What is EtherNet/IP?
EtherNet/IP stands for Ethernet Industrial Protocol. The "IP" is not Internet Protocol; it stands for Industrial Protocol. EtherNet/IP adapts the Common Industrial Protocol (CIP) to run over standard IEEE 802.3 Ethernet hardware, using TCP and UDP as transport layers. It was developed in the late 1990s, standardized by ODVA in 2000, and is today one of the most widely deployed industrial Ethernet protocols in the world.
EtherNet/IP is an open standard. Any vendor whose device passes ODVA conformance testing can legitimately claim EtherNet/IP compatibility, and two ODVA-certified devices from different vendors can communicate using the same protocol without vendor-specific software bridges. ODVA's membership includes Rockwell Automation, Omron, Schneider Electric, Honeywell, Endress+Hauser, Bosch Rexroth, Cisco, Fanuc, Mitsubishi Electric, ABB, Emerson, Beckhoff, and hundreds of others.
The core of EtherNet/IP is CIP. CIP defines how industrial devices organize and expose their data as objects, how those objects are accessed using standardized service codes, and how connections between devices are established and managed. EtherNet/IP provides the Ethernet and TCP/UDP transport beneath CIP: TCP port 44818 for explicit messaging (request-response configuration and data access) and UDP port 2222 for implicit messaging (cyclic I/O). The CIP application layer is shared with three other industrial networks in the CIP family.
EtherNet/IP uses standard Ethernet hardware, but the protocol is defined by CIP above it. Standard Ethernet switches, cables, and NICs work with EtherNet/IP without modification. However, two devices on the same Ethernet switch do not communicate using EtherNet/IP unless they both implement CIP. Using EtherNet/IP requires driver software on the host system that understands the CIP object model and generates correct service requests, not just standard TCP/IP socket communication.
The CIP protocol family
CIP is a media-independent application layer protocol managed by ODVA. The same CIP object model, the same service codes, and the same device profiles work across four different physical network types. Engineers working in brownfield facilities will encounter all of them.
CIP over standard Ethernet (TCP/UDP). The dominant industrial Ethernet protocol in North America and increasingly global. Runs on standard network infrastructure. TCP port 44818 (explicit) and UDP port 2222 (implicit).
CIP over CAN bus. Simple device-level connectivity for sensors, actuators, and drives. Up to 64 nodes, max 500 kbps. Large installed base of legacy DeviceNet devices in discrete manufacturing still in service.
CIP over a CTDMA coaxial or fiber topology. Deterministic scheduled communication between controllers and I/O where timing guarantees are critical. Found in older Rockwell and Omron installations.
CIP over a bit-strobe serial network for high-density, lower-cost sensor and actuator I/O. Up to 384 nodes. Most common in Japan and in OEM machine applications from Japanese vendors.
EtherNet/IP in the OSI model
EtherNet/IP deliberately uses unmodified standard Ethernet at Layers 1 through 4. This is what allows it to run on commodity network infrastructure rather than requiring proprietary cabling or switches.
CIP (Common Industrial Protocol)ODVA standard
Object model, device profiles, service codes (Get_Attribute_Single, Set_Attribute_Single, Forward_Open...), Assembly objects, EDS files. This is where EtherNet/IP differs from plain Ethernet, and where all CIP family protocols share a common specification.
CIP Encapsulation ProtocolEtherNet/IP specific
Defines the session-layer wrapper that carries CIP messages over TCP. Specifies the encapsulation header format, command codes, and session management for establishing and maintaining TCP connections between EtherNet/IP nodes.
CIP connection management (Forward_Open / Forward_Close)
CIP I/O connections are established using the Forward_Open service and released with Forward_Close. Each connection carries a Connection ID and defines the Requested Packet Interval (RPI) for cyclic I/O data exchange.
TCP port 44818 (explicit) / UDP port 2222 (implicit I/O)
Explicit messaging uses TCP for reliable, ordered delivery. Implicit I/O uses UDP because it is cyclic and time-sensitive; the application tolerates occasional dropped packets better than TCP retransmission latency. UDP also supports multicast for one-to-many I/O.
IPv4 (standard Internet Protocol)
Standard IP routing. EtherNet/IP devices have standard IPv4 addresses, configurable via DHCP or static assignment, and are reachable through standard routers and switches. No proprietary network layer required.
IEEE 802.3 Ethernet (standard)
Standard Ethernet MAC and framing. Standard 10/100/1000 Mbps Ethernet infrastructure works without modification. Industrial deployments often use managed switches with IGMP snooping to control multicast I/O traffic scope.
Standard Ethernet cabling (Cat5e, Cat6, fiber)
Standard copper or fiber Ethernet. No special cables required. Industrial environments often use ruggedized M12 Ethernet connectors and DIN-rail mounted managed switches rated for the operating temperature and EMI environment of the plant floor.
The CIP object model
CIP is an object-oriented protocol. Every piece of data and every function in a CIP device is represented as an object. This model is the same across every EtherNet/IP device regardless of vendor, which is what enables a single driver to communicate with PLCs, drives, sensors, and robots from different manufacturers using the same underlying service structure.
The CIP object model uses three levels of addressing: classes, instances, and attributes.
Class: A category of objects sharing a common attribute set and service set. The Identity class (0x01), Assembly class (0x04), and Connection Manager class (0x06) are defined in the ODVA standard and implemented identically by every EtherNet/IP device.
Instance: A specific occurrence of a class. A device with four valve channels would have four instances of the valve class, one per channel. Instance 0 is reserved for class-level attributes that apply to all instances.
Attribute: A specific data item within an instance, accessed using CIP service codes such as Get_Attribute_Single (0x0E) to read or Set_Attribute_Single (0x10) to write.
CIP object addressing: class, instance, attribute across any EtherNet/IP device
Mandatory ODVA objects (present in every EtherNet/IP device):
Class 0x01/Instance 1/Attr 1Identity Object: Vendor ID
Class 0x01/Instance 1/Attr 7Product Name
Class 0x04/Instance 1/Attr 3Assembly: Input data
Class 0x06/Instance N/Attr 1Connection Manager
Vendor-specific and device-profile objects (vary by device type):
Get_Attribute_Single→Omron NJ: drive speedDrive class
Symbolic tag read→AB ControlLogix: FlowRateLogix tags
The EDS (Electronic Data Sheet) file is a text file provided by the device manufacturer that describes all the device-specific CIP objects, their classes, instances, attributes, data types, and valid ranges. Configuration tools and OPC servers use EDS files to understand vendor-specific parameter access without reverse-engineering the device. Standard ODVA objects (Identity, Assembly, Connection Manager) are defined in the specification and do not require an EDS file.
Explicit messaging and implicit messaging
CIP defines two fundamentally different communication models. Understanding which one applies to a given integration is essential for correct EtherNet/IP configuration.
Non-real-time, on-demand
Explicit messaging
| Transport | TCP (port 44818): reliable, ordered delivery |
| Pattern | Request / response. Each message includes source address, destination address, ConnectionID, CIP service code, and the object path (class / instance / attribute). |
| Data access | Any CIP attribute: configuration parameters, process variables, diagnostics, status, firmware info, recipe writes, device identification. |
| Timing | Triggered by the application on demand. Not periodic. The client controls when requests are sent. |
| Primary use | SCADA polling, OPC server tag reads, historian data collection, MES parameter queries, diagnostic tools, device configuration changes. |
| Roles | Client (initiates: OPC server, SCADA, HMI) / Server (responds: PLC, drive, sensor) |
Real-time, cyclic I/O
Implicit messaging (I/O)
| Transport | UDP (port 2222): low overhead, supports multicast for one-to-many I/O delivery |
| Pattern | Producer / consumer. A Forward_Open establishes the connection once; data then flows cyclically at the RPI without repeated addressing overhead per packet. |
| Data access | Assembly objects: pre-defined input/output data structures. The meaning of the data is fixed by the connection configuration, not encoded in each packet (hence "implicit"). |
| Timing | Cyclic (fixed RPI), change-of-state, or polled. RPI typically 1 ms to 500 ms. |
| Primary use | Controller-to-remote-I/O, controller-to-drive command/feedback, robot I/O, safety I/O, controller-to-controller produced/consumed tags. |
| Roles | Scanner (initiates connection: PLC, motion controller) / Adapter (responds: I/O module, drive, robot) |
SCADA and OPC servers use explicit messaging exclusively. When an OPC server or SCADA system reads data from an EtherNet/IP device, it uses explicit messaging over TCP. The device's implicit I/O connections (to its control network: remote I/O, drives, safety systems) continue unaffected. These are separate communication paths. Adding or removing an OPC server connection does not interact with the cyclic I/O connections that the device's control logic depends on.
