The Domain Name System (DNS) has served as the foundational directory service of the Internet since RFC 1034/1035 (1987). Its original design predates the modern threat landscape and lacks mechanisms to prevent redirection of users to malicious infrastructure. Protective DNS (P-DNS), championed by CISA and NSA, addresses this gap by inserting a policy-enforcing recursive resolver upstream of an agency's existing DNS infrastructure. This paper provides a technical overview of classical DNS operation, describes the P-DNS architecture and its Zero Trust alignment per NIST SP 800-207, surveys the federal vendor landscape, and discusses deployment considerations for large federal agencies. Informed by practical experience supporting network modernization at a major federal agency.
David C. Flynn (Mon,) studied this question.