You monitor, control, and protect communications at the edges of your CUI environment.
What it actually means
This is your firewall-and-segmentation control. Traffic at the external boundary (and key internal boundaries — like between your CUI enclave and the rest of the network) is monitored, filtered, and controlled. A defined, defended perimeter is what makes 'out of scope' actually mean something.
Pass or fail — an assessor needs a "yes" to each
- Firewalls/boundary devices control traffic at external and key internal boundaries.
- The CUI environment is segmented from out-of-scope networks.
- Boundary traffic is monitored.
What to have ready
- Network/data-flow diagram showing boundaries
- Firewall rule sets
- Segmentation between CUI and non-CUI networks
Where teams trip up
- Flat network with no segmentation around CUI
- Permissive firewall rules ('allow any')
- No monitoring at the boundary
See where this control puts your score
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More in System & Communications Protection (3.13)
3.13.2 — Build security in by design3.13.3 — Separate user and admin functions3.13.4 — Stop data leaking through shared resources3.13.5 — Wall off your public-facing systems3.13.6 — Deny all, permit by exception3.13.7 — Block split tunneling on VPNs3.13.8 — Encrypt CUI in transit3.13.9 — Drop idle network sessions3.13.10 — Manage your encryption keys3.13.11 — FIPS-validated cryptography3.13.12 — Control cameras and microphones3.13.13 — Control mobile code3.13.14 — Control and monitor VoIP3.13.15 — Protect session authenticity3.13.16 — Encrypt CUI at rest