The EtherNet/IP vendor ecosystem
EtherNet/IP is vendor-neutral by design. ODVA's conformance testing program ensures that any device bearing the EtherNet/IP logo implements CIP in a compatible way. The protocol is used across every major category of industrial device, from many different manufacturers.
Programmable controllers
PLCs and PACs
The largest category. EtherNet/IP is native to Rockwell/Allen-Bradley Logix and Micro800 families, Omron NJ/NX/CP/CJ series, Schneider Electric Modicon M340/M580, AutomationDirect Productivity series.
Rockwell, Omron, Schneider, AutomationDirect
Motion and drives
VFDs and servo drives
Drives from many manufacturers expose speed references, current feedback, fault status, and parameter access via EtherNet/IP. Assembly objects carry I/O data for the cyclic command/feedback loop.
Bosch Rexroth, Yaskawa, ABB, Danfoss
Robotics
Industrial robots
Robot controllers support EtherNet/IP as a primary I/O exchange mechanism with the cell PLC. Provides digital and analog I/O exchange as well as register/position data access.
Fanuc, KUKA, ABB, Yaskawa Motoman
Discrete I/O
Remote I/O and couplers
Distributed I/O systems that extend controller I/O over EtherNet/IP to remote locations. The PLC (scanner) polls the I/O modules (adapters) using implicit I/O connections.
Rockwell POINT I/O, WAGO, Turck, Beckhoff
Process instruments
Smart sensors and transmitters
Process instruments with native EtherNet/IP connectivity expose measurements, device status, and configuration via CIP. Common in food, beverage, and pharmaceutical.
Endress+Hauser, Keyence, Cognex, Banner
CNC and machining
CNC controllers
CNC controllers support EtherNet/IP for integration with cell PLCs and MES systems. TOP Server's Fanuc FOCAS driver addresses Fanuc CNC Ethernet connectivity.
Fanuc, Mitsubishi CNC, Okuma, Mazak
EtherNet/IP vs Modbus TCP
EtherNet/IP and Modbus TCP both run over standard Ethernet, but they differ fundamentally in capability and complexity. The right choice depends on the device types involved and the integration requirements.
| Dimension | EtherNet/IP (CIP) | Modbus TCP |
|---|
| Data model | Object-based. Classes, instances, and attributes carry data type and structure information. EDS files describe vendor-specific extensions. | Register-based. Flat coil and register address space. Type and meaning defined only by device manual. |
| Real-time I/O | Native implicit I/O messaging over UDP at configurable RPI. Producer/consumer model; UDP multicast. | No native push or cyclic mechanism. Clients must poll registers. No multicast. |
| Device discovery | EDS files, identity object for device identification, Logix tag database import. | No standard discovery mechanism. Register map from documentation. |
| Implementation | Higher complexity. CIP object model, connection management, device profiles. | Lower complexity. Simple register map, minimal configuration. |
How TOP Server connects to EtherNet/IP devices
TOP Server provides dedicated EtherNet/IP drivers organized by vendor and device family, plus general-purpose options for devices not covered by a named driver. All drivers use explicit messaging over TCP and do not require proprietary vendor communication middleware to be installed on the OPC server host.
Rockwell / AB
Allen-Bradley Suite (ControlLogix, CompactLogix, Micro800, legacy)
The most complete driver suite for Rockwell/Allen-Bradley hardware. The ControlLogix Ethernet driver connects to the full Logix family over EtherNet/IP/CIP, with automatic tag database generation from the connected controller or an exported .L5X file, no RSLinx license required, and up to 256 simultaneous device channels.
Omron
Omron Communications Suite
Connects to Omron PLCs including NJ, NX, CP, CJ, and CS series controllers over EtherNet/IP and the FINS protocol. Omron's NJ/NX series natively supports EtherNet/IP as both a scanner and adapter, and the TOP Server driver accesses Omron controller variables directly by name.
Fanuc CNCs
Fanuc FOCAS Ethernet driver
Connects to Fanuc CNC controllers over Ethernet using the Fanuc FOCAS (1 and 2) interface for machine data collection. Provides access to CNC program data, axis positions, tool offsets, alarm status, and production counters.
Multi-vendor
TOP Server EtherNet/IP driver (generic CIP)
For EtherNet/IP devices not covered by a named vendor driver, TOP Server includes a generic EtherNet/IP driver that accesses any ODVA-conformant device by class, instance, and attribute address with EDS file support for device-specific parameter mapping.
