How the Windows Update client determines which proxy server to use to connect to the Windows Update Web site (900935)


The information in this article applies to:

  • Microsoft Windows Update

INTRODUCTION

The Microsoft Windows Update client program requires Microsoft Windows HTTP Services (WinHTTP) to scan for available updates. Additionally, the Windows Update client uses the Background Intelligent Transfer Service (BITS) to download these updates. Microsoft Windows HTTP Services and BITS run independently of Microsoft Internet Explorer. Both these services must be able to detect the proxy server or proxy servers that are available in your particular environment. This article describes the various proxy server detection methods that are available. Additionally, this article describes the situations where Windows Update uses a particular proxy server detection method.

MORE INFORMATION

The Automatic Updates service is configured to download and install updates from the Microsoft Windows Update Web site

The Automatic Updates service can automatically download and install updates from the Windows Update Web site. The Automatic Updates service does not require user interaction because this service runs in the context of the Local System account. The Automatic Updates service does not have access to the user-specific proxy server settings that may be configured in Internet Explorer. The Automatic Updates service can only discover a proxy server by using one of the following methods:
  • The proxy server is manually configured by using the Proxycfg.exe tool. For more information about how to use the Proxycfg.exe tool, click the following article number to view the article in the Microsoft Knowledge Base:

    289481 You may need to run the Proxycfg tool for ServerXMLHTTP to work

  • Web Proxy Auto Detect (WPAD) settings are configured in either of the following locations in the network environment:
    • The Domain Name System (DNS) options
    • The Dynamic Host Configuration Protocol (DHCP) options
    For more information about a related topic, click the following article number to view the article in the Microsoft Knowledge Base:

    816320 How to configure firewall and Web proxy client Autodiscovery in Windows Server 2003

Internet Explorer is used to access the Windows Update Web site

If you use Internet Explorer to access the Windows Update Web site, the Windows Update client program discovers a proxy server by using the following methods in the order that they appear in.

Method 1: Internet Explorer is configured to automatically detect settings

If the Automatically detect settings check box is selected in Internet Explorer, the Windows Update client uses the WPAD feature to locate a proxy server. To view the Automatically detect settings check box, follow these steps:
  1. Start Internet Explorer.
  2. On the Tools menu, click Internet Options.
  3. Click the Connections tab.
  4. If you connect to the Internet by using a proxy server on the local area network, click LAN Settings. If you connect to the Internet by using a proxy server for a dial-up connection or a VPN connection, click that connection, and then click Settings.
For more information about a related topic, click the following article number to view the article in the Microsoft Knowledge Base:

816320 How to configure firewall and Web proxy client Autodiscovery in Windows Server 2003

Method 2: Internet Explorer is configured to use an automatic configuration script

If the following conditions are true, the Windows Update client locates the proxy server by processing the automatic configuration script:
  • Internet Explorer cannot discover the proxy server by using Method 1.
  • The Use automatic configuration script check box is selected in Internet Explorer.
To view the Use automatic configuration script check box, follow these steps:
  1. Start Internet Explorer.
  2. On the Tools menu, click Internet Options.
  3. Click the Connections tab.
  4. If you connect to the Internet by using a proxy server on the local area network, click LAN Settings. If you connect to the Internet by using a proxy server for a dial-up or VPN connection, click that connection, and then click Settings.

Method 3: Internet Explorer is configured by using a user-defined proxy server value

If the following conditions are true, the Windows Update client uses the user-defined proxy server to connect to the Internet:
  • The Windows Update client cannot locate a proxy server by using automatic detection or by using an automatic configuration script.
  • A proxy server is defined in Internet Explorer.
To view the user-defined proxy server value, follow these steps:
  1. Start Internet Explorer.
  2. On the Tools menu, click Internet Options.
  3. Click the Connections tab.
  4. If you connect to the Internet by using a proxy server on the local area network, click LAN Settings. If you connect to the Internet by using a proxy server for a dial-up or VPN connection, click that connection, and then click Settings.
  5. Note the value that appears in the Address box under Proxy server.

Method 4: A proxy server is not specified in Internet Explorer

If no proxy server is defined in Internet Explorer, the Windows Update client uses the proxy server that was configured by using the Proxycfg.exe tool. For more information about how to use the Proxycfg.exe tool, click the following article number to view the article in the Microsoft Knowledge Base:

289481 You may need to run the Proxycfg tool for ServerXMLHTTP to work

Method 5: No proxy server is configured

If the following conditions are true, the Windows Update client tries to connect to the Windows Update Web site directly:
  • No proxy server is configured by using the Proxycfg.exe tool.
  • No proxy server is manually defined in Internet Explorer.
In this scenario, if a proxy server is required to connect to the Internet, the Windows Update client cannot successfully connect to the Windows Update Web site.

A description of the Web Proxy Auto Detect (WPAD) feature

The WPAD feature lets services locate an available proxy server by querying a DHCP option or by locating a particular DNS record. For more information about the advantages and disadvantages of using DNS instead of DHCP for WPAD, click the following article number to view the article in the Microsoft Knowledge Base:

816320 How to configure firewall and Web proxy client Autodiscovery in Windows Server 2003

A description of the Proxycfg.exe tool

The Proxycfg.exe tool configures WinHTTP to use a specific proxy server by modifying the following registry entry:

HKEY_LOCAL_MACHINE\ SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\Connections\WinHttpSettings

The Proxycfg.exe tool is useful if you cannot implement WPAD. Additionally, you can use this tool to help you troubleshoot proxy server discovery problems in the network. In this situation, you can use this tool to help verify that an issue occurs because of a failure to discover a proxy server by using the other discovery methods, such as WPAD. For more information about a related topic, click the following article number to view the article in the Microsoft Knowledge Base:

298481 You may need to run the Proxycfg tool for ServerXMLHTTP to work

To view the command-line parameters that the Proxycfg.exe tool supports, type proxycfg.exe /? at a command prompt, and then press ENTER. If you run the proxycfg.exe command by using no command-line parameters, the current settings are displayed. In this situation, you receive results that are similar to one of the following results.

Settings where no proxy server is configured

Microsoft (R) WinHTTP Default Proxy Configuration Tool
Copyright (c) Microsoft Corporation. All rights reserved.

Current WinHTTP proxy settings under:
  HKEY_LOCAL_MACHINE\
    SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\Connections\
      WinHttpSettings :

     Direct access (no proxy server).

Settings where a proxy server is configured

Microsoft (R) WinHTTP Default Proxy Configuration Tool
Copyright (c) Microsoft Corporation. All rights reserved.

Current WinHTTP proxy settings under:
  HKEY_LOCAL_MACHINE\
    SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\Connections\
      WinHttpSettings :
	
       Proxy Server   =	    <myproxyserver>
       Bypass List    =

To configure a proxy server by using the Proxycfg.exe tool

To use the Proxycfg.exe tool to configure a proxy server, follow these steps:
  1. Click Start, click Run, type cmd, and then click OK.
  2. At the command prompt, type proxycfg -p proxyservername:portnumber, and then press ENTER. In this command, replace proxyservername with the fully qualified domain name of the proxy server. Replace portnumber with the port number for which you want to configure the proxy server. For example, replace proxyservername with proxy.domain.example.com and replace portnumber with 80.
If the proxy server is successfully configured, the following results appear: 

Microsoft (R) WinHTTP Default Proxy Configuration Tool
Copyright (c) Microsoft Corporation. All rights reserved.

Current WinHTTP proxy settings under:
  HKEY_LOCAL_MACHINE\
    SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\Connections\
      WinHttpSettings :
	
       Proxy Server   =	    <myproxyserver>
       Bypass List    =

To remove a proxy server by using the Proxycfg.exe tool

To use the Proxycfg.exe tool to remove a proxy server and to configure "direct access" to the Internet, follow these steps:
  1. Click Start, click Run, type cmd, and then click OK.
  2. At the command prompt, type proxycfg -D, and then press ENTER.
Note If one of the following conditions is true, a proxy server does not appear in the results of the proxycfg.exe command:
  • The proxy server is manually configured in Internet Explorer.
  • The proxy server is configured by using a configuration script.
The proxycfg.exe command is only used to manually configure the proxy server that WinHTTP uses. If you use WPAD to specify a proxy server, or if you use Internet Explorer to specify a proxy server, the results of the proxycfg.exe command should indicate a value of Direct access (no proxy server).

Supported .pac files

For more information about the supported types of .pac files, visit the following Microsoft Web site:

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/winhttp/http/winhttp_autoproxy_support.asp

Modification Type:MajorLast Reviewed:6/3/2005
Keywords:kbwindowsupdatev6 kbhowto kbinfo KB900935 kbAudITPRO
©2004 Microsoft Corporation. All rights reserved.