CMMC Practice CA.2.157: Develop, document, and periodically update system security plans that describe system boundaries, system environments of operation, how security requirements are implemented, and the relationships with or connections to other systems.
A system security plan (SSP) is a document that outlines how an organization implements its security requirements. An SSP outlines the roles and responsibilities of security personnel. It details the different security standards and guidelines that the organization follows. An SSP should include high-level diagrams that show how connected systems talk to each other. The organization should outline in its SSP its design philosophies. Design philosophies include defense-in-depth strategies as well as allowed interfaces and network protocols. All information in the SSP should be high-level. Include enough information in the plan to guide the design implementation of the organization’s systems. Reference existing policies and procedures in the SSP.