What is EtherNet/IP and CIP
EtherNet/IP as CIP over standard Ethernet: scanners and adapters, explicit and implicit messaging, the object model, EDS files and the ports used.
CIP on Ethernet
EtherNet/IP (IP = Industrial Protocol) carries the Common Industrial Protocol (CIP), maintained by ODVA, over standard Ethernet and TCP/UDP. The same CIP object model is used by DeviceNet (CAN) and ControlNet, so tools and device profiles are shared across these networks. It is the dominant fieldbus in Rockwell Automation (Allen-Bradley) systems and widely supported by drives, robots and I/O from other vendors.
Roles
| Role | Meaning | Example |
|---|---|---|
| Scanner (originator) | Opens I/O connections and owns the data exchange | ControlLogix / CompactLogix controller |
| Adapter (target) | Device that serves I/O data | POINT I/O, drive, valve terminal |
A device can be both, e.g. a PLC that is an adapter for a line controller.
Two kinds of messaging
| Explicit messaging | Implicit (I/O) messaging | |
|---|---|---|
| Purpose | Request/response: parameters, configuration, diagnostics | Cyclic process data |
| Transport | TCP port 44818 (encapsulation), or UDP 44818 for some services | UDP port 2222, unicast or multicast |
| Addressing | Class / Instance / Attribute path | Assembly instances agreed at connection time |
| Timing | On demand (MSG instruction) | Every RPI |
Object model
Data is organized in CIP objects: class → instance → attribute. Every device implements, for example, Identity (class 0x01: vendor, product code, serial number), Message Router (0x02), Assembly (0x04: groups of I/O data), Connection Manager (0x06), TCP/IP Interface (0xF5) and Ethernet Link (0xF6). An explicit "Get_Attribute_Single" on class 0x01, instance 1, attribute 7 returns the product name.
EDS files
An Electronic Data Sheet (EDS, text, .eds) describes the device: identity, supported connections, assemblies and parameters. The engineering tool uses it to add the device; many controllers can also work with a "generic Ethernet module" defined only by assembly numbers and sizes.
Connections
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Sources
Updated 2026-10-02