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A Strategic Approach to SCADA Cyber Security - Water and Wastewater Network Architecture and Segmentation

Network security for Water sector Process Control Systems (PCS) such as Supervisory Control and Data Acquisition (SCADA) systems continues to be increasingly important and ever evolving due to the need for secure and reliable control systems. Additionally, PCS systems continue to grow and the management of network connected devices and expansion of PCS networks can be difficult and cumbersome. To properly secure PCS networks, a multi-stage process is needed incorporating risk assessment, planning, design, implementation, and maintenance for a comprehensive defense-in-depth strategy. A critical aspect of defense-in-depth is the overall network system architecture and the network segmentation plan. A properly planned and executed network architecture and segmentation strategy lays the foundation for security and simplifies expansion and maintenance of the network. This paper will discuss industry accepted methods for Industrial Control System network architecture and segmentation strategies as related to Water sector PCS and SCADA systems. Industry standard techniques, based on recently published standards and network design guides, will be discussed showing a layered network architecture approach to security and the use of logical subnets and VLANs for segmentation. The advantage of this approach is that it allows for simpler configuration of network security appliances and for simpler management and expansion of the network leading to increased network availability and a reduction in threat risk. A case study will be used to provide examples of actual methods implemented for a water sector utility.