Industrial automation networks (often called OT – operational technology) should be separated from office or business networks (IT) because they have different priorities, protocols, and risks. Mixing them into one flat network greatly increases the chance that a normal office issue, such as malware, a misconfiguration, or a bandwidth spike, can shut down production or even create a safety incident.
Segmentation means dividing the overall environment into smaller, controlled zones, such as corporate IT, plant operations, production lines, and machine or PLC networks. Traffic between these zones is tightly controlled using firewalls, access control lists, or VLANs so that only what is necessary is allowed.
Office or IT networks focus on data confidentiality, user productivity, and access to business applications and the internet. These systems can usually tolerate short delays or brief outages, such as someone waiting a few minutes for email or a file server. Industrial or OT networks focus on safety, deterministic timing, and continuous availability. Even a short delay to a PLC, drive, or robot can cause scrap, equipment damage, or injury, so the tolerance for disruption is very low.
Industrial Ethernet and related technologies are designed for real‑time behavior and high reliability, often in harsh environments with electrical noise, vibration, and temperature extremes. Office networks are designed for throughput and flexibility and are not built to guarantee hard real‑time control of physical processes.
Common industrial protocols, at a high level, include the following. EtherNet/IP is widely used in Rockwell and Allen‑Bradley ecosystems and uses different message types for real‑time I/O and for configuration. PROFINET is commonly used in Siemens environments and supports real‑time and motion control communication with tight synchronization. Modbus TCP and similar protocols use a simple master‑slave style of communication to read and write registers and coils in devices. These protocols expect stable latency, minimal jitter, and often reserved bandwidth. Typical office traffic such as backups, video, and cloud synchronization on the same segment can easily disrupt them and lead to timeouts, nuisance trips, or process shutdowns.
Segmenting the industrial network from the office network reduces both cyber and operational risk. It limits attack paths, because malware or phishing that compromise a user’s laptop are less likely to reach PLCs or SCADA servers if there is a firewall or demilitarized zone between IT and OT. It also contains failures, because a misconfigured office application, a broadcast storm, or a backup job will not flood the control network if VLANs and access control lists isolate production segments. In addition, managed industrial switches can enforce quality of service and isolate critical control traffic from non‑critical traffic to keep machine I/O stable.
A common architecture uses several layers, such as corporate IT, an industrial demilitarized zone that hosts shared services, a plant operations network, line or cell networks, and finally PLC or machine networks. As traffic moves closer to the process, access becomes more restricted. If an incident occurs, such as ransomware, a bad patch, or a simple network loop, this layered and segmented design keeps the blast radius small and helps avoid a plant‑wide shutdown.
Even if the office network is upgraded with faster links or newer switches, running OT and IT on a single flat network is still not recommended. The first reason is that they have different risk tolerance. The IT environment can usually accept reboots, patches, and changes during business hours, but the OT environment often cannot accept any unplanned downtime. Second, the change control and patching processes are different. IT systems are patched frequently, while OT systems often require long validation cycles and are patched less often to avoid unexpected behavior in production. Third, security and compliance expectations for industrial systems often follow standards that explicitly call for segregation of OT from IT and for protection of control system zones. Finally, even a fast shared network can introduce variable latency, congestion, or broadcast traffic that breaks deterministic industrial protocols.
Upgrading an office network mostly improves capacity and speed. It does not fix the fundamental mismatch in timing, safety, and security requirements between business systems and real‑time control systems. Treating them as one network also means changes driven by office needs can unintentionally affect production.
Here are simple examples. In the first example, a user opens a phishing email and their laptop becomes infected with ransomware. If IT and OT share one flat network, the malware can scan and encrypt file shares, historian servers, and possibly engineering workstations used to program PLCs, which can force production lines to stop. With a segmented design and OT firewalls, the infection is more easily contained to the office segment and production can continue while IT handles cleanup. In the second example, at noon a cloud backup or software update generates heavy traffic across the office LAN. On a shared flat network, that traffic competes with industrial I/O packets and can cause timeouts that trip drives or robots. On a segmented OT network with quality of service settings and isolated VLANs, the backup traffic never touches the control VLANs, so machines remain stable.
When planning network upgrades, it is better to upgrade the office network for productivity, cloud access, and user applications, and separately design or upgrade the industrial network. The industrial network should be designed for deterministic performance through quality of service and suitable topologies, resilience through redundant rings and industrial‑grade switches, and strong security zoning at the IT and OT boundary. This approach matches modern guidance for securing control systems and greatly reduces the chance that an office‑driven change unintentionally shuts down production.