Microsoft KB Archive/820780

= Internet Explorer always prompts for authentication when browsing to Web sites already logged on to =

Article ID: 820780

Article Last Modified on 11/15/2007

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APPLIES TO

 Microsoft Internet Explorer 6.0 Microsoft Internet Explorer 6.0 Service Pack 1, when used with:  Microsoft Windows XP Home Edition

 Microsoft Windows XP Professional

 Microsoft Windows 2000 Server

 Microsoft Windows 2000 Professional Edition</li></ul>

 Microsoft Windows NT Server 4.0 Standard Edition</li></ul>

 Microsoft Windows NT Workstation 4.0 Developer Edition</li></ul>

 Microsoft Windows Millennium Edition</li></ul>

 Microsoft Windows 98 Standard Edition</li></ul>

 Microsoft Windows 98 Second Edition</li></ul> </li></ul>

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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

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SYMPTOMS
When you connect through a caching ISA Proxy that has anonymous access, and you try to perform a NT LAN Manager (NTLM) Authentication with an IIS4 or IIS5 Web server, Microsoft Internet Explorer 6 may not automatically authenticate with NTLM pre-authorization (PreAuth). Instead, you may be continually prompted to authenticate.

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RESOLUTION
A supported hotfix is now 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 service pack that contains this hotfix.

To resolve this problem, submit a request to Microsoft Online Customer Services to obtain the hotfix. To submit an online request to obtain the hotfix, visit the following Microsoft Web site:

http://go.microsoft.com/?linkid=6294451

Note If additional issues occur or 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. To create a separate service request, visit the following Microsoft Web site:

http://support.microsoft.com/contactus/?ws=support

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 tool in Control Panel. <pre class="fixed_text">  Date         Time   Version        Size     File name ---  06-Aug-2003  13:15  6.0.2800.1243  586,240  Wininet.dll 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.

This hotfix uses the following registry information to determine how to treat the socket during a 401 Authentication. To use the hotfix, set the registry value to 0. To turn off the hotfix and revert to the original behavior, set the value to 1. By default, the installation of this hotfix package sets the value to 0.

To set the registry value to 0, follow these steps: <ol> Click Start, click Run, type regedit, and then click OK.</li> Locate and then click either of the following keys in the registry:

</li> On the Edit menu, point to New, and then click DWORD.</li> Type ReleaseSocketDuring401Auth, and then press ENTER.</li> <li>On the Edit menu, click Modify.</li> <li>Type 0, and then click OK.</li></ol>

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WORKAROUND
To work around this problem, edit all the &quot;401&quot; response pages in your IIS deployment so they are larger than 1460 bytes. 1460 bytes is the size of one TCP packet.

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STATUS
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the &quot;Applies to&quot; section.

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MORE INFORMATION
If the &quot;401&quot; response page content is smaller than 1460 bytes, Internet Explorer closes the current connection and tries to re-use a previous connection from the keep-alive pool for that server. Because ISA (or any other proxy) has closed the related connection between ISA and the IIS server, the re-use of the Internet Explorer connection does not work. As a result, Internet Explorer produces an authentication prompt.

When the &quot;401&quot; response page is larger than 1460 bytes, Internet Explorer must maintain the current connection so that it can drain the socket of all pending data. This causes Internet Explorer to re-use this socket for the later NTLM authentication traffic. As a result, the connection works seamlessly.

Keywords: kbhotfixserver kbqfe kbie600sp2fix kbie600presp2fix kbfix kbbug KB820780

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