"General Network error", "Communication link failure", or "A transport-level error" message when an application connects to SQL Server

Applies to: Microsoft SQL Server 2005 Standard EditionMicrosoft SQL Server 2005 Workgroup EditionMicrosoft SQL Server 2005 Developer Edition More

Summary

This article discusses the following topics:

  • General information about the Microsoft Scalable Networking Pack (SNP)
  • Errors that your application may receive when it connects to an instance of Microsoft SQL Server that is hosted on a Windows-based computer that has some of or all the networking performance improvements enabled

    Note This article also includes recommendations for preventing these errors on computers that are running various versions of Windows.
  • Additional references
Note The guidance in this article also applies to the host and guest operating systems in virtualization environments.

More Information

Scalable Network Pack

The SNP is a set of high-speed networking features that were introduced as part of Windows Server 2003 Service Pack 2 (SP2). These features also were included as part of Windows Server 2008 and later versions.

Note Because these features are part of the base TCP/IP stack in Windows Server 2008 and later versions, they are no longer known as Scalable Networking Pack features.

The important SNP features relevant to this article are as follows:

  • TCP Chimney Offload This feature transfers TCP/IP protocol processing from the CPU to a network adapter during network data transfer.
  • Receive Side Scaling This feature enables the network load from a network adapter to be distributed across multiple CPUs in a multiprocessor computer.
  • NetDMA This feature provides services for offloading the memory copy operation that is performed by the networking subsystem to a dedicated direct memory access (DMA) engine when receiving network packets.

Error messages when an application connects to SQL Server

You may receive one or more of the following error messages when your network hardware is incompatible with SNP features.

Note You may receive one or more of these error messages when one of the following conditions is true:

  • The computer on which the hardware is installed hosts the instance of SQL Server.
  • An application connects to the instance of SQL Server by using TCP/IP.
Error message 1
 
[Microsoft][ODBC SQL Server Driver][DBNETLIB] General Network error. Check your network documentation

Error message 2
 
ERROR [08S01] [Microsoft][SQL Native Client]Communication link failure

Error message 3
 
System.Data.SqlClient.SqlException: A transport-level error has occurred when sending the request to the server. (provider: TCP Provider, error: 0 - An existing connection was forcibly closed by the remote host.)

You may also receive one of these error messages when the network load on SQL Server is high. For example, you may receive one of these error messages when you replicate databases in SQL Server. Or, you may receive one of these error messages when a multiple-user application accesses databases in SQL Server.

Verify the current configuration

To display the current TCP global parameters, at a command prompt, type the following command, and then press Enter:
 
Netsh int tcp show global

The output of this command resembles the following:

The output of this command resembles the following



To display the network adapters that have the TCP Chimney Offload feature enabled, at a command prompt, type the following command, and then press Enter:
 
Netsh int tcp show chimneystats

The output of this command resembles the following:

The output of this command resembles the following



Recommendations for using SNP or other network offload features in SQL Server environments

If you receive intermittent network errors as described in this section, refer to the following tables for guidance on how to realize the maximum benefits when you use the networking performance improvement features in SQL Server environments.

Table 1: Common guidance for all versions of Windows Server
 
Operating-system version Recommendations
All versions of Windows starting with Windows Server 2003 Service Pack 2
  1. Ask the hardware vendor whether the following updates are available:
    • The latest basic input/output system (BIOS) update for the server
    • The latest firmware update for the network adapter
    • The latest driver update for the network adapter
  2. Update antivirus software to the latest versions or engines and definitions.

Table 2: Windows Server version-specific guidance.
 
Operating-system version Recommendations
Windows Server 2003 Service Pack 2 We recommend that you disable SNP features by installing the hotfix that is documented in the following article in the Microsoft Knowledge Base:
948496 Update to turn off SNP features for Windows Server 2003 and Windows SBS 2003
If network performance is very important, we recommend that you consider migrating to a later version of Windows Server that is included with the next generation of the TCP/IP stack. If you cannot immediately upgrade to a newer version but have to maximize network performance, we recommend that you follow these steps on all the affected servers:
  1. Disable SNP as described in the following article in the Microsoft Knowledge Base:

    948496 Update to turn off SNP features for Windows Server 2003 and Windows SBS 2003
  2. Install the hotfix that is described in the following article in the Microsoft Knowledge Base:
    950224 A Scalable Networking Pack (SNP) hotfix rollup package is available for Windows Server 2003
  3. Enable the Receive feature. By using Regedit.exe

HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
EnableRSS=1 (Dword)
Windows Server 2008
  1. Install Windows Server 2008 Service Pack 2 (SP2). For more information about Windows Server 2008 SP2, go to the following Microsoft website:
    http://www.microsoft.com/en-us/download/details.aspx?id=16468
  2. Install the hotfix that is described in the following article in the Microsoft Knowledge Base:
    979614 Description of a reliability update for the TCP Chimney Offload feature in Windows Server 2008 and in Windows Vista
  3. Install the hotfix that is described in the following article in the Microsoft Knowledge Base:
    967224 Some TCP/IP parameters in the registry are changed to incorrect values when you use the netsh command to change TCP/IP global parameters on a computer that is running Windows Server 2008 or Windows Vista
  4. Re-enable Receive Side Scaling (RSS) in the operating system and network adapters. For information about how to re-enable RSS, click the following article number to view the article in the Microsoft Knowledge Base:
    967224 Some TCP/IP parameters in the registry are changed to incorrect values when you use the netsh command to change TCP/IP global parameters on a computer that is running Windows Server 2008 or Windows Vista
    Note By default, the TCPChimney feature is disabled in Windows Server 2008.
Windows 7 and Windows Server 2008 R2
  1. Install Windows 7 and Windows Server 2008 R2 Service Pack 1 (SP1). For information about to download and install Windows 7 and Windows Server 2008 R2 SP1, go to the following Microsoft website:
    http://www.microsoft.com/en-us/download/details.aspx?id=5842
  2. Install the hotfix that is described in the following article in the Microsoft Knowledge Base:
    2775511 An enterprise hotfix rollup is available for Windows 7 SP1 and Windows Server 2008 R2 SP1
    Note If Windows 7 or Windows Server 2008 R2 SP1 is not installed, install the hotfixes that are described in the following articles in the Microsoft Knowledge Base:
    977977 RSS network throughput performance decreases on Windows Server 2008 R2-based computers that have more than 32 processors
    979612 RSS network throughput performance decreases on Windows Server 2008 R2-based computers that have more than 32 processors
    If the TCP Chimney Offload feature is enabled, install the hotfix that is described in the following article in the Microsoft Knowledge Base:
     
    2525390 The SACK option is always set to "true" even if network adapter does not support SACK for offloaded connections in Windows 7 or in Windows Server 2008 R2
  3. If it is necessary, re-enable RSS in the operating system and network adapters. For information about how to re-enable RSS, click the following article number to view the article in the Microsoft Knowledge Base:

    967224 Some TCP/IP parameters in the registry are changed to incorrect values when you use the netsh command to change TCP/IP global parameters on a computer that is running Windows Server 2008 or Windows Vista

    Note By default, the TCP Chimney Offload feature is set to Auto. This means that the chimney does not offload all connections. Instead, it selectively offloads the connections that meet the following criteria:
    • The connection is established through a 10 gigabits per second (Gbps) Ethernet adapter.
    • The mean round-trip link latency is less than 20 milliseconds.
    • At least 130 kilobytes (KB) of data were exchanged over the connection.

    Note     By default, the TCP Chimney Offload feature is disabled in virtualized clients.
Window 8 and Windows Server 2012 Currently, there are no known issues. We recommend that you use the default configuration for high-speed networking features.

Note By default, the TCP Chimney Offload feature is disabled in Windows Server 2012.

Turn off SNP/high-speed networking features

We do not recommend that you turn off SNP features on newer versions of Windows Server. However, you may have to disable SNP on your Windows Server-based computer as a troubleshooting step or because you lack hardware support for all the RSS features. For more information, see the following table:
 
Windows Server version More information
Windows Server 2003 See the following article in the Microsoft Knowledge Base:
948496 Update to turn off SNP features for Windows Server 2003 and Windows SBS 2003
Windows Server 2008 See the following article in the Microsoft Knowledge Base:
951037 Information about the TCP Chimney Offload, Receive Side Scaling, and Network Direct Memory Access features in Windows Server 2008
Windows Server 2008 R2 Do not disable
Windows Server 2012 Do not disable

Note We recommend that you use the default configuration for the high-speed networking features in Windows Server 2008 R2 and Windows Server 2012 environments. However, you can disable the TCP Chimney Offload feature if you know that you do not want to use it or if you want to keep settings consistent across a mix of different operating systems in your environment.

References

For more information about the Scalable Network Pack, go to the following WindowsITPro website:
http://www.windowsitpro.com/article/networking/give-microsofts-scalable-networking-pack-140350

For information about Receive Side Scaling, go to the following Microsoft TechNet website:
Using Receive Side Scaling

For more information about how to deploy high-speed networking features, go to the following TechNet website:
Networking Deployment Guide: Deploying High-speed Networking Features


For more information about the high-speed networking features in Windows Server 2008 R2, click the following article number to view the article in the Microsoft Knowledge Base:

951037 Information about the TCP Chimney Offload, Receive Side Scaling, and Network Direct Memory Access features in Windows Server 2008
 

For information about how to troubleshoot high-speed networking issues, click the following article number to view the article in the Microsoft Knowledge Base:

2643970 Troubleshooting advanced network performance features (RSS, NetDMA et al.)

For more information about how to deploy and monitor high-speed networking features, go to the following Microsoft website:
 
http://download.microsoft.com/download/8/E/D/8EDE21BC-0E3B-4E14-AAEA-9E2B03917A09/HSN_Deployment_Guide.doc
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