Is 'Packet Mirroring' safe enough for OT environment?

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Is 'Packet Mirroring' safe enough for OT environment?

Packet mirroring is widely used in OT security because it provides deep visibility into network traffic without actively interfering with communication. However, OT environments are highly sensitive to latency, jitter, and packet loss, so it’s crucial to ensure that mirroring does not introduce risks to system stability. Below is a detailed breakdown of why packet mirroring is safe, as well as best practices to avoid communication interruptions.

1. Why Packet Mirroring is Safe for OT Networks?

Packet mirroring passively copies traffic and does not alter the original data flow. It differs from active security solutions (e.g., inline firewalls, Intrusion Prevention Systems (IPS)) that process and potentially drop or delay packets.

Reasons Why Packet Mirroring is Generally Safe in OT

Non-Intrusive Monitoring

  • Mirroring creates a copy of traffic without modifying the original communication.

  • No risk of blocking or altering data unless misconfigured.

No Direct Impact on Network Latency

  • Unlike inline security devices (IPS, DPI-based firewalls), mirroring does not introduce delays.

  • The original OT traffic flows without interruption, reducing the risk of network disruptions.

No Single Point of Failure

  • If the mirroring system fails, it does not impact the live OT network.

  • Even if the monitoring tool crashes, production systems continue to operate normally.

Resilience Against Processing Overloads

  • Mirrored traffic is processed separately from control system operations.

  • Network TAPs (Test Access Points) do not introduce computational load on OT devices.

However, improper configuration and deployment can cause network issues. Below are key areas to be careful about.

2. What to Be Careful About When Setting Up Mirroring in OT?

To ensure mirroring does not cause communication problems, consider the following:

Do Not Overload Network Switches with Mirroring

  • If a switch is not designed to handle multiple mirroring sessions, it can become overloaded.

  • Some managed switches drop packets when mirroring too much traffic to a single port.

  • Solution: Use high-performance switches or dedicated packet brokers to handle mirroring without performance degradation.

Avoid Mirroring Too Much Traffic to a Single Port

  • If multiple ports are mirrored to one destination, the port’s bandwidth might become a bottleneck.

  • Example: A 1 Gbps mirror port cannot handle multiple 1 Gbps mirrored sources without packet loss.

  • Solution:

    • Use load balancing or multiple mirror ports for high-bandwidth networks.

    • Utilize packet aggregation switches for handling multiple mirroring points.

Be Cautious with SPAN (Switch Port Analyzer) Configuration

  • Some switches prioritize production traffic over mirrored traffic—which is good.

  • However, others drop mirrored traffic first when resources are low, leading to incomplete monitoring.

  • Solution:

    • Use TAPs (Test Access Points) instead of relying only on switch-based SPAN.

    • If using SPAN, ensure QoS (Quality of Service) settings are optimized for mirroring.

Choose the Right Mirroring Technology (SPAN vs. TAPs vs. Aggregation Switches)

TechnologyProsConsBest Use Case in OT
SPAN (Port Mirroring)No extra hardware cost, easy to configureCan overload the switch, potential packet lossLow-traffic OT environments where performance impact is minimal
TAP (Network TAP)Zero impact on network performance, full packet captureRequires physical installation, costlierHigh-security OT environments (e.g., power grids, refineries)
Aggregation SwitchCollects multiple mirroring points into a single outputCan become a bottleneck if overloadedLarge-scale OT monitoring environments

3. Best Practices for Safe OT Packet Mirroring

Use TAPs instead of SPAN when possible

  • TAPs do not rely on the switch’s CPU, avoiding performance degradation.

Mirror both TX & RX traffic for complete visibility

  • Helps detect bidirectional threats (e.g., malware beaconing, abnormal SCADA commands).

Set up dedicated mirroring ports to avoid bandwidth overload

  • Example: If monitoring a 1 Gbps network, ensure the mirror port is also 1 Gbps or higher.

Regularly monitor the switch’s CPU and memory usage

  • If mirroring causes high CPU load, consider alternative methods or hardware upgrades.

Use aggregation switches for high-traffic networks

  • Prevents excessive load on single ports and provides better scalability.

Avoid mirroring time-sensitive industrial control protocols

  • If necessary, mirror at the network boundary instead of inside the real-time control loop.

Ensure monitoring tools can handle mirrored traffic effectively

  • Intrusion Detection Systems (IDS) and Security Information & Event Management (SIEM) should be optimized for OT traffic analysis.

Recap: Packet mirroring is safe as long as it is properly configured. Since it is passive and non-intrusive, it does not directly interfere with OT communications. However, misconfiguration or excessive mirroring can overload network devices and affect performance.

To ensure safe deployment, always:

  1. Use the right technology (TAPs > SPAN where possible)

  2. Avoid excessive load on network switches

  3. Monitor system performance to prevent CPU/memory overload

By following these best practices, OT security teams can gain deep visibility into industrial networks without compromising system stability.

#CPS #OT #XIoT #IoT #IIoT #IoMT #CPSSecurity #OTSecurity #IoTSecurity #CPS보안 #OT보안 #IoT보안

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