Web Proxy Auto-Discovery (WPAD) may not succeed when Internet Explorer 6 sends a DHCPInform request that includes the class ID of the client computer in Windows XP

On a computer that is running Microsoft Windows XP, Web Proxy Auto-Discovery (WPAD) may not succeed when Internet Explorer 6 sends a DHCPInform request that includes the class ID of the client computer.

This problem occurs when one of the following conditions is true:

• The computer is running Microsoft Windows XP with Service Pack 2 (SP2).
• The computer is running Microsoft Windows XP with Service Pack 1 (SP1), and the 837206 hotfix is applied to the computer. For more information about the 837206 hotfix, click the following article number to view the article in the Microsoft Knowledge Base:
  837206  (http://support.microsoft.com/kb/837206/ ) The ClassID value may be lost or overwritten when you set the ClassID value for a DHCP-enabled network adapter on a Windows XP-based computer

This problem occurs because the client computer does not pass Option 252 information to Internet Explorer, even though the client computer receives this information.

To work around this problem, disable the DHCP class ID on the client computer. Then, restart the computer.

For more information about how to disable the DHCP class ID, click the following article number to view the article in the Microsoft Knowledge Base:

Internet Explorer sends a DHCPInform request that includes the class ID of the DHCP client to the DHCP server. The DHCP server verifies the class ID and returns the Option 252 information to the client. This information includes the address of the proxy server.

Microsoft Knowledge Base article 919250 describes a hotfix for this problem. For more information, see the following Knowledge Base article: