ISA Server may cause non-paged pool memory peaks

In Microsoft Internet Security and Acceleration (ISA) Server 2000, you may experience slow response or be completely unable to establish sessions through ISA. For example, you may experience slow response or be unable to connect to Web sites through ISA.

When you monitor memory usage on the ISA Server by using, for example, Performance Monitor, you may see extensive peaks in user mode and non-paged pool memory consumption.

Additionally, you may see events similar to the following logged in the Event Viewer.

Event message 1Event message 2 Note that you may not see all of these symptoms.

The peak in the memory usage may be seen when the data retrieval rate between ISA and the Web server that hosts the content is faster than the data sending rate between ISA and the requesting client. Typically this may be seen when content is served from the Web Proxy cache or if the link between ISA and the Web server that hosts the content is faster than the link between ISA and the internal client that sends the request.

This hotfix for the HTTP redirector application filter limits the number of pending sends on the internal socket between the HTTP client and ISA.

You must install ISA Server Service Pack 1 (SP1) before you apply the following hotfix. For more information about how to obtain the latest ISA Server service pack, click the following article number to view the article in the Microsoft Knowledge Base: This issue has been fixed in ISA Feature Pack 1. For more information about how to obtain Feature Pack 1, click the following article number to view the article in the Microsoft Knowledge Base: 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. To install the fix, run the self-extracting file. You do not have to restart the ISA Server computer. If the computer is part of an ISA Server array, you do not have to shut the whole array down; you can still install this fix on a one-by-one basis.

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. This fix also applies to the French, German, Spanish, and Japanese versions of ISA Server.

The binary fix for the issue that is described in this article is Httpfltr.dll. The hotfix does, however, include updates to three binaries, because the hotfix package also resolves another issue that is referenced in the "More Information" section.

Instead of installing this hotfix, you can disable the HTTP redirector application filter if it is not required.

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

Warning Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall your operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk.
This issue has been fixed in ISA Feature Pack 1.

To implement the functionality in this fix and then enable it, follow these steps after you have installed the fix:

1. Stop the Firewall service.
2. Start Registry Editor.
3. Locate and select the following registry key:
   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Fpc
4. Under Fpc, create a new key named PluginHTTP.
5. Locate and select the following registry key:
   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Fpc\PluginHTTP
6. Create a new DWORD value named MaxPendingSendsPerConnection. Give this new value a data value of 20 (Decimal).
7. Restart the Firewall service.

To revert to the original configuration, either remove the MaxPendingSendsPerConnection registry value or change its data value to FFFFFFFF (Hexadecimal). After you make either change, restart the Firewall service.