One of the best practices of the DiD strategy is to isolate the Control Network (CN), which is also often called the Process Control Network (PCN), from the corporate and internet systems using firewalls. While firewalls are widely used in the traditional IT sector, their adoption in CN/PCN environments is quite recent. Most IT firewalls are generally unaware of industrial-control protocols and may introduce unacceptable latency into time-critical systems. They may also face operational constraints that are not typical in the IT world. The reality is that firewalls can be complex devices that need careful design, configuration, and management to be efficient and effective. In this section, we are going to look at some basic information about firewalls and how they are usually deployed in the factory to segregate the control network and protect industrial devices.
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