Where should directory servers used for authentication be located according to security guidelines?

The recommendation to locate directory servers used for authentication within the Electronic Security Perimeter (ESP) of the Bulk Electric System (BES) Cyber System is grounded in the principles of safeguarding critical infrastructure. The ESP is designed to provide a secure boundary around critical assets, ensuring that only authorized devices and users can interact with those assets. By placing directory servers within this perimeter, organizations can better control access and mitigate risks associated with unauthorized attempts at authentication.

This configuration enhances the overall security posture by ensuring that sensitive data such as authentication credentials are protected from external threats. Additionally, having the authentication systems within the ESP allows for robust monitoring and response capabilities, which are vital for timely detection and mitigation of any security incidents.

The alternative choices may fall short in terms of security best practices. For example, placing servers in any public cloud environment could introduce risks associated with external threats and loss of control over data security. Similarly, positioning them outside the regulatory compliance zone or at the corporate office can create vulnerabilities by reducing the defenses that are critical to protect such sensitive functions in an operational environment dedicated to the BES. Therefore, the correct approach aligns with placing authentication directory servers within a well-defined and secure ESP.