19 October 2010

TMG Auto Proxy Configuration Part II - Using DHCP

In part one of this post I highlighted why it is important to use proxy auto configuration.  There are various way to get your clients to use your auto configuration. In this part I will go through using DHCP and the WPAD option

Step 1 - Verify

  • Verify that your TMG server is publishing the auto configuration script.
  • Using your browser connect to http://proxyaddress/wpad.dat or http://proxyaddress:8080/wpad.dat
  • If you are promtped to download the file you know it is working.
  • Test this by opening the Internet options, click lan setting from the connections tab
  • Make sure only the "Use Automatic configuration script" is checked and then enter the tested url from above.
  • Test for internet connectivity etc.

Step 2 - Configure DHCP

  • From the DHCP server's DHCP mmc console
  • Expand IPv4
  • Right click IPv4 and click "Set Predefined Options"
  • Click a Add
  • In the Option type specify the following
  • Name - WPAD
  • Code - 252
  • Data - String
  • String - The tested url from step 1 - make sure wpad.dat is in lowercase

Step 3 - Apply to Server or Scope
Test your setting on a scope before implementing a server option

  • Expand to the scope where you want to implement
  • Right click Scope options and click Configure options
  • Click advanced and then Vendor Class, standard options
  • Form the Available options select 252 WPAD and click OK

Step 4 - Test a client

  • Log onto a client machine that is in the defined DHCP scope
  • Open Internet explorer and make sure that only the "Automatically detect settings" check box is checked.
  • Restart IE
  • Test for internet connectivity.

For more reference you can check out http://technet.microsoft.com/en-us/library/cc940962(WS.10).aspx


  • A DHCP WPAD entry will take precedence if there is also a WPAD DNS entry.
  • In IE - Specifying "Automatically detect settings" will take precedence over  "Use Automatic configuration script"
  • In IE - The automatic automatic configurations will take precedence over manual configuration

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