CA-9 covers connections inside your own system boundary. Its sibling CA-3 handles connections to other systems. CA-9 is about the links between the parts of one system, including development components, and it asks for four things.
- Authorize internal connections of the components you define.
- Document, for each connection, the interface characteristics, the security and privacy requirements, and the nature of the information communicated.
- Terminate internal connections after a condition you define.
- Review the continued need for each connection, at a frequency you define.
800-53 binds US federal systems and reaches others through contract. For a small or mid size company it works as a reference, and this control often shows up as a questionnaire line about network segmentation and service to service access.
What it means in practice
NIST's guidance says internal connections include mobile devices, laptops, tablets, printers, copiers, scanners, sensors and servers. It also says you do not have to authorize each one individually. You can authorize a class of components that share a configuration, such as all printers with a given capability, or all phones with a baseline setup.
Think of it as an approved list of how things talk to each other. The review question is whether a connection still supports a business function. If not, it should end.
Evidence to collect
- A data flow or architecture diagram showing connections between components, with a date and an owner.
- A connection register with source, destination, protocol, data type and the approver.
- The class level authorizations, for example a baseline for managed laptops.
- Firewall, security group or service mesh rules that enforce the register.
- Review records showing someone checked the list and removed stale entries.
Common gaps
- The diagram exists but nobody has touched it since launch.
- Test and development components connect to production with no record.
- Service accounts and API links are not in any register.
- Review happens when something breaks, not on a schedule.
- Connections are authorized, but nothing terminates them when a project ends.
How to implement it
Start with the asset list, since you cannot register links between things you have not counted. Group components into classes with common settings. Record each class connection once, and give one-off links their own row.
Set a review cadence, quarterly is common, and tie it to a ticket so there is a trail. Where you can, generate the register from infrastructure code and firewall rules, so it reflects what is real. CA-9.1, Compliance Checks, is the enhancement that adds verification that connections meet the documented requirements.
Quick check
Do I need to authorize every internal connection one by one?
No. The guidance allows authorization for a class of components with common characteristics or configuration, as long as it is documented.
