Microsoft KB Archive/312955

= Windows Update or Microsoft Update may not work in Windows XP if an authenticating Web proxy is used =

PSS ID Number: 312955

Article Last Modified on 6/17/2005

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The information in this article applies to:


 * Microsoft Windows Update, when used with:
 * Microsoft Windows XP Professional
 * Microsoft Update
 * Microsoft Proxy Server 2.0
 * Microsoft Internet Security and Acceleration Server 2000

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This article was previously published under Q312955



SYMPTOMS
When you use a Windows XP-based computer to connect to the Microsoft Windows Update Web site (at http://windowsupdate.microsoft.com) or to the Microsoft Update Web site (at http://update.microsoft.com/microsoftupdate/v6/muoptdefault.aspx?ln=en&returnurl=http://update.microsoft.com/microsoftupdate/v6/default.aspx?ln=en-us), the connection may not succeed if you connect to the Web site through a firewall or through an authenticating Web proxy that uses integrated (NTLM) proxy authentication.



CAUSE
Windows Update and Microsoft Update use ActiveX controls to determine which updates are installed on your computer. These ActiveX controls do not properly use HTTP keep-alive headers if Microsoft Internet Explorer is configured to use HTTP 1.0. Because integrated (NTLM) proxy authentication requires a persistent connection to authenticate the client, the connection may not succeed when NTLM authentication is performed with the Web proxy.



RESOLUTION
To resolve this issue:
 * 1) Start Internet Explorer.
 * 2) On the Tools menu, click Internet Options.
 * 3) Click the Advanced tab.
 * 4) Select the Use HTTP 1.1 through Proxy Connections check box, and then click OK.
 * 5) Quit and then restart Internet Explorer, and then try again to connect to the Windows Update Web site or to the Microsoft Update Web site.

Because HTTP 1.1 uses persistent connections by default, the entire NTLM handshake takes place on the same TCP connection and the proxy authentication succeeds.



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

Additional query words: 407 proxy-authenticate proxy-authorization isa proxy

Keywords: kbwindowsupdatev6 kbenv kbprb KB312955

Technology: kbAudDeveloper kbISAS2000 kbISAServSearch kbmsupdate kbProxyServ200 kbProxyServSearch kbWinUpdate kbWinUpdateSearch kbWinXPPro kbWinXPProSearch kbWinXPSearch

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