Edge to UNS
N3uron (EtherNet/IP to MQTT/Sparkplug B)
N3uron includes an EtherNet/IP client module that connects directly to EtherNet/IP devices without requiring TOP Server. For architectures where EtherNet/IP device data should be published to an MQTT broker using Sparkplug B for a Unified Namespace, N3uron handles the collection, ISA-95 data modeling, and publication pipeline.
Frequently asked questions
Is EtherNet/IP the same as regular Ethernet? Can I use my existing network switches?+−
EtherNet/IP uses standard IEEE 802.3 Ethernet at the physical and data link layers, so the same Cat5e, Cat6, or fiber cabling and standard managed or unmanaged switches that connect office computers will physically carry EtherNet/IP traffic. You do not need special industrial Ethernet switches specifically for EtherNet/IP compatibility.
However, for production environments, managed industrial switches are strongly recommended. Implicit I/O connections use UDP multicast; without IGMP snooping enabled on managed switches, multicast packets flood all switch ports rather than being delivered only to subscribing devices.
What is the Requested Packet Interval (RPI) and how is it configured?+−
The Requested Packet Interval (RPI) is the interval at which data is exchanged on an implicit I/O connection. It is configured when the connection is established using the Forward_Open service. For a PLC (scanner) connecting to a remote I/O module or drive (adapter), the RPI is set in the controller's I/O configuration, typically in the range of 2 ms to 20 ms for discrete I/O and 10 ms to 100 ms for analog I/O.
RPI is a property of implicit I/O connections only. For explicit messaging, the update rate is controlled by the polling interval configured in the OPC server or SCADA system, not by the EtherNet/IP connection.
What is an EDS file and do I always need one?+−
An Electronic Data Sheet (EDS) file is a text file provided by the device manufacturer that describes the CIP objects a specific device implements. Whether you need one depends on what you want to access. Every EtherNet/IP device must implement the mandatory ODVA objects (Identity, Assembly, Connection Manager, TCP/IP), and you can always read the Identity object and access Assembly objects without an EDS file. But to access vendor-specific parameters, you typically need the EDS file.
For Allen-Bradley ControlLogix and CompactLogix PLCs, TOP Server imports the tag database directly from the controller over CIP.
Can EtherNet/IP cross network segments through routers and firewalls?+−
Explicit messaging (TCP port 44818) crosses standard IP routers and firewalls without any special handling, exactly like any TCP application. You need to allow TCP port 44818 through a firewall to reach EtherNet/IP devices on the other side.
Implicit I/O messaging (UDP port 2222) is more complex. UDP multicast traffic does not cross standard IP routers unless multicast routing is configured. In practice, implicit I/O connections are typically kept within a single subnet, while explicit messaging from SCADA and OPC servers can reach devices across routed boundaries.
Does CIP routing work across different CIP network types?+−
Yes. One of CIP's key architectural features is seamless routing across different CIP network types. A device on EtherNet/IP can communicate with a device on DeviceNet or ControlNet by passing through an intermediate node that has connections to both networks.
For TOP Server users, this means the ControlLogix Ethernet driver can be configured to route through a ControlLogix chassis to reach legacy PLC-5 and SLC 500 controllers on DH+ networks (via a 1756-DHRIO module) or on ControlNet (via a 1756-CNB module), using the ControlLogix chassis as a CIP bridge.
How does EtherNet/IP compare to PROFINET?+−
EtherNet/IP and PROFINET are the two dominant industrial Ethernet protocols globally, with EtherNet/IP strongest in North America and PROFINET strongest in Europe and in Siemens-heavy installations worldwide. Both run over standard Ethernet hardware and use standard TCP/UDP transport, but they implement different application layers and device models that are not interoperable.
Key differences include the object model (CIP object/class/instance/attribute addressing in EtherNet/IP versus PROFINET's GSD/GSDML profile files and slot/subslot addressing), the I/O mechanism (CIP producer/consumer with Forward_Open versus PROFINET's AR/CR relationship model), and the vendor ecosystem (ODVA for EtherNet/IP versus PI International for PROFINET). TOP Server supports both.
Connecting to EtherNet/IP devices?
TOP Server provides EtherNet/IP drivers for PLCs, drives, CNCs, and sensors from across the ODVA vendor ecosystem. Talk to an engineer about connecting to your devices without proprietary communication middleware.
