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OT (Operational Technology) diodes are crucial for securing industrial control systems by enforcing one-way data flow. They come in different types, each with unique characteristics and use cases.
Types of OT Diodes
Hardware Diodes
- One-way physical path (e.g., fiber optic)
- No software, reducing attack surface
- Example command to check fiber link status (Linux):
ethtool <interface_name>
Software-Based Diodes
- Virtual enforcement using firewall rules
- Example iptables rule to block reverse traffic:
iptables -A OUTPUT -d <destination_IP> -j DROP
Hybrid Diodes
- Combines hardware with software rules
- Useful for compliance-heavy environments
Why Use OT Diodes?
- Prevent data exfiltration
- Enforce one-way telemetry (e.g., SCADA to historian)
- Meet compliance (NIST, IEC 62443)
Pros & Cons
| Pros | Cons |
|||
| ✅ One-way traffic only | 🔻 No return path (hard to troubleshoot) |
| ✅ Low attack surface | 🔻 Expensive (hardware diodes) |
| ✅ Ideal for critical zones | 🔻 Requires packet reconstruction tools |
You Should Know:
1. Testing a Hardware Data Diode
Use `ping` and `tcpdump` to verify one-way traffic:
ping -c 4 <target_IP> tcpdump -i <interface> icmp
If no replies are captured, the diode is working.
2. Simulating a Software Diode in Linux
Block reverse traffic using `nftables`:
nft add rule ip filter output ip daddr <monitored_IP> counter drop
3. Windows Firewall One-Way Rule
New-NetFirewallRule -DisplayName "Block Reverse Traffic" -Direction Outbound -Action Block -RemoteAddress <target_IP>
4. Verifying Fiber Optic Diode Integrity
Check light levels (requires SFP module):
sudo ethtool -m <interface>
5. Reconstructing Packets After a Diode
Use `tcpreplay` to simulate traffic:
tcpreplay -i <interface> captured_packets.pcap
What Undercode Say
OT diodes are essential for air-gapped and critical infrastructure networks. While hardware diodes provide the strongest security, software-based solutions offer flexibility. Always verify diode functionality using network monitoring tools like Wireshark or tcpdump.
For ICS/OT security, consider combining diodes with:
- Network segmentation (
iptables, VLANs) - Strict access controls (RBAC, MAC)
- Traffic logging (
syslog-ng, Splunk)
Expected Output: A secure one-way data flow with no unauthorized reverse traffic.
Prediction: As OT/IoT convergence grows, demand for hybrid diodes with AI-driven anomaly detection will rise.
(URLs if needed: NIST ICS Security, IEC 62443)
References:
Reported By: Zakharb Ot – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
