Forefront TMG uses Active Directory (AD) Marker for automatic detection of the location of Forefront TMG. The TmgAdConfig tool is an autodiscovery tool which configures Active Directory with a marker key that points to the Forefront TMG computer. This key is used by the Forefront TMG Client to locate and connect to the Forefront TMG computer.
This is a really great feature that I don’t see used enough – learn more about it over at:
http://technet.microsoft.com/en-us/library/ee658145.aspx
HTH,
Deb