An effective security control monitoring strategy for an information system includes Response:

Monitoring interconnecting systems' controls is important, but doing so outside the scope of authorization implies a lack of proper governance and agreements.

Effective security control monitoring, as part of the NIST Risk Management Framework (RMF) Step 6 (Monitor), emphasizes the ongoing involvement of the Authorizing Official (AO) in the management of the information system's security. This active involvement ensures that the system's security posture is continuously assessed and maintained, aligning with the concept of ongoing authorization.

Annual assessment of all controls is a periodic activity, but an effective monitoring strategy goes beyond just annual assessments to include continuous and near real-time monitoring.

While NIST SP 800-53 controls are foundational, simply listing all controls from an outdated revision (Rev 3) does not define an effective monitoring strategy; the focus is on implementation and ongoing assessment.