Storm Control in Industrial Networks — Preventing Broadcast Floods and Protecting PLC Communications

Introduction

In Industrial Ethernet networks, reliability is everything. PLCs, HMIs, drives, and I/O modules rely on timely and consistent communication to maintain process control and safety. One of the most common—but often overlooked—threats to this reliability is the broadcast storm.

Broadcast storms occur when excessive broadcast or multicast traffic overwhelms the network, consuming bandwidth and CPU resources on every connected device. Even a single malfunctioning node can bring a production line to a halt.

Storm control—a core feature of managed industrial switches—helps prevent these disruptions by detecting and limiting abnormal traffic levels before they cause a network-wide failure

What Causes Broadcast Storms?

In automation environments, several common scenarios can trigger a storm:

• Faulty or misconfigured devices repeatedly sending broadcast packets. This results in broadcast frames being forwarded to all ports by switches, consuming bandwidth and crippling network performance until devices can no longer handle legitimate data.
• Network loops created by incorrect cabling, such as connecting a switch port back to itself or to another port on the same switch, or unmanaged switches without spanning tree protection, can create a loop.
• Multicast-heavy protocols (such as EtherNet/IP or PROFINET) when too many devices respond simultaneously. Additionally, some network devices, like certain BACnet devices or those using protocols like ARP, inherently use broadcasts to discover and communicate with others. When combined with other issues, this can lead to an overload of broadcasts, especially in a large network.

Unlike enterprise networks, where these issues might just slow things down, an automation storm can cause loss of control or safety shutdowns if PLCs can’t exchange I/O data in time.

How Storm Control Works

Storm control continuously monitors incoming broadcast, multicast, and unknown unicast traffic on each port. When traffic exceeds a configured threshold (measured in packets per second or percentage of bandwidth), the switch can:

• Drop excess packets automatically.
• Rate-limit broadcast/multicast traffic to a safe level.
• Generate an SNMP trap or alarm to alert maintenance personnel.

This ensures that even if a single device behaves abnormally, the disturbance is contained to one port—not the entire network.

Example: Containing a Faulty Camera

Imagine a machine vision camera on a packaging line that starts sending continuous multicast packets due to a firmware fault.

Without storm control, those packets propagate across the entire network, flooding PLC communication with I/O devices.

Machines stop responding, HMIs freeze, and alarms trigger.

With storm control enabled:
• The switch detects the excessive multicast rate.
• It throttles or blocks traffic from that specific port.
• The rest of the network—including PLCs, drives, and sensors—continues operating normally.

Best Practices for Implementation

1. Set conservative thresholds. Start with 1–5% of port bandwidth or the normal observed broadcast rate, and adjust as needed.
2. Monitor before enforcing. Most managed switches allow you to monitor traffic for a period before applying limits.
3. Document configurations. In industrial environments, where devices are added or replaced frequently, maintaining consistent storm control settings across all switches helps prevent accidental gaps.
4. Combine with loop protection. Use features like RSTP or MRP in tandem to address root causes of broadcast storms. Watch our tutorial on How to Use Loop Detection to Protect your Network

Why it Matters

Storm control may seem like a small configuration option, but in a 24/7 production environment, it can be the difference between uninterrupted operation and hours of downtime. By automatically isolating traffic anomalies, it protects deterministic communication channels that industrial automation depends on.

In short, storm control is the first line of defense for keeping industrial Ethernet stable, predictable, and production-ready.

Learn more with Maple Systems

Whether building complex industrial networks or setting up your first network switch, Maple Systems has an expansive library of technical and educational resources to support your success. Explore our support pages for tutorials, technical notes, and sample projects on a variety of topics. 

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