Automation Glossary • EtherNet/IP

What Is EtherNet/IP?

Merobix Engineering • • 4 min read

EtherNet/IP is a widely used industrial Ethernet protocol built on the Common Industrial Protocol (CIP) and managed by ODVA. The name stands for EtherNet/Industrial Protocol - not internet protocol - and it is the native network of Rockwell Automation Allen-Bradley controllers, making it one of the most common protocols in North American plants.

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EtherNet/IP in one line: EtherNet/IP is an industrial Ethernet protocol that runs the Common Industrial Protocol (CIP) over standard TCP/IP and UDP/IP, using explicit messaging for configuration and data reads and implicit (I/O) messaging for real-time cyclic control data.

CIP, Implicit and Explicit Messaging

EtherNet/IP adapts the Common Industrial Protocol to standard Ethernet. CIP is an object-oriented, media-independent application layer also used by DeviceNet and ControlNet, which means the same device profiles and object model carry across those networks. On EtherNet/IP, CIP messages travel two ways. Explicit messaging uses TCP for request/response transactions - reading a tag, changing a parameter, uploading configuration - where timing is not critical.

Implicit messaging (also called I/O messaging) uses UDP for real-time, cyclic data such as the produced/consumed I/O between a PLC and remote I/O racks or drives. UDP is used because its low overhead suits the repetitive, time-sensitive nature of control data, with connection setup and health monitoring handled by CIP. For deterministic motion, CIP Sync and CIP Motion add time synchronization on top.

EtherNet/IP in Oil and Gas SCADA

Because Allen-Bradley ControlLogix and CompactLogix processors use EtherNet/IP natively, it is extremely common on oil and gas skids, compressor packages, pump stations, and separator control panels across North America. A SCADA system typically reads controller tags over EtherNet/IP explicit messaging or through an OPC server that speaks the protocol.

For cloud SCADA, an edge gateway or driver reads the PLC's tags over EtherNet/IP locally and forwards a curated set upward over a routable, outbound connection. Merobix supports EtherNet/IP among its device protocols, so an operator running Allen-Bradley controllers can bring wellhead, compressor, or pump-station data into cloud dashboards, alarms, and a historian - polling the PLC locally and pushing data outbound, with no inbound ports opened on the site firewall.

Frequently Asked Questions

Does EtherNet/IP mean internet protocol?

No. The IP in EtherNet/IP stands for Industrial Protocol, referring to the Common Industrial Protocol (CIP) it carries. It does run over standard TCP/IP and UDP/IP Ethernet, but the name is about CIP, not the internet.

What is the difference between implicit and explicit messaging?

Explicit messaging uses TCP for on-demand request/response transactions like reading a tag or changing a parameter, where timing is flexible. Implicit (I/O) messaging uses UDP for real-time cyclic control data between controllers and I/O, where low, repeatable latency matters more than guaranteed delivery of every packet.

Which controllers use EtherNet/IP?

EtherNet/IP is the native protocol of Rockwell Automation Allen-Bradley controllers such as ControlLogix and CompactLogix, and it is supported by many drives, I/O, and instruments from ODVA member vendors. It is especially common in North American oil, gas, and manufacturing plants.

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