FIX: The Http.sys file does not include the Cache Control: max-age header when the Http.sys file sends an HTTP 304 response in IIS 6.0

In Microsoft Internet Information Services (IIS) 6.0, the HTTP protocol stack (that is, the Http.sys file) does not include the Cache Control: max-age header when the Http.sys file sends an HTTP 304 response.

This issue occurs because of a code defect in the Http.sys file.

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 this specific problem. 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

You must have Microsoft Windows Server 2003 Service Pack 2 or Service Pack 1 installed to apply this hotfix.

Restart requirement

You do not have to restart your computer after you apply this hotfix.

Hotfix replacement information

This hotfix does not replace any other hotfixes.

File information

The English version of this hotfix has the file attributes (or later file attributes) that are listed in the following table. The dates and times for these files are listed in Coordinated Universal Time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time item in Control Panel.

Microsoft Windows Server 2003 Service Pack 2, Itanium architecture

Microsoft Windows Server 2003 Service Pack 2, x64

Microsoft Windows Server 2003 Service Pack 2, x86

Microsoft Windows Server 2003 Service Pack 1, Itanium architecture

Microsoft Windows Server 2003 Service Pack 1, x64

Microsoft Windows Server 2003 Service Pack 1, x86

To work around this issue, disable kernel mode caching. To disable kernel mode caching across the system, follow these steps:

1. Open the Machine.config configuration file. This file is located in the following folder:
   Drive:\WINDOWS\Microsoft .NET\Framework\ Version \CONFIG
   Note Drive is a placeholder for the drive where the operating system is installed. Version is a placeholder for the version number of the Microsoft .NET Framework that is installed.
2. In the configuration file, locate the <httpRuntime> element, and then add the following attribute:
   enableKernelOutputCache="false"

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

The issue that is described in the "Symptoms" section can cause excessive network traffic between the Web server and the client. When the content reaches the expiration date on the client, the client determines whether the content has been updated on the Web server. If the content has not been updated, and if the files are cached in the Http.sys file, the Http.sys file sends an HTTP 304 response to the client. Because the HTTP 304 response that is sent to the client does not include the Cache Control: max-age header, the expiration date for the content is not updated on the client computer. Therefore, the client continues to check for updated content on the Web server until the expiration date is updated.

If the content is not cached in the Http.sys file, IIS 6.0 includes the Cache Control: max-age header as expected.