AC-4(21)

Requirement

Separate information flows logically or physically using [Assignment: organization-defined mechanisms and/or techniques] to accomplish [Assignment: organization-defined required separations by types of information].

Discussion

Enforcing the separation of information flows associated with defined types of data can enhance protection by ensuring that information is not commingled while in transit and by enabling flow control by transmission paths that are not otherwise achievable. Types of separable information include inbound and outbound communications traffic, service requests and responses, and information of differing security impact or classification levels.

NIST 800-53A Assessment Guidance

Examine

[SELECT FROM: Information flow enforcement policy; information flow control policies; procedures addressing information flow enforcement; system design documentation; system configuration settings and associated documentation; list of required separation of information flows by information types; list of mechanisms and/or techniques used to logically or physically separate information flows; system audit records; system security plan; other relevant documents or records].

Interview

[SELECT FROM: Organizational personnel with information flow enforcement responsibilities; system/network administrators; organizational personnel with information security responsibilities; system developers].

Test

[SELECT FROM: Mechanisms implementing information flow enforcement functions].

ID	Assessment Objectives
AC-04(21)[01]	information flows are separated logically using <AC-04(21)_ODP[01] mechanisms and/or techniques> to accomplish <AC-04(21)_ODP[03] required separations>;
AC-04(21)[02]	information flows are separated physically using <AC-04(21)_ODP[02] mechanisms and/or techniques> to accomplish <AC-04(21)_ODP[03] required separations>.

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