Research has shown that information infrastructures across many public and private domains share several common attributes in IT deployment and data communications for control systems. A majority of the systems use robust architectures to enhance business and reduce costs by increasing the integration of external, business, and control system networks. However, multi-network integration strategies often lead to vulnerabilities that greatly reduce the security of an organization, and can expose mission-critical control systems to cyber threats. This document provides guidance and direction for developing 'defense-in-depth' strategies for organizations that use control system networks while maintaining a multi-tier information architecture that requires:

• Maintenance of various field devices, telemetry collection, and/or industrial-level process systems
• Access to facilities via remote data link or modem
• Public facing services for customer or corporate operations