## 2 Related Work  
Our general hypothesis argues for the potential benefits of adoption of purely software-based industrial testbeds or in combination with low-cost hardware, for cybersecurity research purposes. Furthermore, we believe that these need to be based, as far as possible, on realistic simulations of the controlled physical processes and of the communications networks used, both in its OT and IT dimensions. In this way, we will be able to minimize the cost, difficulty, and complexity while maximizing the accuracy, reproducibility, and scalability of this type of experimental setup. From this perspective, we list below some related work (this does not focus on the uses of a HIL configuration for training purposes such as [8]); by way of example and without any attempt to exhaust the list of initiatives in the area. At the same time, we recognize that some of these works consider testbed development to be only a preliminary step to achieve diverse specific research goals. Nonetheless, we believe that the principles that guided the development of our testbed can be of value to the cybersecurity community in general. [PERSON], 2011 [9], suggested an open-source software framework to setup a SCADA testbed where the network would be provided by the application GNS3, connecting at one end a Modbus client simulator (ModRSsim2) and at the other end a SCADA server (Free Scada). The author indicates the possibility of performing DoS attacks from a VM situated in the same network against port 502 of the Modbus client. The article presents some good ideas, but does not offer further elaboration or describe practical results eventually obtained. [PERSON], 2015 [10], designed a virtual SCADA laboratory where the physical process (gas pipeline) was modeled out of complex mathematical equations simulated by the Simulink/Matlab software [11]. This allows for a more complete study of the behavior of a physical system during a cyber-attack. The control logic expressed in ladder language was emulated by Python programming. The communication via Modbus/TCP by Python libraries (modbus_tk). The SCADA was partly implemented with a proprietary solution (GE iFix) and partly by Python libraries (TKInter). The pervasive use of Python on the testbed, while positive from a monetary perspective, could have contributed to diminishing the realism of the proposed virtual lab. Furthermore, the use of proprietary software should be avoided, if possible, in our view. [PERSON] et al., 2018 [12], present the development of a SCADA testbed to be used for cybersecurity research. Their setup was dedicated to controlling a water storage tank in a HIL configuration via the Modbus protocol. The effects of reconnaissance industrial network cyber-attacks on the testbed were assessed and used to train machine learning (ML) algorithms, in order to develop an automated IDS. However, the choice of the industrial subprocess to be simulated is too simple, and thus limits the possible practical applications of the model. Furthermore, it resorts to specific commercial hardware such as the Schneider PLC model M241 CE40, which restricts the generality of its conclusions and complicates the reproducibility of the experiment. [PERSON] et al., 2019 [13], in order to test their proposal to improve the security of the Modbus protocol, have built a virtual testbed, containing TCP/IP software network elements (firewall, routers and switches) made available by Cisco for use in the network simulator GNS3. Since the authors' approach was based on applying the Transport Layer Security (TLS) technique to traditional Modbus TCP/IP protocol, they assumed that the cybersecurity of the model is guaranteed by design. It then remained to evaluate possible problems arising from implementation flaws and low performance, which could be verified with the help of the arranged setup. This article shows the power and flexibility of virtualized testbeds, for exploring various aspects of cybersecurity of industrial control systems (ICS).