Computer Networking Basics for Industrial Technicians

Modern industrial systems rely heavily on computer networks.

PLCs, HMIs, SCADA systems, variable speed drives, remote I/O, intelligent instruments and engineering workstations all need to communicate.

You do not need to be a network engineer to work with these systems, but understanding a few basic networking concepts can make troubleshooting much easier.

What is an IP address?

An IP address identifies a device on a network.

A typical IPv4 address looks like this:

192.168.1.20

Each device on the same network normally needs its own unique IP address.

If two devices use the same address, communication problems can occur.

What is a subnet mask?

A subnet mask helps determine which devices are considered to be on the same local network.

A common example is:

255.255.255.0

With that subnet mask, devices such as:

192.168.1.10
192.168.1.20
192.168.1.50

are normally on the same local network.

A device at:

192.168.2.20

would usually be on a different network.

What is a default gateway?

The default gateway is the address a device uses when it needs to communicate outside its local network.

In a small industrial network, a gateway might be:

192.168.1.1

Not every isolated control network needs a gateway, but it becomes important when communicating with other networks.

What is Ethernet?

Ethernet is the most common physical and data-link technology used in modern industrial networks.

Devices may connect using:

copper Ethernet cable
fibre optic cable
industrial switches
routers
wireless links

Industrial Ethernet systems often use the same basic networking principles as office networks, but the equipment and design may need to withstand heat, vibration, dust and electrical noise.

What is a network switch?

A network switch connects devices together.

For example, a switch may connect:

a PLC
an HMI
a SCADA computer
a variable speed drive
an engineering laptop

The switch directs Ethernet traffic between connected devices.

Managed industrial switches may also provide extra features such as diagnostics, VLANs, redundancy and port monitoring.

What is a router?

A router connects different networks together.

For example:

Industrial control network → Router → Site network

Routers are important when devices need to communicate between different IP address ranges.

What is a MAC address?

A MAC address is a hardware address associated with a network interface.

It normally looks something like:

00:1A:2B:3C:4D:5E

IP addresses may be changed, but a MAC address is generally tied to the device’s network interface.

MAC addresses can be useful when identifying equipment connected to a switch.

Static IP addresses

Industrial equipment is often configured with static IP addresses.

That means the address is manually assigned and remains the same.

This is useful because SCADA systems and PLC programs usually need to know exactly where another device is located.

For example:

PLC — 192.168.1.10
HMI — 192.168.1.20
VSD — 192.168.1.30
SCADA — 192.168.1.40

Keeping an accurate network address list is extremely helpful.

DHCP

DHCP automatically assigns IP addresses.

It is common in office and home networks.

Some industrial networks also use DHCP, but many control systems prefer static addresses so equipment remains predictable.

What does ping do?

Ping is a simple troubleshooting tool.

It checks whether one IP device can reach another.

For example:

ping 192.168.1.20

If the device responds, that tells you there is at least some level of network communication.

If it does not respond, the problem may involve:

incorrect IP settings
disconnected cable
failed switch port
firewall settings
power failure
routing
device configuration

A failed ping does not always mean the device is faulty.

Ethernet ports and link lights

Always check the simple things first.

Most Ethernet ports have link and activity lights.

A link light usually indicates that a physical connection has been established.

No link light may point to:

damaged cable
unplugged connector
failed switch port
failed device port
device without power

This is often one of the fastest checks you can make.

Industrial communication protocols

Once the basic network is working, industrial protocols use that network to exchange useful information.

Examples include:

Modbus TCP
DNP3
EtherNet/IP
PROFINET
OPC UA
IEC 60870-5-104

These protocols operate on top of the underlying Ethernet and IP network.

That distinction is important.

A PLC may have a perfectly good Ethernet connection but still fail to communicate because the industrial protocol settings are wrong.

Ports and protocols

Network applications often use TCP or UDP port numbers.

For example, Modbus TCP commonly uses:

TCP port 502

A firewall can block traffic even when the devices can ping each other.

This means successful ping tests do not prove that the application itself will work.

Firewalls

Firewalls control which network traffic is allowed through.

They are an important part of industrial cybersecurity.

However, a badly configured firewall can also stop legitimate industrial communications.

When troubleshooting, confirm that the required communication ports are permitted.

Do not disable security controls unnecessarily just to make a system work.

Network diagrams

A simple network diagram is one of the most useful documents you can have.

It should show:

equipment names
IP addresses
switches
routers
communication links
network ranges
important ports or protocols

Even a basic diagram can save hours during troubleshooting.

A practical troubleshooting approach

When an industrial Ethernet device is not communicating, work through the problem logically:

Check that the device is powered.
Check the Ethernet link lights.
Check the cable.
Confirm the device IP address.
Confirm the subnet mask.
Check for duplicate IP addresses.
Try a ping test.
Check the switch port.
Confirm the industrial protocol settings.
Check firewall or routing rules.
Confirm the application is using the correct port.
Check logs and diagnostic information.

Avoid changing several settings at once.

Change one thing, test it, and then move to the next possibility.

The simple explanation

The easiest way to think about industrial networking is:

The network provides the path. The industrial protocol provides the conversation.

If the path is broken, the devices cannot communicate.

If the path is working but the protocol settings are wrong, they still cannot understand each other.

Understanding both layers makes industrial communication faults much easier to diagnose.

ITIAN Knowledge Hub provides practical, plain-English technical training for industrial communications, SCADA, networking, electrical systems and water infrastructure.