03.13.06: Network Communication by Exception

Beyond CMMC Level 1

The free web app covers the 17 CMMC Level 1 practices. This requirement is part of the full NIST 800-171 set — get the desktop app to work on all 110 requirements with SPRS scoring. Previously saved data is shown read-only below, and your data always remains exportable in full.

Get the desktop app

Security Requirements for 03.13.06 Network Communication by Exception

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.

Assessment GuidanceExamine 0/7

How an assessor determines this requirement is met. Source: CMMC Assessment Guide – Level 2, Version 2.13 (NIST SP 800-171 Rev. 2).

Discussion

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.

Examples

Example 1
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.

Assessment Methods

Examine

The process of reviewing, inspecting, observing, studying, or analyzing assessment objects (e.g., policies, procedures, plans, system designs, mechanisms) to facilitate understanding, achieve clarification, or obtain evidence.Example: An assessor reads the access control policy and inspects system configuration settings to confirm they match.

Not all of the evidence listed is required to meet this requirement — check the items your organization has collected.

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

Interview

The process of holding discussions with individuals or groups within an organization to facilitate understanding, achieve clarification, or identify the location of evidence.Example: An assessor asks a system administrator to describe how user accounts are approved, reviewed, and disabled.

System or network administrators
Personnel with information security responsibilities
System developer
Personnel with boundary protection responsibilities

Test

The process of exercising assessment objects (e.g., activities, mechanisms) under specified conditions to compare actual behavior with expected behavior.Example: An assessor attempts to sign in with a disabled account to confirm that access is denied.

Mechanisms implementing traffic management at managed interfaces

Potential Assessment Considerations

Are network communications traffic on relevant system components (e.g., host and network firewalls, routers, gateways) denied by default (e.g., configured with an implicit deny rule that takes effect in the absence of any other matching traffic rules) [a]?
Are network communications traffic on relevant system components (e.g., host and network firewalls, routers, gateways) allowed by exception (e.g., configured with explicit allow rules that takes effect only when network traffic matches one or more rules) [b]?

Key References

NIST SP 800-171 Rev. 2 3.13.6

Overview