Why VLAN Is Becoming More Important in Industrial Networks

The number of devices on industrial sites keeps growing. PLCs, sensors, HMIs, servers — a mid-sized workshop can easily have several hundred devices that need to be networked.

As device counts rise, network traffic follows. Broadcast messages take up bandwidth, devices spend more processing power on network overhead, and congestion starts to appear. At the same time, security requirements are tightening — data from different production areas needs to be isolated, and not everyone should have access to everything.

Virtual Local Area Networks (VLANs) are designed to address these issues.

What Is a VLAN

Simply put, a VLAN lets you split a single physical switch into multiple isolated virtual subnets. Each VLAN operates like an independent network with its own broadcast domain and security policies.

For example: a factory puts its office network, production network, and warehouse network on the same physical infrastructure but uses VLANs to separate them. Computers in the office can't see real-time data from production equipment, and the warehouse system doesn't get flooded with broadcast traffic from the office network.

This isolation isn't achieved by rewiring — it's done through switch configuration. Devices still connect to the same physical switch, but once VLANs are configured, devices in different VLANs can't communicate directly, as if they were on separate switches.

Why Industrial Sites Need VLANs

Industrial networks have stricter requirements for real-time performance and reliability compared to office networks. VLANs address two main challenges in industrial settings:

Traffic Management

Industrial communication generates a lot of broadcast traffic. Device discovery, IP address assignment, and service announcements all produce broadcast frames. With a small number of devices, this isn't a problem. But when you have several hundred nodes on site, broadcast traffic can consume a noticeable portion of bandwidth and device processing capacity.

VLANs split the network into smaller broadcast domains. Broadcast messages stay within their own VLAN and don't propagate across the entire network. This helps real-time control traffic (like communication between PLCs) by reducing unnecessary interference.

Network Security

In industrial networks, different zones have different security levels. For example, devices on the office network have lower privileges than devices on the control network. VLAN isolation limits access between zones, so even if a machine on the office network gets infected, malicious traffic can't reach the control network.

In addition, operators, engineers, and third-party service providers can be assigned VLAN access based on their roles, reducing the risk of accidental misoperation and insider threats.

How VLANs Are Divided

The three most common division methods are:

Port-based: Each port on the switch is assigned to a VLAN. A device plugged into port A belongs to VLAN 10; a device plugged into port B belongs to VLAN 20. This is the simplest and most commonly used approach.

MAC-based: Devices are assigned to VLANs based on their MAC addresses, regardless of which port they're connected to. This offers greater flexibility but is more complex to configure and maintain.

Protocol-based: Devices are divided by network protocol type. This is less common.

In industrial settings, port-based VLANs are the most practical — simple to configure and easy to understand.

How Do VLANs Communicate with Each Other

By default, different VLANs cannot communicate. If a production management system needs to read data from the control network, routing is required to enable inter-VLAN communication.

The typical approach is to configure inter-VLAN routing on the core switch or router, assign a sub-interface to each VLAN, and let the router forward packets across VLANs.

One thing to keep in mind: inter-VLAN communication introduces some latency. For most data collection and monitoring scenarios this isn't an issue, but if real-time control is involved, it's better to keep devices that need frequent interaction in the same VLAN to avoid routing delays.

Things to Watch When Deploying VLANs

VLANs aren't new — they've been used in commercial networks for over two decades. But when deploying them in industrial settings, a few points are worth thinking about upfront:

Do a network assessment first. Which devices need to talk to each other? Which need to be isolated? Which traffic is real-time? Clarify the requirements before planning the VLAN structure.

Avoid overcomplicating things. More VLANs aren't necessarily better. Too many subdivisions increase management overhead and make troubleshooting harder. As a general guideline, divide by functional zones (control network, monitoring network, office network) and communication needs.

Plan for future expansion. Devices will be added over time. Reserve some VLAN IDs and ports so you don't have to reconfigure the entire network when you expand.

Keep configurations updated. On-site equipment changes frequently — new devices added, existing devices relocated — and VLAN configurations need to be updated accordingly, or new devices may not get the correct network access rights.

Not All Devices Support VLANs

VLANs require managed switches. Standard unmanaged switches don't support VLAN configuration. If your site uses unmanaged switches, you'll need to upgrade them to use VLAN functionality.

Also, older devices may not recognize VLAN tags (802.1Q). Ports connecting to such devices need to be configured as untagged ports or set to Access port mode.

Final Thoughts

VLANs aren't a new technology, but they're becoming increasingly useful in industrial networks. As device counts grow, traffic increases, and security requirements tighten, you naturally need a tool to organize and manage the network more effectively.

VLANs don't solve every problem, but they do address two very practical issues: network isolation and broadcast control. For medium to large industrial sites that are expanding or upgrading their networks, VLANs are a basic capability worth considering.