An Introduction to
ETHERNET/IP
What is EtherNet/IP?
EtherNet/IP is an open industrial communication standard designed to deliver the Common Industrial Protocol (CIP) application layer over traditional IEEE802.3 Ethernet networks. By leveraging standard Internet Protocol (IP) alongside TCP and UDP transport layers, EtherNet/IP provides fast, practically deterministic and scalable communication across complex automation environments.
It has gained global acceptance because it utilizes the exact same physical infrastructure and software framework found in standard commercial IT applications and is supported by the world’s leading control manufacturers.
Ethernet vs. EtherNet/IP
Most people who work in an office associate the term “Ethernet” with the physical cable behind their desk that connects their office PC to a local printer, a corporate server, or the Internet. This cable is only the physical part of Ethernet. On that commercial wire sits a standard suite of office protocols like HTTP for web browsing or SMTP for email. These work well in office environments, but lack the mechanics required for machine automation.
EtherNet/IP is a specialized industrial application protocol that adapts standard Ethernet to meet the demands of the factory floor, like accessing data and communicating in real time (or very close to it).
| Feature/Demand | Standard Commercial Ethernet (Office IT) | Industrial EtherNet/IP (Factory Floor OT) |
|---|---|---|
| Primary Role | File sharing, internet access and corporate communication | Accessing real-time data embedded in drive systems, operator workstations and I/O blocks |
| Timing | Time-Insensitive: Users can wait for webpages or emails to load without consequence | Practical Determinism: Devices must operate in real-time (or very close to it) with sub-millisecond precision |
| Data Payload | Large, sporadic blocks of data | Small, continuous streams of data at high frequency |
| Network Infrastructure | Standard unmanaged switches, corporate routers and unshielded cabling | Industrial-grade managed switches, Layer 3 isolation routers and ruggedized shielded cabling |
Traditionally, Ethernet faced limited acceptance in industrial automation due to high hardware costs, a lack of intelligent switches and routers and the market dominance of proprietary vendor fieldbuses.
Today, the ubiquity of high-speed Ethernet hardware, powerful PCs and smart switching has made Ethernet the most common network standard for modern industrial automation.
The EtherNet/IP Stack: How EtherNet/IP Works
EtherNet/IP can be thought of as having multiple layers working together. Unlike proprietary industrial networks that invent their own hardware transport mechanisms (e.g., EtherCAT or PROFINET IRT), EtherNet/IP relies entirely on standard commercial Ethernet infrastructure.
While the ODVA documentation describes EtherNet/IP using the 7-layer OSI model, when applied to a practical, real-world EtherNet/IP architecture, the protocol stack collapses into the 4-layer TCP/IP model which will be used throughout this document. To understand why the automation world treats these frameworks differently, you can read our full breakdown on the differences between the OSI and TCP/IP models.
When applied to EtherNet/IP, the TCP/IP model breaks down as follows:
- CIP (Application layer)
- TCP/IP and UDP (Transport layer)
- IP (Internet layer)
- Network hardware (Network Access layer)
The Application Layer: An Overview of CIP
Common Industrial Protocol (CIP) is a network-independent, application-layer protocol that provides a suite of network functionality designed to establish unified data representation, connection management and messaging, enabling seamless interoperability between devices from multiple vendors.
CIP provides three core functions:
- Unified, Object-based Data Representation: Data and functions inside CIP devices are presented as objects with well-defined attributes, services and behaviors, enabling a single driver to communicate across entirely different devices.
- Connection Management: CIP establishes dedicated data pipelines between controllers and devices, predefining network parameters to ensure a predictable data flow and reliable fault detection.
- Vendor Interoperability: By utilizing standardized object data structures, system integrators can use CIP-enabled hardware from different manufacturers without the need for custom drivers.
Because CIP is completely media-independent, it serves as the universal upper-layer language for an entire family of networks:
- CIP on Ethernet technology = EtherNet/IP
- CIP on CAN technology = DeviceNet
- CIP on CTDMA technology = ControlNet
- CIP on TDMA technology = CompoNet
The Transport Layer: TCP/UDP Protocols and EtherNet/IP Ports
At the Transport layer, CIP messages are encapsulated into an Ethernet message and sent across the network using either Transmission Control Protocol (TCP) or User Datagram Protocol (UDP), utilizing specific registered destination port numbers.
Depending on the operational priority of the data, EtherNet/IP routes traffic across two distinct pathways:
- Explicit Messaging (TCP Port 44818): Used for non-time-critical data like configuration, troubleshooting and uploading programming logic. Because it uses TCP, it establishes a formal connection handshake and includes strict error checking to guarantee accurate delivery.
- Implicit Messaging (UDP Port 2222): Used to stream real-time, time-critical I/O data from field devices directly to controllers. By using UDP, the network bypasses the processing overhead of TCP, prioritizing raw speed and determinism over delivery verification.
The Internet Layer: Internet Protocol (IP)
The Internet layer is responsible for addressing and routing packets across the network. Because EtherNet/IP uses standard Internet Protocol (IP), it treats every industrial device like a standard network node.
However, routing must be carefully managed via routers and managed switches to maintain strict separation between factory floor control traffic and the rest of the enterprise network.
The Network Access Layer: Ethernet Frames, Hardware and Topologies
EtherNet/IP uses standard IEEE 802.3 Ethernet technology to define its physical media, frame format and media access rules. Using the TCP/IP model, this layer is comprised of the Data Link and Physical layers of the OSI model.
Data Link Layer
The Data Link layer is responsible for moving frames between devices across the local network. It relies on the Media Access Control (MAC) protocol to dictate how devices share the physical wire.
- MAC Addressing: Identifies the unique source node sending the frame and the destination node receiving the data.
- Multicast Addressing: Allows a single implicit I/O message to be sent to multiple destination nodes simultaneously.
- Full-duplex Ethernet: Allows networked devices to send and receive data at the same time, eliminating data collisions and providing the high throughput required for automation.
Physical Layer
Because the physical layer uses standard commercial Ethernet standards, EtherNet/IP networks can use standard commercial copper wire (Cat5e or later) or fiber optic cabling. To withstand harsh factory environments, EtherNet/IP deployments utilize ruggedized hardware including heavily shielded twisted pair cables or sealed connectors with an IP67 rating.
EtherNet/IP Network Topologies
EtherNet/IP networks can accommodate a virtually unlimited number of nodes and a variety of topologies:
- Star Topology: In a star topology, all network devices are individually connected to a central switch, which is then connected to a higher-level network access point. Star topology is one of the most prevalent topologies used in control networks.
- Linear Segments: Devices in linear networks feature embedded three-port switches, allowing engineers to wire Ethernet-enabled devices in a daisy chain, exactly like RS-485 serial networks.
- Ring Topology and Device Level Ring (DLR): In a ring topology, devices are daisy chained together in a ring, allowing messages to travel in either direction. Utilizing the Device Level Ring (DLR) protocol, EtherNet/IP networks can detect failures and quickly change to function as 2 linear segments.
- Hybrid Topology: Some manufacturers choose to combine two or more topologies within a single EtherNet/IP network, taking advantage of different technologies. However, this adds complexity and can be more difficult to maintain.
The 7 Things You Must Know About the EtherNet/IP Protocol
Your Guide to Understanding EtherNet/IP
People often ask, “What is EtherNet/IP?” or “Can you give me a quick introduction to the EtherNet communication protocol?” Here are the top 7 things you need to know about EtherNet/IP: (Note: David Letterman had his Top Ten, but I’m only 65% as good as David Letterman.)
- EtherNet/IP is an application layer protocol transmitted within a TCP/IP packet. Essentially, EtherNet/IP defines how data is organized inside a TCP or UDP packet. For information on what TCP or UDP is, get my Industrial Ethernet book.
- All devices on an EtherNet/IP network present their data as attributes grouped into objects.
- There are EtherNet/IP required objects – identity, TCP, router – that every device must have. The EtherNet/IP specification defines those objects.
- There are EtherNet/IP application objects that have the data for your specific device. For example, an EtherNet/IP drive device has a motor object. EtherNet/IP devices that support specific devices all have the same set of EtherNet/IP application objects.
- There are two types of messages exchanged between an EtherNet/IP scanner device (which opens connections and initiates data transfers) and EtherNet/IP adapter devices (which provide data to scanners). These are explicit messages (asynchronous and on-demand) and I/O messages (data messages that are continuously transferred).
- EtherNet/IP is part of the Common Industrial Protocol (CIP). CIP defines the object structure and specifies the message transfer. CIP protocol over CAN is DeviceNet. CIP protocol over Ethernet is EtherNet/IP.
- Our company, Real Time Automation (RTA), is the leading supplier of EtherNet/IP technology. RTA can supply royalty-free EtherNet/IP Source Code Stacks (for both scanners and adapters), EtherNet/IP PCBs and Modules.
EtherNet/IP
The EtherNet/IP standard (often shortened to E/IP or EIP) is the application layer protocol that can provide what the industry is looking for. Four independent groups have joined forces to develop and promote EIP as a public domain Ethernet application layer for industrial automation. These groups include ODVA, the Industrial Open Ethernet Association (IOANA), Control Net International (CI) and the Industrial Ethernet Association (IEA). The goal of their efforts is to illustrate how EIP provides a wide-ranging, comprehensive, certifiable standard suitable to a wide variety of automation devices.
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- Ethernet/IP uses the tools and technologies of traditional Ethernet. Ethernet/IP uses all the transport and control protocols used in traditional Ethernet including TCP, IP and the media access and signaling technologies found in off-the-shelf Ethernet interface cards. Building on these standard PC technologies means that EIP works transparently with all the standard off-the-shelf Ethernet devices found in today’s marketplace. It also means that EIP can be easily supported on standard PCs and all their derivatives. Even more importantly, basing EIP on a standard technology platform ensures that EIP will move forward as the base technologies evolve in the future.
- Ethernet/IP is a certifiable standard. The groups supporting EIP plan to ensure a comprehensive, consistent standard by careful, multi-vendor attention to the specification and through certified test labs as has been done with DeviceNet and ControlNet. Certification programs modeled after the programs for DeviceNet and ControlNet will ensure the consistency and quality of field devices.
- EIP is built on a widely accepted protocol layer. EIP is constructed from a very widely implemented standard used in DeviceNet and ControlNet called CIP (mentioned earlier) and is illustrated in the attached drawing. This standard organizes networked devices as a collection of objects. It defines the access, object behavior and extensions that allow widely disparate devices to be accessed using a common mechanism. Hundreds of vendors now support the CIP protocol in present-day products. Using this technology in EIP means that EIP is based on a widely understood, widely implemented standard that does not require a new technology shakedown period.
An Overview of CIP
The Common Industrial Protocol is a communications protocol for transferring automation data between two devices. In the CIP protocol, every network device represents itself as a series of objects. Each object is simply a grouping of the related data values in a device. CIP does not specify at all how this object data is implemented, only what data values or attributes must be supported and that these attributes must be available to other CIP devices.
There are three types of objects defined by the CIP protocol.
1. EtherNet/IP Required Objects
Required objects are required by the specification to be included in every CIP device. These objects include the identity object, a message router object and a network object.
A. The identity object contains related identity data values called attributes. Attributes for the identity object include the vendor ID, date of manufacturer, device serial number and other identity data.
B. The message router object is an object which routes explicit request messages from object to object in a device.
C. The network object contains the physical connection data for the object. For a CIP device on DeviceNet the network object contains the MacID and other data describing the interface to the CAN network. For EIP devices, the network object contains the IP address and other data describing the interface to the Ethernet port on the device.
Common CIP Objects |
|
| IDENTITY OBJECT CLASS 0x01 | REQUIRED OBJECT |
| The identify object provides the Identifying information for the CIP Node and includes the vendor ID, the product code, the software revision information, the serial number and the product name among other items. The identity object is a required object and there is usually only a single instance. | |
| MESSAGE ROUTER OBJECT CLASS 0x02 | REQUIRED OBJECT |
| The message router object provides a mechanism for external devices to access objects in a CIP device. Messages sent over Explicit connections are directed to the target object by the message router object.9 | |
| CONNECTION OBJECT CLASS 0x05 | REQUIRED OBJECT |
| The connection object is where the characteristics of a connection are maintained in a CIP device. An instance of the connection object is generated for every connection. That instance identifies the connection as explicit or implicit, sets the packet rate on implicit connections and holds other descriptive information on the connection. A connection object is removed when the connection is closed. | |
| ASSEMBLY OBJECT CLASS 0x04 | OPTIONAL |
| The assembly object provides the interface to CIP devices communicating with a device over an implicit connection. Instances of an assembly object organize the data exchanged with external devices. An input assembly instance manages data sent to external devices, while an output assembly instance handles data received from external devices. Multiple assembly instances can be defined, allowing an external device to select the specific instance (by instance ID) for data transfer. An explicit message-only device, however, does not have any assembly instances. | |
| PARAMETER OBJECT CLASS 0x0F | OPTIONAL |
| A parameter object provides a standard mechanism for a CIP device to make its configuration parameters publicly available to external devices. It provides complete identifying information for the configuration parameters of a CIP device. | |
| NETWORK SPECIFIC LINK OBJECT CLASS 0xNN | REQUIRED OBJECT |
| The network specific link object provides the information on the specific link (DeviceNet, EtherNet/IP, ControlNet) used to implement the CIP device. The object specifies attributes that describe the link, such as the node addresses and data rates. See the Chapter on EtherNet/IP operation over CIP for more details on the Link object for EtherNet/IP. | |
| APPLICATION OBJECT CLASS IDs 0x64 to 0Xc7 | OPTIONAL |
| Application objects organize the specific data and services of a device. Vendors building CIP devices can choose to implement no application objects, one application object with all the data for a device or any number of application objects. | |
2. Application Objects
Application objects are the objects that define the data encapsulated by the device. These objects are specific to the device type and function. For example, a motor object on a drive system has attributes describing the frequency, current rating and motor size. An analog input object on an I/O device has attributes that define the type, resolution and current value for the analog input.
These application layer objects are predefined for a large number of common device types. All CIP devices with the same device type (drive systems, motion control, valve transducer, etc.) must contain an identical series of application objects. The series of application objects for a particular device type is known as the device profile. A large number of profiles for many device types have been defined. Supporting a device profile allows a user to easily understand and switch from a vendor of one device type to another vendor with that same device type.
A device vendor can also group application layer objects into assembly objects. These super objects contain attributes of one or more application layer objects. Assembly objects form a convenient package for transporting data between devices. For example, a vendor of a temperature controller with multiple temperature loops may define assemblies for each of the temperature loops and an assembly with data from both temperature loops. The user can then pick the assembly that is most suited for the application and how often to access each assembly. For example, one temperature assembly may be configured to report every time it changes state while the second may be configured to report every one-second regardless of a change in state.
Assemblies are usually predefined by the vendor, but CIP also defines a mechanism in which the user can dynamically create an assembly from application layer object attributes.
3. Vendor Specific Objects
Objects not found in the profile for a device class are termed vendor specific. The vendor includes these objects as additional features of the device. The CIP protocol provides access to these vendor extension objects in exactly the same method as either application or required objects. The data is entirely determined by the vendor and organized in a way that suits their needs. Besides defining how device data is represented on the network, the CIP protocol outlines various methods for accessing this data, including cyclic, polled, and change-of-state access.
Advantages to EtherNet/IP
The advantages of the CIP protocol layer over Ethernet are numerous. Consistent device access means that a single configuration tool can configure CIP devices on different networks from a single access point without using vendor-specific software. Classifying all devices as objects reduces the training and startup time needed when new devices come online. EtherNet/IP provides improved response time and greater data throughput than DeviceNet and ControlNet. EtherNet/IP links devices from the sensor bus level to the control level to the enterprise level with a consistent application layer interface.
There are numerous application layer competitors to the EtherNet/IP protocol including Modbus/TCP from Groupe Schneider, Profinet from Siemens, and EtherCAT from Beckhoff. Unfortunately, space prevents a detailed review of each of these products. However, none of these competitors can provide the vendor support, flexibility and total architecture support offered by the implementation of CIP over Ethernet.
User Challenges of EtherNet/IP
EtherNet/IP protocol implementation is not without challenges. Two of the most important challenges to the first-time user include training and network configuration. One common problem is the lack of trained staff who understand both the IT fundamentals and the automation network. Successfully implementing the EtherNet/IP protocol requires a collaborative effort between IT and automation staff.
A second challenge is proper network configuration. Planning your Ethernet factory automation infrastructure is essential. Careful identification of all your control loops, choosing the correct routers, switches and paths and documenting your network properly are requisites for a communications network that meets your production goals and requires little ongoing maintenance.
Detractors of Ethernet applications on the factory floor often cite the lack of inherent determinism in Ethernet communications protocol to keep it out of automation applications. While true in the past, recent developments in intelligent switches have largely eliminated this argument. These switches create separate collision domains that offer the determinism required of almost all but the most demanding of automation applications.
