In order to find a rogue DHCP server use the following procedure:
1.Go to the Interfaces Config option on the XRoads Gateway and choose Secondary IP's:
2.Add the detected secondary address to the LAN interface as a slash 24.
3.Then ping the secondary address, which will then generate the associated MAC in the ARP table.
4.Then go to the Tools tab, select ARP table then click on the Show Arp button to find the offending MAC.
Please ensure you remove the secondary address from the table so as to not create network conflicts.
You will then have to go through your switch tables to find and lockout the port. Ideally, you want to enable port protection so a rogue dhcp device cannot broadcast its presence in the first place but older switches does not have this capability.