SC-46 asks you to put a policy enforcement mechanism between the physical or network interfaces of connecting security domains. Think of a guard between a classified and an unclassified network, or between two systems that must never exchange data freely.
800-53 binds US federal systems and their contractors. Most small and mid size companies will not need SC-46 as written. It matters if you work with government data at different classification levels, or if a customer contract names it.
What it means in practice
NIST says that for a logical mechanism you avoid creating any path that bypasses it. For a physical one, the isolation may need to rule out covert channels. The record also points readers to a US government office for more information, which tells you this is specialist territory.
Evidence to collect
- A diagram of the domains and the single enforcement point between them.
- Rule sets and change records for that point.
- Test results showing traffic that should be blocked is blocked.
Common gaps
A second, undocumented path such as a VPN or file share that goes around the guard.
How to implement it
If you only need strong separation, for example production from corporate, start with SC-7 boundary protection. Reach for SC-46 only when a contract demands it.
Quick check
What is the main risk SC-46 guards against?
A path between the two domains that bypasses the enforcement mechanism.
