Level 2 · System and Communications Protection
SC.L2-3.13.6
Network Communication by Exception
Default-deny communication requires a rule set that permits justified traffic and rejects the rest.
Official reference
The requirement
Deny network communications traffic by default and allow network communications traffic by exception (i.e., deny all, permit by exception).
DoD CMMC Assessment Guide, Level 2, version 2.13. SC.L2-3.13.6; requirement and objectives, printed page 223 ↗
Assessment objectives
What must be established
Determine if each applicable objective is satisfied. The labels below follow the cited DoD assessment guide.
- [a]
network communications traffic is denied by default; and
- [b]
network communications traffic is allowed by exception.
MET requires evidence that all applicable objectives are satisfied. Final, approved evidence is needed. A NOT APPLICABLE determination needs a scope-based basis and is equivalent to MET for scoring. Enduring exceptions and temporary deficiencies have specific conditions under 32 CFR 170.24; they are not a general permission to defer implementation.
GAVII Cybersecurity assessment approach
Connect the objective to the evidence
Evaluate relevant boundaries and enforcement points, including cloud security groups and host controls. A final deny rule is ineffective if an earlier broad allow rule admits unnecessary traffic.
Assessment focus: objectives [a], [b]. Use the methods together; a single example does not establish every objective.
Examine
Review traffic authorizations, rule sets, default actions, and change approvals.
Interview
Who approves a new allowed flow, and how are broad or obsolete rules identified?
Demonstrate or test
Compare an approved flow with a safe unapproved flow and show the expected enforcement and record.
Evidence gaps to look for
- Any-to-any rules override the stated default.
- The rule inventory cannot connect allowed traffic to a business or security need.
GAVII Cybersecurity’s examples illustrate ways to examine, interview, and test. They are not a mandatory artifact list or a guarantee of an assessment result. Combine methods and address every applicable objective in the actual scope.
Assessment constraints
Scoring and POA&M eligibility
Score: 5
If this requirement is NOT MET, deduct 5 points from the Level 2 maximum of 110. The deduction applies to the requirement, not separately to each objective.
Scoring rule ↗POA&M: Not eligible
This requirement has a deduction greater than 1 point and does not qualify for the limited encryption exception. It cannot be deferred on the POA&M used for Conditional Level 2 status.
POA&M rule ↗Conditional Level 2 requires a score of at least 88 out of 110 and satisfaction of every eligibility condition. A 1-point requirement is not automatically eligible. The permitted POA&M must be closed through the appropriate closeout assessment within 180 days of the Conditional CMMC Status Date. An operational remediation plan does not confer Conditional Status.
Assessment planning
Location and observation
Not specifically listed in CAP P.11
This requirement is not specifically listed in CAP P.11. That does not establish that remote assessment is sufficient: the Lead CCA and C3PAO determine an adequate approach for the actual scope and evidence.
CAP §P.11, pages 10–11 ↗Check the source
References and related requirements
- DoD CMMC Assessment Guide, Level 2 ↗SC.L2-3.13.6; requirement and objectives, printed page 223. 2.13, September 2024.
- 32 CFR 170.24: Assessment findings and scoring ↗170.24(b) and (c)(2). Current electronic Code of Federal Regulations.
- 32 CFR 170.21: POA&M eligibility and closeout ↗170.21(a)(2) and (b). Current electronic Code of Federal Regulations.
- NIST SP 800-171 Rev. 2 ↗Requirement 3.13.6. February 2020, updated January 2021.
- NIST SP 800-171A ↗Assessment procedure 3.13.6. June 2018.
- Cyber AB CMMC Assessment Process (CAP) ↗P.11, printed pages 10-11; Level 2 certification assessment-location planning. 2.0, December 2024.
Program timing and contract applicability can change independently of these requirements. Check current DoD program notices and your solicitation or contract before making a compliance decision. Open the official DoD resource hub.