IP autoconfiguration

Unconfigured brand new PortServer TS 16 got IP address from the virtual IP of the NLB cluster in the same network segment.
Changed ARP tables in the machines connected to that virtual IP. NLB cluster sends multicast to all ports in the same switch. DHCP service was available.

How was that possible?

Something on the network is serving up the IP address. The PortServer units have DHCP, RARP and Ping-ARP activated by default. A server on the network appears to be responding to one of these service requests.