn't specified correctly.



You looked for a few additional alerts connected to it in the Windows Event Viewer:


The login packet used to open the connection is structurally invalid; the connection has been closed.

Please contact the vendor of the client library. [CLIENT: 10.10.10.91]

Error: 17832, Severity: 20, State: 2.



Length specified in network packet payload did not match number of bytes read; the connection has been closed.

Please contact the vendor of the client library. [CLIENT: 10.10.10.91]

Error: 17836, Severity: 20, State: 17.



The prelogin packet used to open the connection is structurally invalid; the connection has been closed.

Please contact the vendor of the client library. [CLIENT: 10.10.10.91]




If you have different SQL instances which you are trying to connect from other machine, so before that you must provide alternate customized port to all the instances (i.e. 1434, 1435,1437 etc.). Don't provide dynamic ports.


Please Click here how to configure port  




Use the following text in SSMS or a native client once you've specified a specific port to connect instances.



<Server Name or IP>\<Instance Name>,<port Number>


Example : Server Name ----- xyz

                   IP ---- 10.10.10.91

                   Instance Name ---- instance1

                   Port Given To Instance ------ 1437


Then string will be below


xyz\instance1,1437    or     10.10.10.91\instance1,1437






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Posted By : Kamlesh Gaur

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