Network Infrastructure
for EtherNet/IPTM:
Introduction andConsiderations

Network Infrastructure for EtherNet/IP™
Publication Number: PUB00035R0
Copyright © 2007 Open DeviceNet Vendor Association, Inc. (ODVA). All rights reserved. For
permission to reproduce excerpts of this material with appropriate attribution to the author, please contact
ODVA at:
ODVA, Inc.
4220 Varsity Drive, Suite A
Ann Arbor, MI 48108-5006 USA
Phone +1 734.975.8840
Fax +1 734.922.0027
E-mail odva@odva.org
Web www.odva.org
The right to make, use, or sell product or system implementations described herein is granted only under
separate license pursuant to a Terms of Usage Agreement or other agreement. Terms of Usage
Agreements for individual CIP Networks are available, at standard charges, over the Internet at thefollowing web sites:www.odva.org Terms of Usage Agreements for DeviceNet, CompoNet, and EtherNet/IP along withgeneral information on DeviceNet, CompoNet, and EtherNet/IP networks and their extensions, and theassociation of ODVA.
www.controlnet.org Terms of Usage Agreement for ControlNet along with general information on
ControlNet and ControlNet International.
NOTE: Because the technologies described herein may be applied in many diverse situations and in
conjunction with products and systems from multiple vendors, the user and those responsible for
specifying these technologies must determine for themselves their suitability for the intended use. ALL
INFORMATION PROVIDED BY ODVA IS PROVIDED ON AN “AS IS” BASIS. NO
WARRANTIES, EXPRESSED OR IMPLIED, INCLUDING WITHOUT LIMITATION ANYWARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, ARE
BEING PROVIDED BY THE PUBLISHER OR ODVA. The figures and examples in this guide aredesigned to demonstrate general concepts for planning and installing a network. The user should always
verify interconnection requirements to and from other equipment, and confirm installation andmaintenance requirements for their specific application. IN NO EVENT SHALL THE PUBLISHER ORODVA, THEIR OFFICERS, DIRECTORS, MEMBERS, AGENTS, LICENSORS, OR AFFILIATES BE
LIABLE TO YOU, ANY CUSTOMER, OR THIRD PARTY FOR ANY DAMAGES, DIRECT OR
INDIRECT, INCLUDING BUT NOT LIMITED TO LOST PROFITS, DEVELOPMENT EXPENSES,OR ANY OTHER DIRECT, INDIRECT, INCIDENTAL, SPECIAL, OR CONSEQUENTIAL
DAMAGES.
CIP™, Common Industrial Protocol™, EtherNet/IP CONFORMANCE TESTED™, and DeviceNet™ are
trademarks of ODVA, Inc.
EtherNet/IP™ is a trademark used under license by ODVA.
All other trademarks are the property of their respective owners.
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Note from the Publisher
The application of Ethernet and Internet technologies is permeating every aspect of manufacturing
automation today—control, safety, configuration and diagnostics, synchronization and motion, andinformation. To realize the benefits of these technologies, the network infrastructure is critical andrepresents a long-term investment for users that requires thorough analysis of performance requirements
along with technology choices and trends.
Network Infrastructure for EtherNet/IP™ provides an introduction to the network infrastructure used in
EtherNet/IP networks and gives users a framework for identifying the considerations that are most criticalto their specific applications. It represents the combined knowledge of experts from companies that areleading the industry in the application of Ethernet on the factory floor. ODVA wishes to recognize themany hours of hard work provided by people from these contributing companies:
•
•
•
•
•
•
•
•
•
•
•
•
•

BeldenCisco Systems
Contemporary Controls
General Motors
HARTING
Hirschmann
Kendall Electric
McNaughton-McKay Electric Company
Phoenix Contact
Rockwell Automation
RuggedCom
The Siemon Company
WAGO

To learn more about EtherNet/IP, visit the ODVA web site at www.odva.org where you’ll find many
more resources to help you apply the world’s leading Ethernet network for manufacturing automation.
Sincerely,

Katherine Voss
Executive Director
ODVA

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Contents
Preface.......................................................................................................................................................viii
1

INDUSTRIAL ETHERNET… NOT JUST ANOTHER FIELDBUS ........................................1-1
1.1
Industrial Networks ................................................................................................................................... 1-1
1.2
Introduction to EtherNet/IP ....................................................................................................................... 1-1
1.2.1
Industrial Ethernet and Traditional Fieldbuses.................................................................................... 1-3
1.2.2
Infrastructure for EtherNet/IP Applications ........................................................................................ 1-4
1.2.3
Security Issues..................................................................................................................................... 1-4

2

UNDERSTANDING THE BASICS OF NETWORK PROTOCOLS ........................................2-5
2.1
2.2
2.3

3

The TCP/IP Suite....................................................................................................................................... 2-6
User Datagram Protocol............................................................................................................................. 2-9
Data Exchange Models ............................................................................................................................ 2-10

PLANNING THE INFRASTRUCTURE....................................................................................3-12
3.1
Segmentation vs. Trunk-and-Drop........................................................................................................... 3-12
3.1.1
Implications of Multiple and Higher Data Rates............................................................................... 3-13
3.1.2
Frame Size......................................................................................................................................... 3-13
3.1.3
Implications of Multiple Protocols .................................................................................................... 3-13
3.2
Ethernet System Components.................................................................................................................. 3-14
3.2.1
Ethernet Hubs.................................................................................................................................... 3-14
3.2.2
Ethernet Switches .............................................................................................................................. 3-14
3.2.3
Switches: Key System Elements ....................................................................................................... 3-15
3.2.4
How Switches Add Flexibility .......................................................................................................... 3-15
3.2.5
Media Converters .............................................................................................................................. 3-16
3.2.6
Routers .............................................................................................................................................. 3-16
3.3
Ethernet Cabling Systems........................................................................................................................ 3-17
3.3.1
Star Topology: The Standard Approach............................................................................................ 3-17
3.3.2
Implementation of Mixed Cable Systems ......................................................................................... 3-17
3.3.3
Applicable IEEE Standards for Twisted-pair Ethernet...................................................................... 3-17
3.3.3.1 Unshielded Category 5e Cable ....................................................................................................... 3-17
3.3.3.2 Shielded Category 5e Cable ........................................................................................................... 3-18
3.3.3.3 Connectors and Pre-terminated Cables........................................................................................... 3-18
3.3.3.4 Crossover vs. Straight-through Cables ........................................................................................... 3-18
3.3.3.5 Other Options ................................................................................................................................. 3-19
3.3.3.6 Future Options................................................................................................................................ 3-19
3.3.4
Applicable IEEE Standards for Fiber-Optic Ethernet........................................................................ 3-19
3.3.4.1 Glass Fiber Cable ........................................................................................................................... 3-19
3.3.4.2 Plastic Fiber Cable.......................................................................................................................... 3-20
3.3.4.3 More Cabling Resources ................................................................................................................ 3-20
3.3.5
Wireless Ethernet .............................................................................................................................. 3-20
3.4
Ethernet Data Connections ...................................................................................................................... 3-20
3.4.1
IP Addressing of Industrial Ethernet Devices ................................................................................... 3-21
3.4.2
Important Ethernet Tools and Protocols ............................................................................................ 3-21
3.5
Diagnostics via Infrastructure Components............................................................................................. 3-22
3.5.1
Simple Network Management Protocol ............................................................................................ 3-22
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3.5.2
Traps.................................................................................................................................................. 3-22
3.5.3
Network Management and Web-based Management Software......................................................... 3-23
3.6
Isolated vs. Integrated Networks ............................................................................................................. 3-23
3.6.1
Security Issues................................................................................................................................... 3-24
3.6.1.1 Firewalls ......................................................................................................................................... 3-24
3.6.1.2 Routers and Switches ..................................................................................................................... 3-24
3.7
Traffic Management with VLANs........................................................................................................... 3-24
3.7.1
How VLANs Work ........................................................................................................................... 3-24
3.7.2
VLAN Benefits ................................................................................................................................. 3-25
3.8
Topologies to Provide Ethernet Network Redundancy............................................................................ 3-25
3.8.1
IEEE Standard Network Redundancy Options.................................................................................. 3-26
3.8.1.1 Spanning Tree Protocol Method..................................................................................................... 3-26
3.8.1.2 Link Aggregation ........................................................................................................................... 3-27
3.8.2
Ring Redundancy .............................................................................................................................. 3-27
3.8.3
Dual Homing ..................................................................................................................................... 3-28

4

DESIGNING THE INFRASTRUCTURE ..................................................................................4-29
4.1
Network Design Method.......................................................................................................................... 4-29
4.1.1
Design Steps for Isolated EtherNet/IP Networks .............................................................................. 4-29
4.1.2
Definition of Application Requirements ........................................................................................... 4-30
4.1.3
Logical Network Design ................................................................................................................... 4-31
4.1.4
Physical Network Design .................................................................................................................. 4-31
4.2
Non-Isolated EtherNet/IP Networks ........................................................................................................ 4-32
4.2.1
Definition of Application Requirements ........................................................................................... 4-32
4.2.2
Logical Network Design ................................................................................................................... 4-33
4.2.3
Physical Network Design .................................................................................................................. 4-34
4.2.4
Design Verification ........................................................................................................................... 4-34
4.2.5
Summary of Key Points on EtherNet/IP Design ............................................................................... 4-34
4.3
EtherNet/IP Infrastructure Design Issues................................................................................................. 4-35
4.3.1
Full-Duplex vs. Half-Duplex Implications ........................................................................................ 4-35
4.4
Layout and Wiring Considerations .......................................................................................................... 4-36
4.4.1
Length of Run and Category of Cable............................................................................................... 4-36
4.4.2
Cable Routing.................................................................................................................................... 4-38
4.4.3
Categories of Conductors/Wiring...................................................................................................... 4-38
4.4.4
General Design Wiring Guidelines.................................................................................................... 4-38
4.4.5
Wiring External to Enclosures........................................................................................................... 4-39
4.4.6
Wiring Inside Enclosures .................................................................................................................. 4-40
4.4.7
Cable Grounding Considerations ...................................................................................................... 4-40
4.5
Industrial Ethernet Connectors ................................................................................................................ 4-42
4.5.1
Attributes of Industrial Ethernet Cables ............................................................................................ 4-42
4.5.1.1 Oil-resistant Jackets........................................................................................................................ 4-42
4.5.1.2 Plenum-rated Cables....................................................................................................................... 4-43
4.5.1.3 Weld Splatter-Proof Cables............................................................................................................ 4-43
4.5.1.4 High Flex........................................................................................................................................ 4-43
4.5.1.5 Ambient Temperature..................................................................................................................... 4-43
4.6
Performance Considerations: The Need for Switches ............................................................................. 4-43
4.6.1
Performance of Switches................................................................................................................... 4-43
4.7
Switching Technologies........................................................................................................................... 4-44
4.8
IGMP Snooping ....................................................................................................................................... 4-45
4.8.1
Joining a Multicast Group ................................................................................................................. 4-47
4.8.2
Leaving a Multicast Group................................................................................................................ 4-48
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4.8.3
Immediate-Leave Processing............................................................................................................. 4-48
4.9
Quality of Service in a Switched Network............................................................................................... 4-49
4.9.1
QoS Flow........................................................................................................................................... 4-50
4.9.2
Class of Service ................................................................................................................................. 4-50
4.9.3
Priority Mechanisms.......................................................................................................................... 4-51
4.10 Virtual Local Area Networks................................................................................................................... 4-52
4.10.1 VLAN Trunking ................................................................................................................................ 4-53
4.11 Multilayer Ethernet Switches................................................................................................................... 4-54
4.11.1 Layer 2 and Layer 3 Switching ......................................................................................................... 4-54
4.12 Achieving Deterministic Behavior .......................................................................................................... 4-56
4.13 Managing the Interface between Control and IT ..................................................................................... 4-56

5

DEPLOYING THE NETWORK .................................................................................................5-58
5.1
Validating the Integrity of the Physical Layer ......................................................................................... 5-58
5.1.1
Link and Other Diagnostic LEDs ...................................................................................................... 5-59
5.1.2
Ping Checks for TCP/IP Continuity .................................................................................................. 5-60
5.1.3
Switch Configuration and Management ............................................................................................ 5-61
5.2
Putting Traffic on the Network................................................................................................................ 5-62
5.2.1
Characterization of EtherNet/IP Traffic ............................................................................................ 5-62
5.2.2
IP Addressing in EtherNet/IP Networks............................................................................................ 5-63
5.2.2.1 IP Addressing Example .................................................................................................................. 5-63
5.2.3
IP Multicast Traffic in EtherNet/IP Networks................................................................................... 5-64
5.3
Deployment Summary ............................................................................................................................. 5-64

6

INFRASTRUCTURE APPLICATION SCENARIOS ..............................................................6-65
6.1
General Application Considerations ........................................................................................................ 6-66
6.1.1
Multicast Traffic Management within a Control System .................................................................. 6-66
6.1.2
Control Device Sensitivity to Extraneous Traffic ............................................................................. 6-66
6.1.2.1 Potential for Traffic Overload ........................................................................................................ 6-66
6.1.2.2 Varying Sensitivity by Device Type .............................................................................................. 6-67
6.1.3
Configurable Isolation of Enterprise and Control Traffic ................................................................. 6-67
6.2
Isolated Control Network with a Single Controller ................................................................................. 6-67
6.2.1
Systems with Low Device Counts..................................................................................................... 6-68
6.2.1.1 Use of Unmanaged Switches.......................................................................................................... 6-68
6.2.2
Systems with High I/O Count............................................................................................................ 6-71
6.3
Isolated Network with Multiple Controllers ............................................................................................ 6-74
6.3.1
Multiple Single-Controller Systems without Data Sharing ............................................................... 6-74
6.3.2
Multiple Single-Controller Systems with Data Sharing .................................................................... 6-75
6.3.3
Isolated Systems Summary................................................................................................................ 6-75
6.4
Enterprise-Connected and Integrated Control Systems ........................................................................... 6-76
6.4.1
Networks Connected via CIP Gateways............................................................................................ 6-76
6.4.2
Networks Integrated with Routers (or Layer 3 Switches) ................................................................. 6-77
6.4.3
Two Types of Integration .................................................................................................................. 6-77
6.4.3.1 Non-Interlock Connections ............................................................................................................ 6-77
6.4.3.2 Interlock Connections..................................................................................................................... 6-78
6.5
Application Summary.............................................................................................................................. 6-79

7

SELECTING COMPONENTS ....................................................................................................7-80
7.1
Sealed Connectors: Key to Successful Operation.................................................................................... 7-80
7.1.1
Approved Sealed Version of RJ-45 Connectors................................................................................ 7-80
7.1.2
M12 “D”-Coded Connector for EtherNet/IP ..................................................................................... 7-82
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7.1.3
Fiber-Optic Connectors ..................................................................................................................... 7-82
7.2
Cabling Considerations: Twisted-Pair vs. Fiber-Optic Cable.................................................................. 7-83
7.2.1
When to Use Shielded Twisted-Pair Cabling .................................................................................... 7-83
7.2.2
Terminating Copper Cable ................................................................................................................ 7-84
7.2.3
When to Use Fiber-Optic Cabling ..................................................................................................... 7-85
7.2.4
Types of Optical Fiber....................................................................................................................... 7-85
7.2.5
Bend Radius / Pull Force of Fiber ..................................................................................................... 7-85
7.2.6
Terminating Fiber-Optic Cable ......................................................................................................... 7-86
7.3
Key Switch Selection Issues .................................................................................................................... 7-86
7.3.1
Address Table Size Limits Control Device Quantity ........................................................................ 7-87
7.3.2
Auto-negotiation vs. Manual Setting of Switched Port Data Rates................................................... 7-87
7.3.3
Multicast Messaging Handling Option.............................................................................................. 7-87
7.3.4
Quality of Service Options ................................................................................................................ 7-87
7.3.5
Security Options ................................................................................................................................ 7-87
7.3.6
Broadcast or Multicast Threshold Filters .......................................................................................... 7-88
7.3.7
Additional Functions ......................................................................................................................... 7-88
7.4
Distributed Enclosures and Environmental Considerations..................................................................... 7-88
7.4.1
Environmental Specification Considerations .................................................................................... 7-88
7.4.2
Temperature ...................................................................................................................................... 7-88
7.4.3
Electrical noise .................................................................................................................................. 7-89
7.4.4
Shock and Vibration.......................................................................................................................... 7-89
7.4.4.1 Certifications .................................................................................................................................. 7-89

Appendix A

Recommendations for Ethernet Switches in EtherNet/IP Systems ...........................A-1

Personnel for System Start-Up and Maintenance .................................................................................................. A-1
Isolated Systems: Small Scale ............................................................................................................................... A-2
Isolated Systems: General Use .............................................................................................................................. A-2
Large-scale Control and Enterprise Networking ................................................................................................... A-4
Summary ............................................................................................................................................................... A-7

Appendix B

Overview of the OSI Model, EtherNet/IP and CIP ..................................................... B-1

Characteristics of the OSI Layers...........................................................................................................................B-1
Communication between Systems..........................................................................................................................B-2
OSI Layer Services..............................................................................................................................................B-3
OSI Model Layers and Information Exchange .......................................................................................................B-3
Information Exchange Process............................................................................................................................B-4
Physical Layer.....................................................................................................................................................B-5
Data Link Layer ..................................................................................................................................................B-5
Network Layer ....................................................................................................................................................B-6
Transport Layer...................................................................................................................................................B-6

Appendix C

EtherNet/IP and International Standards ...................................................................C-1

Internet and Ethernet Standards..............................................................................................................................C-1
Protocols and Profiles.............................................................................................................................................C-1
Electronic Data Sheets (EDS).................................................................................................................................C-2

Appendix D
Appendix E

Glossary of Terms ..........................................................................................................D-1
Ingress Protection (IP) Codes........................................................................................ E-1

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Preface
About This Publication

Advances in Ethernet technology and reduced component costs are fueling the growth of Ethernet in plant
floor networks. EtherNet/IP™, the adaptation of the Common Industrial Protocol™ (CIP™) provides
users with the tools to deploy standard Ethernet technology for manufacturing applications while enabling
Internet and enterprise connectivity… anytime, anywhere. The unique performance and environmental
requirements of manufacturing applications require users to select appropriate network infrastructure.
This publication provides an overview of the technologies used to deploy EtherNet/IP and provides
guidelines for deploying infrastructure devices in EtherNet/IP networks.
Related Publications

For more information on how to plan for, design, implement, and maintain networks incorporating
EtherNet/IP, refer to the current versions of the following publications:•

ODVA, The EtherNet/IP™ Specification•

ODVA, EtherNet/IP™ Media Planning and Installation Guide•

IAONA, Industrial Ethernet Planning and Installation Guide•

IEEE 802®, IEEE Standard for Information Technology –Telecommunications andInformation Exchange between Systems – Local and Metropolitan Area Networks

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1 Industrial Ethernet… Not Just AnotherFieldbus
Using the Common Industrial Protocol (CIP™), EtherNet/IP provides the backbone for acompletely open, vendor-neutral communication network for the full range ofmanufacturing applications, and can integrate these applications with one another andthe enterprise. Unlike traditional fieldbuses, EtherNet/IP has an active infrastructure thatuses the standard Ethernet physical layer and standard Ethernet and Internet protocols.
This chapter provides the background to understand the application of industrial
networks and their special needs along with an introduction to the unique aspects ofdeploying Ethernet networks.

1.1 Industrial Networks
Industrial communication networks have been deployed on the factory floor since the 1980s. Initiallyused as remote input/output (I/O) and controller-level networks, they now interconnect a wide range ofindustrial automation devices, from sensors and actuators, to controllers, human-machine interface (HMI)
workstations, and computers. Today, these networks are capable of supporting real-time control as well as
plant-floor information systems.
The characteristics of industrial networks differ from commercial or residential networks in two ways:
1.

They provide the additional real-time performance capabilities needed for a majority of
manufacturing applications.

2.

They meet the requirements for survival in various types of industrial environments, normallycharacterized by higher levels of electrical noise, shock, vibrations, ambient temperature,humidity, etc.

1.2 Introduction to EtherNet/IP
By the early 1990s, Ethernet networks were used successfully in manufacturing environments, mainly in
non-time-critical applications. The evolution of the Ethernet technology from a 10-Mbps, half-duplex,
bus/tree topology to a 100-Mbps and 1-Gbps, full-duplex, switch/router-based star topology has paved theway for using Ethernet to support time-critical applications in industrial networks.
EtherNet/IP is a communication network designed for use in industrial environments and time-criticalapplications. Using the Common Industrial Protocol™ (CIP™), it has many unique features that give it
advantages over other Ethernet-based industrial networks.

