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Many modern critical mon is a widely adopted reference in the energy
infrastructures rely on Ethernet sector based on an architecture developed at Pur-
“technology. However, this due University known as the Purdue model.
The Purdue model separates the complex archi-
technology was not originally tecture of an ICS into fi ve different levels (see table
designed to supply the level 1).
of performance, reliability, Although Level 3.5 is located in the middle of the
Purdue model, it represents a crucial layer, as it is
and cybersecurity required the access gateway providing IT access for go-
by modern industrial control vernance function and support. It creates a barrier
between the IT and OT networks and can also help
systems (ICSs) prevent infections within the IT environment from
spreading to OT systems and vice versa.
Multiple cyber attacks reported in the past were
single device. The complete architecture of any IT/ successful due to a lack of segmentation betwe-
OT system needs to be designed following a pro- en IT and OT; in many cases, the attackers could
per cyber-risk assessment. Among the most com- move through the IT network and reach the OT in- Table 1

Enterprise resource planning (ERP), databases, e-mail servers, and
Level 4/5 Enterprise/business level other systems to manage the planning and manufacturing and busi-
ness decisions
Provides separation between
Level 3.5 Demilitarized zone
IT (Levels 4–5) and OT (Levels 1–3)
Advanced system for visualization, archiving and engineering of geo-
graphically distributed control and/or manufacturing systems
Level 3 Centralized control center
(i.e., dispatch centers and wide-area
monitoring systems)
Devices that control the entire pro- Human-machine interfaces (HMIs) and supervisory control and data
Level 2
cesses (locally) acquisition (SCADA)
Devices that monitor and send control
Level 1 equipment PLCs, RTUs, and intelligent electronic devices (IEDs)
at Level 0
Physical components of Motors, pumps, sensors, circuit breakers,
Level 0
the process and transformers

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