0 Enable IP address conflict detection in DHCP.

Recently I noticed, that some PC's trying to get IP addresses , that are in use.
So after checking, found out that this option was turned out.
"Sweet" legacy from previous administrator :)

Right-click the IPv4 node in the DHCP management console and select the Advanced tab.
Set “Conflict detection attempts” to 1 or 2.
This ensures that the DHCP service will ping every IP address to check if it is really available before it is assigned to the client. Note that each additional conflict detection attempt delays the DHCP server response by 1. second.