NIST SP 800-171 Rev 2 · 3.13 System & Communications Protection

3.13.6 Deny by default, allow by exception

Deny network communications traffic by default and allow network communications traffic by exception (i.e., deny all, permit by exception).

SPRS weight

5

5 points deducted from 110 when not implemented.

CMMC level

L2

Level 2 only; not among the 17 Level 1 practices.

Assessment objectives

2

From NIST SP 800-171A, each one a “determine if” an assessor answers.

What an assessor checks

NIST SP 800-171A breaks 3.13.6 into 2 objectives. Every one has to be met for the requirement to be met; a partial answer scores as not implemented.

1. [a]Determine if network communications traffic is denied by default.
2. [b]Determine if network communications traffic is allowed by exception.

Examine

[SELECT FROM: System and communications protection policy; procedures addressing boundary protection; security plan; system design documentation; system configuration settings and associated documentation; system audit logs and records; other relevant documents or records].

Interview

[SELECT FROM: System or network administrators; personnel with information security responsibilities; system developer; personnel with boundary protection responsibilities].

Test

[SELECT FROM: Mechanisms implementing traffic management at managed interfaces].

If it is open: POA&M eligibility

A POA&M is only permitted at a score of 88 or above, and closes in one 180-day window. Check a full gap list or compute your score.

Where 3.13.6 maps

Query it from your own tools

This page and the MacTech CMMC MCP server render the same dataset. Ask your assistant and it will answer from the methodology, not from memory.

lookup_control 3.13.6
get_assessment_objectives 3.13.6
generate_poam_entries ["3.13.6"]

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