CMMC Practice SI.2.216
Monitor organizational systems, including inbound and outbound communications traffic, to detect attacks and indicators of potential attacks.
Bold Coast Security Guidance
In order to comply with this practice you can rely on your SIEM (deployed as part of the AU Domain) to conduct real time analysis on your network, but you should also consider adding an Intrusion Detection/Prevention System (IDS/IPS). An IDS will simply notify you when an alert is triggered, while the IPS will actively take steps to block the activity.
This system normally resides on the perimeter, but most systems also have sensors to be deployed at key points of the network to monitor netflow traffic and identify malicious or suspicious activity.
Create a policy identifying your strategy to monitor your network, and identify those specific tools in your plan, along with who is responsible for monitoring those systems. You should also include any subscription or renewal fees for budgetary purposes. When conducting internal and external penetration tests, review these systems and verify they have detected and properly alerted to the simulated attack.
DRAFT NIST SP 800-171 R2
System monitoring includes external and internal monitoring. External monitoring includes the observation of events occurring at the system boundary (i.e., part of perimeter defense and boundary protection). Internal monitoring includes the observation of events occurring within the system. Organizations can monitor systems, for example, by observing audit record activities in real time or by observing other system aspects such as access patterns, characteristics of access, and other actions. The monitoring objectives may guide determination of the events. System monitoring capability is achieved through a variety of tools and techniques (e.g., intrusion detection systems, intrusion prevention systems, malicious code protection software, scanning tools, audit record monitoring software, network monitoring software). Strategic locations for monitoring devices include selected perimeter locations and near server farms supporting critical applications, with such devices being employed at managed system interfaces . The granularity of monitoring information collected is based on organizational monitoring objectives and the capability of systems to support such objectives.
System monitoring is an integral part of continuous monitoring and incident response programs. Output from system monitoring serves as input to continuous monitoring and incident response programs . A network connection is any connection with a device that communicates through a network (e.g., local area network, Internet). A remote connection is any connection with a device communicating through an external network (e.g., the Internet). Local, network, and remote connections can be either wired or wireless.
Unusual or unauthorized activities or conditions related to inbound/outbound communications traffic include internal traffic that indicates the presence of malicious code in systems or propagating among system components, the unauthorized exporting of information, or signaling to external systems. Evidence of malicious code is used to identify potentially compromised systems or system components. System monitoring requirements, including the need for specific types of system monitoring, may be referenced in other requirements.
NIST SP 800-94 provides guidance on intrusion detection and prevention systems.