Listen to this Post
Introduction:
Operational Technology (OT) and Industrial Control Systems (ICS) cybersecurity cannot be secured by simply layering on Zero Trust or AI-driven anomaly detection without mastering the foundational building blocks. As Mike Holcomb emphasizes, learning to crawl before you walk—starting with networking, firewalls, remote I/O, and the Purdue Model—is the only path to resilient defense in critical infrastructure.
Learning Objectives:
- Understand why fundamental IT and OT concepts (VLANs, DMZ, packet analysis) must precede advanced frameworks like Zero Trust and AI anomaly detection.
- Execute hands-on commands in Linux and Windows to analyze network traffic, configure firewall rules, and map Purdue Model layers.
- Apply step‑by‑step guides for OT protocol abuse testing, incident response playbooks, and secure remote access setup.
You Should Know:
- Learn Networking Before OT/ICS Cybersecurity – And Build a Lab to Prove It
Most OT environments run on legacy Ethernet and serial protocols. Without a solid grasp of IP addressing, subnets, ARP, and routing, you cannot segment an ICS network or troubleshoot a dropped PLC connection.
Step‑by‑step guide to map your OT network:
- On Linux: Use
ip addr show,arp -a, and `nmap -sn 192.168.1.0/24` to discover live hosts. For a safer, passive approach on a live OT network, run `sudo tcpdump -i eth0 -nn -s 1500 -c 1000 -w ot_traffic.pcap` to capture initial traffic without active scanning. - On Windows: Launch PowerShell as admin and execute
Get-NetNeighbor, `Test-NetConnection-Port 502` (Modbus default port), and tracert <HMI_IP>. - Use Wireshark to filter for OT protocols: type
modbus,dnp3, or `s7comm` in the display filter bar. Analyze packet timing to identify normal vs. anomalous polling intervals.
- Learn Firewalls Before Quantum Encryption – Configure Stateful Inspection for Purdue Levels
Quantum encryption is irrelevant if a misconfigured firewall allows a ransomware to jump from the IT zone to the control zone. Start with stateful firewalls and access control lists (ACLs) that enforce the Purdue Model.
Step‑by‑step guide to harden a Linux iptables firewall for Level 3 to Level 2 traffic:
Flush existing rules sudo iptables -F sudo iptables -X Set default policies: drop incoming, allow outgoing sudo iptables -P INPUT DROP sudo iptables -P FORWARD DROP sudo iptables -P OUTPUT ACCEPT Allow established/related traffic from Level 2 (control) back to Level 3 sudo iptables -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT Allow Modbus TCP from Level 3 (DMZ historian) to Level 2 (PLC) only sudo iptables -A FORWARD -s 192.168.3.0/24 -d 192.168.2.0/24 -p tcp --dport 502 -j ACCEPT Log dropped packets for forensics sudo iptables -A FORWARD -j LOG --log-prefix "OT-FW-DROP: " --log-level 4
On Windows Defender Firewall with Advanced Security, create inbound rules restricting access to Engineering Workstations by source IP range and port (e.g., 102 for S7, 20000 for DNP3).
- Learn Remote I/O Before Edge Computing – Understand Fieldbus Fundamentals
Edge computing collects and processes data near the source, but if you don’t know how remote I/O racks (e.g., ET 200SP, Flex I/O) communicate with a PLC over Profinet or EtherNet/IP, you’ll misconfigure edge nodes and introduce latency or unsafe states.
Step‑by‑step tutorial to simulate remote I/O polling with Python (use only in lab):
import socket
Modbus TCP read holding registers (simulated remote I/O)
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect(('192.168.2.10', 502)) PLC IP
Modbus PDU: 0x03 read holding registers, starting address 0, quantity 10
pdu = bytes([0x03, 0x00, 0x00, 0x00, 0x0A])
mbap = bytes([0x00, 0x01, 0x00, 0x00, 0x00, len(pdu), 0x01])
sock.send(mbap + pdu)
response = sock.recv(1024)
print(f"Remote I/O values: {response.hex()}")
Understanding this raw polling helps you troubleshoot cable breaks, scan cycles, and I/O bus errors before deploying edge AI.
- Learn OT Protocol Abuse Before Counting CVEs – Manual Exploitation on Modbus/DNP3
CVEs tell you a vulnerability exists, but without knowing how to abuse the protocol, you cannot test mitigations. The most common OT risk is lack of authentication and authorization in protocols like Modbus (no concept of user or password).
Step‑by‑step guide to perform a legitimate write coil attack in a controlled lab (Do not use on live systems):
– Use `nmap` to identify Modbus devices: `nmap –script modbus-discover -p 502
– Install `modbus-cli` or pymodbus: `pip install pymodbus`
– Read a coil: `python -c “from pymodbus.client import ModbusTcpClient; c=ModbusTcpClient(‘192.168.2.10’); print(c.read_coils(0,10).bits)”`
– Write to a coil (simulate valve command): `c.write_coil(0, True)`
– To mitigate: Deploy Modbus TCP to serial converters, use firewalls to restrict source IPs, and monitor for write operations via IDS rules (e.g., Snort rule: alert tcp $HOME_NET 502 -> any any (msg:"Modbus Write Coil"; content:"|FF 05|"; depth:2; sid:1000001;)).
- Learn Packet Analysis Before AI Anomaly Detection – Capture and Decode OT Traffic
AI models flag deviations from normal traffic, but if you never learned to manually inspect a PCAP, you cannot validate if an anomaly is a cyberattack, a machine failure, or a misconfigured engineering laptop.
Step‑by‑step tutorial using Wireshark and tshark:
- Capture traffic on a mirrored switch port: `sudo tshark -i eth0 -f “port 502 or port 20000” -c 10000 -w ot_capture.pcap`
– Open in Wireshark and apply a custom column for Modbus function codes: Edit → Preferences → Columns → Add fieldmbtcp.func_code. Use a filter `mbtcp.func_code == 5` to highlight all write single coil commands. - For command line analysis: `tshark -r ot_capture.pcap -Y “modbus.func_code == 15” -T fields -e ip.src -e ip.dst -e modbus.word_cnt`
– Compare against a baseline captured during normal production. Any write function from an unknown source IP should trigger an incident response.
- Learn the Expanded Purdue Model Before Zero Trust Principles – Map Layers 0‑5
Zero Trust says “never trust, always verify,” but in OT you cannot constantly re‑authenticate every packet on a real‑time control loop. The expanded Purdue Model (Level 0‑5, plus DMZ) gives you a physical and logical architecture to apply Zero Trust only where it makes sense (e.g., between Levels 3 and 4, not inside Level 1).
Step‑by‑step guide to map your environment:
- Level 0 (Physical): Motors, valves, sensors. No IP stack.
- Level 1 (Local control): PLCs, RTUs, DCS controllers.
- Level 2 (Supervisory): HMIs, SCADA servers.
- Level 3 (Operations): Historians, asset management, application servers.
- Level 4 (Enterprise IT): Business networks, ERP.
- Level 5 (External): Cloud, partners.
- DMZ: Jump hosts, patch management, secure remote access gateways.
Action: Draw a data flow diagram between levels. Label every firewall rule and VLAN. For each rule, answer “Does this flow require mutual authentication?” – if yes, implement using IEC 62443‑4‑2 compliant security levels, not a blanket Zero Trust overlay.
- Learn Incident Response Before Penetration Testing – Build a Playbook for a PLC Compromise
Penetration testing finds holes, but incident response stops the bleeding. In OT, you cannot reboot a PLC that controls a blast furnace without a predefined response that includes manual backup, forensic acquisition, and safe‑state transition.
Step‑by‑step playbook for a suspected Modbus anomaly:
- Detect: Alert from SNORT rule or SIEM. Capture live traffic with `sudo tcpdump -i eth0 -G 300 -W 48 -w ot_rotate_%Y%m%d_%H%M.pcap` (rotates every 5 minutes).
- Contain: Isolate the suspicious IP by adding a block rule on the switch or firewall (e.g.,
sudo iptables -A INPUT -s <offending_IP> -j DROP). Do not pull the network cable if the PLC is controlling a process – use ACLs that preserve safety functions. - Eradicate: Reflash the PLC firmware from a known‑good backup. Verify using `fciv` (Windows) or `sha256sum` (Linux) against the original image.
- Recover: Restore the control logic and force a manual walk‑down of the physical process before returning to auto mode.
- Document: Log every command into a tamper‑proof journal (e.g., using
systemd-journal-remote).
What Undercode Say:
- Key Takeaway 1: Fundamentals are not optional; skipping network basics and the Purdue Model leads to failed Zero Trust deployments and expensive breaches.
- Key Takeaway 2: Active learning through commands, packet captures, and protocol abuse in a lab environment is the only way to internalize OT defense.
Analysis: Mike Holcomb’s list resonates because the OT/ICS industry is flooded with hype around AI, quantum, and Zero Trust while operational teams still struggle to segment a flat Layer 2 network. The conversation with Donald Green highlights a genuine tension: IT cybersecurity professionals already understand Zero Trust principles, yet applying them in OT requires unlearning the “trust nothing” extreme because real‑time control loops cannot tolerate per‑packet authentication overhead. Stuardo Rodriguez’s audit perspective reinforces that assessors must first verify Purdue level mapping and data flows before recommending any advanced framework. Steve Jones adds a dose of reality – learning is messy and often arrives as a crisis. However, a structured, command‑by‑command approach as outlined above gives defenders a repeatable methodology. The “grease‑smudged notebook” metaphor perfectly captures the hands‑on, roll‑up‑your‑sleeves ethos that the community needs to embrace.
Prediction:
Within 3‑5 years, OT/ICS security certifications will require practical exams that include manual Modbus frame crafting, firewall rule debugging, and Purdue Model mapping, similar to how OSCP demands live exploitation. The vendors selling AI anomaly detection will be forced to integrate baseline packet analysis modules because customers will demand transparency. Meanwhile, organizations that ignore fundamentals will suffer a major incident (likely a ransomware that pivots from IT to OT via an unsegmented historian), triggering regulatory mandates for minimum competency testing before any Zero Trust deployment in critical infrastructure.
▶️ Related Video (74% Match):
🎯Let’s Practice For Free:
IT/Security Reporter URL:
Reported By: Mikeholcomb Learn – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
