The ever growing penetration of Distributed Energy Resources (DERs), involving both conventional and renewable technologies, is changing the power system face. International Standards are being revised for including new requirements for DERs such as wider voltage amplitude and frequency protection thresholds and new local P=f and Q=V power regulation. This scenario has led to an increasing concern about the problem of uncontrolled islanding on distribution networks. The purpose of this paper is to describe a hardware in the loop (HIL) test-bed, where the effects of the DER inverter control actions and of the physical interface protection systems (IPSs) on the unintentional islanding can be addressed. The analysis has shown that the frequency measurement under transient conditions is very important, influencing the P=f DER control action and the IPS tripping. Thus, the preliminary results on the HIL test-bed suggest the need of standardization for the frequency measurement. This solution would be of fundamental importance to predict system behavior of distribution network having large DER diffusion and its protection system during unintentional islanding and other transient conditions.