Having a DHCP Server on you network that not managed by a IT department is a security issue.
Microsoft has released a new tool for free that you can download that will show you all your DHCP servers that are Authorized and then show you what is not approved This is a Graphic Tool that test by subnet.
Rogue detection tool is a GUI tool that checks if there are any rogue DHCP servers in the local subnet.
See what you have
Choose your network
Following are the features with this tool:
1. The tool can be run one time or can be scheduled to run at specified interval.
2. Can be run on a specified interface by selecting one of the discovered interfaces.
3. Retrieves all the authorized DHCP servers in the forest and displays them.
4. Ability to validate (not Authorize in AD) a DHCP server which is not rogue and persist this information
5. Minimize the tool, which makes it invisible. A tray icon will be present which would display the status.
You can download this tool here