You may be continually prompted to authenticate in Internet Explorer 6 when you browse Web sites that you already logged on to in Windows Server 2003

When you connect through a caching ISA Proxy that has anonymous access, and you try to perform NTLM authentication with an Microsoft Internet Information Services (IIS) 5.0-based Web server, Microsoft Internet Explorer 6 may not automatically authenticate with NTLM pre-authorization (PreAuth). Instead, you may be continually prompted to authenticate.

Hotfix information

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.

Prerequisites

No prerequisites are required to install this hotfix.

Restart requirement

You do not have to restart your computer after you apply this hotfix.

Hotfix replacement information

This hotfix does not replace any other hotfixes.

Hotfix file information

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.

Windows Server 2003, 32-Bit Edition

Windows Server 2003, 64-Bit Edition

Additional steps

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 to 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:

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.

1. Exit Internet Explorer 6.0.
2. Click Start, click Run, type regedit, and then click OK.
3. Locate and then click to select the following registry subkey:
   HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings
4. On the Edit menu, point to New, and then click DWORD Value.
5. Type ReleaseSocketDuring401Auth, and then press ENTER.
6. Right-click ReleaseSocketDuring401Auth, and then click Modify.
7. In the Value data box, type 0, and then click OK.
8. On the File menu, click Exit to exit Registry Editor.

To work around this problem, edit all the "401" response pages in your IIS deployment so they are larger than 1,460 bytes. 1,460 bytes is the size of one TCP packet.

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

If the "401" response page content is smaller than 1,460 bytes, Internet Explorer closes the current connection and tries to reuse a previous connection from the keep-alive pool for that server. Because the ISA proxy, or any other proxy, has closed the related connection between the ISA proxy and the IIS server, you cannot reuse the Internet Explorer connection. Therefore, Internet Explorer produces an authentication prompt.

When the "401" response page is larger than 1,460 bytes, Internet Explorer must maintain the current connection so that it can drain the socket of all pending data. This behavior causes Internet Explorer to reuse this socket for the later NTLM authentication traffic. Therefore, the connection works seamlessly.

For additional information, click the following article number to view the article in the Microsoft Knowledge Base: