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CIP

The Common Industrial Protocol (CIP) is an industrial application-layer protocol developed by ODVA that provides a common, object-oriented communication model for industrial automation devices. Unlike register-based protocols such as Modbus, CIP represents every device as a collection of objects, each containing attributes, services, and behaviours. CIP is the foundation of EtherNet/IP, DeviceNet, and ControlNet, allowing vendors to support multiple industrial networks without redesigning the application protocol.

Overview

The Common Industrial Protocol (CIP) is an industrial application protocol developed by ODVA that provides a common object-oriented communication model for industrial automation devices.

Unlike protocols such as Modbus, which simply read and write registers, CIP represents every device as a collection of objects, each containing attributes, services, and behaviours.

One of CIP's biggest advantages is that the same application protocol works across multiple physical networks, allowing different network technologies to communicate using identical services.

CIP is the foundation of:

• EtherNet/IP
• DeviceNet
• ControlNet
• CompoNet (legacy)

This allows vendors to support multiple industrial networks without redesigning the application protocol.

Why CIP Was Developed

Prior to CIP:

• Vendors created proprietary protocols.
• Different networks required different software.
• Devices were difficult to integrate.
• Limited interoperability existed.

CIP solved these issues by defining:

• Common device models
• Standard services
• Standard object classes
• Common messaging methods

As a result, PLCs, drives, sensors, robots, HMIs, and safety devices from different manufacturers can communicate consistently.

CIP Architecture

CIP separates communications into two layers:

Application
-----------------------
CIP
-----------------------
EtherNet/IP
DeviceNet
ControlNet
-----------------------
Physical Network

The lower network handles:

• cables
• routing
• switching
• timing

CIP handles:

• device information
• commands
• diagnostics
• alarms
• configuration
• motion
• safety

Object-Oriented Design

Everything inside a CIP device is represented as an Object.

A device consists of multiple object classes.

Example:

PLC

Identity Object
Connection Object
Assembly Object
TCP/IP Object
Ethernet Link Object
Message Router
Application Objects

Each object contains:

• Attributes (data)
• Services (functions)
• Behaviour

CIP Object Model

Every object contains:

Class

Defines the object type.

Example: Identity Object

Instance

A specific copy of the object.

Example:

Identity Object

Instance 1

Attributes

Data belonging to the object.

Example:

• Vendor ID
• Device Type
• Product Code
• Serial Number
• Revision
• Status

Services

Commands that operate on the object.

Examples:

• Read Attribute
• Write Attribute
• Reset
• Start
• Stop

Example Identity Object

Identity Object

Attributes

Vendor ID
Device Type
Product Code
Revision
Status
Serial Number
Product Name

Every CIP device contains an Identity Object.

This allows engineering software to automatically identify devices.

CIP Messaging Types

CIP defines two communication methods.

Explicit Messaging

Used for:

• Configuration
• Programming
• Diagnostics
• Reading parameters
• Writing parameters
• Status information

Characteristics:

• Request/Response
• Reliable
• TCP
• Non time-critical

Example:

PLC

Read Parameter

↓

Drive

Returns Parameter

Implicit Messaging

Used for:

• Real-time I/O
• Motion
• Safety
• Fast updates

Characteristics:

• Cyclic
• Scheduled
• UDP
• Low latency

Example:

PLC

Output Data →

Drive

Input Data →

This is how PLCs continuously exchange I/O data with field devices.

CIP Connection Model

Unlike Modbus polling, CIP creates logical connections.

Example:

PLC
   │
Connection
   │
Drive

Once established:

• Data transfers automatically.
• No repeated requests are required.
• Lower network overhead.
• Deterministic performance.

Producer-Consumer Model

One of CIP's major innovations is the Producer-Consumer Model.

Traditional polling:

PLC

Request

Device 1

Request

Device 2

Request

Device 3

Every device must be polled individually.

CIP:

Producer

↓

Network

↓

Consumer 1

Consumer 2

Consumer 3

The producer sends one packet.

Multiple devices receive it simultaneously.

Benefits:

• Lower bandwidth
• Faster communications
• Better scalability
• Lower PLC workload

CIP Services

Common services include:

Common CIP Objects

CIP Communication Path

Typical communication:

PLC

↓

EtherNet/IP

↓

TCP/IP

↓

Switch

↓

Drive

↓

Message Router

↓

Assembly Object

↓

Application

CIP over Different Networks

EtherNet/IP

Uses:

• TCP
• UDP
• IP
• Ethernet

Most common modern implementation.

