NIST SP 800-171 Rev. 3·Requirement 3.13.6·critical·Component: Situational Awareness

What this control requires

This control mandates denying all network communications traffic by default and allowing traffic only by exception. It applies to both inbound and outbound traffic at the system boundary and within identified system points, ensuring that only essential and approved connections are permitted. This control supports the Traffic Control System capability within the Situational Awareness (3.13) family.
— NIST SP 800-171 Rev. 3, Requirement 3.13.6

In plain English

This control mandates denying all network communications traffic by default and allowing traffic only by exception. In practice, this means you can prove you configuration management-level controls on a defined cadence.

Why it matters

DoD contractors and their subcontractors must implement all 100 SP 800-171 requirements to keep CUI handling contracts. Gaps are scored against the SPRS scoring methodology; below a 110-point starting score, each unmet requirement deducts points and a below-threshold score can disqualify a bid.

This control is rated critical in the source catalogue. Treat gaps here as production incidents in the risk register, not housekeeping.

What an auditor looks for

A C3PAO conducting a CMMC Level 2 assessment uses NIST SP 800-171A objectives. They expect a System Security Plan (SSP), Plan of Action & Milestones (POA&M) for any gaps, and objective evidence (configurations, ticket records, training records) for every requirement.

Within Situational Awareness, the assessor will trace your implementation back to the catalogue reference (Requirement 3.13.6) and look for objective evidence on the latest two assessment cycles.

How to implement

Cloud Posture

CSPM. Run Wiz / Prisma / Defender for Cloud / Security Command Center over every account; auto-ticket findings above your accepted-risk threshold.

Network Security

AWS. VPC Flow Logs to S3, default-deny security groups, AWS Network Firewall for north-south, and Transit Gateway for hub-and-spoke segmentation.

Azure. NSGs with deny-by-default, Azure Firewall Premium with TLS inspection, Private Endpoints for PaaS, and Microsoft Defender for Cloud's secure score for drift.

GCP. VPC Service Controls perimeters around sensitive APIs, Cloud NGFW Enterprise for L7 inspection, Private Service Connect for managed services.

Configuration Management

Policy-as-code. Codify the control as Service Control Policies (AWS), Azure Policy initiatives, or Organisation Policy (GCP) so the platform enforces what the document promises.

IaC. Gate Terraform / Pulumi / CloudFormation changes with Checkov / tfsec / OPA so misconfigurations never reach production.

Drift. Run a CSPM (Wiz / Prisma / Defender for Cloud / Security Command Center) over every account and route findings to a single risk register.

Operational checklist

  • Configuration. Document the trigger, the owner and the cadence.
  • System. Document the trigger, the owner and the cadence.
  • Security. Document the trigger, the owner and the cadence.
  • Boundary. Document the trigger, the owner and the cadence.
  • Network. Document the trigger, the owner and the cadence.
  • Scope: management, configuration, security.

Evidence to collect

  • Infra Scan. Continuous infrastructure-posture telemetry — AWS Config, Azure Policy compliance, GCP Organisation Policy, Wiz / Prisma findings.

Infrastructure posture tooling (AWS Config, Azure Policy, Nessus) verifies platform hardening. Focus: Network Communications - Deny by Default - Allow by Exception.

Common pitfalls

  • Treating CSPM findings as a backlog instead of a hot queue: findings older than the policy SLA accumulate until the auditor asks why.
  • Default-allow egress rules; East-West traffic with no segmentation; jump hosts on the public internet with password auth.
  • Manual cloud-console changes that never make it back to Terraform — drift accumulates until the next outage forces a reconciliation.

How it maps to other frameworks

Computed from shared tags, control component and key-operation subjects — handy when you are reconciling controls across an audit.

Related controls in NIST SP 800-171 Rev. 3

References

Topics: network securitycloud postureconfiguration management