Requirement
NIST SP 800-171 REV.2 / CMMC 2.0 Level 2 - Control - SI.L2-3.14.6 – Monitor organizational systems, including inbound and outbound communications traffic, to detect attacks and indicators of potential attacks.
Understanding the Requirement
This control from NIST SP 800-171 REV.2 / CMMC 2.0 Level 2 requires you to actively watch your systems and network traffic—both inbound and outbound—to identify attacks or suspicious behaviors early. Practically, that means deploying intrusion detection capabilities (hardware, appliances, or open-source tools such as Snort), collecting and reviewing alerts, and ensuring both incoming and outgoing communications are inspected so exfiltration or command-and-control activity can be detected. The objective is continuous visibility and timely detection so incidents can be contained before they cause harm.
Technical Implementation
- Placement and data collection: Deploy an intrusion detection system (IDS) at network choke points—typically between your LAN and the internet (on the firewall/edge or behind a network tap/span). For cloud environments, enable VPC flow logs, mirror traffic to a monitoring instance, or use cloud-native IDS/IPS capabilities so you capture both east-west and north-south traffic.
- Choose and configure detection tooling: Use a supported IDS/IPS or an open-source option like Snort or Suricata. Configure signatures and/or anomaly rules to detect common threats; enable both network and protocol-specific rules. Keep signatures and detection rules updated on a regular schedule (automated if possible).
- Monitor inbound and outbound indicators: Tune rules and alerts for inbound threats (scans, exploit attempts) and outbound indicators (large uploads, suspicious DNS, persistent connections to known command-and-control). Create rules or detections that flag unusual destinations, unexpected encryption patterns, or anomalous data flows from endpoints.
- Logging, aggregation and alerting: Forward IDS alerts and network logs to a centralized log store or lightweight SIEM. Define alerting thresholds and notify the responsible person/team via email, messaging, or ticketing. Maintain an alert triage playbook so alerts are classified and escalated consistently.
- Tuning and false-positive management: Regularly review and tune detections to reduce noise. Use baseline traffic profiling for your environment and whitelist known benign services. Schedule quarterly reviews of rules and incident data to refine detections and reduce alert fatigue.
- Staffing and fallbacks: If you lack in-house security staff, use a managed detection and response (MDR) service or a trusted MSSP to handle monitoring, initial triage, and 24/7 alerts. Ensure clear SLAs and access for incident response when needed.
Example in a Small or Medium Business
An SMB with about 75 employees installs a Linux server running Snort at the network edge, connected to a network tap so all internet traffic is mirrored to the IDS. The IT manager configures Snort with a baseline signature set and adds rules for outbound DNS anomalies and large file uploads, which could indicate exfiltration. IDS alerts are forwarded to a cloud-based log collector and a lightweight SIEM where alerts generate tickets for the IT team. The company documents an alert triage checklist that tells the on-call admin how to investigate suspicious outbound connections and when to isolate a host. Quarterly, the team updates signatures and reviews false positives to refine rule thresholds. For off-hours coverage they contract an MSSP to watch high-priority alerts and escalate incidents. When a malware beacon was detected in outbound traffic, the on-call admin followed the playbook to isolate the affected workstation and preserve logs for forensic review, preventing further data loss.
Summary
Monitoring both inbound and outbound communications with an IDS/IDS-capable appliance, centralized logging, tuned detection rules, and an established alert triage process gives SMBs the visibility to detect attacks and indicators of compromise. Combining technical controls (placement, rule management, logging) with documented procedures and either in-house or managed monitoring ensures timely detection and containment—meeting the intent of SI.L2-3.14.6 while remaining practical and affordable for small and medium organizations.
