When HTTP compression is enabled in Web publishing rules in ISA Server 2006, the compression filter may be unable to handle HTTP responses

Consider the following scenario:

• Some Web sites are published in Microsoft Internet Security and Acceleration (ISA) Server 2006.
• HTTP compression is enabled in the Web publishing rules.

In this scenario, the compression filter may be unable to handle HTTP responses after the memory that is allocated for compression reaches its limit.

The following event is logged in the Application log:

Event ID: 23006
Description:
The Compression filter cannot handle a response because the allocated memory currently used for compression reached its limit. The memory allocated for compression is specified by the following registry values under the HKLM\Software\Microsoft\RAT\Stingray\Debug\W3Filter key: COMPRESS_MEMORY_ALLOC_MBYTES (by default, 256) and COMPRESS_MEMORY_POOL_BLOCKS (by default, 200).

Additionally, you receive a "Compression failure (Allocated Memory Exhausted)" message in the ISA Server Management console.

In certain scenarios, the ISA Server proxy layer does not identify the end of HTTP responses that are coming from the published Web server. This behavior causes a leak of ISA Server internal memory structures.

This memory leak occurs in one of the following situations:

• The Web server sends an HTTP/1.1 response that does not have a content-length header. Then, the Web server closes the TCP session when the response ends.
• The Web server sends an HTTP/1.1 response that has a content-length header. However, the server closes the TCP session before all content is sent.

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

To apply this hotfix, you must have the ISA Server 2006 Supportability Update package installed. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

Restart requirement

You do not have to restart the computer after you apply this hotfix. However, services that are related to ISA Server 2006 automatically restart 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 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: