Network Communication By Exception
Deny network communications traffic by default and allow network communications traffic by exception (i.e., deny all, permit by exception).
What gets scored, the objectives
SC.L2-3.13.6 is met only when every one of these 2 objectives, from NIST SP 800-171A, is satisfied. A single missed objective makes the whole requirement not met.
- a.network communications traffic is denied by default
- b.network communications traffic is allowed by exception
How this is assessed
NIST SP 800-171A defines three assessment methods. For SC.L2-3.13.6, whoever assesses it, including your own team in a self assessment, uses these:
System and communications protection policy; procedures addressing boundary protection; system security plan; system design documentation; system configuration settings and associated documentation; system audit logs and records; other relevant documents or records
System or network administrators; personnel with information security responsibilities; system developer; personnel with boundary protection responsibilities
Mechanisms implementing traffic management at managed interfaces
What it means, in context
This requirement applies to inbound and outbound network communications traffic at the system boundary and at identified points within the system. A deny-all, permit-by-exception network communications traffic policy ensures that only those connections which are essential and approved are allowed.
Block all traffic entering and leaving the network , but permit specific traffic based on organizational policies, exceptions, or criteria. This process of permitting only authorized traffic to the network is called whitelisting and limits the number of unintentional connections to the network. This requirement, SC.L2-3.13.6, requires a deny-all permit by exception approach for all network communications. In doing so, it adds specifics for SC.L2-3.13.1, which only requires monitoring, control, and protection of communication channels. Example You are setting up a new environment to house CUI. To properly isolate the CUI network, you install a firewall between it and other networks and set the firewall rules to deny all traffic [a]. You review each service and application that runs in the new environment and determine that you only need to allow http and https traffic outbound [b]. You test the functionality of the required services and make some needed adjustments, then comment each firewall rule so there is documentation of why it is required. You review the firewall rules on a regular basis to make sure no unauthorized changes were made.
What passing evidence looks like
Deny by default at the boundary: the firewall's outbound and inbound posture denying except allowed exceptions, from the rule table itself.
Common ways contractors fail SC.L2-3.13.6
- !Five points. Inbound deny by default is nearly universal; OUTBOUND deny by exception is the half shops miss. If full egress filtering is impractical, a risk acceptance memo alone does not make this met: put in an outbound control you can show, such as DNS filtering or an egress allowlist, or record it as a gap with a dated remediation plan.
The step by step walkthrough for Microsoft 365 GCC High, Google Workspace, and on premises setups, plus the exact evidence to capture, lives inside the CMMC Level 2 plan.
Prove SC.L2-3.13.6, and the other 109
The Level 2 workspace walks your team through all 110 requirements at the objective level, drafts your SSP section by section from your own record for your team to read and accept, gives a prime or your own internal auditor a read only seat on the same record, and a credentialed officer reviews every step.
Book a free advisory callNo credit card, and Level 1 and Level 2 are both open, so sign up for the level your contracts call for. Self assessed and self attested: you score yourself in SPRS on a three year cycle and your senior official affirms it every year. As of September 3, 2026 a class deviation directs contracting officers to remove third party assessment from contracts. The program rule still provides for it, so your solicitation sets the track. Your team builds the same evidence either way. DFARS 252.204-7012 is unaffected, and the NIST SP 800-171 Rev 2 baseline is unchanged.
SC.L2-3.13.6 questions, answered
How many points is CMMC requirement SC.L2-3.13.6 worth?+
SC.L2-3.13.6 is worth 5 points in the CMMC Level 2 score under 32 CFR 170.24. If it is not met, you lose 5 from your total of 110.
Can SC.L2-3.13.6 be placed on a POA&M?+
No. SC.L2-3.13.6 must be fully met before you can file. It cannot be deferred to a POA&M, so it is a gate on your assessment.
What family does SC.L2-3.13.6 belong to?+
SC.L2-3.13.6 is in the System & Communications Protection (SC) family, one of the 14 families of NIST SP 800-171 that make up CMMC Level 2.
- NIST SP 800-171 Rev. 2 3.13.6