DeviceNet

Uses:

• CAN Bus

Suitable for field devices.

ControlNet

Uses:

• Deterministic scheduled network.

Suitable for high-speed control.

CIP Motion

CIP Motion provides:

• Servo synchronization
• Motion control
• Electronic gearing
• Camming
• Coordinated multi-axis control

Widely used in packaging and robotics.

CIP Safety

CIP Safety extends standard CIP with:

• Redundant safety checks
• Time expectations
• CRC protection
• Safety sequence counters
• Diagnostic coverage

Allows safety traffic and standard traffic to coexist on the same network while remaining logically separated.

Applications include:

• Emergency stops
• Safety PLCs
• Safety drives
• Safety I/O

CIP Sync

CIP Sync is based on the Precision Time Protocol.

Provides:

• Microsecond clock synchronization
• Motion coordination
• Distributed clocks
• Timestamp accuracy

Required for:

• Motion control
• Robotics
• High-speed automation

CIP Security

CIP Security enhances communications by adding:

• Authentication
• Device identity verification
• Encryption
• Confidentiality
• Integrity protection
• Secure session establishment

Typically implemented using:

• Transport Layer Security for TCP communications
• Datagram Transport Layer Security for UDP communications
• Certificate-based authentication using X.509 certificates

Benefits:

• Prevents unauthorized devices joining the network
• Protects against message tampering
• Encrypts sensitive industrial communications
• Supports secure remote access

Advantages

• Vendor independent
• Object-oriented architecture
• Supports multiple physical networks
• Excellent interoperability
• High-speed cyclic communications
• Real-time I/O
• Motion support
• Functional safety support
• Time synchronization
• Strong diagnostics
• Scalable
• Widely adopted in industrial automation

Limitations

• More complex than Modbus
• Object model has a steeper learning curve
• Larger protocol overhead
• Configuration can be more involved
• Requires a solid understanding of connections and objects for troubleshooting

Relationship to EtherNet/IP

A common misconception is that CIP and EtherNet/IP are the same protocol.

In simple terms: CIP defines what industrial devices communicate, while EtherNet/IP defines how those CIP messages are transported across an Ethernet network.

Cybersecurity Considerations (IEC 62443)

CIP networks should be secured using a defence-in-depth strategy aligned with the principles of IEC 62443.

Key recommendations include:

• Segment industrial networks into security zones and conduits.
• Restrict CIP services using industrial firewalls and access control lists.
• Disable unused services and unnecessary object access.
• Use CIP Security where supported for authentication and encryption.
• Implement role-based access control for engineering workstations.
• Monitor explicit messaging for abnormal configuration changes.
• Inspect implicit messaging for unexpected traffic rates or destinations.
• Synchronise clocks (for example using CIP Sync) to support accurate event correlation.
• Continuously monitor networks with intrusion detection systems that understand industrial protocols.
• Maintain firmware and apply vendor security updates through a controlled change management process.

Typical Applications

• PLC to Remote I/O
• PLC to Variable Speed Drives (VSDs)
• PLC to Robots
• PLC to Safety Controllers
• PLC to HMIs
• PLC to SCADA
• Motion Control Systems
• Packaging Machines
• Automotive Manufacturing
• Food & Beverage Plants
• Mining Automation
• Oil & Gas Facilities
• Process Industries

Key Takeaways

• CIP is an application-layer industrial protocol that provides a common communication model across multiple industrial networks.
• It uses an object-oriented architecture with standardised classes, instances, attributes, and services.
• Two messaging types are used: Explicit Messaging for configuration and diagnostics, and Implicit Messaging for high-speed real-time I/O.
• The Producer-Consumer model improves efficiency by allowing one transmission to be consumed by multiple devices.
• EtherNet/IP is the most common transport for CIP, but the protocol also operates over DeviceNet and ControlNet.
• Extensions such as CIP Motion, CIP Safety, CIP Sync, and CIP Security add advanced capabilities for modern industrial automation.
• When deployed in OT environments, CIP should be protected using the layered security practices defined by IEC 62443 to reduce cyber risk and improve operational resilience.

Related Topics

• OSI Model
• Modbus
• Defence in Depth