I recently found this little gem on petri.co.il and subsequently discovered its origin at the DHCP technet blog. MAC Filter Callout DLL is a free dll file which allows a windows 2003 DHCP server to check a requesting client’s MAC address against a list of allowed or denied hosts before issuing an IP address.
This tool proved extremely useful in an environment I worked at where for whatever reason a client had two active directory forests setup in the same IP subnet. The forests domain controllers were connected via a trust relationship and for local exchange email connectivity, the servers needed to communicate with each other. Without Callout Dll there was no way to keep clients from one domain from grabbing IP addresses off of the other domains DHCP server.
With Callout Dll and two lists of MAC addresses (one for each forest easily obtained from the DHCP MMC) keeping the clients registered to their respective forest was an easy task without the need for expensive routing/switching equipment or an IP address block change.
Here’s how to install and use Callout DLL:
There it is, now you CAN have multiple DHCP servers on the same network.