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

If Internet Security and Acceleration (ISA) Server 2000 is chained to an upstream Web proxy server, you may experience unexpected delays, incomplete pages, random authentication warning messages, and so forth, when you browse the Web.

This behavior does not occur if the upstream proxy server requires NTLM authentication and the routing rule on the downstream server is configured to provide Integrated Authentication credentials to the upstream Web proxy server.

This behavior can occur if all of the following conditions are true:

• The downstream ISA Server computer is configured to require integrated authentication (NTLM).
  
  -and-
• The upstream Web proxy server is not configured to require authentication (anonymous).
  
  -and-
• You are using Internet Explorer as your client browser.

Under certain circumstances, Internet Explorer sends an extraneous NTLM authentication header on a connection that has already been authenticated with the downstream ISA Server computer by using integrated authentication. This may cause the downstream ISA Server computer to pass those credentials to the upstream Web proxy server. Because these credentials are for the downstream ISA Server computer, the upstream proxy server may return unexpected delays or responses because it is unable to process the NTLM credentials. The downstream ISA Server computer then passes this HTTP response back to the Web browser, resulting in unexpected delays, authentication warning messages, or other effects on the client computer (running Internet Explorer).

Note that you must have ISA Server 2000 Service Pack 1 (SP1) installed on your computer before you apply the following fix.

For additional information about how to obtain ISA Server 2000 SP1, click the article number below 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.
The English-language version of this fix should have the following file attributes or later:

Microsoft has confirmed that this is a bug 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 and then enable it, follow these steps after you have installed the fix:

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

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

For additional information, click the article numbers below to view the articles in the Microsoft Knowledge Base: