Incomplete HTML Pages and Random Authentication Prompts If ISA Server Is Chained to Upstream Proxy

If Internet Security and Acceleration (ISA) Server 2000 is chained to an upstream Web proxy server, you may receive incomplete HTML pages and random authentication prompts in the Web browser.

These symptoms may occur if the downstream ISA Server computer is configured to require integrated authentication and if the upstream Web proxy server is also configured to require proxy authentication. In addition, the Routing rule on the downstream ISA Server computer is configured to provide Basic Authentication credentials to the upstream Web proxy server.

This behavior does not occur if the downstream ISA Server computer is not configured to provide any credentials or if it is configured to provide Integrated Authentication credentials to the upstream Web proxy server.

Under certain circumstances, Web browsers may try to authenticate a connection with the downstream ISA Server computer that has already been authenticated by using integrated authentication. This may cause the downstream ISA Server computer to pass those credentials to the upstream Web proxy server. Because the credentials are for the downstream ISA Server computer and not for the upstream Web proxy server, the server returns a "407 Proxy authentication required" HTTP response. The downstream ISA Server computer then passes this HTTP response back to the Web browser, causing the authentication prompt on the client computer. Because the client is unable to authenticate this request, it may cause incomplete HTML pages on the Web browser client.

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. The English version of this fix should have the following file attributes or later:

Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article.

WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

To implement the functionality in this fix, create the following registry value:

1. Stop the Web Proxy service.
2. Start Registry Editor.
3. Locate and click the following registry key:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W3Proxy\Parameters
4. Create a new DWORD value named RemoveRedundantProxyAuthorization. Give this new value a data value of 1.
5. Start the Web Proxy service.

To revert to the original configuration, either remove the RemoveRedundantProxyAuthorization registry value, or change its data value to 0 (zero). After making either change, restart the Web Proxy service.

If you see the same symptoms when the upstream Web Proxy Server is running without any Access Control (it is using Anonymous access), then instead of installing this fix, implement the fix described in the following Microsoft Knowledge Base article: