# EtherNet/IP

**EtherNet/IP** (Ethernet Industrial Protocol) is an industrial Ethernet network protocol that adapts the [Common Industrial Protocol](https://www.edgepedia.org/common-industrial-protocol) (CIP) to standard Ethernet and TCP/IP technologies for manufacturing and process automation communication. It was introduced in 2001 and is managed by ODVA, a standards development organization founded in 1995 whose members are industrial automation companies.<sup>[1](https://www.odva.org/publication_download/ethernet-ip-technology-overview/)</sup><sup> • </sup><sup>[2](https://www.odva.org/about/structure/)</sup> The "IP" in the name stands for "Industrial Protocol," not [Internet Protocol](https://www.edgepedia.org/internet-protocol).<sup>[3](https://literature.rockwellautomation.com/idc/groups/literature/documents/um/857-um005_-en-p.pdf)</sup>

| Key fact | Detail |
|---|---|
| Full name | Ethernet Industrial Protocol; "IP" refers to Industrial Protocol, not Internet Protocol<sup>[3](https://literature.rockwellautomation.com/idc/groups/literature/documents/um/857-um005_-en-p.pdf)</sup> |
| Introduced | 2001<sup>[1](https://www.odva.org/publication_download/ethernet-ip-technology-overview/)</sup> |
| Upper layers | Common Industrial Protocol (CIP), an object-oriented, media-independent protocol implemented at the OSI Session layer and above<sup>[1](https://www.odva.org/publication_download/ethernet-ip-technology-overview/)</sup> |
| Transport | Explicit messages over TCP/IP (TCP port 44818); implicit I/O messages over UDP/IP (UDP port 2222)<sup>[4](https://literature.rockwellautomation.com/idc/groups/literature/documents/um/842e-um001_-en-p.pdf)</sup><sup> • </sup><sup>[5](https://literature.rockwellautomation.com/idc/groups/literature/documents/td/enet-td022_-en-p.pdf)</sup> |
| Communication model | Producer-consumer: data identified by CIP Connection ID plus IP multicast group address, so one transmission serves many consumers<sup>[1](https://www.odva.org/publication_download/ethernet-ip-technology-overview/)</sup> |
| Device classes | Messaging Class, Adapter Class, and Scanner Class, based on communication capabilities<sup>[1](https://www.odva.org/publication_download/ethernet-ip-technology-overview/)</sup> |
| Governing body | ODVA (founded 1995), which publishes the specification and runs conformance and interoperability testing<sup>[2](https://www.odva.org/about/structure/)</sup> |
| Topologies | Star, linear, and Device Level Ring (DLR) single-fault-tolerant rings<sup>[6](https://www.odva.org/library_proceedings/high-availability-guidelines-for-use-of-dlr-in-ethernet-ip-networks/)</sup> |

## Architecture

EtherNet/IP follows the Open Systems Interconnection (OSI) seven-layer model. Like all CIP Networks, it implements CIP at the [Session layer](https://www.edgepedia.org/session-layer) and above and adapts CIP to Ethernet technology at the [Transport layer](https://www.edgepedia.org/transport-layer) and below. The Physical and Data Link layers use standard IEEE 802.3 Ethernet, and the Network and [Transport](https://www.edgepedia.org/transport) layers use the standard TCP/IP suite, so CIP messages are encapsulated inside ordinary Ethernet frames and pass through standard switches and routers.<sup>[1](https://www.odva.org/publication_download/ethernet-ip-technology-overview/)</sup>

This reliance on unmodified commercial Ethernet is a deliberate design principle. Ethernet's active infrastructure of Layer 2 and Layer 3 switches can accommodate a very large number of point-to-point nodes, unlike the passive infrastructures of many traditional industrial networks, and embedded switch technology extends it to linear and ring topologies.<sup>[1](https://www.odva.org/publication_download/ethernet-ip-technology-overview/)</sup> Facilities can use commercial off-the-shelf products or industrial-grade devices rated for harsh environments, with CAT 5E or later cabling recommended for noise immunity in manufacturing applications.<sup>[1](https://www.odva.org/publication_download/ethernet-ip-technology-overview/)</sup>

## Messaging: explicit and implicit

CIP defines two message types, and EtherNet/IP maps each to a different transport protocol.<sup>[1](https://www.odva.org/publication_download/ethernet-ip-technology-overview/)</sup>

**Explicit messages** carry request/reply, client-server style transactions for non-time-critical information such as configuration, diagnostics, and data collection. Each message describes its own meaning, which makes transmission less efficient but very flexible. Explicit messaging uses TCP/IP, whose connection-oriented, acknowledged delivery suits reliable transfer of both large and small data quantities.<sup>[1](https://www.odva.org/publication_download/ethernet-ip-technology-overview/)</sup><sup> • </sup><sup>[7](https://www.odva.org/wp-content/uploads/2020/05/PUB00213R0_EtherNetIP_Developers_Guide.pdf)</sup> A client initiates a TCP connection on port 44818 followed by a Connection Manager Forward_Open request to the server.<sup>[5](https://literature.rockwellautomation.com/idc/groups/literature/documents/td/enet-td022_-en-p.pdf)</sup>

**Implicit messages** carry time-critical I/O data at regular intervals. The two devices agree in advance on the data format, so the format is "implied" and interpretation is fast. Implicit connections use UDP/IP, typically on port 2222, because UDP's connectionless, low-overhead packets are small and support multicasting.<sup>[1](https://www.odva.org/publication_download/ethernet-ip-technology-overview/)</sup><sup> • </sup><sup>[4](https://literature.rockwellautomation.com/idc/groups/literature/documents/um/842e-um001_-en-p.pdf)</sup> Once an I/O connection is established there is no request/response cycle; data is produced and consumed at intervals set by the production trigger, which can be Cyclic (the most common), Change of State, or Application.<sup>[7](https://www.odva.org/wp-content/uploads/2020/05/PUB00213R0_EtherNetIP_Developers_Guide.pdf)</sup> The requested packet interval (RPI) parameter specifies the update rate for implicit data.<sup>[8](https://support.rockwellautomation.com/ci/okcsFattach/get/525866_4)</sup>

Connections are opened with the ForwardOpen service of the Connection Manager object and closed by a ForwardClose request or by a timeout at either endpoint.<sup>[7](https://www.odva.org/wp-content/uploads/2020/05/PUB00213R0_EtherNetIP_Developers_Guide.pdf)</sup> Unconnected messaging, handled by a device's Unconnected Message Manager (UCMM), is used for connection establishment and infrequent, low-priority explicit messages.<sup>[1](https://www.odva.org/publication_download/ethernet-ip-technology-overview/)</sup>

## Producer-consumer model

CIP's producer-consumer communication model uses network resources more efficiently than a pure source-destination model: a producing device transmits data once regardless of how many devices consume it, and all interested consumers receive the same data. In EtherNet/IP a produced message is identified by the combination of the CIP Connection ID and an [IP multicast](https://www.edgepedia.org/ip-multicast) group address rather than by a destination address.<sup>[1](https://www.odva.org/publication_download/ethernet-ip-technology-overview/)</sup><sup> • </sup><sup>[7](https://www.odva.org/wp-content/uploads/2020/05/PUB00213R0_EtherNetIP_Developers_Guide.pdf)</sup> The CIP Connection mechanism supplies timeout detection for data delivery problems on these transfers.<sup>[1](https://www.odva.org/publication_download/ethernet-ip-technology-overview/)</sup>

## Device classes

EtherNet/IP supports three device classes based on communication capability.<sup>[1](https://www.odva.org/publication_download/ethernet-ip-technology-overview/)</sup>

- **Messaging Class** products handle explicit messaging only; examples include HMI configuration tools, network diagnostic tools, and software applications that need no real-time I/O.
- **Adapter Class** products are targets of real-time I/O connection requests from scanners; examples include I/O blocks, drives, robots, and weigh scales. They do not originate I/O connections or store the connection parameters.<sup>[1](https://www.odva.org/publication_download/ethernet-ip-technology-overview/)</sup>
- **Scanner Class** products originate I/O data connections to adapters and other scanners; examples include PLCs, PC-based controls, and robot controllers.<sup>[1](https://www.odva.org/publication_download/ethernet-ip-technology-overview/)</sup>

Devices are configured using electronic data sheet (EDS) files, simple text files supplied by the manufacturer that describe a product's device type, revision, and configurable parameters so that configuration tools can identify and commission the device on the network.<sup>[9](https://www.rockwellautomation.com/en-mde/support/documentation/electronic-datasheets.html)</sup>

## Distinctive CIP services

Because EtherNet/IP shares CIP with [DeviceNet](https://www.edgepedia.org/devicenet), ControlNet, and [CompoNet](https://www.edgepedia.org/componet), it inherits a suite of application services spanning control, safety, security, energy, synchronization, motion, configuration, and information.<sup>[1](https://www.odva.org/publication_download/ethernet-ip-technology-overview/)</sup><sup> • </sup><sup>[10](https://www.odva.org/technology-standards/key-technologies/common-industrial-protocol-cip/)</sup>

**CIP Motion** delivers deterministic, closed-loop multi-axis motion control over standard, unmodified Ethernet. Ethernet's CSMA/CD data layer cannot by itself deliver the sub-microsecond jitter that precise speed and position control requires, so CIP Motion instead entrusts the end devices with the timing: clocks in the drives are tightly synchronized using CIP Sync, the IEEE 1588-compliant precision clock synchronization, and messages are time-stamped, so small variations in arrival time do not matter. [Clock synchronization](https://www.edgepedia.org/clock-synchronization) of better than 200 ns can be achieved, and the network needs no special switches or gateways.<sup>[11](https://www.odva.org/technology-standards/distinct-cip-services/cip-motion/)</sup>

**CIP Safety** extends safety communication to EtherNet/IP, encoding a Production Identifier in each safety packet to confirm that each message reaches the correct consumer, and using the Forward_Open connection mechanism to establish producer-consumer connections locally or across routed links.<sup>[12](https://www.odva.org/publication_download/cip-safety-safety-networking-for-today-and-beyond-pub-110/)</sup>

## Security

EtherNet/IP's use of standard TCP/IP gives it enterprise connectivity, which also makes it a target, and ODVA addresses this with CIP Security, a network extension that lets devices protect themselves from malicious communications. CIP Security provides integrity, authenticity, and authorization, and leverages the IETF-standard TLS (RFC 5246) protocol for TCP-based communications, including the encapsulation layer, UCMM, and transport class 3, and DTLS (RFC 6347) for the UDP-based transport class 0/1 communications.<sup>[13](https://www.odva.org/technology-standards/distinct-cip-services/cip-security/)</sup>

Secure transport attributes include device authentication using X.509 certificates or pre-shared keys, message integrity and authentication via the TLS message authentication code (HMAC), and optional message encryption negotiated during the TLS handshake. User authentication uses [OpenID Connect](https://www.edgepedia.org/openid-connect). Devices declare their capabilities through Security Profiles such as the EtherNet/IP Confidentiality Profile, the CIP User Authentication Profile, and a Resource-Constrained profile for limited devices; ODVA states that CIP Security can help users comply with [IEC 62443](https://www.edgepedia.org/iec-62443) and the EU Cyber Resilience Act.<sup>[13](https://www.odva.org/technology-standards/distinct-cip-services/cip-security/)</sup>

Beyond device-level security, industrial guidance recommends the usual defense-in-depth measures for networks carrying EtherNet/IP: segmenting control networks from business networks, using DMZs and VLANs, restricting internet exposure of control system devices, and applying patch management adapted to ICS operational constraints.<sup>[14](https://www.cisa.gov/sites/default/files/2023-01/NCCIC_ICS-CERT_Defense_in_Depth_2016_S508C.pdf)</sup><sup> • </sup><sup>[15](https://www.cisa.gov/ncas/alerts/aa22-083a)</sup>

## Specification and conformance

The EtherNet/IP specification is part of ODVA's CIP Networks Library; the EtherNet/IP Adaptation of CIP is Volume 2 of that library.<sup>[16](https://www.odva.org/subscriptions-services/specifications/)</sup> Vendors must sign ODVA's license agreement, obtain a Vendor ID, and subscribe to the specification to build EtherNet/IP products.<sup>[2](https://www.odva.org/about/structure/)</sup> ODVA operates conformance testing and a PlugFest event in which devices are tested against the EtherNet/IP Interoperability Test Procedures (Pub 95), covering EDS verification, network and I/O interoperability, device performance measures such as the fastest supported cyclic production rate and jitter, and optional tests for DLR, CIP Security, and CIP Safety.<sup>[17](https://www.odva.org/subscriptions-services/learning-tools/plugfest/)</sup> Conformance testing is also available for EtherNet/IP devices communicating over the Ethernet-APL physical layer for process automation, announced by ODVA in November 2022.<sup>[18](https://www.odva.org/news/odva-conformance-testing-available-for-ethernet-ip-devices-on-the-ethernet-apl-physical-layer-for-process-automation/)</sup>

## References

1. [EtherNet/IP Technology Overview (Pub 138), ODVA](https://www.odva.org/publication_download/ethernet-ip-technology-overview/)
2. [About ODVA, ODVA](https://www.odva.org/about/structure/)
3. [EtherNet/IP Configuration Details for 857/865 Protection System User Manual, Rockwell Automation](https://literature.rockwellautomation.com/idc/groups/literature/documents/um/857-um005_-en-p.pdf)
4. [EtherNet/IP Absolute Encoder User Manual (842E-UM001), Rockwell Automation](https://literature.rockwellautomation.com/idc/groups/literature/documents/um/842e-um001_-en-p.pdf)
5. [Deploying CIP Security within a Converged Plantwide Ethernet Architecture (ENET-TD022), Rockwell Automation](https://literature.rockwellautomation.com/idc/groups/literature/documents/td/enet-td022_-en-p.pdf)
6. [High Availability: Guidelines for Use of DLR in EtherNet/IP Networks, ODVA](https://www.odva.org/library_proceedings/high-availability-guidelines-for-use-of-dlr-in-ethernet-ip-networks/)
7. [EtherNet/IP Quick Start for Vendors Handbook (PUB213R0), ODVA](https://www.odva.org/wp-content/uploads/2020/05/PUB00213R0_EtherNetIP_Developers_Guide.pdf)
8. [EtherNet/IP Implicit vs. Explicit Messaging White Paper, ProSoft Technology / Rockwell Automation](https://support.rockwellautomation.com/ci/okcsFattach/get/525866_4)
9. [Electronic Data Sheets, Rockwell Automation](https://www.rockwellautomation.com/en-mde/support/documentation/electronic-datasheets.html)
10. [Common Industrial Protocol (CIP), ODVA](https://www.odva.org/technology-standards/key-technologies/common-industrial-protocol-cip/)
11. [CIP Motion, ODVA](https://www.odva.org/technology-standards/distinct-cip-services/cip-motion/)
12. [CIP Safety: Safety Networking for Today and Beyond (Pub 110), ODVA](https://www.odva.org/publication_download/cip-safety-safety-networking-for-today-and-beyond-pub-110/)
13. [CIP Security, ODVA](https://www.odva.org/technology-standards/distinct-cip-services/cip-security/)
14. [Recommended Practice: Improving Industrial Control System Cybersecurity with Defense-in-Depth Strategies, CISA](https://www.cisa.gov/sites/default/files/2023-01/NCCIC_ICS-CERT_Defense_in_Depth_2016_S508C.pdf)
15. [Tactics, Techniques, and Procedures of Indicted State-Sponsored Russian Cyber Actors Targeting the Energy Sector (AA22-083A), CISA](https://www.cisa.gov/ncas/alerts/aa22-083a)
16. [Network Specifications, ODVA](https://www.odva.org/subscriptions-services/specifications/)
17. [PlugFest, ODVA](https://www.odva.org/subscriptions-services/learning-tools/plugfest/)
18. [ODVA Conformance Testing Available for EtherNet/IP Devices on the Ethernet-APL Physical Layer, ODVA](https://www.odva.org/news/odva-conformance-testing-available-for-ethernet-ip-devices-on-the-ethernet-apl-physical-layer-for-process-automation/)

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*Topic: Encyclopedia › Technology and the built world › Computing and digital systems › Networks and security › Ethernet › Carrier and specialized Ethernet › EtherNet/IP*

*Initially written Sep 17, 2026 · Reviewed: Sep 17, 2026; Oct 15, 2026 · Edited: Oct 15, 2026 · Last review: Oct 15, 2026*

*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*

License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license