Incomplete HTML Pages and Random Authentication Prompts If ISA Server Is Chained to Upstream Proxy (297080)

IMPORTANT: This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:

256986 Description of the Microsoft Windows Registry

SYMPTOMS

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.

CAUSE

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.

RESOLUTION

A supported fix is now available from Microsoft, but it is only intended to correct the problem that is described in this article. Apply it only to computers that are experiencing this specific problem. This fix may receive additional testing. Therefore, if you are not severely affected by this problem, Microsoft recommends that you wait for the next Product Name service pack that contains this hotfix.

To resolve this problem immediately, contact Microsoft Product Support Services to obtain the fix. For a complete list of Microsoft Product Support Services phone numbers and information about support costs, visit the following Microsoft Web site:

http://support.microsoft.com/default.aspx?scid=fh;EN-US;CNTACTMS

NOTE: In special cases, charges that are ordinarily incurred for support calls may be canceled if a Microsoft Support Professional determines that a specific update will resolve your problem. The typical support costs will apply to additional support questions and issues that do not qualify for the specific update in question.

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

   Date      Time     Version      Size     File name  
   ----------------------------------------------------
   5/6/2001  02:03PM  3.0.1200.64  373,520  W3proxy.exe

MORE INFORMATION

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:

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

317822 FIX: Problems with Web Browser if ISA Server 2000 Is Chained to an Upstream Web Proxy Server