What is an EtherNet/IP Network?

EtherNet/IP network

That would seem like an odd question to ask. I’ve been involved with EtherNet/IP for over twenty years now. Our company, Real Time Automation, was the very first company, even before Allen-Bradley, to certify an EtherNet/IP adapter. We’ve sold hundreds of EtherNet/IP adapter and EtherNet/IP scanner toolkits to developers of EtherNet/IP products. And now I’m asking, “What is an EtherNet/IP network?”

It’s sounds like an easy question to answer, but is it? For example, is the following sub-network on this switch an EtherNet/IP network? It is certainly a Modbus TCP network, but should you call it an EtherNet/IP network since it has an (unused) EtherNet/IP adapter.

What about the case of a Rockwell ControlLogix PLC and an EtherNet/IP adapter where the PLC is not using the adapter? Is that an EtherNet/IP network? What about the following diagram where we have two scanners? Each scanner controls one adapter. Is that one EtherNet/IP network or two EtherNet/IP networks?

Is the network, the IP subnet? If all four devices are part of the same subnet, is that one network or is it two networks? If I add a Modbus TCP Master and a 50 Modbus TCP Slaves to it, is that network an EtherNet/IP network, two EtherNet/IP networks or a Modbus TCP networks, or just a control network?

It’s clear that there have to be some rules about what is and what is not an EtherNet/IP network (or you could ask the same about a Modbus TCP network or PROFINET IO network). It’s certainly not as clear as a Modbus RTU network. I haven’t seen anyone else do it, so I’ll do it here. All the following must be true to call something an EtherNet/IP network:

  1. There are one or more EtherNet/IP scanner devices actively controlling one or more EtherNet/IP adapter devices.
  2. All the devices in the network are part of the same IP subnet. For example, all devices in a network are addressed as 192.168.1.x.
  3. All devices in the network are part of the same broadcast domain.

That last rule means I would not call a scanner in one subnet,, accessing an adapter in another subnet,, an EtherNet/IP network.

These are my rules as of today and they are subject to change. Feel free to contact me with your thoughts.