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Consider the following scenario. You enable the AuthNoEncap policy to handle large payloads in a network environment. Then, you perform a network operation on a computer that is running Windows 7 or Windows Server 2008 R2 in the network environment. In this scenario, you may experience a significant decrease in network performance.

This issue occurs because the TCP stack uses the IPsec slow path instead of the IPsec fast path when the TCP stack processes AuthNoEncap traffic.

Hotfix information

A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing the problem described in this article. This hotfix might receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next software update that contains this hotfix.

If the hotfix is available for download, there is a “Hotfix download available” section at the top of this Knowledge Base article. If this section does not appear, contact Microsoft Customer Service and Support to obtain the hotfix.

Note If additional issues occur or if any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft Web site:

Note The “Hotfix download available” form displays the languages for which the hotfix is available. If you do not see your language, it is because a hotfix is not available for that language.

Prerequisites

To apply this hotfix, you must be running one of the following operating systems:

• Windows 7
• Windows 7 Service Pack 1 (SP1)
• Windows Server 2008 R2
• Windows Server 2008 R2 Service Pack 1 (SP1)

For more information about how to obtain a Windows 7 or Windows Server 2008 R2 service pack, click the following article number to view the article in the Microsoft Knowledge Base:

Registry information

To use the hotfix in this package, you do not have to make any changes to the registry.

Restart requirement

You must restart the computer after you apply this hotfix.

Hotfix replacement information

This hotfix does not replace a previously released hotfix.

File information

The global version of this hotfix installs files that have the attributes that are listed in the following tables. The dates and the times for these files are listed in Coordinated Universal Time (UTC). The dates and the times for these files on your local computer are displayed in your local time together with your current daylight saving time (DST) bias. Additionally, the dates and the times may change when you perform certain operations on the files.

Windows 7 and Windows Server 2008 R2 file information notes

Important Windows 7 hotfixes and Windows Server 2008 R2 hotfixes are included in the same packages. However, hotfixes on the Hotfix Request page are listed under both operating systems. To request the hotfix package that applies to one or both operating systems, select the hotfix that is listed under “Windows 7/Windows Server 2008 R2″ on the page. Always refer to the “Applies To” section in articles to determine the actual operating system that each hotfix applies to.

• The files that apply to a specific product, milestone (RTM, SPn), and service branch (LDR, GDR) can be identified by examining the file version numbers as shown in the following table:

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  Version	Product	Milestone	Service branch
  6.1.760 0.21xxx	Windows 7 and Windows Server 2008 R2	RTM	LDR
  6.1.760 1.21xxx	Windows 7 and Windows Server 2008 R2	SP1	LDR

• GDR service branches contain only those fixes that are widely released to address widespread, critical issues. LDR service branches contain hotfixes in addition to widely released fixes.
• The MANIFEST files (.manifest) and the MUM files (.mum) that are installed for each environment are listed separately in the “Additional file information for Windows 7 and for Windows Server 2008 R2″ section. MUM and MANIFEST files, and the associated security catalog (.cat) files, are critical to maintaining the state of the updated component. The security catalog files, for which the attributes are not listed, are signed with a Microsoft digital signature.

For all supported x86-based versions of Windows 7

For all supported x64-based versions of Windows 7 and of Windows Server 2008 R2

For all supported IA-64-based versions of Windows Server 2008 R2

Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:

To work around this problem, disable Large Send Offload (LSO) in the TCP/IP protocol. To do this, follow these steps:

1. Click Start

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   , type regedit in the Search programs and files box, and then press Enter.

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   If you are prompted for an administrator password, type the password. If you are prompted for confirmation, provide confirmation.

2. Locate and then click the following registry subkey:

   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesTcpipParameters

3. On the Edit menu, point to New, and then click DWORD Value.
4. Type DisableLargeSendOffload, and then press Enter.
5. Right-click DisableLargeSendOffload, and then click Modify.
6. In the Value data box, type 1, and then click OK.
7. Exit Registry Editor.
8. Restart the computer.

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the “Applies to” section.

For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base:

Additional file information

Additional file information for Windows 7 and for Windows Server 2008 R2

Additional files for all supported x86-based versions of Windows 7

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File name	X86_63b2417eb9dd62e0eb1139be82c86eca_31bf3856ad364e35_6.1.7600.21006_none_5fee7b79ebde9cca.manifest
File version	Not applicable
File size	702
Date (UTC)	12-Jul-2011
Time (UTC)	09:21
Platform	Not applicable
File name	X86_a24ff779972a7e2a89a2bd8ffa8d1fe4_31bf3856ad364e35_6.1.7601.21768_none_4630e7eeeb8d371b.manifest
File version	Not applicable
File size	702
Date (UTC)	12-Jul-2011
Time (UTC)	09:21
Platform	Not applicable
File name	X86_microsoft-windows-tcpip-binaries_31bf3856ad364e35_6.1.7600.21006_none_b3d5668ae095d505.manifest
File version	Not applicable
File size	3,834
Date (UTC)	12-Jul-2011
Time (UTC)	04:57
Platform	Not applicable
File name	X86_microsoft-windows-tcpip-binaries_31bf3856ad364e35_6.1.7601.21768_none_b57d0c7addeae803.manifest
File version	Not applicable
File size	3,834
Date (UTC)	12-Jul-2011
Time (UTC)	06:20
Platform	Not applicable

Additional files for all supported x64-based versions of Windows 7 and of Windows Server 2008 R2

Collapse this tableExpand this table

File name	Amd64_64de594551836357dfd1d976aeb0e347_31bf3856ad364e35_6.1.7601.21768_none_478f19f3354ca5a0.manifest
File version	Not applicable
File size	706
Date (UTC)	12-Jul-2011
Time (UTC)	09:21
Platform	Not applicable
File name	Amd64_e2ddea40f744287622ae42f8e4b38fc3_31bf3856ad364e35_6.1.7600.21006_none_131570faab66a0a9.manifest
File version	Not applicable
File size	706
Date (UTC)	12-Jul-2011
Time (UTC)	09:21
Platform	Not applicable
File name	Amd64_microsoft-windows-tcpip-binaries_31bf3856ad364e35_6.1.7600.21006_none_0ff4020e98f3463b.manifest
File version	Not applicable
File size	3,838
Date (UTC)	12-Jul-2011
Time (UTC)	05:59
Platform	Not applicable
File name	Amd64_microsoft-windows-tcpip-binaries_31bf3856ad364e35_6.1.7601.21768_none_119ba7fe96485939.manifest
File version	Not applicable
File size	3,838
Date (UTC)	12-Jul-2011
Time (UTC)	07:11
Platform	Not applicable

Additional files for all supported IA-64-based versions of Windows Server 2008 R2

Collapse this tableExpand this table

File name	Ia64_0289f3c0cf5086b1b5f86369e0ba37f7_31bf3856ad364e35_6.1.7600.21006_none_4e515909ccd19c1a.manifest
File version	Not applicable
File size	704
Date (UTC)	12-Jul-2011
Time (UTC)	09:21
Platform	Not applicable
File name	Ia64_7558328428d6e0808c0f4aa357866d35_31bf3856ad364e35_6.1.7601.21768_none_c15e4cc30c7da21f.manifest
File version	Not applicable
File size	704
Date (UTC)	12-Jul-2011
Time (UTC)	09:21
Platform	Not applicable
File name	Ia64_microsoft-windows-tcpip-binaries_31bf3856ad364e35_6.1.7600.21006_none_b3d70a80e093de01.manifest
File version	Not applicable
File size	3,836
Date (UTC)	12-Jul-2011
Time (UTC)	05:55
Platform	Not applicable
File name	Ia64_microsoft-windows-tcpip-binaries_31bf3856ad364e35_6.1.7601.21768_none_b57eb070dde8f0ff.manifest
File version	Not applicable
File size	3,836
Date (UTC)	12-Jul-2011
Time (UTC)	07:02
Platform	Not applicable