Modbus TCP vs EtherNet/IP
Why “Both Ethernet Anyway” Almost Ruins Your Decision
THE INSIGHT
I keep hearing it in meetings: “Use Modbus TCP. It’s cheaper, and they’re both Ethernet anyway.”
Such a statement should raise serious concerns. This is not because either protocol is inherently flawed, but rather because it exposes a fundamental misconception about the process of selecting between them.
Here’s what I’ve learned after 36+ years of watching these decisions play out: the most important information isn’t what these protocols are; it’s why they were built the way they are.
Think about this timeline. Modbus was designed in 1979. EtherNet/IP in the 1990s. That’s not just a date difference; it’s a gulf in technology, in our understanding of networks, in what cybersecurity means, and in what we expect from automation systems.
Modbus was born to solve a very specific problem: how do you get a few devices to talk to each other in an isolated factory with simple serial connections? It was elegant for that job. When Ethernet came along, someone said, “Let’s wrap our Modbus messages in TCP packets.” And that’s exactly what they did, an adaptation, not a redesign.
EtherNet/IP was different. It was purpose-built from the ground up for modern networks. The architects already knew about cybersecurity, about scaling to dozens of devices, and about real-time control. The design reflects that.
This is the mental model that matters: every strength and every weakness of a protocol traces back to what problem it was built to solve.
When you understand that, a lot of confusion disappears.
Why is Modbus TCP simpler? Because it was designed for simplicity.
Why does EtherNet/IP have more complex capabilities? Because it was designed for connected systems where those capabilities matter.
Why can one handle synchronized motion and the other can’t? Because one was built with that capability in mind from day one, and the other wasn’t.
The takeaway isn’t, “EtherNet/IP is better.” It’s this: before you choose a protocol, understand what era it was built for and what problem it was designed to solve. That understanding will tell you if it’s the right fit for your project, not just whether it costs less upfront.
QUICK WIN
Next time someone says, “they’re both Ethernet anyway,” slow down and ask yourself these three questions before moving forward:
What era was this protocol designed for? What was the state of industrial networks when it was created?
What specific problems was it trying to solve? Simple point-to-point communication? Connected systems? Real-time control?
Which aspects were not a concern for the designers? For older protocols: cybersecurity, scaling, advanced capabilities. For newer ones: backward compatibility with legacy systems.
Your answers will tell you whether the protocol’s design philosophy matches your actual needs.
FROM THE FIELD
A few years ago, a mid-sized manufacturer brought me in to help plan a modernization project. They’d already decided on Modbus TCP, mainly because it was cheaper and they saw it as “simple Ethernet.”
After eight months, they encountered a roadblock.
They needed integrated safety-rated communication for their new emergency systems. Modbus TCP doesn’t have that capability. Not out of the box, not with better configuration, not at all, it wasn’t designed for it. So they had to run a separate safety network alongside their Modbus TCP network. Different cables, different controllers, double the cost.
Then they realized they needed real-time synchronization for a new coordinated motion system. Again, the protocol they had chosen did not allow for real-time synchronization. Another separate network.
By the end, they had three networks doing what one, properly chosen architecture, could have done.
The frustrating part? If someone had asked, “What are we building this for?” instead of “What’s the cheapest protocol?” if they’d understood that Modbus TCP was designed for something different, they would have seen these limitations coming.
The protocol wasn’t bad. The decision was.
Until next issue,
Alana