Microsoft KB Archive/931490

= 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 =

Article ID: 931490

Article Last Modified on 12/3/2007

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APPLIES TO


 * Microsoft Internet Information Services 6.0

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SYMPTOMS
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.



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



Hotfix information
A supported hotfix is now 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 service pack that contains this hotfix.

To resolve this problem, submit a request to Microsoft Online Customer Services to obtain the hotfix. To submit an online request to obtain the hotfix, visit the following Microsoft Web site:

http://go.microsoft.com/?linkid=6294451

Note If additional issues occur or 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. To create a separate service request, visit the following Microsoft Web site:

http://support.microsoft.com/contactus/?ws=support

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 1, x86


WORKAROUND
To work around this issue, disable kernel mode caching. To disable kernel mode caching across the system, follow these steps:  Open the Machine.config configuration file. This file is located in the following folder:



Note is a placeholder for the drive where the operating system is installed. is a placeholder for the version number of the Microsoft .NET Framework that is installed. In the configuration file, locate the  element, and then add the following attribute:

enableKernelOutputCache=&quot;false&quot;





STATUS
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the &quot;Applies to&quot; section.



MORE INFORMATION
The issue that is described in the &quot;Symptoms&quot; 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.

Keywords: kbbug kbfix kbqfe kbpubtypekc kbhotfixserver KB931490

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