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A device with appropriate mechanisms that: (i) facilitates the adjudication of different interconnected system security policies (e.g., controlling the flow of information into or out of an interconnected system); and/or (ii) provides information system boundary protection.
CNSSI 4009-2015 from NIST SP 800-53 Rev. 4
NIST SP 800-53 Rev. 4 [Superseded] under Boundary Protection Device
A device (e.g., gateway, router, firewall, guard, or encrypted tunnel) that facilitates the adjudication of different system security policies for connected systems or provides boundary protection. The boundary may be the authorization boundary for a system, the organizational network boundary, or a logical boundary defined by the organization.
NIST SP 800-53 Rev. 5