How Network Traffic Logs Help You Comply with CMMC and IEC 62443
Discover how network traffic logs support compliance with CMMC and IEC 62443 standards, ensuring security, auditability, and incident response in critical environments.
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How Network Traffic Logs Help You Comply with CMMC and IEC 62443
For CISOs, IT Directors, and the growing crowd of engineers tasked with safeguarding industrial and critical environments, the discipline of logging and traffic monitoring is anything but glamorous. Yet, in modern security postures—especially under frameworks like CMMC (Cybersecurity Maturity Model Certification) and IEC 62443 (for Industrial Automation and Control Systems)—network traffic logs are not only foundational but increasingly mandated. This article aims to dissect why, explore network architectures supporting proper traffic logging, and get granular about making these logs actionable (and compliant) in operational environments.
Why Do Network Traffic Logs Matter for Compliance?
In both CMMC and IEC 62443, evidence is king. Controls and policies are only as good as the ability to prove their existence and effectiveness. Network traffic logs serve several compliance and operational purposes:
Demonstrate oversight of asset communications (CMMC AC.2.013, IEC 62443-2-1:2009, Section 4.2.3)
Facilitate incident response with forensic evidence (CMMC IR.2.092, IEC 62443-2-4:2015, SR 7.1-7.5)
Enable detection of anomalous behavior, lateral movement, or unauthorized system access
Provide a historical record for auditability and accountability — a key expectation of both standards
But logging isn’t simply copying everything and dumping it somewhere. The value is in structured, reliable, and context-rich logs, with a focus on retention, integrity, and accessibility.
Historical Context: How Logging Became the Backbone of Auditable Security
If you go back to the early 1980s, networked systems such as those built around Novell NetWare and DECnet would generate rudimentary connection logs—enough for troubleshooting, not really for incident forensics. As networks expanded and threats evolved, the 1990s gave birth to more formal security event logs: UNIX’s syslog (RFC 3164) and Windows’ Event Logs. However, real "network traffic logs"—packet capture (pcap) and flow data (NetFlow, sFlow)—largely originated in core routing and backbone operations, especially in telecom. It wasn’t until worms (Code Red, Slammer) began traversing enterprise networks in seconds that security logging for traffic analysis became a staple recommendation.
In critical infrastructure and OT, system uptime trumped logging for decades—historian logs outpaced security logs until regulations like NERC CIP, then IEC 62443, pushed the issue forward. Today, CMMC (initially a DoD initiative) takes this even further, requiring not only event but also session and flow logs to prove the absence of compromise.
Clarifying the Requirements: What Do CMMC and IEC 62443 Actually Demand?
CMMC Logging Requirements
CMMC encapsulates both NIST 800-171 controls and DoD-specific mandates. The requirements you absolutely need traffic logs for are:
AU.2.041: Ensures that audit logs capture enough information for traceability—who did what, from where, and when.
AU.3.046: Requires you to review and update audit processes, including traffic logging methodologies, upon significant changes or incidents.
IR.2.092: Stipulates collection and retention of data to support incident response, which explicitly references network traffic data—not just endpoint events.
IEC 62443 Logging Controls
IEC 62443 is structured around zones and conduits, with logging required at both endpoints and inter-zone boundaries:
SR 7.1: Generating audit records for security-relevant events, including access and data movement across network segments.
SR 7.2: Retaining logs securely for evidence in post-incident analysis (with recommendations on duration and access control).
SR 2.1/2.2: Monitor communication channels for unauthorized traffic, making flow or even packet-level logs mandatory where appropriate.
Getting Technical: What Makes a "Good" Network Traffic Log?
A network traffic log suitable for compliance and forensics should display:
Timestamp Accuracy: Synchronized with trusted NTP sources for event correlation.
Source and Destination: IP addresses and ideally device names (requires asset inventory tie-in).
Session Metadata: Protocol, port, session duration, bytes transferred.
Integrity Controls: Hashing/signing of logs to detect tampering.
Contextual Annotations: Classification (e.g., "between IT/OT boundary", "remote access"), ideally with geo-IP or role-based enrichment.
Packet captures (pcaps) are only required in rare circumstances, but flow logs (NetFlow, IPFIX, or SDN controller logs) are mandatory at security boundaries. Correlating these logs with authentication data (RADIUS, Windows Event IDs, LDAP logs) is optimal for auditability.
Architectural Deployment: Where and How to Log Within Segregated Environments
IT vs. OT Segmentation: The Classic Challenge
Modern critical environments have at least three zones (IT, DMZ, OT), with specific conduits between them. Each boundary, especially the IT/OT firewall, is a requisite logging point. Despite decades of "air gap" talk, remote management, cloud historians, and enterprise integration mean these boundaries are now porous.
Best Practice:
Locate passive traffic loggers (SPAN ports or network taps) at all significant inter-zone boundaries.
Where encrypted tunnels are unavoidable (e.g., VPNs for remote maintenance), ensure logging both before and after decryption—in practice, this may require agent-based logs on jump hosts or inspection proxies in the DMZ.
Have a retention and backup policy for these logs—typically 90 days minimum (CMMC) and up to a year for IEC 62443 audits.
Centralization and Integrity of Traffic Logs
Network log centralization is standard in enterprise IT (SIEM, syslog-NG, ELK/Graylog stacks) but is often overlooked in isolated OT environments. For regulatory success:
Bridge logs using high-security data diodes or transfer protocols such as IEC 60870-5-104 gateways.
If full centralization is impossible, deploy local log servers per zone, with periodic (and integrity-checked) secure transfer to a central repository.
Collaboration and Role Delineation: IT/OT Logging Responsibilities
Log management is a locus of tension between IT and OT, especially as log data can be sensitive or operationally disruptive. CMMC and IEC 62443 both push for clearly defined roles:
IT: Typically runs infrastructure, SIEM, and enterprise network devices. Responsible for interzone and perimeter logging, SIEM integration, and incident response logs.
OT: Owns device logs (PLCs, DCS, field devices), historian integration, and often the DMZ. Must ensure network logs don’t disrupt real-time performance—mirror port oversubscription is a classic pitfall.
Collaboration mechanisms include shared asset inventories, regular cross-team audits, and joint runbooks for log review and retention.
Annotation: The Greatest Practical Obstacles
Lack of consistent timestamping in legacy OT devices; consider NTP-over-DTLS or GPS-based time sources.
Proprietary or vendor-specific logs; strong case for open logging standards (syslog, CEF, LEEF, IPFIX).
Operational silos—without unified dashboards or review routines, logs become digital landfill instead of compliance lifelines.
Deploying Secure Network Traffic Logging: A Pragmatic Checklist
Map the network, segment by segment.
Document every firewall, switch, and OT field device interface.
Select logging points.
Use physical taps for critical boundaries; fallback to SPAN/port-mirroring if taps are impractical.
Choose the right logging technology.
NetFlow/IPFIX for flow metadata; syslog for event logs; packet capture for exceptional cases.
Sync clocks religiously.
Misaligned timestamps are a common audit failure point.
Establish log review procedures.
Assign dual-responsibility (IT/OT) for high-stakes zones.
Implement log integrity checks.
Hash/sign log files and retire them to WORM storage if possible.
Regularly test incident response using logs.
Your logs only matter if you can actually trace an incident with them.
Final Observations for Security Leaders and Network Operators
Logs are not a compliance checkbox; they're a mirror to your actual security posture. While both CMMC and IEC 62443 mandate logs for a reason, the real world is full of poorly-implemented or unreviewed logs that only add risk and complexity. Proper network traffic logging supports not just audits, but smarter incident response, operational troubleshooting, and continuous improvement.
As the separation between IT and OT becomes more of a gradient than a wall, cross-disciplinary skillsets—think network engineering with an eye for security operations—are the new standard. If you haven’t walked your own log path from field device to SIEM, start now. When your next audit lands or your next event escalates, you’ll want to be speaking from evidence, not from theory.
In other words: build your logging like you’ll have to debug the system yourself, at 2AM, on an oil rig, with a regulator on the conference line. That’s what compliance actually means.
Further Reading & References
RFC 3917: Requirements for IP Flow Information Export (IPFIX)
US CERT: ICS Cybersecurity Resources
