Stacked, not parallel
The single most important thing to understand: FedRAMP and the DoD CC SRG are not competing authorizations you choose between. The SRG is built on top of FedRAMP.
FedRAMP is the federal government's standardized cloud security authorization — the baseline that lets any federal agency consume a cloud service. The DoD Cloud Computing Security Requirements Guide takes that FedRAMP foundation and adds DoD-specific requirements as Impact Levels for defense workloads.
Roughly: FedRAMP Moderate corresponds to IL2. FedRAMP High is the foundation that IL4 and IL5 build on, each adding DoD overlay controls (CUI handling at IL4; National Security Systems controls at IL5). IL6 reaches into Secret-classified workloads on isolated infrastructure. So the SRG is a defense-specific extension of the federal-wide FedRAMP framework, not a substitute for it.
Who needs which — and who needs both
The customer determines the requirement.
Civilian agency customers → FedRAMP, usually standalone. A CSP whose federal customers are civilian agencies (GSA, HHS, Treasury, and the like) needs FedRAMP at the appropriate baseline. The DoD CC SRG is not relevant to that market.
DoD component customers → FedRAMP plus an Impact Level. A CSP whose customer is a DoD component needs the relevant Impact Level. For anything above IL2, that means FedRAMP (typically High) as the foundation, with the DoD overlay on top. FedRAMP alone is insufficient for DoD CUI or mission-critical workloads.
Both markets → both authorizations. Commercial CSPs entering the federal market broadly often pursue FedRAMP first for civilian reach, then add DoD Impact Levels for defense customers. The work compounds — see the sequencing point below.
Sequencing — FedRAMP work accelerates the DoD authorization
Because the SRG builds on FedRAMP, the two authorizations share most of their substance. A CSP that has done FedRAMP High has already implemented the foundation that IL4 and IL5 extend.
We sequence engagements so the FedRAMP work directly accelerates the DoD CC SRG authorization rather than duplicating effort. A single canonical System Security Plan documents the FedRAMP implementation, with a DoD overlay annex capturing the Impact Level-specific controls. The evidence pipeline serves both. The 3PAO assessment can be coordinated to cover both in phases.
The economics resemble the broader multi-framework pattern: running FedRAMP and a DoD Impact Level together is meaningfully less than the sum of running them separately. For the FedRAMP-to-IL4/IL5 upgrade path specifically, see our [upgrade path article](/insights/fedramp-to-il4-il5-upgrade/); for the Rev 5 and IL5 v1r3 overlap, the [overlap analysis](/insights/fedramp-rev-5-il5-overlap/).