You cannot connect to the Internet from a Windows Vista-based computer that uses a local .pac file

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Article ID: 937151 - View products that this article applies to.
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SYMPTOMS

When you try to connect to the Internet from a Windows Vista-based computer that uses a local proxy autoconfiguration (.pac) file, the proxy server is not detected successfully. Therefore, you cannot connect to the Internet.

CAUSE

By default, in Windows Vista, the Network Connectivity Status Indicator (NCSI) feature tries to determine whether you are connected to the Internet or to a smaller network. Before NCSI can report on Internet connectivity, NCSI must verify the connection to the proxy server. To do this, NCSI uses the WinHTTP feature to find the proxy server. However, WinHTTP is unable to process locally stored .pac files. Because NCSI cannot find the proxy server, the Windows Vista-based computer is reported as having only local connectivity.

Other Windows features may also be affected by this limitation unless they can access the Internet without identifying a proxy server.

RESOLUTION

To resolve this issue, you can use one of the following methods.

Method 1: Use the Web Proxy Autodiscovery (WPAD) protocol

The WPAD protocol lets Windows Vista-based computers automatically discover proxy servers on the network. For more information about the WPAD protocol, visit the following Microsoft Web site:
http://technet.microsoft.com/en-us/library/cc713344.aspx
For more information, visit the following Internet Engineering Task Force (IETF) Web site:
http://www.ietf.org/
Microsoft provides third-party contact information to help you find technical support. This contact information may change without notice. Microsoft does not guarantee the accuracy of this third-party contact information.

Method 2: Use the netsh command to manually specify the proxy server

Note The netsh command is independent of the proxy settings that are specified in Microsoft Internet Explorer. After you set the proxy server by using the netsh command, you must still configure the Internet Explorer proxy settings by using the Local Area Network (LAN) Settings dialog box.
  1. Click Start
    Collapse this imageExpand this image
     Start button
    , click All Programs, click Accessories, right-click Command Prompt, and then click Run as administrator.
  2. At the command prompt, type the following command, and then press ENTER:
    netsh winhttp set proxy ProxyServer:PortNumber
    For example, type netsh winhttp set proxy Proxy1:80.
  3. To set the Internet Explorer proxy settings in the Local Area Network (LAN) Settings dialog box, follow the steps in the "How to manually set proxy settings" section.

How to manually set proxy settings

If you manually set the proxy settings by using the Local Area Network (LAN) Settings dialog box in Internet Explorer, you may experience the following limitations:
  • The proxy settings can only be read by NCSI when a user logs on to the Windows Vista-based computer.
  • If each user who logs on to the Windows Vista-based computer has different proxy settings, the proxy settings of the last user who logged on are used.
  • If the proxy settings specify a .pac file, the .pac file must be located on an HTTP server before NCSI can successfully process the .pac file.
To manually set the proxy settings by using the Local Area Network (LAN) Settings dialog box in Internet Explorer, follow these steps:
  1. In Internet Explorer, click Tools, and then click Internet Options.
  2. Click the Connections tab, and then click LAN Settings.
  3. Click to enable the Use automatic configuration script check box, and then make sure that you include the Web address of the proxy server in the Address box. For example, use the following address:
    HTTP://Proxy_Server_URL

Properties

Article ID: 937151 - Last Review: October 31, 2007 - Revision: 1.6
APPLIES TO
  • Windows Vista Starter
  • Windows Vista Home Basic
  • Windows Vista Home Premium
  • Windows Vista Business
  • Windows Vista Enterprise
  • Windows Vista Ultimate
  • Windows Vista Ultimate 64-bit Edition
  • Windows Vista Home Premium 64-bit Edition
  • Windows Vista Home Basic 64-bit Edition
  • Windows Vista Enterprise 64-bit Edition
Keywords: 
kbtshoot kbprb kbexpertisebeginner KB937151

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