Client Conflict Detection
Windows 2000 or 98-based client computers also check to determine if an address is already in use before completing address configuration with the DHCP server. If the client detects a conflict, it sends a DHCPDecline message to the DHCP server. The DHCP server attaches a BAD_ADDRESS value to the IP address in the scope, as detailed in "Server-Side Conflict Detection." The client begins the lease process again, and is offered the next available address in the scope.
For networks that include clients that are not running Windows 2000 or 98, server-side conflict detection should be enabled.