Admin Tips
- Windows Server 2008/2003/2000/XP/NT Administrator Knowledge Base
  - Windows 2003
    - Admin Tips
      - Network
        W2K3 DHCP vs. SBS2K3 DHCP

Section(s): Network
Published on Aug 03, 2005.
Last Modified on Aug 03, 2005.
Last Modified by Mitch Tulloch.
Rated 4.4 out of 5 based on 12 votes.

There's an important difference in how DHCP works on a W2K3 DHCP server as compared to a Small Business Server 2003 (SBS2K3) box.

If you boot up an SBS2K3 box and it finds another DHCP server somewhere on the network, the SBS box will shut down its DHCP service. That's a good way of finding a rogue DHCP server on your network if your company has under 75 seats and uses SBS--check the event log for DHCP service failure. SBS checks for rogue DHCP servers once an hour.

Rogue DHCP detection on W2K3 DHCP servers is more complicated. If your DHCP server belongs to an Active Directory domain, then it checks AD for a list of authorized DHCP servers. If it finds itself in the list, the DHCP service starts. But if your W2K3 DHCP server belongs instead to a workgroup, it broadcasts DHCPINFORMS when it starts up and if it receives a response (DHCPACK) then it does the following:

If the response is from a DHCP server belonging to an AD domain, the workgroup DHCP server doesn't start its DHCP service.
If the response is from any other DHCP server (or if there's no response at all) then its DHCP service starts up.

About Mitch Tulloch

Mitch Tulloch was lead author for the Windows Vista Resource Kit from Microsoft Press, which is the book for IT pros who want to deploy, maintain and support Windows Vista in mid- and large-sized network environments. Mitch was also the author of Introducing Windows Server 2008 and technical project lead for the Microsoft Office Communications Server 2007 Resource Kit, both books also from Microsoft Press. For more information on these and other books by Mitch, see www.mtit.com .