The DHCP clients may not obtain the configuration script when you use DHCP Option 252 to automatically configure Internet Explorer (911072)


The information in this article applies to:

  • Microsoft Windows Server 2003, Standard Edition
  • Microsoft Windows Server 2003, Enterprise Edition
  • Microsoft Internet Security and Acceleration Server 2004, Standard Edition
  • Microsoft Internet Security and Acceleration Server 2004, Enterprise Edition

SYMPTOMS

When you use Dynamic Host Configuration Protocol (DHCP) Option 252 to automatically configure Microsoft Internet Explorer by using a Wpad.dat file, the DHCP clients may not obtain the configuration script.

This behavior occurs when all the following conditions are true:
  • The DHCP client and the DHCP server belong to different subnets.
  • The DHCP relay agent is configured on a computer that is running Microsoft Windows Server 2003.
  • Microsoft Internet Security and Acceleration (ISA) Server 2004 and the DHCP relay agent are both running on the same computer.
  • The virtual private network (VPN) configuration is not enabled on the computer that is running ISA Server.
When all these conditions are true, ISA Server takes control on the server that is running the Routing and Remote Access service. Then, ISA Server stops the Routing and Remote Access service. Therefore, no DHCP relay agent is running on the network segment, and Internet Explorer cannot find its configuration script.

CAUSE

This behavior occurs because the VPN Client access option is not enabled in ISA Server. By default, ISA Server controls the Routing and Remote Access service. If the VPN Client access option is not enabled in ISA Server, the Routing and Remote Access service does not start. When the Routing and Remote Access service does not start, the DHCP datagrams are not relayed to the DHCP server.

RESOLUTION

To resolve this behavior, use one of the following methods:
  • Use a DHCP relay agent on the default gateway for the subnet. Then, remove the DHCP relay agent from the computer that is running ISA Server.
  • Use a DHCP relay agent on a computer that is not running ISA Server. Then, remove the DHCP relay agent from the computer that is running ISA Server.
  • If you have to use the DHCP relay agent and ISA Server at the same time, enable the VPN Client access option on the computer that is running ISA Server. This prevents ISA Server from stopping Routing and Remote Access.

STATUS

This behavior is by design.

MORE INFORMATION

After you install and then configure the DHCP relay agent on a computer that is running Windows Server 2003 and then install ISA Server, the DHCP relay agent configuration is reset to the default values. You can use the Netsh utility to dump the DHCP relay agent configuration before you install ISA Server. You can then reapply the DHCP relay agent configuration after you finish installing ISA Server.

To dump the DHCP relay agent configuration by using the Netsh utility, type the following command at the command prompt:

netsh routing dump


The following is sample output of this command: 

# ----------------------------------
# DHCP Relay Agent configuration
# ----------------------------------
pushd routing ip relay
uninstall
install
set global loglevel=ERROR 
add dhcpserver server=10.30.40.50
add dhcpserver server=10.30.40.51 

#
#DHCP Relay Agent configuration for interface "Local Area Connection"
#
add interface name="Local Area Connection"
set interface name="Local Area Connection" relaymode=enable maxhop=16 minsecs=0 
popd
# End of DHCP Relay configuration

For more information about the Netsh utility, visit the following Microsoft Web site:

http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/netsh.mspx

For more information, click the following article numbers to view the articles in the Microsoft Knowledge Base:

307502 "Automatically Detect Settings" does not work if you configure DHCP Option 252

309814 How to configure firewall and Web proxy client Autodiscovery in Windows 2000

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

252898 How to enable Proxy Autodiscovery in Windows 2000

For more information about how to configure the DHCP relay agent in ISA Server, visit the following Microsoft Web site:

http://www.microsoft.com/technet/prodtechnol/isa/2004/plan/isadhcprelay.mspx

Modification Type:MajorLast Reviewed:12/16/2005
Keywords:kbtshoot kbprb KB911072 kbAudDeveloper
©2004 Microsoft Corporation. All rights reserved.