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Industrial Ethernet… Not Just Another Fieldbus

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EtherNet/IP:•

offers producer-consumer services that enable users to control, configure, and collect datafrom over a single network or to use the network as a backbone for multiple distributed
networks.

•

provides robust physical layer options for industrial environments and includes the use of
sealed RJ-45 and M12-4 “D” Coded connectors.

•

uses existing Institute of Electrical and Electronics Engineers (IEEE) standards for
Ethernet physical and data link layers.

•provides flexible installation options leveraging commercially available industrial
infrastructure products, including copper, fiber, fiber ring, and wireless solutions.

•

incorporates the TCP/IP suite—the Ethernet standard.

•is compatible with accepted communication standards, including OPC1 and Internet
protocols such as Hypertext Transfer Protocol (HTTP), Simple Network Management
Protocol (SNMP), File Transfer Protocol (FTP), and Dynamic Host Configuration
Protocol (DHCP).

It is useful to understand the architecture of EtherNet/IP in terms of the seven-layer Open System
Interconnection (OSI) Reference Model developed by the International Organization forStandardization (ISO) as shown in Figure 1-1. Appendix B provides an introduction to the ISO OSI Modelwith references to appropriate standards.

Figure 1-1

How EtherNet/IP Relates to the OSI Model.

In EtherNet/IP and all CIP Networks, exchange of time-critical data is based on the producer-consumer
messaging model whereby a transmitting device produces data on the network, and one or more

1

Information on the OPC Foundation and its open specifications can be found at www.opcfoundation.org.
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receiving devices can consume this data simultaneously. Implementation of this model in CIP is
supported by the Internet Protocol (IP) multicast service which, in its turn, is supported by the Ethernet
multicast service. The primary benefit of a producer-consumer network is its more efficient use of
bandwidth. When a message is produced on the network, it is identified not by its destination address, but
by its connection ID. Multiple nodes may then consume the data to which the connection ID refers. As aresult, if a node wants to receive data, it only needs to ask for it once in order to consume the data eachtime it is produced. And, if a second (third, fourth, etc.) node wants the same data, all it needs to know is
the connection ID to receive the same data simultaneously with all other nodes.
Conversely, using the source-destination model, nodes receive only the packets that contain theirdestination node number. If more than one node needs the same data, it must be transmitted multiple
times, which is inherently inefficient. This can also cause synchronization problems, as nodes that require
the same data obtain it at slightly different times.

1.2.1 Industrial Ethernet and Traditional Fieldbuses
Since the mid-1990s, the use of fieldbuses, such as DeviceNet™, has grown significantly. At the sametime, advances in Ethernet switching technology and significant cost reductions fueled by the expanded
use of PCs and the Internet now allow industrial Ethernet to be used in more manufacturing applications.
Depending on the application, it may be desirable to combine Ethernet networks with fieldbus-type
networks. CIP Networks, such as EtherNet/IP and DeviceNet, support seamless bridging and routing
between multiple CIP Networks.
Implementing an industrial Ethernet system is different than implementing a device-level network, suchas DeviceNet. Whether installing a homogeneous EtherNet/IP network architecture or a heterogeneous
CIP Network architecture, users must be aware of the basic differences between Ethernet networks, suchas EtherNet/IP, and typical fieldbuses, such as DeviceNet, as highlighted in Table 1-1.
Table 1-1

Comparison of Device-level Networks and Industrial Ethernet Implementations

Control System Issue
Device capacity andwiring flexibility

Data rate vs. distance

Typical Device-level
Network Capability

Industrial Ethernet
Capability

Industrial Ethernet
Differences

Trunk-and-drop,
typically 10s of devices

Star configuration withpotential for 100s or
1000s of devices

Infrastructure devices
required

Limited total network
distance

Virtually unlimited total
network distance

Network management
tools may be needed

100s kbps, up to 500
meters (1600 ft) for
copper cable runs,
trading lower speed for
longer distance

10 Mbps to 100 Mbps,
up to 100 meters (328 ft)
for copper runs and up
to 2000 meters (6561 ft)
for fiber

Cable types and noise
immunity

Greater need for a mix
of fiber and copperwithin a system
Protocols

Single protocol

Coexistence of multiple
protocols

Coexistence of multiple
protocols

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1.2.2 Infrastructure for EtherNet/IP Applications
A communication network can be viewed as a utility for providing services that allow devices, or humans
operating these devices, to exchange information. A typical modern communication network isfunctionally a mix of computer, telecommunication, and broadcast networks capable of supporting voice,data, video, and image communication. Such a network normally consists of two basic components:
nodes and infrastructure (i.e., network = nodes + infrastructure). The same is true for industrial networks.
In the world of industrial networks, two types of infrastructures can be identified: passive and active.
Fieldbuses typically have a passive infrastructure, which is essentially a cable system. In contrast,
Ethernet networks, including those using EtherNet/IP, have an active infrastructure. At its core is aninterconnection of Ethernet Layer 2 (OSI data link layer) and Layer 3 (OSI network layer) switches.
Layer 2 switches allow all protocols to pass, but Layer 3 switches behave like routers, allowing only
designated protocols to pass through to certain locations.
The following examples present approaches that could be used to design a network with active
infrastructure. For Ethernet to function in control applications, it has to satisfy end-to-end response timerequirements for each transaction. Because processing delays in the network infrastructure are usually
negligible in comparison with delays in end-devices (nodes), performance bottlenecks are still located in
end-devices. Some of these end-devices (e.g., controllers) have to support time-critical as well as nontime-critical traffic and are frequently equipped with two separate Ethernet interfaces. But there is noneed to create two physical networks to separate devices with time-critical data from devices with nontime-critical traffic. This can be achieved by applying switches that support virtual LAN (VLAN)
functionality, thus making it possible to create separate virtual networks on the same wire. The
performance of many commercial and industrial switches manufactured today is sufficient to handle thiscombined traffic.
When an EtherNet/IP network is integrated with a plant’s enterprise network, network designers must
consider a set of issues never previously considered by designers of industrial networks. For instance,
EtherNet/IP infrastructure devices must have features that, when enabled, will not allow propagation oftime-critical traffic onto the plant’s enterprise network. This would bog down the enterprise network.
Conversely, extraneous enterprise network traffic must not propagate onto the EtherNet/IP network.

1.2.3 Security Issues
The deployment of Ethernet networks for manufacturing applications brings all of the issues andconsiderations for network security to the factory floor. The coexistence of multiple protocols and IP
addressing mean that network systems designers must take additional steps to ensure secure operation of
the manufacturing applications. Not only is it important that enterprise traffic be kept out of the plantfloor network, but it is also important to keep viruses, Trojans, and worms from infecting manufacturingcomputers. In addition, access to the plant-floor network controllers must be restricted to prevent
inappropriate changes in controller configurations and programs.
Fortunately, the active infrastructure needed for EtherNet/IP can help factory-floor applications be moresecure. Proper installation of managed (configurable) switches, routers, and firewalls provide mechanisms
for managing traffic to achieve a more secure network installation.

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2 Understanding the Basics of Network
Protocols
The following discussion includes information on the TCP/IP suite, focusing on theTransmission Control Protocol (TCP), the Internet Protocol (IP) and the User Datagram
Protocol (UDP).
The OSI Model provides a conceptual framework for communication between computers, but the model
itself is not a method of communication. Actual communication is made possible by using
communication protocols. In the context of data networking, a protocol is a formal set of rules andconventions that govern how computers exchange information over a network medium. A protocol
implements the functions of one or more of the OSI Model layers. (See Appendix B for more
information.)
A wide variety of communication protocols exist. Some of these protocols include Local Area Network(LAN) protocols, Wide Area Network (WAN) protocols, network protocols, and routing protocols. LAN
and WAN protocols operate at the physical layer (Layer 1) and data link layer (Layer 2) of the OSI
Model and define communication over the various LAN media. Routing protocols are network-layer
protocols that are responsible for exchanging information between routers, so the routers can select theproper path for network traffic. Finally, network protocols are the various upper-layer protocols thatexist in a given protocol suite. (See Figure 2-1.)

OSI Layer
7

Application
FTP

4
3
2
1
Figure 2-1

SMTP

Telnet

SNMP

TCP
ARP

Ethernet

RARP

TFTP

HTTP

UDP
IP

ICMP

IBS

LAP
X.21

ISDN

Relationship of the Internet Protocol Suite to the OSI Reference Model.

Many protocols rely on the existence of others for operation. For example, CIP uses Internet Protocol(IP), UDP, and TCP. This concept of building upon other existing layers is the foundation of the OSI
Model.

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2.1 The TCP/IP Suite
EtherNet/IP incorporates the TCP/IP suite, utilizing TCP for explicit messaging and UDP for implicit or
I/O messaging. These widely adopted protocols are implemented at the network layer (IP) and thetransport layer (UDP and TCP) of the OSI Model, and are the basic networking technology for
EtherNet/IP.
Transmission Control Protocol (TCP)
Transmission Control Protocol (TCP) is a connection-oriented transport protocol that
sends data as an unstructured stream of bytes. By using sequence numbers andacknowledgment messages, TCP can provide a sending node with delivery information about
packets transmitted to a destination node. EtherNet/IP uses TCP for explicit messaging (i.e., device
configuration).
TCP’s multiplexing allows simultaneous upper-layer conversations to be multiplexed over a single
connection. TCP provides connection-oriented, end-to-end reliable packet delivery by sequencing bytes
with a forwarding acknowledgment number that indicates to the destination the next byte the source
expects to receive. Bytes not acknowledged within a specified time period are retransmitted. The
reliability mechanism of TCP allows devices to deal with lost, delayed, duplicate, or misread packets.
For example, if data is lost in transit from source to destination, TCP can retransmit the data until either atimeout condition is reached or successful delivery is achieved. TCP can also recognize duplicate
messages and appropriately discard them. If the sending computer is transmitting too fast for the receiving
computer, TCP can employ flow control mechanisms to slow data transfer. TCP can also communicatedelivery information to upper-layer protocols and applications. Figure 2-2 shows the TCP packet fields.

Figure 2-2

TCP Packet Fields.

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The following descriptions summarize the TCP packet fields.
•

Source Port and Destination Port: Identifies the source and destination processes that are
to receive TCP services.

•

Sequence Number: Typically specifies the number assigned to the first byte of data in thecurrent message.

•

Acknowledgment Number: Contains the sequence number of the next byte of data thesender expects to receive.

•

Data Offset: Indicates the number of 32-bit words in the TCP header.

•

Reserved: Reserved for future use.

•

Flags: Carries a variety of control information used for connection establishment, andtermination.

•

Window: Specifies the size of the buffer space available for incoming data.

•

Checksum: Indicates if a header or data was damaged in transit.

•

Urgent Pointer: Points to the first non-urgent data byte in the packet.

•

Options: Specifies various TCP options.

•

Data: Contains upper-layer information.

Internet Protocol (IP)Internet Protocol (IP) is the primary Layer 3 protocol in the TCP/IP suite. In addition tointer-network routing, IP provides error reporting as well as fragmentation and reassembly of
information units called datagrams for transmission over networks with different maximum data
unit sizes. IP represents the foundation of the TCP/IP suite.

Public IP addresses are globally unique, 32-bit numbers assigned by the Network Information Center(NIC). Globally unique addresses permit IP networks anywhere in the world to communicate with eachother. In control networks, users may assign IP addresses within “private” IP address ranges. Examples of“private” IP address ranges include 10.x.x.x, 172.16-31.x.x, and 192.168.x.x. The IP addresses in these“private” control networks must be assigned so that they are also unique on the network. The setting ofidentical addresses on the same network will disrupt proper operation.
An IP address is divided into three parts. The first part designates the network address, the second part
designates the subnet address, and the third part designates the host address.

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IP addressing supports three different network classes. Class A networks are intended mainly for use

with a few very large networks because they provide only 8 bits for the network address field. Class B
networks allocate 16 bits, and Class C networks allocate 24 bits for the network address field. Class C
networks provide only 8 bits for the host field, so the number of hosts per network may be a limiting
factor. In all three cases, the leftmost bit(s) indicate the network class. IP addresses are written in dotted
decimal format (e.g., 34.0.0.1.). Table 2-1 shows the address formats for Class A, B, and C IP networks.
Table 2-1
Class

IP Address Formats for Class A, B, and C Networks
Leading Bits

Start

End

Class A0

0.0.0.0

127.255.255.255

Class B10

128.0.0.0

191.255.255.255

Class C110

192.0.0.0

223.255.255.255

Class D (multicast2)1110

224.0.0.0

239.255.255.255

Class E (reserved)1111

240.0.0.0

255.255.255.255

IP networks can be divided into smaller units called subnetworks or subnets. Subnets provide extra
flexibility for the network administrator. For example, assume that a network has been assigned a Class A
address, and all the nodes on the network use a Class A address. Further assume that the dotted decimal
representation of this network’s address is 34.0.0.0. (All zeros in the host field of an address specify theentire network.) The administrator can subdivide the network using subnetting. This is done by“borrowing” bits from the host portion of the address and using them as a subnet field.
If the network administrator has chosen to use 8 bits of subnetting, the second octet of a Class A IP
address provides the subnet number. In our example, address 34.1.0.0 refers to network 34, subnet 1;
address 34.2.0.0 refers to network 34, subnet 2, and so on as shown in Figure 2-3.

Figure 2-3

Subdividing a Network.

The number of bits that can be borrowed for the subnet address varies. To specify how many bits are used
and where they are located in the host field, IP provides subnet masks. Subnet masks use the sameformat and representation technique as IP addresses as shown in Table 2-2.

2

A packet with a special destination address, which multiple nodes on the network may be willing to receive. Source: RFC 1983.
Internet Users’ Glossary. G. Malkin. August 1996. http://rfc.net/rfc1983.html
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Subnet Masks

Dot-decimal Address

BinaryFull Network Address

192.168.5.10

11000000.10101000.00000101.00001010

Subnet Mask

255.255.255.0

11111111.11111111.11111111.00000000

Network Portion

192.168.5.0

11000000.10101000.00000101.00000000

Subnet masks have ones in all bits except those that specify the host field. For example, the subnet maskthat specifies 8 bits of subnetting for Class A address 34.0.0.0 is 255.255.0.0. The subnet mask thatspecifies 16 bits of subnetting for Class A address 34.0.0.0 is 255.255.255.0. Both of these subnet masks
are pictured in Figure 2-4. Subnet masks can be passed through a network on demand such that newnodes can learn how many bits of subnetting are being used on their network.
As IP subnets have grown, administrators have looked for ways to use their address space more
efficiently. Traditionally, all subnets of the same network number used the same subnet mask. In otherwords, a network manager would choose an eight-bit mask for all subnets in the network. This strategy iseasy to manage for both network administrators and routing protocols. However, this practice wastes
address space in some networks.
Some subnets have many hosts and some have only a few, but each consumes an entire subnet number.
Serial lines are the most extreme example because each has only two hosts that can be connected via a
serial line subnet.
On some media, such as LANs designed to IEEE Std 802®,3 IP addresses are dynamically discovered
through the use of two other members of the Internet protocol suite: Address Resolution Protocol(ARP) and Reverse Address Resolution Protocol (RARP).
ARP uses broadcast messages to determine the hardware layer Media Access Control (MAC) address
corresponding to a particular network-layer address. ARP is sufficiently generic to allow use of IP with
virtually any type of underlying media-access mechanism.
RARP uses broadcast messages to determine the network-layer address associated with a particular
hardware address. RARP is especially important to diskless nodes, for which network-layer addresses
usually are unknown at boot time.4

2.2 User Datagram Protocol
The User Datagram Protocol (UDP) is a connectionless transport-layer protocol (Layer 4) that belongs to
the TCP/IP suite. UDP is an interface between IP and upper-layer processes. UDP protocol ports
distinguish multiple applications running on a single device from one another.
3

IEEE 802, IEEE Standard for Information Technology –Telecommunications and Information Exchange between Systems –Local and Metropolitan Area Networks. http://standards.ieee.org/getieee802/portfolio.html

4

Information on ARP/RARP courtesy of Cisco Systems, Inc. Protocol Brief: TCP/IP. 1996.

http://www.cisco.com/warp/public/535/4.html
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Unlike the TCP, UDP adds no reliability, flow-control, or error-recovery functions to IP. Because of
UDP’s simplicity, UDP headers contain fewer bytes and, therefore, consume less network overhead thanTCP.
UDP is useful in applications where efficiency of data delivery takes precedence over verification of datadelivery, such as in cases where a higher-layer protocol might provide error and flow control.
User Datagram Protocol (UDP)

User Datagram Protocol (UDP) is the transport protocol for several well-known application-layer
protocols, including Network File System (NFS), Simple Network Management Protocol (SNMP),
Domain Name System (DNS), and Trivial File Transfer Protocol (TFTP). EtherNet/IP uses UDP for
implicit (real-time control) messaging.

The UDP packet format contains four fields, as shown in Figure 2-4. These include Source Port,
Destination Port, Length, and Checksum fields.
32 Bits
Source Port

32 Bits
Destination Port

Figure 2-4

LengthChecksum

Data

UDP Packet Format.

Source Port and Destination Port fields contain the 16-bit UDP protocol port numbers used to demultiplex datagrams for receiving application-layer processes. A Length field specifies the length of the
UDP header and data. Checksum provides an (optional) integrity check on the UDP header and data.

2.3 Data Exchange Models
EtherNet/IP uses the producer-consumer data exchange model. A data exchange model, or
architecture, describes a set of mechanisms by which data is exchanged between application programs
running in two or more computing devices. Each mechanism, depending on its function, uses unicast,multicast, or broadcast communication or some combination of these. The most popular data exchange
models today are point-to-point, client-server, publisher-subscriber, and producer-consumer.
Since present networks support a variety of multimedia information services, it is sometimes difficult todetermine whether a particular device supports more than one data exchange model or if one model is a
special case of the other one. EtherNet/IP has the flexibility to support these different types of dataexchanges to meet application needs that may arise.
Point-to-point communication is the simplest data exchange model. Classical examples of point-topoint connections are communication between two people over a phone and two computers over a TCP/IP
connection.
Client-server communication implies a central server connected to many clients. This is a one-to-manymodel. One could argue that a client-server system is actually a collection of point-to-point connections.
Client-server communication (or client-server computing) is popular in office networks and transaction
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processing systems. Office network examples are file, print, mail, and database servers. Examples related
to EtherNet/IP networks are DHCP/BOOTP, DNS, and web servers.
Publish-subscribe communication is a one-to-many model. In these systems, devices subscribe to data

they need and publish information they produce. Common examples of publish-subscribe systems include
newspapers, magazines, cable television, and various multimedia information services available over theInternet, such as breaking news. The publish-subscribe model is used in some control networks forperiodic broadcasts of relatively large amounts of data (e.g., 1000 bytes).
Producer-consumer communication also is a one-to-many model. Information produced by one device

can be consumed by a group of other devices. In comparison with the models mentioned above, theproducer-consumer model is the most applicable for I/O messaging (transport classes 0 and 1) on
EtherNet/IP, which includes cyclic and change-of-state event-type messages, message size, and rate.
Refer to The EtherNet/IP™ Specification5 for more details.
Advantages of the Producer-Consumer Model

The primary benefit of a producer-consumer network is its more efficient use of bandwidth. When amessage is produced onto the network, it is identified not by its destination address, but by its
connection ID. Multiple nodes may then consume the data to which the connection ID refers. As aresult, if a node wants to receive data, it only needs to ask for it once in order to consume the data
each time it is produced. And, if a second (third, fourth, etc.) node wants the same data, all it needs
to know is the connection ID to receive the same data simultaneously with all other nodes.
Conversely, using the source-destination model, nodes receive only the packets that contain theirdestination node number. If more than one node needs the same data, it must be transmitted multiple
times, which is inherently inefficient. This can also cause synchronization problems as nodes that
require the same data obtain it at slightly different times.

5

ODVA, The CIP Networks Library, Vol. 1 and 2, The EtherNet/IP™ Specification. Ann Arbor: ODVA, Inc., 2006.

www.odva.org. CD-ROM.

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3 Planning the Infrastructure
The most significant differences between industrial Ethernet networks and device-levelnetworks are presented here with information on how industrial EtherNet/IP networks
are designed and built.
Open device-level networks have been a key element of building modular manufacturing systems. The
networks’ quick response times, low connect costs, and simplicity fuel their growth. At the same time,industrial Ethernet infrastructure components, low-cost embedded Ethernet devices, and better
performance due to higher data rates (100 Mbps to 1 Gbps), are increasing the real-time control capabilityof industrial Ethernet.

3.1 Segmentation vs. Trunk-and-Drop
There are significant differences in the topology of industrial Ethernet networks and device-levelnetworks as shown in Figure 3-1. Device-level networks are often laid out in a trunk-and-drop system.

Figure 3-1

Device-level Networks are Trunked. Ethernet Networks are Segmented.

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These networks can connect more than 60 devices with communication cable without using any othercomponents. Bus extenders or bridges increase the network length or add layout flexibility, but they are
optional.
Industrial Ethernet uses “star” topology to connect infrastructure components to each other and to end
devices. While industrial Ethernet requires that the cost and use of infrastructure components beconsidered in the total automation system design, the star topology provides almost unlimited flexibility
for connecting to devices wherever they are located.

3.1.1 Implications of Multiple and Higher Data Rates
Device-level networks offer choices of several data rates versus distance options. Once these parameters
are chosen for a particular network, all attached devices must be configured to operate at the same data
rate. Industrial Ethernet, however, allows a mix of data rates within the same network, for example, 10
Mbps, 100 Mbps, and 1000 Mbps (1 Gbps). Higher speeds are generally used for connections (uplinks)
between infrastructure components, such as switches and routers. For backward compatibility purposes,
many industrial Ethernet devices are offered with both 10-Mbps and 100-Mbps capabilities, or all three
speeds.
The ability to mix 10-Mbps, 100-Mbps, and 1-Gbps data rates in the same system allows engineers tobalance the 1-Gbps benefits of maximizing throughput with the 10-Mbps benefits of higher immunity toelectrical noise and lower sensitivity to custom cable and connector termination variances. The lower data
rates of device-level networks allow long copper wire cable lengths of 500 meters (about 550 yards).
With the higher data rates of industrial Ethernet, fiber-optic cable and/or infrastructure components arenecessary for long distances.

3.1.2 Frame Size
A single frame of data on a device-level network is usually small (e.g., a CAN-based network contains
only up to 8 bytes of data). A single frame of industrial Ethernet can contain up to 1500 bytes of data. The
combination of high speed and high data capacity makes industrial Ethernet increasingly attractive as
more intelligence is embedded into smaller and less expensive devices.

3.1.3 Implications of Multiple Protocols
Device-level networks are designed to communicate using one protocol. Even in cases where the sameunderlying technology is used for multiple networks (e.g., CAN technology for both DeviceNet and
CANopen), placing one device of a different protocol on the network causes errors that prevent
communication. However, IEEE Std 802.3-based Ethernet technology and infrastructure components
handle multiple protocols.6
One advantage to open-standards-based Ethernet technology is that the user can choose a cabling
approach and cable layout design, and select protocols no matter which vendors supply the products.
Another advantage is the seamless connection between the plant floor, office, and Internet/Intranet
worlds. With this connection, however, comes a challenge: keeping the enterprise and Internet network
message traffic off the plant-floor control system. To prevent this traffic from slowing the industrial

6
IEEE 802.3, IEEE Standard for Information Technology –Telecommunications and Information Exchange between Systems –Local and Metropolitan Area Networks -- Specific Requirements – Part 3: Carrier Sense Multiple Access with Collision
Detection (CSMA/CD) Access Method and Physical Layer Specifications (Incorporates IEEE Std 1802.3D).
http://standards.ieee.org/getieee802/portfolio.html

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network’s response time, infrastructure components and addressing techniques provide connectivity while
segregating plant-floor traffic.

3.2 Ethernet System Components
Industrial Ethernet systems require various infrastructure components to connect all the segments
together. These include hubs, switches (especially managed switches), media converters, cables, androuters.
Classification of Ethernet Infrastructure Components

Ethernet infrastructure components are also known as Data Communications Equipment (DCE).
Control devices that send and receive messages, such as variable frequency drives, PLCs, PCs,
HMIs, machine vision devices, etc. are typically classified as Data Terminal Equipment (DTE).

3.2.1 Ethernet Hubs
Ethernet hubs, also referred to as repeaters or repeater hubs, are inexpensive electronic “repeaters” of
Ethernet data packets; they have no built-in intelligence. They amplify the signal and can extend the
distance and quantity of devices on a segment. All connected network devices hear all Ethernet data
packets on all of the Ethernet hub ports. Also, all network devices connected to a hub must communicate
at the same data rate.
Unlike switches, hubs only operate in a half-duplex communications mode, so they retransmit
collisions to other devices. (See 4.3.1 Full-Duplex vs. Half-Duplex Implications.) The cost of hubs
initially was significantly lower than that of switches, so hubs were used as a lower-cost method of
adding devices to the segments connected by switches. Switch products—thanks to home and officeneeds—have become ubiquitous, with prices dropping accordingly. Because switches do more and are
relatively inexpensive, hubs have lost favor and are disappearing from vendor catalogs and store shelves.
Industrial switches, borrowing on the technology of their commercial counterparts, provide an attractive
connect cost per device. It is possible to use switches (with all their performance benefits) in places wherecost constraints formerly resulted in the use of hubs. It is recommended that switches be used throughout,and where economically feasible, managed switches (configurable) or routers should be used.

3.2.2 Ethernet Switches
Ethernet switches are intelligent connection devices that generally use high-speed hardware to buffer
messages, analyze data frames, and connect the sending and receiving nodes in a virtual one-to-one
connection. Switches are a fundamental part of most networks. They make it possible for several users tosend information over a network at the same time without slowing each other down.
Ethernet Switch Terminology

Ethernet switches were historically referred to as bridges, multi-port bridges, or switching hubs.
The simple term switch is now the industry’s generally accepted term.
Switches are typically OSI Layer 2-type devices that allow all protocols to pass through. The Ethernet
switch is the most effective means of setting up Ethernet systems, especially on machine-control systems
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on the manufacturing floor. In fact, the use of Ethernet switches is the preferred means of Ethernet
interconnect of EtherNet/IP systems. Typical industrial switches can connect four or more network
segments or Ethernet devices. Each of these connections (ports) typically supports both 10-Mbps and100-Mbps data rates. Many of the newer switches will support 1-Gbps data rates as well.

3.2.3 Switches: Key System Elements
Switches are the key components that provide the determinism and throughput required for control
applications. They do this through several key features:•

Switches learn which device addresses are connected to each of their several ports. They
then send data received at one port only to the port that is connected to the target station.
This reduces unnecessary traffic.

•

If a switch is connected to a segment containing half-duplex devices (which may beconnected via hubs), collisions from that segment are isolated to that segment and are notpassed on to other devices or segments connected to other ports.

•

The Ethernet connections (ports) on switches typically support and automaticallyconfigure themselves for either half-duplex or full-duplex communications. Using fullduplex communications from a switched port directly to a device turns off the traditional
Carrier Sense Multiple Access with Collision Detection (CSMA/CD) mechanism sothat collisions are impossible.

The switch’s ability to eliminate collisions is the most important mechanism to provide real-time
capability for Ethernet-based control systems. If the data load increases on any one segment such that
performance is affected, a switch may be added to split the data load between two or more segments,
resulting in higher throughput. In addition, managed switches can prioritize traffic with up to eight trafficclasses, allowing the preferential handling of real-time traffic over supervisory traffic (e.g., file transfer,
web sessions, etc.).

3.2.4 How Switches Add Flexibility
The capabilities of switches increase the flexibility of the overall system in a number of ways:•

Switches can simultaneously communicate with and pass network messages between
devices or segments operating at different data rates (10 Mbps, 100 Mbps, or 1 Gbps).

•

Provided with both types of ports, they can connect to both fiber-optic and twisted-paircables, allowing developers to use a mix of media in the same system.

•

Managed switches come with added functions. Each has its own IP address, throughwhich users can enable/disable or configure the added functions. The features included
with a managed switch vary from vendor to vendor. Some vendors offer managed
switches that provide added diagnostics, addressing functions, and redundancy. Others
can be configured to help manage traffic through configuration optimization of Ethernet
features (e.g., virtual LANs, Quality of Service), bandwidth allocation, user
authentication, and other sets of features.

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Managed Switches

Managed switches provide the basic switching capabilities of unmanaged switches, plus they offer
additional diagnostic or traffic-management functions.

In essence, a managed switch is configured or tailored for a particular part of the overall application. The
different switches in an application can each have different configurations that the user must maintain. If
a managed switch is replaced, the particular configuration settings must be downloaded or entered into the
new switch. Unmanaged switches, however, perform only the basic switch functions and do not need tobe reconfigured if they are replaced. Since managed switches perform the basic switching functions “outof the box,” they can be used as “plug-and-go” replacements for unmanaged switches. For more specificdetails on the requirements for switches in EtherNet/IP networks, see Appendix A Recommendations for
Ethernet Switches in EtherNet/IP Systems.

3.2.5 Media Converters
Hubs and switches that allow connection of fiber and twisted-pair wire to the same device may bepurchased. In cases where the mix of ports does not match the requirements, twisted-pair to fiber-media
converters are available for converting a single cable of one type to another.

3.2.6 Routers
Routers provide added functionality not usually found in switches. A hub or a switch will pass along any
broadcast or multicast packets they receive to all the other segments, but a router will not. A four-way
traffic intersection is a good example. With a hub or unmanaged switch, all of the traffic passes throughthe intersection no matter where it is going. If, however, this intersection is at an international border, therules are different. To pass through the intersection, the driver must provide the border guard with a
specific destination address. If the driver doesn’t have a specific destination address, the guard will not let
the vehicle pass.
Routers work the same way. Without a specific address of a destination device, the router will not let thedata packet through. This is good for keeping networks separate from each other, but is less desirable
when different parts of the same network need to communicate. Switches allow different devices on thesame network to talk to each other.
Routers are typically used when traffic from two different networks needs to be interconnected. Routers
direct traffic based on the network address (OSI Layer 3) information of the packet. Routers can help the
performance of factory-floor Ethernet networks by blocking Ethernet multicast and broadcast data traffic.
Routers can isolate the traffic of other connected but unrelated Ethernet networks, which could otherwise
reduce the performance of factory-floor systems. Routers also can determine the optimal path along
which network traffic should be forwarded and can be used to help implement network security.
Routers normally do not have as many interfaces (ports) as switches, but like managed switches, theyrequire setup and configuration. Most switches add very little latency (or delay) to the messages that passthrough them. However, based on the added functions a router performs and the specific vendor’s
hardware implementation, added latency may be introduced. Engineers need to check the latency
specifications of a router if real-time control information will pass through it.
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3.3 Ethernet Cabling Systems
New Ethernet installations are based on twisted-pair and fiber-optic cables. The following presents
general guidelines and an overview of cabling schemes. The use of industrial grade Ethernet cable iscritical for withstanding exposure to harsh environments.

3.3.1 Star Topology: The Standard Approach
Industrial Ethernet systems are laid out in a point-to-point cabling scheme with one cable used for eachdevice being connected. These individual connections are coordinated through an Ethernet switch in acabling topology known as a star configuration.
The star configuration simplifies troubleshooting for device, cable, and connection installation problems.
With this star approach, multiple infrastructure components are interconnected, and each infrastructurecomponent connects in a star fashion to a group of individual control devices. This approach provides aflexible, distributed control architecture.
Most manufacturers offer pre-made or custom “patch” cables in a wide variety of lengths. Typically abackbone of switches will be connected with copper cables up to 100 meters (328 ft) in length or longer
fiber-optic cables, where each switch isolates a machine or major part of a machine. The other ports of theswitch connect to the control devices using twisted-pair or fiber cables for that part of the machine or
manufacturing process.
In a situation where there are more devices than switch ports to accommodate them, connecting one of thefirst switch’s ports over to a port on a second switch effectively adds more ports to the first switch. Some
active infrastructure components have a modular hardware-expansion capability where additional ports
may be added (without using a device connection port) by plugging together port expansion modules.
Another option is to select a switch with additional ports and use the smaller switch elsewhere. It is often
wise to choose a larger switch than necessary and leave a few open ports. This way, when it comes time
to add sensors, actuators or subnetworks, it will not be necessary to replace the switch.

3.3.2 Implementation of Mixed Cable Systems
Infrastructure components, such as media converters, allow copper wire (twisted-pair) and fiber-optic
cables to be mixed in the same system. Industrial Ethernet systems may require the use of fiber optics tocover the longer cable-run distances that would previously be implemented with copper wire at lower
data-rate settings in device-level networks. Also, the added noise immunity of fiber, especially at the 100Mbps and 1-Gbps rates, can reduce start-up surprises. This is especially true when routing wires near
welders, larger horsepower drives, motors, or motor starters.

3.3.3 Applicable IEEE Standards for Twisted-pair Ethernet
The major IEEE standards that apply to industrial twisted-pair Ethernet installations are 10 Base-T for 10Mbps connections and 100 Base-TX for 100-Mbps or fast Ethernet operation. The term “fast Ethernet”
applies to the standards that support 100-Mbps operation. Gigabit Ethernet (1000 Base-T) operates at1000 Mbps.7
3.3.3.1 Unshielded Category 5e Cable
The Unshielded Twisted Pair (UTP) wiring standard, which allows for flexibility and ease of installationand maintenance, is the most prevalent cabling scheme in use today. There are two twisted-pair (four7IEEE Std 802.3. http://standards.ieee.org/getieee802/portfolio.html
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wires) and four twisted-pair (eight wires) UTP cables. Two twisted-pair cables support network speeds of
10 Mbps as well as the 100-Mbps. Industrial Ethernet systems with 1-Gbps speeds use four twisted-paircables with a maximum cable length of 100 meters (328 ft). Pre-configured Category 5e (CAT 5e) cables
are available in required lengths. Field terminations may require manual work with crimping tools, bulk
cable, and connectors.
The quality of the cable and of the connector termination is particularly important at the high data rates
and in the electrically noisy environments of industrial Ethernet.
Only the highest quality, industrial grade Category 5e (or higher) cable should be used in industrial
Ethernet applications. Category 5e (e for enhanced) has superseded the older CAT 5 designation for 100Mbps systems. CAT 5e can contain either two twisted pairs (four wires) or four twisted pairs (eightwires). The added wires and improved signal transmission characteristics allow CAT 5e cables to be used
for 1-Gigabit Ethernet and all power-over-Ethernet applications. However, two twisted-pair cables havethe advantages of compatibility with M12 (IP65 and IP67 grade) connectors and, in 100-Mbps
applications where only two pairs carry communications, this reduces the chance of electrical noiseinterference.8
3.3.3.2 Shielded Category 5e Cable
Shielded cable should be considered for use in high noise environments. It also is the prevalent cable usedin European installations. See 4.4 Layout and Wiring Considerations for more information.
3.3.3.3 Connectors and Pre-terminated Cables
The RJ-45 connector is the standard for twisted-pair cabling. The IEEE Std 802.39 and TIA Std TR42.910
industry standards groups are in the process of specifying IP65 and IP67 versions of industrialized
Ethernet connectors.
“D”-coded M12 connectors with four wires are used to create IP65 and IP67 fluid-resistant, sealed
connections. These connectors allow removable connections to panels and connection of machine-mountcontrol devices. See 7.1.2 M12 “D”-Coded Connector for EtherNet/IP for more information.
The use of pre-terminated cables should get serious consideration, especially for 100-Mbps and 1-Gbps
connections. Improperly terminated cables can degrade the signal or provide a path for electrical noise toenter, causing intermittent communications or reduced system throughput as the devices are forced to retransmit a higher percentage of messages.
3.3.3.4 Crossover vs. Straight-through Cables
Unlike device-level networks, different types of Ethernet devices require different pin-to-pin connections.
Some devices require the use of crossover cables where the transmit pins at one end of the cable areconnected to the receive pins of the other connector. Other devices require a 1:1 (straight-through) cable
where the transmit pins at one end are connected to the transmit pins of the other.

8
The Ingress Protection (IP) code IP65 refers to equipment that is dust-tight and protected against water jets. IP67 refers toequipment that is dust-tight and protected against immersion in water. See Appendix E for more information.

9

IEEE 802.3, http://standards.ieee.org/getieee802/portfolio.html

10

TIA TR42.9, Industrial Telecommunications Infrastructure Standard. www.tiaonline.org
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Recommended Cable PracticeDifferent cable types can be distinguished through the use of different colored outer cable jackets.
Most infrastructure components automatically compensate for the type of device connected. This is
known as auto-crossover or auto MDI/X capability.
There are two classes of Ethernet devices: Data Communications Equipment (DCE) refers to
infrastructure components, and Data Terminal Equipment (DTE) refers to control devices. The following
connection schemes normally apply:•

DCE to DCE (infrastructure components connected to infrastructure components):
crossover cable•

DTE to DTE (control devices connected to control devices): crossover cable•

DTE to DCE (control devices connected to infrastructure devices): 1:1 straight-throughcable

3.3.3.5 Other Options
Like device-level networks, a variety of cable options are available for easier wiring in specificapplication situations (e.g., in cabinets versus outside of cabinets). See 4.4 Layout and Wiring
Considerations for more details.
3.3.3.6 Future Options
The IEEE Std 802.3af task group is working on DTE powering, which will enable switches and other
DCE equipment with integrated power supplies to provide dc power for unpowered DTE equipment.11
Power will be carried either by signal pairs 1 & 2 and 3 & 6, or by unused pairs 4 & 5 and 7 & 8. This
capability can provide power to sensors and video equipment as well as security devices and wirelessaccess points, extending the flexibility of subnetworks.

3.3.4 Applicable IEEE Standards for Fiber-Optic Ethernet
Fiber-optic cable mediums provide longer distance runs than wire as well as immunity from electrical andradio frequency (RF) noise. The major IEEE standards that apply to industrial fiber-optic Ethernet
installations are 10 Base-FL for 10 Mbps connections and 100 Base-FX for 100-Mbps (fast Ethernet)
operation; 1000 Base-SX refers to IEEE Std 802.3z for 1-Gbps (or Gigabit Ethernet).12
3.3.4.1 Glass Fiber Cable
The fiber-optic cable typically used in both 10-Mbps and 100-Mbps industrial Ethernet applications isbased on 62.5-micron duplex multimode glass cable. Also available are 50- and 100-micron fibers.
Maximum cable lengths are based on the type of cables used and whether full-duplex or half-duplex

11

IEEE 802.3, http://standards.ieee.org/getieee802/portfolio.html

12IEEE 802.3, http://standards.ieee.org/getieee802/portfolio.html
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communications is used. Cable lengths of 2000 meters (6562 ft) are possible using multimode fiber infull-duplex, 100-Mbps applications. The use of pre-terminated glass fiber-optic cables is recommended.
Fiber-optic cables are terminated using SC, ST, or MTRJ connectors. Like twisted-pair wiring, the use ofhalf-duplex communications has additional restrictions as to how many hubs can be used between thesending and receiving devices. These issues are covered in more depth in 4 Designing the Infrastructure.
3.3.4.2 Plastic Fiber Cable
For cabling within cabinets or over short distances in conjunction with media converters, plastic fiber
optics provide noise immunity and easier connection capability, especially if custom cables need to be
used. Polymer (980/1000 um) fiber cables can be used for lengths up to 50 meters (164 ft), while HCS(200/230 um) fiber cables can be used for up to 100 meters (328 ft).
3.3.4.3 More Cabling Resources
An overview of characteristics to consider when selecting connectors and cables suitable for industrial
applications can be found in 7 Selecting Components. For complete connector, cabling, and layout
information, refer to the EtherNet/IP™ Media Planning and Installation Guide available from ODVA.13

3.3.5 Wireless Ethernet
Wireless Ethernet network systems use radio frequency (RF) transmitters and receivers to send andreceive data. Like any system based on radio, performance and interference issues need to be addressed
for use on the plant floor. Wireless systems are based on the IEEE Std 802.11b and other standards;
however, this remains an emerging area for industrial Ethernet applications and is not covered here.

3.4 Ethernet Data Connections
Ethernet data packets are sent in the format shown in Figure 3-2.

Figure 3-2

Typical Layout of an Ethernet Data Packet.

This data format is used to implement the Media Access Control (MAC) protocol that allows a device to“talk” on the Ethernet network. Each MAC device has a unique Source Address (SA) comprised of a 6byte number (48 bits or 12 hexadecimal digits) that was assigned to it at the time of manufacture. The
13

ODVA, Inc., EtherNet/IP™ Media Planning and Installation Guide, Ann Arbor: 2006. www.odva.org
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Destination Address (DA) is the target MAC address for which the packet of data is intended. Setting

the first bit to a “1” in the DA field, indicates a packet of data for multiple destinations. This enables an
Ethernet device to transmit one packet that can be received by multiple other devices.
There are a number of different types of Ethernet packets that can be sent and received on an Ethernet
network. Some of these protocols are Novell’s IPX/SPX, DECNET, UDP, TCP/IP, FTP, TELNET, andso on. All of these unique protocols use the MAC to do the physical sending and receiving of data
packets. However, by defining how the “DATA” portion of the data packet is organized, different
protocols and functions are created.

3.4.1 IP Addressing of Industrial Ethernet Devices
One of the more common protocols familiar to many is TCP/IP, which stands for Transmission Control
Protocol/Internet Protocol. EtherNet/IP uses the TCP/IP suite to send messages between devices. The
TCP portion of this protocol suite allows for reliable connections on the Ethernet and the quick streamingof data from one Ethernet node to another. It has become the most popular protocol implemented on
Ethernet networks.
The Internet Protocol (IP) portion of the TCP/IP suite is its routing mechanism. All devices on anindustrial Ethernet-based system must be assigned an IP address. Infrastructure components with added
diagnostic capabilities (managed switches and hubs) also require an assigned IP address. It is mostcommonly identified by the 4-byte address listed in the network properties on personal computers that use
TCP/IP as their Ethernet network connection. (See 2 Understanding the Basics of Network Protocols forexamples). IP addresses create unique, high-level identifiers for IP networks, such as the Internet.
Media Access Control (MAC) Address

Unlike device-level networks where the physical layer address also is the address that the user sets,
Ethernet devices are addressed by assigning an IP address to that particular device’s MAC address.
The MAC address is the lowest level address and resides at the data link layer for Ethernet.
Each Ethernet device vendor sets a unique MAC address into each product that is shipped. Before startingup the system, the engineer must first assign an IP address to a plant-floor Ethernet device as a part of its
configuration. See 4.6 Performance Considerations: The Need for Switches for more information.

3.4.2 Important Ethernet Tools and Protocols
EtherNet/IP uses the TCP/IP suite as the basis for sending and receiving the Common Industrial Protocol(CIP) packets of data. CIP is the protocol used by DeviceNet, ControlNet, and EtherNet/IP to facilitate
the I/O control, programming, startup, operation, and maintenance of control systems. By encapsulatingthese CIP messages inside the TCP/IP Ethernet protocols, EtherNet/IP is able to provide a powerfulcontrol system network that can be seamlessly integrated into the business systems of a manufacturing
facility. Control engineers should become familiar with a number of other protocols associated with the
TCP/IP suite:•

UDP - User Datagram Protocol

UDP packets offer a simple method of moving data with minimal overhead. UDP is used by
EtherNet/IP to move connected I/O messages in a very efficient producer-consumer model.

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DHCP - Dynamic Host Configuration Protocol

This is a protocol to allow a device, acting as a DHCP server, to assign 4-byte IP addresses todevices connected to the network.
•

DNS - Domain Name Services

This protocol searches for resources on a TCP/IP network using a database connected to the
TCP/IP network. It makes correlations between computer names, their 4-byte IP addresses,
and the resources and information available in the network. There are many other tools andprotocols available. See 5 Deploying the Network for more information.

3.5 Diagnostics via Infrastructure Components
Industrial Ethernet infrastructure components, like their device-level network counterparts, can provide afull range of diagnostics over displays such as built-in LEDs or seven-segment readouts. Typicaldiagnostics include transmit/receive status by port, port active/cable connected status, and 10-Mbps
versus 100-Mbps operation. Most intelligent infrastructure components perform periodic self-tests andprovide LED indication of failure. Some units also provide a hardware contact that can be wired to an
alarm or nearby industrial controller to signal a device failure.

3.5.1 Simple Network Management Protocol
Simple Network Management Protocol (SNMP) is an industry standard protocol supported by virtually all
infrastructure component manufacturers. Through the SNMP protocol, engineers can set configuration
parameters (e.g., assign IP addresses) and receive diagnostics (i.e., remote monitoring data). This
information, however, only relates to infrastructure components, not to Ethernet embedded controllers,
devices, or I/O. EtherNet/IP is used to access Ethernet control device data.
SNMP drivers are available as standard in virtually all infrastructure-related (network management)
software packages. SNMP allows a software package from vendor X to display and set parameters invendor A, B, and C’s infrastructure components. Managed infrastructure components provide added
diagnostics, such as port status (cable connected/unconnected, communications active/inactive), packet
size, and statistics on the packet type transmitted (unicast, multicast, broadcast), power supply status, etc.
These devices contain a data table called a Management Information Base (MIB) that contains
diagnostic and other information.
The SNMP defines the format and standard types of remote monitoring (RMON) information. This
standard allows multiple vendor diagnostics to be accessed by vendor-independent software. The standard
also allows vendor-specific information to be added. Within a point-to-point tree structure containing
hundreds of connected devices, the ability to quickly locate cabling or other faults in the Ethernet
infrastructure can be key to expediting start-ups. For more information, see 5 Deploying the Network.

3.5.2 Traps
Managed infrastructure devices allow a network engineer to set up SNMP traps. If it is important thatmultiple devices receive diagnostic information, all the extra network traffic could significantly affect the
response time of the control network. Traps concentrate, or “trap,” the diagnostics from a quantity of
infrastructure devices. Without traps, PCs, etc. would have to constantly poll the MIB data from all theinfrastructure devices to determine if errors occurred. Infrastructure components can be configured with
the IP addresses of one or more networked PCs and devices.
When an alarm or error condition happens (some infrastructure diagnostics can determine if a parameter
exceeds a high or low limit), the infrastructure component sends an error message to the trap. This
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concept is similar to the “Change of State” messaging found in CIP. An event, in this case an error,
triggers a message to a specific device, in this case a trap. This “report by exception” approach limits
Ethernet network management traffic, allowing greater network bandwidth to be used for control.

3.5.3 Network Management and Web-based Management Software
Many vendors offer network management software that uses SNMP, Bootstrap Protocol (BootP), andaccessed MIB data to allow an operator to view the status of the entire network. It also allows the IP
addresses to be loaded into the devices. This overview of the installation can be used to identify problem
areas during startup or on an ongoing basis. Detailed information about the devices may also be accessed.
Many devices have an integrated Web-server that allows SNMP data to be accessed using standard
Internet browsers. The combination allows problem areas to be identified using network management
software with the Internet browser to “zoom in” on the device’s web page(s) for access to detailed
information or settings. Some devices also include embedded data sheets or user manuals that can beaccessed.

3.6 Isolated vs. Integrated Networks
Historically, device-level networks have been “isolated” from one another. A single controller, such as a
PLC or PC, is the “master” of a small network of nodes, such as I/O blocks, variable frequency drives(VFDs), barcode readers, servo drives, and so on. This small control network does not have a physicalconnection to any other network other than through the master PLC or PC. As such, communications
between these device-level networks require a separate network port on the PLC or PC and also require
programming in the controller to send and receive data. In this way, the network communications frommachine to machine, from cell to cell, and throughout a manufacturing campus have been isolated to only
what was needed for the specific connected devices.
These isolated networks, while very effective at providing distributed control, do not provide the“seamless” connectivity that industrial Ethernet offers. The ability to connect and communicate between
the business system networks and the plant-floor networks via industrial Ethernet provides a huge
opportunity to reduce work-in-process inventory, improve throughput, find manufacturing bottlenecks,
increase uptime, and improve customer service. The “integrated network,” while providing thesemanufacturing improvement opportunities, demands a conscientious effort at an overall network designand layout for an entire facility. The benefit of Ethernet is that it can be scaled, from small original
equipment manufacturer (OEM) machine control applications, to integrated manufacturing lines. As theapplications become more complex, the quantity, type, and functionality of the required infrastructurecomponents also grows. (See 6 Infrastructure Application Scenarios for more information.)
Typically, manufacturing and OEM control engineers can achieve the goals of a good industrial Ethernet
network design by using robust industrial Ethernet components. First, the industrial Ethernet electronics
and cabling systems should implement full-duplex switching technology, follow proper Category 5e (orhigher) twisted-pair and fiber installation techniques, and address the environmental conditions present
around the equipment. Next, using the proper equipment and building industrial Ethernet control
networks in a “managed network” scheme, manufacturing and OEM control engineers can achievemachine control objectives while adding the benefits of total plant network integration. Finally, when
integrated networks with industrial Ethernet are used, new requirements such as security and network
traffic routing can arise. Additional “higher-level” network equipment and networking techniques may berequired to meet these needs.

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3.6.1 Security Issues
Firewalls are important to the security of integrated networks. Routers and switches may also be
configured to contribute to network security.
3.6.1.1 Firewalls
A firewall is a software and hardware solution that acts as a barrier to protect a network from outside
intruders when connected to a wide area network (WAN), such as an enterprise network or the Internet.
Any plant-floor information (e.g., remote diagnostics) that is accessed from outside the building must firstpass through a firewall.
3.6.1.2 Routers and Switches
Most routers today allow filtering of TCP/IP packets as they approach the internal network from a WAN
or the Internet. Operating at the network layer of the OSI Model, these routers can deny access to theinternal network for packets from specific external sites. They allow access to only certain services (suchas internal web servers) or certain computers in the internal network (such as a mail server). All attempts
to connect to other computers in the internal network will be denied. Although not bulletproof, routers doprovide an added line of defense. Many managed switches also contain the ability to disable unused
physical ports to prevent unauthorized personnel from plugging in and accessing the network.

3.7 Traffic Management with VLANs
A virtual LAN (VLAN) is a switched network segmented by functions or applications on anorganizational basis as opposed to a physical or geographical basis. VLAN addressing mechanisms allow
stations to be assigned to logical groups that communicate across multiple LANs as though they were ona single LAN.
Bridges and switches filter Destination Addresses and forward VLAN frames only to ports that serve the
VLAN to which the traffic belongs. One example is a device-level network with “multi-master”
capability. In this case, two industrial PCs communicate on the same network with a number of devices.
PC #1 may control devices 1, 3 and 5 while PC #2 controls devices 2, 4 and 6.
With industrial Ethernet, all eight devices can be connected together on the same Ethernet network using
several switches. A VLAN approach might place PC #1 and devices 1, 3 and 5 on VLAN 1, and PC #2
with devices 2, 4 and 6 on VLAN 2. Devices or network segments related to VLAN 1 do not receive
messages from VLAN 2, thus reducing overall network traffic.

3.7.1 How VLANs WorkA VLAN is created by “tagging” or inserting a 4-byte VLAN header into the basic Ethernet (MAC Data)frame between the Source Address and Length/Type fields as shown in Figure 3-3.

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VLAN-tagged Frames are Identified when the MAC Finds the LAN Type Value in theNormal Length/Type Field Location.

The VLAN header contains a Tag Control field that defines the transmission priority (0 to 7, where 7 isthe highest) and a VLAN ID that identifies the particular VLAN over which the frame is to be sent. These
provide the means to expedite time-critical network traffic. Ethernet switches or routers use the VLAN
header information to direct the message to the correct port and transmit the frames according to theirpriority. VLAN tagging requires that all infrastructure devices involved with a VLAN group be equippedwith the VLAN option.

3.7.2 VLAN Benefits
The application of VLANs allows the flexibility of using interconnecting devices while reducing
unnecessary network traffic and delay time. In addition to managing network traffic, VLANs provide
added system scalability and security, and they simplify network management by making device adds,
moves, or changes easier to administer. The configuration of a VLAN requires managed infrastructurecomponents.

3.8 Topologies to Provide Ethernet Network Redundancy
Infrastructure components come with a variety of system redundancy options, from redundant power
supplies, to cable and communication path redundancy. Cable and communication path redundancy isoften required in larger scale installations or in cases where an infrastructure component or cable failure
may cause significant scrap of manufactured product or result in damage to a machine or process.
There are both standardized and proprietary methods of achieving redundancy in Ethernet networks thatinvolve variations on standard Ethernet topologies. Standardized methods have the benefits of allowing
the mix of multi-vendor products or the ability to easily change vendors without re-engineering thesystem. Like PLCs, proprietary redundancy methods may offer special features or performanceadvantages in certain applications, but the approach cannot be mixed with multiple vendors’ components.
In addition, special attention needs to be paid to how, and if, the proprietary method can be used inconjunction with standardized redundancy approaches.
If a user mixes proprietary and nonproprietary methods within an overall system, communication loops
can be formed, creating spurious traffic that can overload and effectively shutdown the network. Different
vendors’ equipment should be evaluated based on the type of redundancy offered, the switchover time,and if there is message storage capacity to reduce “lost messages” during switchover time.

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3.8.1 IEEE Standard Network Redundancy Options
The Spanning Tree and Trunking/Aggregation methods are standard, multi-vendor approaches toachieving network redundancy.
3.8.1.1 Spanning Tree Protocol Method
The Spanning Tree Protocol (STP) is a Layer 2 (data link layer) protocol designed to run on bridges
and switches. The specification for STP is IEEE Std 802.1D.14 The main purpose of STP is to ensure that
there are redundant paths while avoiding a loop situation that causes network messages to endlessly cyclearound the loop and repeat, causing the network to saturate and communications to effectively stop.
As shown in Figure 3-4, switches with STP can detect one or more cable cuts and automaticallydetermine the next best path for the data to travel. This capability requires switches that support the
Spanning Tree algorithm, and transmit and receive Spanning Tree configuration messages. Vendors
should be consulted to determine how many bridges/switches can be supported, and to determine thelength of the time lapse from when a break is detected to when the network is reconfigured and normal
communications resume.

Figure 3-4

Using the Spanning Tree Protocol Method, Switches Detect a Cut Cable and Automatically
Determine the Next Best Path for the Data to Travel.

14

IEEE 802.1D, IEEE Standard for Local and Metropolitan Area Networks – LAN/MAN Bridging and Management – Media
Access Control (MAC) Bridges. http://standards.ieee.org/getieee802/802.1.html
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The Rapid Spanning Tree (RSTP) specification (originally IEEE Std 802.1W, now included in IEEE
Std 802.1D) is an enhancement over the original Spanning Tree specification. It allows for faster recovery
times (a few seconds) than Spanning Tree. In Spanning Tree applications, recovery times typically range
from 30 to 60 seconds. Large and complex topologies may result in minutes of recovery time.
3.8.1.2 Link Aggregation
The Link Aggregation method (IEEE Std 802.3AD15) is used to provide redundant communication paths
between two devices when two or more links connect the devices as shown in Figure 3-5. When one linkis broken, the others carry the traffic.
Link Aggregation uses all the links all the time, typically in situations where high traffic volume (such as
uplinks from lower-level networks to higher-level enterprise networks) requires the added bandwidth ofmultiple communication paths. For example, four fast Ethernet links (100 Mbps) produce a bandwidth ofa single 400-Mbps link. In a case where one of the links is cut, traffic continues but at a slower 300-Mbps
equivalent bandwidth.

Infrastructure
Component

Figure 3-5

Infrastructure
Component

When One of Four Fast Ethernet Links between the Two Devices is Broken,
Message Traffic Capacity Decreases but Continues.

3.8.2 Ring Redundancy
Ring redundancy schemes are proprietary in nature and are available from multiple vendors. These
redundancy schemes are not interoperable between different vendors’ infrastructure products.
Redundancy configurations require multiple switches to be connected in a ring manner as shown in
Figure 3-6. These systems allow typical communications recovery times in the 100s of milliseconds
range.

15

IEEE 802.1AD, IEEE Standard for Local and Metropolitan Area Networks – Virtual Bridged Local Area Networks.
http://standards.ieee.org/getieee802/802.1.html
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Ring Redundancy Topology.

3.8.3 Dual Homing
The dual homing approach is typically used to achieve redundancy between routers or network layer(Layer 3) switches that have router-level functions. (See 4.11 Multilayer Ethernet Switches for more
information.) In addition to a simple hub-and-spoke network where a remote router is connected to asingle distribution router, the remote router can be dual-homed to two or more distribution routers. A
dual-homed remote router will have two or more distribution routers.
Figure 3-7 shows a common dual-homed remote topology with one remote router; however, 100 or morerouters could be connected to Distribution Routers 1 and 2. The remote router will use the best route toreach its destination. This approach typically allows flexible configurations, combinations of two ports
with different data rates (10 Mbps, 100 Mbps, or 1000 Mbps) and different media (fiber optic, twistedpair), and typically faster switchover times than the spanning tree method.

Figure 3-7

If Distribution Router 1 Experiences a Failure, the Remote Router Can Use Distribution
Router 2 to Reach the Corporate Network.
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4 Designing the Infrastructure
Network design is a methodical, step-by-step process. It includes the top-down process of
mapping out the network infrastructure required for an application. This systematic
process focuses on the application, technical objectives, and business goals.
When designing the infrastructure for an EtherNet/IP network, it helps to first define a logical view of the
network, including a description of traffic-flow and architectural topology, before designing the physicallayout. With a top-down network design, the emphasis is put on planning before implementation. If thesystem involves a fully integrated control and business network, cooperation between control andInformation Technology personnel cannot be overemphasized. The two groups need to work together.
What follows is a review of the processes and steps involved in network design. This approach considers
both logical and physical network design, takes an in-depth look at infrastructure components, andprovides some guidelines for practical network design.

4.1 Network Design Method
The network design process can be viewed as a sequence of the following steps:
1.

Definition of application requirements

2.

Logical network design

3.

Physical network design

The following sections list activities recommended for consideration during EtherNet/IP network design,
including functional application requirements, project scope, and other factors. To better understand thedesign issues, they are presented in the form of a comparison between industrial networks with active
infrastructures (such as EtherNet/IP) and passive infrastructures.

4.1.1 Design Steps for Isolated EtherNet/IP Networks
Except for the active infrastructure of EtherNet/IP, the design process of an isolated EtherNet/IP network
is similar to a device-level network as shown in Figure 4-1.

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Comparison of Isolated and Integrated EtherNet/IP Networks.
(Courtesy of General Motors.)

An isolated network has no immediate, continuous connection with the rest of the plant floor network or
the enterprise network. Typically, it will connect to a supervisory PC or node, which will then act as agateway to filter out connections from/to the main network. The design process for an isolated network is
broken into three steps, which follow.

4.1.2 Definition of Application Requirements
During this stage, application requirements are identified and analyzed. The collected data is then used as
design input. See Table 4-1. Note that EtherNet/IP networks will require more attention to planning anddesign than proprietary industrial device-level networks, which have many predefined specifications.
Table 4-1

Definition of Application Requirements

Activity

Industrial Network with Passive
Infrastructure

EtherNet/IP

Define project goals and constraints(e.g., budget constraints).

This activity is usually performed.
Controls company may assist.

This activity should be performed.
Bring in IT Dept. and outside help
for expertise if necessary.

Analyze technical goals andconstraints (e.g., scalability,
performance, and device
configuration requirements).

This activity is usually performed.
Controls company may assist; maybe part of overall control scheme
built around proprietary systems.

This activity should be performed.
Bring in IT Dept. and outside help
for expertise if necessary.

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4.1.3 Logical Network Design
Logical network design is a process of creating a logical model of a network infrastructure consisting of
the steps listed in Table 4-2. Begin by designing a network topology.
Table 4-2
Activity

Logical Network Design

Industrial Network with Passive
Infrastructure

EtherNet/IP

Design network topology.

This activity is normally not
performed because network
topology is predefined.

This activity should be performed.
Enlist help of IT Dept., system
integrator, or control engineer
familiar with Ethernet systems.

Define IP addressing andnaming.

A node-addressing model isusually created. Node naming is
usually not supported in these
networks.

This activity should be performed.
May need help from IT Dept.

Develop policies/procedures for
network operation andmaintenance.

Typically performed by plantengineers and maintenancepersonnel.

May be performed by either plantor IT/MIS personnel.

Define switch and routerfeatures.

Not applicable in the context used
in information networks.

This activity should be performed.
Get IT help if necessary.

4.1.4 Physical Network Design
Once application requirements have been determined and a logical network design has been achieved, it istime to design the physical network. See Table 4-3. This stage may be more complex in working with
EtherNet/IP, but it will pay off in the long run if plant-floor connectivity is needed.
Table 4-3
Activity

Select cable system components
and infrastructure devices.

Physical Network Design

Industrial Network with Passive
InfrastructureThis activity is equivalent toselection of the network cablesystem components.

EtherNet/IP

This activity must be performed.
System integrators and IT Dept.
may help.

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4.2 Non-Isolated EtherNet/IP Networks
A non-isolated network as shown in Figure 4-1 is integrated with the rest of the plant floor network andcan communicate upwards to the enterprise network. Since there are more integration concerns (e.g.,working with corporate IT), initial design work will be necessarily more involved. The design steps
follow.

4.2.1 Definition of Application Requirements
During this stage, application requirements are identified and analyzed (Table 4-4). The collected data isthen used as design input. Note that an extra characterization step has been added.
Table 4-4

Definition of Application Requirements

Activity

Industrial Network with Passive
Infrastructure

EtherNet/IP

Define project goals and budget
constraints.

This activity is usually performed
but has not been recognized as aseparate activity.

This activity should be performed,
if appropriate. Work with IT Dept.

Analyze technical goals andconstraints (e.g., scalability,
availability, performance,
security, manageability,
usability, and adaptability).

This activity is usually performed.
Work with controls company.

This activity should be performed.
Get outside help if necessary.
Work with IT Dept. or system
integrator.

Characterize the existing
network.

This activity is rarely performed
since these networks are normallydesigned from scratch.

It is expected that these networks
will normally be designed fromscratch. Therefore, this activity
will be rarely performed.
An interface with the existing
plant/enterprise network should becharacterized instead.

Characterize network traffic.
This activity may include
characterization of traffic flow,
traffic load, traffic behavior,
and Quality of Service.

This activity is usually performed
as part of network planning
activities. Includes transaction
analysis.

Both transaction and traffic
analysis should be performed.
Attention should be paid tomulticast traffic generated by
implicit messaging on
EtherNet/IP.

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4.2.2 Logical Network Design
Logical network design (Table 4-5) is a process of creating a logical model of a network infrastructure
consisting of the steps listed in the table below.
Table 4-5
Activity

Design network topology.

Logical Network Design

Industrial Network with Passive
InfrastructureThis activity is normally not
performed because network
topology is predefined. For
example, proprietary networks use
a fixed and highly-defined
topology.

EtherNet/IP
This activity should be performed.
It is recommended that network
topology be consistent withplant/enterprise network topology.
It is also recommended to address
here, if applicable, how the
EtherNet/IP network under design
will fit into a typical three-layer
hierarchical model of abuilding/campus network withneed for path redundancy, loadbalancing, VLANs, and physicalsecurity.

Design a model for addressing
and naming.

A node-addressing model isusually created. Node naming is
usually not supported in these
networks.

For a non-isolated network thisactivity is usually not performed
because node naming andaddressing must be the same as in
the plant/enterprise network towhich this network will beconnected or integrated.

Define switch and routerfeatures.

Not applicable in the context used
in information networks.

This activity should be performed.
Features are normally selectedbased on results of traffic
analysis.

Set policies/procedures for
network operation andmaintenance.

Typically performed by plantengineers and maintenancepersonnel.

May be performed by either plantor IT/MIS personnel.

Develop network security andmanagement strategies.

Not applicable.

This activity should be performed.
Network security andmanagement strategies should
comply with corporate policies
and procedures and be consistent
with strategies developed for theplant/enterprise network.

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4.2.3 Physical Network Design
Table 4-6
Activity

Physical Network Design

Industrial Network with Passive
Infrastructure

Select cable system components
and infrastructure devices.

This activity is equivalent toselection of the network cablesystem components.

EtherNet/IP

This activity must be performed.
System integrators and IT Dept.
may help.

4.2.4 Design Verification
Design verification activities (Table 4-7) should be performed for both isolated and non-isolated
EtherNet/IP networks and should include testing, optimization, and documentation of the network design.
Table 4-7
Activity

Design Verification

Industrial Network with Passive
Infrastructure

EtherNet/IP

Test network design.

Normally performed, usuallyconsists of a test pilot design andimplementation.

Should be performed and may
consist of design andimplementation of a test pilot.

Optimize network design.

Performed if necessary.

Should be performed if necessary.

Document network design.

Usually performed.

Should be performed or will bedifficult to troubleshoot when key
personnel are no longer available.

A more detailed description of these activities is provided in the following chapters.

4.2.5 Summary of Key Points on EtherNet/IP Design•

EtherNet/IP networks use an active infrastructure; they need routers and switches.

•

EtherNet/IP is used for control applications; subnets can handle real-time applications.

•Control traffic on EtherNet/IP is based on the producer-consumer model, resulting in IP
multicast of critical control data.

•

There are two types of EtherNet/IP networks: isolated and non-isolated.

•

For isolated networks, the network design process is similar to device-level networks.
Non-isolated networks require additional design considerations. Non-isolated networks
interface to enterprise and Wide Area Networks (WANs) and the Internet to provide
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information wherever and whenever it is needed by qualified users, such as plant andmaintenance engineers or managers.

4.3 EtherNet/IP Infrastructure Design Issues
4.3.1 Full-Duplex vs. Half-Duplex Implications
Ethernet is based on Carrier Sense Multiple Access/Collision Detect (CSMA/CD) technology. In its
original design, this technology put all nodes on a common circuit, and they could all “talk” at the sametime, which created a problem—collisions of data—because when nodes talked they could not
simultaneously listen. It was analogous to two-way radios with push-to-talk switches. If two radio
operators simultaneously responded to the same caller, the caller heard nothing but garble from the two
radios transmitting at the same time and interfering with one another. Neither operator had any way ofknowing that the other was talking. Thus, Ethernet nodes had to deal with how collisions were handled
and how connected devices could maximize their ability to transmit Ethernet without monopolizing thetime such that other nodes could not transmit.
The issue was that Ethernet was based on half-duplex (HDX) mode of operation for the connected
devices as shown in Figure 4-2. Thus, a node could only transmit data or receive data. It could not doboth at the same time. Half-duplex mode is similar to the traffic problem created when road construction
causes one lane of a two-lane highway to be closed. Traffic from both directions is trying to use the samelane. This means that traffic coming from one direction must wait until traffic coming from otherdirection stops.
Ethernet Talks and Listens at the Same TimeWith advances in switch technology, Ethernet connections have moved toward full-duplex
operation (FDX), enabling connected devices to both send and receive packets of Ethernet data at
the same time.

Ethernet Half-Duplex (HDX) and Full-Duplex (FDX)

T
X

T
X

Collision

Half-Duplex
Sending simultaneously over one
path leads to collisions.
9

6

3

T
X

Figure 4-2

Full-Duplex
Sending simultaneously over one
path doesn’t lead to collisions.

Full-Duplex Operation Eliminates Collisions.

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All of the Ethernet data communications equipment can be connected to additional switches and routers
to extend the overall physical network size. The use of fiber-optic cabling along with twisted pair helps
extend the Ethernet network. Switches and routers allow full-duplex operation—they transmit over a
dedicated transmit pair of wires (or channel) and receive over a dedicated receive channel. With fullduplex, fully switched installations, collisions will be eliminated, allowing Ethernet to be applied to realtime control applications.

4.4 Layout and Wiring Considerations
There are no rigid guidelines for deciding which type of cable to use or how to route it. However, thefollowing guidelines can make layout and wiring decisions easier by helping users compare the benefits
and limitations of various options to their specific application needs. First, Figure 4-3 provides a look at a
typical design.

Figure 4-3

Layout and Wiring of a Typical System.

4.4.1 Length of Run and Category of Cable
In general, the total length of each cable channel (segment) in an Ethernet system must not exceed 100
meters (328 ft) between any two active devices. (See Table 4-8.) For more information consult the
EtherNet/IP™ Media Planning and Installation Guide.16

16

ODVA, Inc., EtherNet/IP™ Media Planning and Installation Guide, Ann Arbor: 2006. www.odva.org

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Table 4-8

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EtherNet/IP™

Maximum Cable Lengths by TypeCable

Maximum Segment Length

10Base-T

100 meters (328 ft)

100Base-TX

100 meters (328 ft)

10Base-FL

2000 meters (6562 ft)
412 meters (half-duplex) (1352 ft)

100Base-FX (62.5 micron multimode glass fiber)
2000 meters (full-duplex) (6562 ft)
412 meters (half-duplex) (1352 ft)
100Base-FX (single-mode fiber)

15 km or more (full-duplex) (6.2 mi)Consult vendor for cable-specific limits.

1000Base-TX

100 meters (328 ft)

1000Base-SX (62.5 micron multimode glass fiber)

550 meters (1787 ft)
5 km (3 mi) up to 10 km (6 mi) based on cable type

1000Base-LX (single-mode fiber)
Consult vendor for cable-specific limits.

1000Base-LH (single-mode fiber)

Up to 120 km (75 mi) based on cable type andsignal frequency (1310 nm vs. 1550 nm)
Consult vendor for cable-specific limits.

These are maximum suggested cable lengths. For more specific Ethernet wiring rules, refer to
ANSI/TIA/EIA Std 568-B.1.17 For fast Ethernet, low noise, high-performance 24 AWG cables andconnectors are highly recommended. Any degradation in noise rejection will degrade an entire link
between a switching device and the peripheral equipment.
For Gigabit operation, the increase in speed also increases the potential for data corruption by electricalnoise, and requires additional attention to the cabling layout of the installation. Cat6 data cable isrecommended for use with Gigabit Ethernet for higher noise immunity. Be aware of distance constraints
for multimode fiber as it is typically no more than 550 meters (about 600 yds) for Gigabit Ethernet. Thisis compared to 2 km (1 mi) or more for 100-Mbps Ethernet.
17

ANSI/TIA/EIA-568-B Series, Commercial Building Telecommunications Cabling – Part 1: General Requirements.

http://www.tiaonline.org/
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4.4.2 Cable Routing
A proper cable routing plan is essential. EtherNet/IP or any network cables should not be routed nearequipment that generates strong electric or magnetic fields. In particular, routing network cables near andaround the following should be avoided:•

Lights, especially those using ballasts such as mercury vapor, sodium, or fluorescent•

Motors—any size, especially if their speeds are controlled by variable frequency drives•

Drive controllers•

Arc welders•

Conduit carrying high-voltage/high currents

4.4.3 Categories of Conductors/Wiring
There are three categories of conductors for wiring in any manufacturing facility.
Category One consists of

•
•
•
•

ac power lines,
high-power digital ac I/O,
high-power digital dc I/O, andpower connections (conductors) from motor drives to motors.

Category Two consists of

•
•
•
•
•

analog I/O lines,
dc power lines for analog devices,low-power digital ac/dc I/O lines,
low-power digital I/O lines, andEtherNet/IP.

Category Three typically includes••

low-voltage dc power lines andcommunication cables between system components within the same enclosure.

4.4.4 General Design Wiring Guidelines
The following guidelines should be followed for wiring all EtherNet/IP cables:•

If an EtherNet/IP cable must cross power lines, it should do so at right angles.

•

EtherNet/IP cabling should be routed at least 1.5 meters (5 ft.) away from high-voltage
enclosures or sources of radio frequency (RF)/microwave radiation.

•

If the EtherNet/IP cable is running through a metal wire-way or conduit, each section of
the wire-way or conduit must be bonded to each adjacent section so that it has electrical
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continuity along its entire length. It also must be bonded to the enclosure at the entry
point.
For more information on general wiring guidelines, see Industrial Automation Wiring and Grounding
Guidelines18 and the Telecommunications Industry Association publication ANSI/TIA/EIA-607,
Grounding and Bonding Requirements.19

4.4.5 Wiring External to Enclosures
Cables that run outside protective enclosures may be relatively long. To minimize cross-talk from nearby
power lines, it is good practice to maintain maximum separation between the Ethernet cable and otherpotential noise conductors. The following guidelines should be followed for routing network cables near
potential noise-inducing cables.
Within a contiguous metal wire-way or conduit•

Category 1 conductors of less than 20 amps: maintain a 0.08-meter (3-in.) separation
distance.

•

AC power lines of 20 amps or more, up to 100 KVA: maintain a 0.15-meter (8-in.)separation distance.

•

AC power lines greater than 100 KVA: maintain a 0.3-meter (12-in.) separation distance.

In open-air cabling systems•

Category 1 conductors of less than 20 amps: maintain a 0.15-meter (8-in.) separation
distance.

•

AC power lines of 20 amps or more, up to 100 KVA: maintain a 0.3-meter (12-in.)separation distance.

•

AC power lines greater than 100 KVA: maintain a 0.6-meter (24-in.) separation distance.

Local, regional, and national codes regarding the grouping of cables should also be followed. In theabsence of these codes, the general rule for noise protection is a minimum distance of 7.6 cm (3 in.) fromelectric light and power conductors and an additional 2.5 cm (1 in.) for each 100 volts over the 100-volt
level. See Table 4-9 for outside wiring recommendations.

18

Rockwell Automation, Industrial Automation Wiring and Grounding Guidelines. Publication 1770-4.1. Milwaukee: Rockwell
Automation, 1998. http://literature.rockwellautomation.com/

19

TIA-J-Std 607-A, Commercial Building Grounding (Earthing) and Bonding Requirements for Telecommunications.

http://retail.ihs.com/abstracts/tia/tia-j-std-607a.jsp
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Table 4-9

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Outside Wiring

Voltage Level

Minimum Distance

0-100 V

7.6 cm (3 in.)101-200 V

10.2 cm (4 in.)

201-300 V

12.7 cm (5 in.)

301-400 V

15.2 cm (6 in.)401-500 V

17.8 cm (7 in.)

4.4.6 Wiring Inside Enclosures
Cable sections that run inside protective equipment enclosures are relatively short. As with wiringexternal to enclosures, maximum separation between Ethernet cables and Category-1 conductors should
be maintained.
When running cable inside an enclosure, conductors should be routed external to all raceways in the sameenclosure or in a raceway separate from Category-1 conductors. Cable should be routed at least the
distance from the noise source listed in Table 4-10.
Table 4-10
Minimum DistanceRouting Cable Around Various Noise Sources
Strength of Noise Source

0.08 meter (3 in.)Category-1 conductors of less than 20 amps

0.15 meter (8 in.)AC power lines of 20 amps or more, up to 100 KVA

0.6 meter (24 in.)AC power lines greater than 100 KVA

4.4.7 Cable Grounding Considerations
For information regarding grounding and bonding requirements for your network, the appropriate local,
regional, and national or international codes should be followed.

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Grounding of Shielded Cables

Shields play an important role in providing noise immunity for systems. However, an improperly
installed shielded cable can cause problems due to voltage offsets in a grounding system. To
minimize the effects of ground offsets, the shield should be isolated at one end of the cable. In thiscase, the shield should be isolated at the device. The ground can be applied at the switch or otherinfrastructure component. It should be noted that some European wiring practices recommend
grounding the cable shields at both ends, requiring that particular care be taken to avoid groundloops. The quality of a plant’s grounding system must be thoroughly evaluated prior to using thisapproach.
Eliminating ground loops is extremely important in reducing noise interference caused byground offsets or local ground transients. Ground offsets occur when there is a potential difference
between two earth-ground points in a system as shown in Figure 4-4. This potential difference can consistof continuous dc or ac voltages as well as transients.

Figure 4-4

Ground Noise Loop in Shielded Cable.

A cable that connects the two points together provides a secondary travel path for current. The current
through the communications cable’s shield will couple noise into the communications system. This noise
will have a direct impact on the signal-to-noise performance of the system.

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There can be as much as a 45-volt high frequency offset in ground potential between the two ends of a
100-meter (328 ft) cable. This offset can cause noise currents in the shields. Consequently, to eliminate
ground loops, the cable should be grounded at the switch end only as shown in Figure 4-5.

Figure 4-5

Grounding of Cable Shield.

If, for example, a device other than a switch provides a low resistance (<500k ohms) ground at the jack,the shield should not be connected at the device end of the cable. Rather, the shield should be cut backand insulated from the connector plug’s shell to break the ground as shown in Figure 4-6.

Figure 4-6

Null Termination of Shielded Cable.

4.5 Industrial Ethernet Connectors
4.5.1 Attributes of Industrial Ethernet Cables
When selecting network cable, the jacket construction must be compatible with any vibration and thetemperature and chemicals in the environment. It is important not to overlook cable electrical
specifications, such as over-temperature, as many off-the-shelf cables do not meet the TIA/EIA standards
at industrial temperatures. Cable jackets may by easily damaged, even at low temperature ranges.
Chemicals can be absorbed into the jackets and wire insulation, causing plastic deterioration andperformance degradation. Sealed media may be required if connectors or cable jackets are exposed to aharsh environment.
In industrial unshielded cable installations, the use of balanced cables is recommended. If the networking
application is in a high-noise environment, then shielded cable media or fiber-optic cabling should beconsidered.
4.5.1.1 Oil-resistant Jackets
If an application requires control of equipment that uses cutting oils or lubricating chemicals, cables
constructed with oil-resistant jackets should be specified.

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4.5.1.2 Plenum-rated Cables
Plenum installations require special material compounds in the makeup of cables. If an application
requires cables to be run in air-handling space, plenum-rated cables should be used, and may be requiredby local electrical codes. (Often local electrical codes are concerned with voltage and current levels for
power wiring in a heated duct.) Another cautionary note: Many air-handling ducts have sharp edges ofsheet metal throughout—especially at joints and corners, which can easily cut cable when it is pulled
through existing duct work.
4.5.1.3 Weld Splatter-Proof Cables
If an application requires control of welding equipment, cables should be routed to reduce damage fromweld splatter and noise ingress. All cables should be routed to cross over welding and motor control
cables at right angles and should never run parallel to control cables. The cables should be protected fromweld splatter either by adding protective sheath, using conduit, or selecting cables with the proper jacket
insulation.
4.5.1.4 High Flex
Typically, Ethernet cables are constructed of 24-gauge solid copper conductors, which are not suited toconstantly moving machinery, such as robots. High-flex applications require stranded-type conductor
construction to extend the life of a cable in flexing applications. Also note that high-flex cables are rated
differently based on the type of flexing to which they will be exposed. Trailing cable or “C Track”
applications require different cables than applications where cables are exposed to a continuous back andforth, or “tick-tock” type of flexing. Other technologies that can replace wiring in these applications
include wireless and infra-red (IR) communications.
4.5.1.5 Ambient Temperature
The ambient temperature of the environment must be considered in specifying the cables and connectors
to be installed. Some Ethernet cables cannot survive or will not perform to specification in the extreme
hot and cold temperatures of some industrial environments.

4.6 Performance Considerations: The Need for Switches
Managing network traffic involves knowing what hardware to apply, such as a switch versus a router. It
also requires logical segmentation of the network. Using Virtual LANs (VLANs), for instance, can becompared to assigning a lane on a highway for trucks only. Finally, just as a freeway system gives
priority to emergency vehicles, network traffic must be prioritized. The objective is to use various
mechanisms to assure that critical messaging traversing the network will always have enough resources toguarantee it will arrive—and arrive on time.

4.6.1 Performance of Switches
In the past, nodes were simply connected together using hubs wherever possible to keep costs low. Theirlimitations have already been covered. While hubs provide an easy way to add additional nodes andextend the length of the network, they do not break up the actual network into discrete segments. That is a
job for switches.
Switches are a fundamental part of most networks. They make it possible for several users to send
information over a network at the same time without slowing each other down.
In a fully switched network, switches replace all the hubs of an Ethernet network with a dedicatedsegment for every node. Since the only devices on each segment are the switch and the node, the switch
picks up every transmission before it reaches another node. The switch then forwards the frame over the
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appropriate segment. Since any segment contains only a single node, the frame only reaches the intended
recipient. Before switches were used, Ethernet was a half-duplex network. Thanks to managed andunmanaged switches, Ethernet can be a full-duplex network.
Switched Networks and Full-Duplex Ethernet

In a switched network, nodes only communicate with the switch and never directly with each other.
With a dedicated segment for every node, switching allows a network to maintain full-duplex
Ethernet.
Switched networks employ either twisted-pair or fiber-optic cabling, both of which use separate
conductors for sending and receiving data. In this environment, Ethernet nodes can forgo the collision
detection process and transmit at will, since they are the only potential devices that can access themedium.
In other words, traffic flowing in each direction has a lane to itself. This allows nodes to transmit to theswitch at the same time the switch transmits to them, achieving a collision-free environment. Transmitting
in both directions also can effectively double the apparent bandwidth of the network when two nodes areexchanging information. For example, if the speed of the network is 100 Mbps, then each node cantransmit at 100 Mbps at the same time.

4.7 Switching Technologies
Switches usually work at Layer 2 (data link) of the OSI Reference Model using MAC addresses whilerouters work at Layer 3 (network) with Layer 3 addresses (IP, IPX®, or AppleTalk® depending on what
Layer 3 protocols are being used). The algorithm that switches use to decide how to forward packets isdifferent from the algorithms that routers use to forward packets.
One of the differences between the algorithms of switches and routers is how each algorithm handles
broadcasts. On any network, the concept of a broadcast packet is vital to the operability of the network.
Whenever a device needs to send out information but does not know where to send it, it sends out abroadcast. For example, every time a new computer or other device comes onto the network, it sends out
a broadcast packet to announce its presence. Broadcasts are transmitted any time a device needs to makean announcement to the rest of the network or is not sure where to send information.
A switch will pass along any broadcast packets it receives to all other segments in the broadcast domain,
but a router will not. Without the specific address of another device for which a message is intended, arouter will not let the data packet pass through. This is an effective way of keeping networks separate
from each other but is not helpful when different parts of the same network need to communicate with
one another. Switches provide a solution to this problem.

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Ethernet Switches Rely on Packet-Switching.

The switch establishes a connection between two segments and maintains the connection just longenough to send the current packet. Incoming packets, which are part of an Ethernet frame, aresaved to a temporary memory area called a buffer. The MAC address contained in the frame’s
header is read and then compared to a list of addresses maintained in the switch’s lookup table.
Today’s packet-based switches normally use the store-and-forward method of routing traffic. Previously
installed switches may also have used the cut-through, or modified cut-through traffic routing techniques.
The cut-through method of switching is based on the premise that there is no need for the switch to wait
for the arrival of the complete frame. The switch waits only long enough to read the destination address inthe frame before it begins forwarding the frame to its destination.
A switch using store-and-forward will save the entire packet to the buffer and run a Cyclic Redundancy
Check (CRC) to locate transmission and storage errors or other problems. If the packet has an error, thenit is discarded. Otherwise, the switch looks up the MAC address and sends the packet on to thedestination node. Some switches combine the two methods by using cut-through until a certain error levelis reached, then changing over to store-and-forward. Very few switches are strictly cut-through since thisprovides no error detection.
Modified cut-through (also known as fragment-free) switches are an attempt to offer the best of bothstore-and-forward and cut-through switching. In an Ethernet environment, an incoming frame is held until
the first 64 bytes have been received. If the frame is incomplete or corrupt, it can usually be detected
within the first 64 bytes. Therefore, a trade-off between switch latency and error checking is achieved.
Message Types

There are three types of communication in IP networks: unicast, multicast and broadcast. A unicast
packet is addressed to an individual node, a multicast packet is addressed to a group of nodes, anda broadcast packet is addressed to all nodes on a network. Each node, regardless of the type ofcommunication in which it participates, must have a uniquely assigned IP address. When anothernode wants to send a unicast packet to this node, it must use this address as a destination address.
When a node wants to send to this node, or a group of nodes, it must use a multicast packet and a
destination address, a specific address selected from the IP multicast address class (class D). When anode wants to send a broadcast packet addressed to all nodes on the network, it must use, as adestination address, IP address 255.255.255.255.

4.8 IGMP Snooping
Internet Group Management Protocol (IGMP) snooping constrains the flooding of multicast traffic by
dynamically configuring the switch interfaces such that multicast traffic is forwarded only to thoseinterfaces associated with IP multicast devices. In other words, when a multicast message is sent to theswitch, the switch forwards the message only to the interfaces that are interested in this traffic.

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IGMP Snooping

The Internet Group Management Protocol is very important because it reduces the load of traffic
traversing through the network. It also relieves the hosts from processing frames that are not needed.
In the producer-consumer model used by EtherNet/IP, IGMP snooping limits unnecessary traffic from theproducing I/O, such that it only reaches the devices that consume that data. Messages delivered to a given
device (say Device A) that were intended for another device (say Device B) will consume resources,
negatively affecting the performance of Device A.
Networks with multiple multicasting devices will suffer performance issues if IGMP snooping or othermulticast limiting schemes are not implemented. The number of devices that can be supported in a given
network varies with the type of traffic that is present.
When using IGMP snooping, at least one IGMP querier is needed somewhere on the network. A router orswitch can act as the IGMP querier if the device supports this functionality. An IGMP querier periodicallyqueries the multicast receiving devices as to their multicast interest. Once queried, a multicast recipient
will respond with the multicasts it wishes to receive by sending an IGMP Join Report for each multicast
group in which it has interest.
The Ethernet switch snoops on the IGMP traffic coming to that switch and keeps track of multicast
groups and member ports. When the switch receives an IGMP Join Report from a host for a particularmulticast group, the switch adds the host port number to the associated multicast forwarding table entry.
When it receives an IGMP Leave Group message from a host, it removes the host port from the tableentry. After it relays the IGMP queries, it deletes entries periodically if it does not receive any IGMP
membership reports from the multicast clients. A Layer 3 device (router) normally performs the querying
function, but it can also be implemented by another network element designed to take over thisfunctionality.
When IGMP snooping is enabled in a network with Layer 3 devices, the multicast router sends out
periodic IGMP general queries to all VLANs. The switch responds to the router queries with only one
join request per MAC multicast group, and the switch creates one entry per VLAN in the Layer 2
forwarding table for each MAC group from which it receives an IGMP join request. All hosts interested
in this multicast traffic send join requests and are added to the forwarding table entry.
Layer 2 multicast groups learned through IGMP snooping are dynamic. However, in a managed switch, it
is possible to statically configure MAC multicast groups. If a group membership for a multicast groupaddress is specified statically, this setting supersedes any automatic manipulation by IGMP snooping.
Multicast Group Membership Lists can consist of both user-defined and IGMP snooping-learned
settings.
If a port spanning-tree, a port group, or a VLAN ID change occurs, the IGMP snooping-learned multicast
groups from this port on the VLAN are deleted.

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4.8.1 Joining a Multicast Group
When a host connected to the switch wants to join an IP multicast group, it sends an IGMP join request,
specifying the IP multicast group it wants to join. When the switch receives this message, it adds the port
to the IP multicast group port address entry in the forwarding table.
In Figure 4-7, Host 1 wants to join multicast group 224.1.2.3 and multicasts an unsolicited IGMP Join
Report (IGMP join message) to the group with the equivalent MAC destination address of0100.5E01.0203. The switch recognizes IGMP packets and forwards them to the CPU.

Figure 4-7

Initial IGMP Join Message.

When the CPU receives the IGMP report multicast by Host 1, the CPU uses the information to set up amulticast forwarding table entry as shown in Table 4-11. This entry includes the port numbers of Host 1
and the router.
Table 4-11

Multicast Forwarding Table Entry

IP Multicast Forwarding Table Destination Address

Type of Packet

Ports

0100.5E01.0203

!IGMP

1, 2

The switch architecture allows the CPU to distinguish IGMP information packets from other packets forthe multicast group. The switch recognizes the IGMP packets through its filter engine. This prevents the
CPU from becoming overloaded with multicast frames.
The entry in the multicast-forwarding table tells the switching engine to send frames addressed to the0100.5E01.0203 multicast MAC address that are not IGMP packets (!IGMP) to the router and to the hostthat has joined the group.

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Figure 4-8

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Second Host Joining a Multicast Group.

If another host (for example, Host 4 in Figure 4-8) sends an IGMP join message for the same group, theCPU receives that message and adds the port number of Host 4 to the multicast forwarding table as shownin Table 4-12.
Table 4-12

Updated Multicast Forwarding Table Entry

Updated Multicast Forwarding Table Destination Address

Type of Packet

Ports

0100.5E01.0203!IGMP

1, 2, 54.8.2 Leaving a Multicast GroupThe router sends periodic IP multicast general queries, and the switch responds to these queries with one
join response per MAC multicast group. As long as at least one host in the VLAN needs multicast traffic,
the switch responds to the router queries, and the router continues to forward the multicast traffic to the
VLAN. The switch only forwards IP multicast group traffic to those hosts listed in the forwarding table
for that IP multicast group.
When hosts need to leave a multicast group, they can either ignore the periodic general-query requests
sent by the router, or they can send a leave message. When the switch receives a leave message from ahost, it sends out a group-specific query to determine if any devices behind that interface are interested intraffic for the specific multicast group. If, after a number of queries, the router processor receives noreports from a VLAN, it removes the group for the VLAN from its multicast-forwarding table.

4.8.3 Immediate-Leave Processing
IGMP snooping immediate-leave processing allows the switch to remove an interface that sends a leavemessage from the forwarding table without first sending out MAC-based general queries to the interface.
The VLAN interface is pruned from the multicast tree for the multicast group specified in the original
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leave message. Immediate-leave processing ensures optimal bandwidth management for all hosts on aswitched network, even when multiple multicast groups are in use simultaneously.

4.9 Quality of Service in a Switched Network
Phrases like “gigabits of back-plane capacity,” “millions of switched packets per second,” and “nonblocking switch fabrics” reflect the high-performance of today’s Ethernet switches and typically generate
a simple question: Why the need for Quality of Service (QoS)? The answer is congestion.
A switch may be the fastest switch in the world, but if either of the two scenarios in Figure 4-9 is present,
the switch will experience congestion.

Figure 4-9

Inputs Higher in Speed or Quantity than Outputs Cause Congestion.

If the congestion management features on the switch are not up to par during these congested periods,
performance will suffer and packets will be dropped. In a TCP/IP network, packet drops will generate
retransmissions, which then increases network load. In networks that are already congested, this increasein network load further exacerbates existing network performance issues.
Latency-sensitive traffic, such as motion control messages, can be severely affected if transmission delays
occur. Adding more buffers to a switch will not necessarily alleviate congestion problems since latencysensitive traffic needs to be switched as quickly as possible.
To address network congestion issues, different stages of QoS need to be implemented:•

First, identify different traffic types in the network using classification techniques.

•

Next, implement advanced buffer management techniques to avoid high-priority
traffic from being dropped during congestion.

•

Finally, incorporate scheduling techniques to transmit high-priority traffic fromqueues as quickly as possible.

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4.9.1 QoS Flow
The common definition of QoS in Layer 2 switches is to prioritize native encapsulated Ethernet frames or
to honor 802.1p Class of Service (CoS) tagged Ethernet frames.20 However, advanced QoS mechanisms
take this definition a step further. Layer 2 QoS on advanced Ethernet switches entail up to four distinct
stages: classification, policing, marking, and queue/schedule. As shown in Figure 4-10, the first three
represent actions taken at ingress, and queue/schedule is an action taken at egress.

Actions
at Egress

Actions
at Ingress

Classification

Policing

Marking

Classify packet
based on priority
or flag.

Determine if packet
is in profile or out of
profile based onpolicer associatedwith filter.

Based on whether packet
is in or out of profile andconfigured parameters,
determine forwarding
action and act
accordingly.

Figure 4-10

Queue/
Schedule
Based on CoS,
determine into which of
the egress queues toplace packet. Then
service queues
according to configured
weights.

Quality of Service Stages.

Feature-rich switches can be used to study and interpret the flow of QoS traffic through the switch from
ingress, as it gets processed through the switch fabric, and as it flows out (egress).
A switch can be configured to prioritize frames based on given criteria at different layers of the OSI
Model’s stack. For example, priorities may be assigned according to the source MAC Address (Layer 2)or the destination TCP port (Layer 4). Any traffic traveling through the interface to which these criteria
apply will be classified and tagged within the frame header, assigning them a given priority. Once thepacket has been classified, it can be policed/marked down (if necessary), and it will be queued according
to the specified priority. Once it has been placed into the appropriate holding queue for transmission onegress, it will be scheduled based on the configuration of the scheduling algorithm.

4.9.2 Class of Service
Class of Service (CoS) refers to three bits on an 802.1Q header that are used to indicate the priority of the
Ethernet frame as it passes through a switch network. The CoS bits in the 802.1Q header are commonlyreferred to as the 802.1p bits. Not surprisingly, there are three CoS bits that match the number of bits used
for IP Precedence (which is part of the Type of Service [ToS] byte). In many networks, to maintain endto-end QoS, a packet may traverse both Layer 2 and Layer 3 domains, thus the ToS and CoS fields should
be mapped to each other.

20

IEEE Std 802.1p is a Standard used in IEEE Std 802.1D, Standard for Local and Metropolitan Area Networks: Media AccessControl Bridges, and used in IEEE Std 802.1Q, IEEE Standard for Local and Metropolitan Area Networks – Virtual Bridged
Local Area Networks. http://standards.ieee.org/getieee802/802.1.html
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Figure 4-11 depicts an Ethernet frame tagged with an 802.1Q field, which consists of a two-byte
Ethertype and a two-byte 802.1Q Tag. Within the two-byte tag are the user priority bits (known as 802.1p
CoS bits).

Figure 4-11

Details of Ethernet Frames and IP Packet.

4.9.3 Priority Mechanisms
For any QoS services to be applied to data, there must be a way to “tag” or prioritize an IP packet or an
Ethernet frame. The Layer 2 802.1p Class of Service (CoS) and Layer 3 IP Type of Service (ToS) are thefields used to achieve this as shown in Figure 4-12.

Figure 4-12

Prioritization of IP Packets.

There are several parameters to take into account when considering Layer 2 through Layer 4classification. A switch can implement Layer 2 classification (as shown in the “Encapsulated Packet”
diagram within Figure 4-12) by looking at the Layer 2 Header and classifying the frame accordingly. An
advanced managed switch may also view any CoS value that comes tagged on a frame coming into theswitch and will use this information to determine the priority that it should be assigned, then take theappropriate actions. Feature rich switches will also process the packets based on Layer 3 IP address
information as well as Layer 4 (TCP and UDP) information, and the Differentiated Services Code Point(DSCP) value.

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4.10 Virtual Local Area Networks
As networks have grown in size and complexity, many companies have turned to Virtual Local Area
Networks (VLANs) to provide a means for structuring this growth logically. Basically, a VLAN is a
network that is created logically, using software, as opposed to physical cabling. Therefore, only devices
predefined according to a specific criterion for the same broadcast domain will receive a transmission
generated by a station on a VLAN.
A broadcast domain is a network (or portion of a network) that will receive a broadcast packet fromany node located within that network. Since routers do not pass along broadcast messages, in a typical
network everything on the same side of the router is part of the same broadcast domain.
Switches Implemented with VLANs

A switch implemented with VLANs has multiple broadcast domains similar to a router. The
switching device used to construct a VLAN can be an advanced managed Layer 2 switch that
operates at the MAC sub-layer of the OSI Model, or a Layer 3 switch that operates at the network
layer.
Here are some common reasons why a company might want to install VLANs:•

Security. Separating systems with sensitive data from the rest of the network decreases
the chance that someone will gain access to information they are not authorized to see.

•

Projects/special applications. Managing a project or working with a specialized
application can be simplified by using a VLAN to bring all the required nodes together.

•

Performance/bandwidth. Monitoring of network use allows the network administrator
to create VLANs that reduce the number of router hops and increase the apparent
bandwidth for network users.

•

Broadcasts/traffic flow. Since a principle element of a VLAN is that it does not passbroadcast traffic to nodes that are not part of the VLAN, it automatically reduces
broadcasts. Access lists provide the network administrator with a way to control who sees
what network traffic.
•

Departments/specific job types. Companies may want to set up VLANs for

departments that are heavy network users (such as Multimedia or Engineering). A VLAN
dedicated to specific types of employees from different departments (such as managers or
sales people) might also be set up across departments.
While more than one VLAN can exist on a single switch, these VLANs cannot communicate directly witheach other. If they could, it would defeat the purpose of having a VLAN, which is to isolate a part of the
network. Communication between VLANs requires the use of a router.

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VLAN Trunking

VLANs can span across multiple switches and you can have more than one VLAN on each switch. For
multiple VLANs on multiple switches to be able to communicate via a single link between the switches,trunking is needed. Trunking is the technology that allows information from multiple VLANs to be
carried over just one link between switches.
Switches use VLAN trunking protocols to communicate VLAN configuration information between
them. Standardized protocols such as the Group VLAN Registration Protocol (GVRP) allow VLAN
trunk connections between switches from different vendors. Proprietary, vendor-specific trunking
protocols are also available.

Figure 4-13 Devices on Three VLANs Communicate via Trunking Links
between Three Switches and a Router.

In Figure 4-13, each switch has two VLANs. On the first switch, VLAN A and VLAN B are sent througha single port (trunked) to both the router and through another port to the second switch. VLAN C andVLAN D are trunked from the second switch to the first switch and through it to the router. This trunk
can carry traffic from all four VLANs. The trunk link from the first switch to the router can also carry all
four VLANs. In fact, this one connection to the router actually allows the router to appear on all four
VLANs as if it had four different physical ports connected to the switch.
The VLANs can communicate with each other via the trunking connection between the two switches
using the router. For example, data from a computer on VLAN A that needs to get to a computer on
VLAN B (or VLAN C or VLAN D) must travel from the switch to the router and back again to theswitch. Because of the switches’ transparent bridging algorithm and trunking, both PCs and the router
think they are on the same physical segment.

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4.11 Multilayer Ethernet Switches
A multilayer Ethernet switch performs the traditional function of a Layer 2 device but also can performfunctions based on information from other layers of the networking stack. For example, a multilayerswitch can inspect the IP information encapsulated in an Ethernet frame and perform routing decisions
based on it (Layer 3 switching), assign a given priority to the frame (QoS), and deny or permit access(security). A Layer 4-aware switch could do the same based on UDP or TCP ports (source or destination).
This can be a very useful feature in EtherNet/IP networks as a switch can be configured to give highpriority to the Common Industrial Protocol (CIP) traffic based on the UDP port destination/source in the
datagram. It also could prevent unauthorized users from accessing the network by checking their IP
addresses.

4.11.1

Layer 2 and Layer 3 Switching

Switching is the process of taking an incoming frame from one interface and delivering it out throughanother interface. Routers use Layer 3 switching to route a packet, and switches (Layer 2 switches) use
Layer 2 switching to forward frames.
The Difference between Layer 2 and Layer 3 Switching

The difference between Layer 2 and Layer 3 switching is the type of information inside the framethat is used to determine the correct output interface. With Layer 2 switching, frames are switchedbased on MAC address information. With Layer 3 switching, frames are switched based on
network-layer information.
Traditional Layer 2 switching does not look inside a packet for network-layer information as does Layer 3
switching. Layer 2 switching is performed by looking at a destination MAC address within a frame. It
looks at the frame’s destination address and sends it to the appropriate interface if it knows the destination
address location. Layer 2 switching builds and maintains a switching table that keeps track of which
MAC addresses belong to each port or interface.
If the Layer 2 switch does not know where to send the frame, it transmits the frame out on all its ports andis said to flood the ports to learn the correct destination. When the frame’s reply is returned, the switch
learns the location of the new address and adds the information to the switching table.
Layer 2 Addresses

Layer 2 addresses are determined by the manufacturer of the data communications equipment. They
are unique addresses that are derived in two parts: the manufacturing (MFG) code and the unique
identifier. The MFG code is assigned to each vendor by the IEEE. The vendor assigns a unique
identifier to each board it produces. Layer 2 addresses are fixed with a device, whereas Layer 3
addresses can be changed. In addition, Layer 2 addresses assume a flat address space with
universally unique addresses.

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Layer 3 switching operates at the network layer. It examines packet information and forwards packets
based on their network-layer destination addresses. Layer 3 switching also supports router functionality.
As routers operate at Layer 3 of the OSI Model, they can adhere to and formulate a hierarchicaladdressing structure. Therefore, a routed network can tie a logical addressing structure to a physicalinfrastructure, for example, through TCP/IP subnet networks for each segment. Traffic flow in aswitched (flat) network is, therefore, inherently different from traffic flow in a routed (hierarchical)
network. Hierarchical networks offer more flexible traffic flow than flat networks because they can use
the network hierarchy to determine optimal paths and contain broadcast domains.

Figure 4-14

Flow of Inter-subnet Traffic with Layer 2 Switches and Routers.

As shown in Figure 4-14, for the PC client to communicate with Server 1, which is on another subnet, it
must traverse through Switch 1 (a Layer 2 switch), then through the router (a Layer 3 switch) and, finally,
through Switch 2 (a Layer 2 switch). There is the potential for a tremendous bottleneck, which canthreaten network performance, because the inter-subnet traffic must pass from one network to another.
To relieve this bottleneck, network designers can add Layer 3 capabilities throughout the network. By
implementing Layer 3 switching on edge devices, they can alleviate the burden on centralized routers.
Figure 4-15 illustrates how deploying Layer 3 switching throughout the network allows the PC client tocommunicate directly with Server 1 without passing through the router.

Figure 4-15

Flow of Inter-subnet Traffic with Layer 3 Switches.

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4.12 Achieving Deterministic Behavior
Different mechanisms can be implemented to achieve reliable and deterministic behavior on a network.
Scale and criticality are two key factors for determining when to implement such mechanisms. Just as aback country road often can effectively move traffic and manage the potential for collisions with a single
lane, traffic in larger metropolitan areas generally demands multi-lane, multi-level highways. As theamount of traffic increases, the need for mechanisms that can guarantee a given performance becomes
evident.
In general, two factors drive the need to implement performance mechanisms in EtherNet/IP networks.
•

Scale: Small networks that will not be sharing their resources with other applications,such as video, voice, non-control data, etc. have lower potential for congestion andconsequent jitter, latency, and frame losses. As the networks grow and the hosts begin
sharing data through a producer-consumer model, the need for mechanisms such as
IGMP snooping and QoS become indispensable to guarantee a deterministic behavior.

•

Criticality: Some applications can tolerate lost data without any significant impact on the

manufacturing process, and other applications can be adversely affected by even smalllatency or packet loss. Even small disruptions can have a big economic impact on a
manufacturing facility. In these cases, it is normally a requirement to implement costeffective solutions that reduce the potential for a work stoppage.
Large EtherNet/IP deployments or deployments where a line stop is critical should consider
implementing:•A fully switched network. This will eliminate collisions and improve the deterministic
behavior of the data network.

•

Quality of Service (QoS) traffic prioritization. QoS prioritization allows time criticaltraffic to have preferential handling over supervisory traffic.
•

Logical segmentation of the network. VLANs improve security and containbroadcast messaging.
•

IGMP snooping. This will control multicast messages that can slow the performance ofthe network hosts. It also exponentially reduces the amount of traffic on the network,
reducing the chance for congestion and consequent packet loss.

4.13 Managing the Interface between Control and IT
Managing the interface between control and IT requires cooperation between two disparate sets of needs.
Covered here is the technology of integration—connecting EtherNet/IP networks to enterprise networks.
There is no doubt that EtherNet/IP networks can solve the “islands of automation” syndrome that has
plagued manufacturers for so long, but making them work with the enterprise network will require a
commitment for cooperation between a manufacturer’s enterprise Information Technology Department
and plant-floor network engineers.

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It is important to keep in mind that everyone is working for the same team and toward the same goals.
This spirit of cooperation is a prerequisite to achieving an effective plant-floor-to-enterprise information
system. Business leaders also must realize that while engineers from both disciplines share the sameideals—performance, speed, and security—they tend to employ different problem-solving methods toachieve the same ends.
EtherNet/IP networks installed by control engineers will be carefully scrutinized by IT network specialists
before interconnecting them to business-level applications. For example, the IT department probably willinsist that any Ethernet infrastructure devices follow IT guidelines, policies, and procedures.
In addition, the IP addresses used on EtherNet/IP networks will need to be coordinated with an IT IP
address administrator. Network management policies will need to be changed to give IT operations’support personnel access to Ethernet switch configuration parameters. The security threats posed bydevices on the EtherNet/IP networks will require gateway and/or firewall protection for the IT network.
Conversely, control engineers are likely to insist on “owning” the EtherNet/IP network switch hardware
installed on the plant floor. They will require that any piece of communication equipment conveying
control signal traffic be locally monitored, readily accessible, and replaceable by on-site maintenancepersonnel. Control engineers may deem the IT support policies for critical production equipment to be notsufficiently real-time for the uptime demands of the factory floor, and an IT department counter-proposal
to install redundant networks to ensure communication reliability may be deemed too expensive for the
return-on-investment metrics of the plant. Control engineers may complain that the IP addressadministration policies and procedures are not workable for their plant-floor requirements, and may insist
on the ability to modify or expand control system networks without outside interference.
In one respect, IT security practices may be criticized for being too excessive for the control system
environment. Conversely, control system vendors are very cautious about operating system security
patches, and will want to verify that any operating system patches are compatible with control systems
before they are applied. Indiscriminate application of operating system and security patches has been
known to shut down some control system software that has not yet been checked out for operation withthe patches.
Who owns EtherNet/IP networks? This is not a simple question. EtherNet/IP networking issues span boththe information technologies’ and control systems’ organizational boundaries.
Having looked at isolated and non-isolated networks and provided detailed instructions for designing andplanning EtherNet/IP networks, as well as covering wiring issues, network topologies, and factors that
affect network performance, perhaps the most important issue is the “people factor.” Control engineers
and IT engineers need to work together on the top-down approach presented here to build an effectiveplant-wide information system that gets the right data to those who need it wherever they are, and to get
the data to these destinations promptly and securely.

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5 Deploying the Network
EtherNet/IP networks can be tested using relatively inexpensive equipment and software.
There are some quick and easy methods of assuring that EtherNet/IP cables andconnectors are providing connectivity. Deployment also involves configuring the system
for EtherNet/IP traffic.
Methods of self-testing routers and switches make it easy to diagnose the basic issues: Is it connected?
Does it see its signal? Easy software checks can further ensure that the connections are not only made, butthat hardware will communicate over TCP/IP connections. Simple hand-held testers are available, manyof which offer embedded diagnostics. Using such testers, engineers can be assured that a new system willcommunicate without having to spend tens of thousands of dollars on test equipment.
EtherNet/IP provides a large set of simple, universal tools that can be leveraged to increase the speed of
network deployments. It opens the door for remote monitoring via SNMP (potentially from any place inthe world) to improve the productivity of the network users.
From a cabling perspective, deployment of EtherNet/IP is similar to the deployment of DeviceNet;validation of proper connection of the physical layer is vital. Major differences, however, between
EtherNet/IP and DeviceNet include the following:•

EtherNet/IP has a star topology; DeviceNet uses a trunk-line/drop-line topology.

•

The switching infrastructure of EtherNet/IP becomes a part of the network that may need
to be configured to optimize its performance. DeviceNet can be configured as a masterslave or as a distributed control architecture using peer-to-peer communication.

5.1 Validating the Integrity of the Physical Layer
Implementing the physical layer involves four steps: design, installation, cable verification, andcertification or acceptance testing. Performance testing and verification of the EtherNet/IP physical layer
infrastructure, whether copper or fiber-optic cable, is essential after installation and before network
startup. This is similar in practice to testing any industrial network infrastructure, such as DeviceNet orControlNet.
Each cabling segment (consisting of cable and connectors) must be tested to confirm that, after
installation, the segments all conform to The EtherNet/IP™ Specification21 for performance. As noted
earlier, the use of pre-terminated cables is strongly advised to limit problems with field terminations. If
commercially-supplied cables with RJ-45 connectors must be used, they should be kept in tightly-closed
21

ODVA, The CIP Networks Library, Vol. 1 and 2, The EtherNet/IP™ Specification. Ann Arbor: ODVA, Inc., 2006.

www.odva.org. CD-ROM.
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cabinets to protect them from shop-floor environments. For critical applications, the use of more durable
sealed connectors will stand up to the rigors of plant-floor environments.
Testing is easily done with commercially available hand-held network testers. Special adapters may benecessary for sealed connectors. Testing output includes conformance to all electrical requirements
including, but not limited to, attenuation, impedance, return loss, cross-talk, and cable segment length
measurements.

5.1.1 Link and Other Diagnostic LEDs
When deploying EtherNet/IP networks or diagnosing existing networks, engineers can take advantage ofa few low-level, built-in diagnostic “tools” found on switches, routers, hubs, and network adapter cards
on computers or industrial equipment. One of these tools is the built-in link/activity LED.
The link LED indicates a connection between two EtherNet/IP devices. These can be two switches, aswitch and a computer, a switch and a PLC, etc. How the device knows there is a proper link is that each
EtherNet/IP device, when not transmitting data, will transmit a link signal on all of its EtherNet/IP ports.
When either device receives this link signal, it will then turn on the link LED associated with that port.
Therefore, if the wiring is correct between two EtherNet/IP device ports, the appropriate link LEDs will
be enabled on each of the devices at both ends of the cable.
There may also be speed LEDs and type of duplex connection LEDs that indicate the speed (10 Mbps,
100 Mbps, etc.) and the type of duplex connection (half- or full-duplex) between the two devices. Some
devices may use a multicolor LED to indicate speed. For example, amber may indicate 10 Mbps withgreen for 100 Mbps. Both sides of the connection must use the same speed and the same duplex settings
for proper communications. Most equipment will automatically negotiate for the fastest speed and forfull-duplex operation. If both devices connected to a cable show a 10-Mbps and half-duplex setting when
they are rated for 100-Mbps and full-duplex operation, this may be an indication of a defective cable. It isalso possible that there may be a physical problem with the adapter’s circuit at either end, or aconfiguration switch may be set for manual operation, locking in the speed or mode of operation.
Many switches and EtherNet/IP devices also provide an activity LED to indicate data transmission
activity. Sometimes the link LED flashes to indicate either receive or transmit activity. The
manufacturer’s manual should be reviewed for specific details.
The link LED will indicate a working connection between two EtherNet/IP devices. The activity LEDs
will show that one of the two devices is transmitting data. The speed and duplex LEDs can provide
further diagnostic information. Sometimes a single LED will be used to show multiple functions. In somecases a router or switch may even have separate LEDs to show transmit and receive (or upload anddownload) functions. In many cases, there is not consistency from device to device. It’s best to check the
manual to confirm what the various LEDs indicate.
In rare cases, link LEDs can show a proper connection between two devices even though the cable may
be constructed improperly. Communication may still occur over an improperly wired cable, but it may beintermittent or contain errors. A cable tester tool should be used to check all cables to evaluate fully thecable wiring. Fiber-optic cables can have a similar problem, especially if they have to be terminated in thefield under poor lighting or temperature conditions.

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5.1.2 Ping Checks for TCP/IP Continuity
If proper wiring between two devices has been verified, another built-in diagnostic tool that can be used isthe ping. Like the link LEDs built into EtherNet/IP devices, ping is built into TCP/IP software.
A ping is basically an Internet Control Message Protocol (ICMP) echo request and echo response
between two TCP/IP devices. As EtherNet/IP uses TCP/IP, EtherNet/IP devices may support ping.
Managed switches may also have the ability to respond to ping and may be able to send a ping request.
The device sending the ICMP echo request (also called a ping request) will transmit the request, andthe addressed device will provide the echo response or ping response. Ping requires that both devices
have proper IP addresses and that both exist on the same subnet or are connected via one or more routers.
Most all computers—whether Linux/UNIX, DOS, or Windows—support ping, usually from thecommand line, and sometimes from a Graphical User Interface (GUI) application that supports pings. For
example, a Windows 95 or later computer with a proper network configuration can both transmit a pingrequest and respond to a ping request. In an MS-DOS or command-line window, the user types [ping]followed by the IP address of the targeted device as shown in Figure 5-1. In Windows, the ping
application will transmit four ping requests; additional or fewer pings can be requested using [ping –n x
192.168.25.25] where x is the number of pings to be sent to the address that follows. The resulting output
will show the time it took for each response, or it will indicate that the request timed out if the ping was
unsuccessful.

Figure 5-1

Simple Ping Request Sent from the Windows Command Line Using an MS-DOS Prompt.

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Linux and UNIX computers can send pings from the command line as well, but if a count is not specified,the computer will continue to send pings until a terminate command is given by hitting [Ctrl-c]. To
specify a number of pings under UNIX or Linux, type [ping –c x 192.168.25.25] where x is the number ofpings to be sent to the address that follows.
Ping can be used to validate connections and IP addresses and to help determine where connections are
failing. To help locate faults, an engineer can ping end devices, devices located on intermediate points, ormanaged switches between two end devices.
Most TCP/IP devices will respond to a ping request, however, it is possible for a device to ignore pingrequests or to have ping responses disabled. The device’s user manual will usually note if pings or pingrequests can be turned off.

5.1.3 Switch Configuration and Management
EtherNet/IP networks can be optimized to enhance their performance. Most industrial EtherNet/IP
deployments that share the network with other kinds of traffic will require some level of switch
configuration. The configuration process also enables the network to insure a high level of resiliency,
deterministic behavior, and a high degree of security with appropriate access for authorized users. This
process will increase the level of access an authorized user has, potentially allowing for monitoring andconfiguration of devices from anywhere in the world. It also reduces costs as it leverages the existing
Ethernet infrastructure to deliver multiple services and new applications.
Managed vs. Unmanaged Devices

The broad definition of a managed device encompasses any network element that can be configured
to improve performance and/or can be accessed remotely to gather metrics on it. Switches that canbe configured and accessed remotely are normally referred to as managed switches. Network
switches that are not configurable, and therefore cannot be optimized, are generally referred to as
unmanaged switches.
In terms of the EtherNet/IP infrastructure, managed devices may include very basic functions such as
simple network utilization (RMON) to more critical settings that determine who has access to a given setof services or traffic (security). It can also include which traffic should be prioritized (QoS), what amountof bandwidth should be allocated to a given port or application to assure high availability of the network(preventing potential critical situations like a broadcast storm from interfering with control messaging),
how to deal with multicast traffic, etc. The level of management is commensurate with the set of featuresthat may be optimized or the metrics that may be gathered.
Many network elements, such as routers and switches that have been designed as managed devices, areconfigured using Simple Network Management Protocol (SNMP), often with graphical user interfaces.
This is actually no different from programming a PLC or any other control element that has some level of
embedded programmable logic.
Most vendors of Ethernet switches provide some graphical interface utility that can be used for accessing
the device. Many of the vendors also provide a web browsing interface allowing for the configuration of
the devices through the network by pointing the browser to the switch’s IP address. This presumes that
the IP address has already been configured into the device.

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The IP address of the switch can generally be configured using a console cable directly connected to thedevice. Alternatively, a Dynamic Host Configuration Protocol (DHCP) or Bootstrap (BootP) server canbe used.
Managed switches also allow for remote management of the network. There are multiple network
management software vendors that provide solutions to manage Faults (alarms) remotely, Configuration,
Accounting (who is using what resources), Performance, and Security—commonly referred to as FCAPS.
Problems identified during infrastructure testing will be detailed by the network tester so appropriate
corrective action can be taken. Other non-conformance problems and warnings may appear that address
additional issues, such as incorrect termination, faulty components, and high ambient noise. All nonconformance and test warning issues must be resolved before network startup.

5.2 Putting Traffic on the Network
In order to identify features of the EtherNet/IP network infrastructure that help provide the required
performance and connectivity, it is necessary to characterize network traffic, employ IP addressing
techniques, and understand IP multicast traffic.

5.2.1 Characterization of EtherNet/IP Traffic
As has been shown, EtherNet/IP network infrastructure can be defined as a hierarchical interconnection ofLayer 2 and Layer 3 Ethernet switches.
Traffic generated during programming, configuration, and diagnostics of EtherNet/IP devices as well as
during exchange of non-time-critical data is called explicit messaging in EtherNet/IP terminology. It is
normally low-rate traffic that generally has an insignificant impact on network performance. Although it
contains both broadcast and unicast data, this traffic does not require engagement of any special featuresin the EtherNet/IP network infrastructure. Broadcast traffic typically consists of IP packets supporting
Address Resolution Protocol (ARP), BootP, DHCP, SNMP and other protocols of this type. Unicast
traffic consists of Transmission Control Protocol/Internet Protocol (TCP/IP) packets.
Traffic generated during time-critical data exchange is called implicit messaging and consists mostly ofUser Datagram Protocol/Internet Protocol (UDP/IP) unicast and multicast packets. Examples include:•

Input/Output (I/O) data and status produced by a remote I/O device for consumption by
one or more programmable controllers•

Data produced by a programmable controller for consumption by one or moreprogrammable controllers

While the handling of UDP/IP unicast traffic does not require engagement of any special features in the
EtherNet/IP network infrastructure, handling of UDP/IP or IP multicast traffic may require these features.
Although EtherNet/IP supports change-of-state and application reporting, in a typical control system, dataexchange is predominately cyclic. The implicit messaging traffic is normally generated at an aggregate
rate of tens of thousands of packets per second, depending on the number and type of EtherNet/IP devices
and the application. Many EtherNet/IP devices are, for example, capable of generating up to 5000 packets
per second. Normally, this traffic is evenly divided between UDP/IP unicast and multicast packets. Packet
length is typically around 120 bytes.
Normal IP multicast traffic generated in an EtherNet/IP network consists of high-rate, short-packets
generated on a continuous basis. For this reason, EtherNet/IP networks differ considerably from typical
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office networks, where IP multicast traffic is generated sporadically and with much lower packet rates. A
growing exception to this traffic profile may be in the area of multimedia audio and video conferencing
applications.
EtherNet/IP Specification Tip

In accordance with The EtherNet/IP™ Specification, a message producer can send data
encapsulated in either an IP unicast or IP multicast packet.

5.2.2 IP Addressing in EtherNet/IP Networks
In some EtherNet/IP products, transfer of CIP-implicit messages is performed using connectionlesstransport layer protocol, UDP, and multicast services of underlying protocols, namely IP and Ethernet.
Only “heartbeats” are transferred as UDP unicast packets. Therefore, the first half of a transaction
constituting implicit message transfer from a producer to a consumer is a UDP/IP multicast packet
transmitted by the producer, and the second half is a UDP/IP unicast packet transmitted by the consumer.
In the case of multiple consumers, each consumer transmits a “heartbeat” packet to the producer.
If an EtherNet/IP bridge or adapter has a maximum packet rate of 5000 packets per second, it means thata maximum of 2500 packets per second can be transmitted by this device, and a maximum of 2500
packets per second can be received by it. Therefore, the maximum UDP/IP multicast packet rate of thisdevice is 2500 packets per second.
It is important to remember that the destination address of an IP multicast packet is always selected froma specific range, called Class D and, in the case of some EtherNet/IP products, from a specific sub-classwithin it. Therefore, as an example, these products generate IP multicast addresses from 239.192.xxx.xxx
to 239.193.xxx.xxx.
5.2.2.1 IP Addressing Example
Consider an EtherNet/IP network consisting of a programmable controller system acting as a consumer, aremote I/O rail acting as a producer, and a managed switch. Assume that the consumer has been
configured with the IP address 10.88.80.100, the producer has been configured with the IP address
10.88.80.110, and the switch has been configured with the IP address 10.88.80.120. The CIP connection
has been configured with a 10-millisecond (ms) Requested Packet Interval (RPI). See 6.1.1 Multicast
Traffic Management within a Control System for more information.
During the CIP connection establishment process, the consumer sends a CIP Forward_Open Request
packet to the producer. This is a TCP/IP unicast packet with IP Destination Address 10.88.80.110 and IP
Source Address 10.88.80.100. In response, the producer sends a CIP Forward_Open Response packet
back to the consumer, which contains an IP multicast address in its Data field that the producer will use to
send data to the consumer on this CIP connection. The Forward_Open Response packet is also a TCP/IP
unicast packet but with IP Destination Address 10.88.80.100 and IP Source Address 10.88.80.110.
Assume that the IP multicast address generated by the producer is 239.192.1.1. As soon as a CIP
connection has been established, the producer begins multicasting a UDP/IP packet containing the statusof its inputs every 10 ms. The IP Destination Address of this packet is 239.192.1.1, and the IP Source
Address is 10.88.80.110. The consumer responds by sending a “heartbeat” packet, which in this example
contains the output status update. This packet is a UDP/IP unicast packet with the IP Destination Address
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10.88.80.110 and the IP Source Address 10.88.80.100. The packet rate will be 200 packets per second,consisting of 100 multicast and 100 unicast packets per second.

5.2.3 IP Multicast Traffic in EtherNet/IP Networks
To satisfy the performance requirements of the implicit messaging traffic, the following is recommended:•

EtherNet/IP network infrastructure should be based on Ethernet switching technology.

•

Micro-segmentation should be used.

•

Networks should run in 100-Mbps, full-duplex mode.

Ethernet switches (also called Layer 2 or Ethernet Layer 2 switches) should always be used instead of
hubs. Only one device (end-node) should be connected to a switch port, and, if manual-mode setup ispreferred, switch and device ports should be set to 100-Mbps, full-duplex mode. Switches should support
port mirroring and IGMP snooping. Port mirroring is convenient for diagnostic and troubleshooting and iscovered in Appendix A Recommendations for Ethernet Switches in EtherNet/IP Systems. IGMP snooping
helps to manage multicast traffic and is described in 6 Infrastructure Application Scenarios in moredetail. Without the use of special traffic filtering features, an Ethernet Layer 2 switch normallyretransmits each received IP multicast, broadcast, or unknown unicast packet through all ports.

5.3 Deployment Summary
In many ways wiring, testing, and troubleshooting an EtherNet/IP network is not unlike wiring a complex
telephone system. Cable lengths are more important, and proper termination is a must. In addition tosimple hand-held testers, most of the infrastructure components—routers, switches, and otherequipment—provide built-in testing capabilities for both the physical wiring and for TCP/IP testing.
Checking for obvious potential problems before putting the system into use is important. These problems
include cable routing mistakes, environmental concerns, and location of equipment. Once the wiring isfunctioning, the guidelines presented here can be used to check and maintain traffic performance and
flow.

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6 Infrastructure Application Scenarios
Regardless of the specific application, all networks require a design that deals withmulticast traffic to meet the needs of real-time control.
EtherNet/IP supports both the time-critical (implicit) and non-time-critical (explicit) message transfer
services of CIP. With CIP, the exchange of time-critical messages (real-time control or I/O control) isbased on the producer-consumer model where a transmitting device produces data on the network, andmany receiving devices consume this data simultaneously. On EtherNet/IP, this functionality is provided
through IP multicast and Ethernet multicast mechanisms. The use of Ethernet for real-time control isdifferent from typical office and other non-time-critical applications.
In the office world, one of the primary network design objectives is to manage the traffic load on the
network. In the industrial world, the small, embedded control devices have modest CPU capability
compared to the office world’s PCs and workstations. Device CPU resources are needed to process eachbroadcast and multicast message. While managing network bandwidth is always important, correct designand setup of the Ethernet infrastructure must first protect the control devices from multicast and broadcast
floods that can slow or stop operation of these devices.
The recommendations in this section focus on addressing real-time control application needs. These
applications typically use the producer-consumer capabilities of EtherNet/IP, which are based on
multicast Ethernet communications. Monitoring, device configuration management, or explicit message
applications that use unicast communications do not need to follow the recommendations for multicast
traffic outlined in the following scenarios.
There is no single or standard approach to infrastructure implementation will provide the right balance ofperformance, data connectivity, and installed cost for all applications. However, these scenarios address
the general application concerns of four typical types of industrial EtherNet/IP networks.
•

Isolated EtherNet/IP network with a single controller. An isolated EtherNet/IP

network interconnecting devices of a control system with a single controller.
•

Isolated EtherNet/IP network with multiple controllers. An isolated EtherNet/IP
network interconnecting devices of a control system with multiple controllers.

•

EtherNet/IP network connected to the enterprise network. An EtherNet/IP

network connected, via a gateway or equivalent, to the enterprise network. The control
system it serves can be of any complexity.
•

EtherNet/IP network integrated with the enterprise network. An EtherNet/IP

network that is fully integrated with the enterprise network. The control system it serves
can be of any complexity.
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Within each of these four network types, recommendations can be made regarding the types of active
infrastructure components (switches, routers, etc.) and the key functions needed to balance real-time
performance with data connectivity requirements. Appendix A Recommendations for Ethernet Switches in
EtherNet/IP Systems complements this chapter by summarizing the recommended switch functions foreach of the four system types.

6.1 General Application Considerations
There are several key concerns that vary based on the type of system desired.

6.1.1 Multicast Traffic Management within a Control System
Data producers on an EtherNet/IP network can generate a significant amount of multicast traffic,
requiring that particular care be taken to manage it. Managing multicast traffic is the most importantconcern in the design of a high-performance EtherNet/IP network. With EtherNet/IP, implicit messages(I/O control and controller-to-controller communication) use unicast (one-to-one) packets to communicate
output information from a controller to I/O or other control devices. Input information, sent from thesedevices to the controller, is usually transferred using multicast (one-to-many) packets. As noted in 4.7
Switching Technologies, switches normally retransmit multicast packets to all switch ports (flooding), sothat all devices see all the multicast traffic. Without multicast control functions, such as IGMP snooping,
the end devices’ operation is impaired as its CPU becomes overloaded due to discarding extraneous
multicast traffic.
Requested Packet Interval

One of the major controller or scanner setup parameters is the Requested Packet Interval (RPI).
This value is the minimum rate at which control devices will produce the input information neededby the controller. The larger the application (and the number of interconnected control devices) andthe faster the response time needed (lower RPI), the greater the need for IGMP snooping.
The tradeoff here is that managed switches (those typically with web/SNMP diagnostics and message
filtering functions, such as IGMP snooping, VLAN, and others) cost more than simple unmanaged
switches, which do not have message filtering functions, such as IGMP snooping. Systems with thehighest performance requirements and the fewest application timing problems will use all managed
switches with IGMP snooping.

6.1.2 Control Device Sensitivity to Extraneous Traffic
Another consideration related to multicast message control relates to each control device’s sensitivity tounwanted multicast and broadcast traffic. The impact of unwanted traffic is analogous to sorting the “junkmail” from the important mail.
6.1.2.1 Potential for Traffic Overload
Every time a control device receives an Ethernet frame, it takes a tiny bit of its microprocessor/Ethernet
chip resource to look at the address, decide if the message is for it, and discard messages addressed toothers. The rate of incoming unwanted messages (expressed in packets per second) can reach a point
where so much time is spent processing and throwing out junk mail that it can not produce or receive
control messages at the configured RPI value. This will cause an error condition that shuts down
communications and causes the system to go into its fault mode.

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6.1.2.2 Varying Sensitivity by Device Type
Certain devices, such as Windows-based PCs/workstations, may have an extra sensitivity to multicast
traffic. There can be significant variance in sensitivity between the same devices from different vendors,
and between different devices from the same vendor. Direct connection of the sensitive devices toseparate Ethernet ports on controllers or to Ethernet connections via switches capable of IGMP snooping
may be mandatory.

6.1.3 Configurable Isolation of Enterprise and Control Traffic
One of the promises of Ethernet-based systems is shop-floor-to-top-floor connectivity. When connecting
control networks to enterprise networks (i.e., networks supporting mainly office traffic, MES, plant
management, manufacturing line efficiency, quality monitoring , etc.), unwanted enterprise traffic(including multicast and broadcast) must be blocked from disrupting control traffic. Equally important is
the need to prevent EtherNet/IP multicast control traffic from flooding and bogging down the enterprisenetwork. The conventional method used to connect separate fieldbus networks is to use two network
interface cards in a PC. The enterprise and control networks are physically isolated with a PC-based
program used to selectively enable data transfers in both directions.
Of course, any change in the desired data flow requires each of these PCs with two network cards to be
manually reprogrammed. For single connections and relatively stable data flows, this may be acompletely acceptable approach. However, as the quantity of control-to-enterprise connection points growand the need to adapt data flow increases, reprogramming all the intermediate databases becomesunwieldy. In these cases, industrial switches and routers with Virtual LAN (VLAN) capabilities allow
configurable traffic isolation without reprogramming PCs, rewiring network cables, or purchasing
additional network cards. VLAN-capable switches and routers isolate broadcast and multicast traffic,
preventing it from passing into other network areas. These same functions and devices are also used to
implement network security functions. See 4.10 Virtual Local Area Networks for more VLAN
information.
Once traffic is isolated using VLANs, routers (or Layer 3 switches with routing functions) are required toallow data to be selectively transported from one VLAN to another. Other router mechanisms, such as
Time-to-Live (TTL) thresholds and Access Control List (ACL) filtering may be used in conjunction with
VLANs to provide further isolation and protection between plant-floor and enterprise environments.

6.2 Isolated Control Network with a Single Controller
Isolated EtherNet/IP networks are not connected to other plant or enterprise-level networks. Control
system examples built around these networks typically contain one programmable controller, one or moreworkstations, and control devices, which may include I/O nodes and/or drives, etc. Two configurations
are typical: low (usually with 10 or fewer devices) and high (usually with more than 10 devices). The
major performance concerns relate to managing multicast traffic and preventing device overload fromunwanted multicast traffic, which would shut down device communications.

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6.2.1 Systems with Low Device Counts
In the example shown in Figure 6-1, IP multicast traffic is produced by I/O devices and consumed by the
programmable controller. Here, IP multicast traffic produced by I/O1 will be sent to all devices connectedto the switch, including I/O2 through I/O5 and the workstation.

Workstation

Programmable
Controller

8-portEthernet Switch

I/O1

Figure 6-1

I/O5

Isolated Network with One Controller.

EXAMPLE 1

Assume that each device establishes one CIP connection to the controller with a 10-ms RPI. Each device
will generate 100 multicast packets per second and receive 100 unicast (“heartbeats” or output status)
packets per second from the controller. Each device will also receive 400 unwanted multicast packets per
second, and the workstation will receive 500 unwanted multicast packets per second.
EXAMPLE 2

Assume that each control device establishes four CIP connections with the controller. One connection
has a 10-ms RPI, and each of the other three connections has a 50-ms RPI. Each control device will
generate 160 multicast packets per second and will also receive 640 unwanted multicast packets per
second. The workstation will receive 800 unwanted multicast packets per second.
6.2.1.1 Use of Unmanaged Switches
In isolated systems with low device counts (10 or fewer), a low number of CIP connections, and modest
RPIs (higher than 10 ms), the level of unwanted multicast traffic may not cause a device overload
condition. In isolated systems with large device counts and, more importantly, a large number of CIP
connections, the use of unmanaged switches as expansions to managed switches may allow a balance of
cost versus performance. In applications with a low number of CIP connections that have modest RPI
requirements, the use of unmanaged switches can provide product cost savings over the use of all
managed switches. As a general rule, applications requiring fast RPIs and/or more than a few connections
should use managed switches with IGMP snooping capability.

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When using unmanaged switches, follow these guidelines:
Calculate or test the maximum multicast traffic load for each device.
For each device, ask the vendor for the maximum unwanted multicast packets per second rate thatthe device can withstand while maintaining the desired RPI rate. Be sure to use the configuration with thelargest I/O count or most time-critical configuration. If the vendor cannot provide this information, referto the alternative traffic-management approaches presented below.
For each device connected by one or more unmanaged (non IGMP snooping) switches, add all the rates
together to determine the total multicast traffic in the multicast domain, then add in any significant
broadcast traffic from application or network management software, and reduce the total by 5% for adesign buffer. Note that splitting the devices between different unmanaged switches makes no differencein the total multicast domain traffic load as depicted in Figure 6-2.

Figure 6-2

Adding Unmanaged Switches Does Not Reduce the Size of a Multicast Domain.

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Confirm that the total unwanted multicast traffic value is less than each devices’ maximum unwanted
multicast traffic rate. If it is greater, add managed switches. Adding managed switches reduces themulticast domain as shown in Figure 6-3.

Figure 6-3

Use Managed Switches to Reduce the Size of a Multicast Domain.

This is also a key concept for end users who may be interconnecting multiple OEM machines from one ormore vendors. To minimize application timing problems and maximize determinism, separate the traffic
from the different machines with managed switches.
Consider future expansion needs.

In the future, before connecting any additional devices to the unmanaged switches, first determine if theunwanted muticast traffic load of the existing installation (as well as the added device) can withstand theadded device’s traffic. Failure to do this runs the risk of adding one device that shuts down the system. It
is reccommended that any new sections or expansions be connected into a managed switch to add IGMP
snooping capabilities.
Alternative traffic management approaches.

In cases when the prefered calculation approach is not possible and the maximum unwanted multicast
traffic rates cannont be obtained from the device vendors, there are three options:1.

Use all managed switches (with IGMP snooping). This is the best alternative and themost conservative approach to system design because it keeps traffic and application
timing issues to a minimum.
2.

Test the configuration during the design phase. Pre-test each multicast domain(unmanged switch section) to confirm proper operation using the actual application
configuration and controller/scanner RPI value. Be sure to allow time to add managed
switches to the system design if they are needed.

3.

Reconfigure devices to use unicast messages. Some devices may have a userselectable option to produce implicit (I/O) messages using unicast messaging instead of
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multicast messaging. Disabling multicast messages allows the use of unmanaged
switches. This is most effective for systems with one consumer.
In the systems described in these examples, a certain amount of the workstation’s and remote I/O devices’computing power is used to filter the unwanted traffic. If the control engineer concludes that unwanted
multicast traffic affects the performance of these devices and, consequently system performance, then oneof the following recommendations may be considered:
Certain types of devices, such as PCs/workstations, can be more sensitive to unwanted multicast traffic. If
only workstation performance is affected, the controller should be connected via a separate switch as
shown in Figure 6-4. IGMP snooping need not be activated in any of these switches.

Workstation
Programmable
Controller

Switch8-port Switch

8-port Switch 1

Producer 1

Figure 6-4

8-port Switch 4

Producer 6

Producer 19

Producer 24

Isolated Network with One Controller and a Separate Network for HMI.

If both workstation and remote I/O performance is affected, a switch with IGMP snooping should be
used. The switch with IGMP snooping forwards IP multicast packets to consumer ports only. In isolated
multi-switch networks, one switch with the IGMP query function is needed, and the other switches needto support the IGMP snooping function.

6.2.2 Systems with High I/O Count
Isolated systems with high producer device counts (i.e., I/O, drives, sensors, etc.), a large number of CIP
connections, and low RPI rates require the use of managed switches for implicit-messaging-based I/O
control applications. Larger non-time-critical applications (such as monitoring systems) with RPI rates
over 70 ms may be capable of using combinations of managed and unmanaged switches. Use theguidelines in 6.2.1.1 Use of Unmanaged Switches to determine the potential for multicast overloads. As
systems grow larger, the need for web or SNMP diagnostics can considerably reduce initial system startup
times, and provide port-based traffic statistics to help optimize overall system performance. In addition,
as systems grow in complexity and size, the need for network redundancy often grows as well.

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Programmable
Controller

8-port Switch

8-port Switch 1

Producer 1

Figure 6-5

8-port Switch 4

Producer 6

Producer 19

Producer 24

Isolated Network with One Controller.

EXAMPLE 3

In the example shown in Figure 6-5, IP multicast traffic is produced by 24 producers, remote I/O rails
and/or drives, and is consumed by the programmable controller. Assume that each producer establishes
one connection with the controller with a 10 ms RPI, and IGMP snooping is not activated in the switches.
Each producer will generate 100 multicast packets per second and will receive 2300 unwanted multicast
packets per second. The workstation will receive 2400 of unwanted multicast packets per second.
If the engineer concludes that unwanted multicast traffic affects system performance, then one of thefollowing recommendations may be considered:•

If only workstation performance is affected, the workstation can be connected to thecontroller via a separate switch as shown in Figure 6-4. IGMP snooping does not have tobe activated in any of these switches.

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If workstation and remote I/O performance are affected, a switch with IGMP snooping
should be used. In isolated networks, one of the switches will be required to have the
IGMP query function to manage the multicast process as shown in Figure 6-6.

Programmable
Controller

Workstation

24 PortSwitch24-portLayer 3
Switch• IGMP
Query• IGMP Snooping

8-port Switch 1

8-port Switch 4

Switches with IGMP
Snooping
Producer 1

Figure 6-6

Producer 6

Producer 19

Producer 24

Isolated Network with One Controller and a Main Switch with Query Function.

EXAMPLE 4

Figure 6-7 depicts a “daisy chain” configuration similar to and operating under the same conditions as theone shown in Figure 6-5.

Workstation

Programmable
Controller

Switch 1

P1

Figure 6-7

Switch 3

Switch 2

P6

P7

P12

P13

Switch 4

P18

P19

P24

Isolated Network with One Controller and a Daisy Chain Configuration.

Here, each producer establishes one connection with the controller with 10-ms RPIs. Each producer
will generate 100 multicast packets per second and will receive 2300 unwanted multicast packets per
second. The workstation will receive 2400 unwanted multicast packets per second and each switch willprocess 2400 multicast packets per second.

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In this example, if producer traffic is unicast instead of multicast, then switch 4 will process 600
packets per second, switch 3 will process 1200 packets per second, switch 2 will process 1800 packets
per second, and switch 1 will process 2400 unicast packets per second. It is important to note:•

In this unicast environment, no matter how many packets a switch will process, no nodes
will receive extraneous traffic, thus eliminating the potential of a multicast traffic loading
problem.

•

In a daisy-chain connection of switches in this unicast environment, switch 1 has very
high loading. To reduce the additive loading from switch to switch, a star topology withswitch 1 in the middle is recommended instead of the daisy chain configuration. This will
also decrease the individual port loading on switch 1.

In this example, if the produced traffic is multicast, and both workstation and remote I/O performance
are affected, switches with IGMP snooping should be used. To even loading across the network, a star
topology is used instead of a daisy-chain topology.

6.3 Isolated Network with Multiple Controllers
EtherNet/IP networks can consist of multiple programmable controllers (or other controllers such as
motion) and still remain isolated—not connected to other networks. One example is the VLAN approachshown in Figure 6-8 and Figure 6-9 where two programmable controllers use a single switch to connect totheir I/O.

6.3.1 Multiple Single-Controller Systems without Data Sharing
Figure 6-8 depicts two small, separate control systems sharing the same managed switch. Programmable
Controllers 1 and 2 are not sharing data. Also, each of the I/O devices produces data for only one
programmable controller. In other words, this represents two single-consumer systems that share amanaged switch. To prevent one system’s unwanted multicast traffic from appearing on the other system,
managed switches with VLAN functionality must be used.

Programmable
Controller 2

Programmable
Controller 1
Workstation 1

Workstation2

12-port Switch

I/O11

I/O12

I/O13

I/O21

I/O22

Figure 6-8

Two Single-Controller Systems Sharing a VLAN-enabled Managed Switch.

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Figure 6-9 depicts the logical view of the system set up as two VLANs. Here, ports 1, 3, 4, 5, and 6
belong to VLAN 1; ports 2, 7, 8 and 9 belong to VLAN 2. For more distributed applications, VLANs canalso be implemented across multiple switches.

Programmable
Controller 1

Programmable
Controller 2

Workstation 1

2

1

3

Workstation 2

9SwitchVLAN 1

4

I/O11

5

VLAN 2

6

I/O12

7

I/O13

8

I/O21

I/O22

Figure 6-9

Logical View of Two Single-Controller Systems Sharing a VLAN-enabled Managed Switch.

6.3.2 Multiple Single-Controller Systems with Data Sharing
Consider the example shown in Figure 6-9 but with the need for data sharing. If programmable controllers
need to share data or if input data produced by one more of the I/O devices needs to be shared, VLANs
are not an option. Infrastructure requirements for a network serving these applications are the same as for
an isolated network with a single controller as described in 6.2.2 Systems with High I/O Count. Even with
one switch, the number of devices connected to the network and the number of CIP connections demand
IGMP snooping and query to prevent a multicast overloading of devices.

6.3.3 Isolated Systems Summary
In small isolated EtherNet/IP networks with a single controller, control of IP multicast traffic using IGMP
snooping may not be required. In these cases, unmanaged switches may be used, given that the overall
multicast traffic load is calculated or the system pre-tested to prevent device shutdown from multicast
traffic overloads. In cases when unwanted multicast traffic affects performance of HMI workstations, aseparate network for controller-HMI communication should be used.
In large isolated networks when unwanted multicast traffic also affects the performance of traffic
producers (remote I/O, drives, etc.), managed switches with IGMP snooping could be used in
combination with unmanaged switches to lower total system cost. For maximum system performance, allmanaged switches with IGMP snooping should be used. When IGMP snooping is used, one of theswitches must support the IGMP query function.
In isolated networks with multiple controllers that do not share data between them, managed switcheswith VLAN functionality may be used to increase control performance by isolating traffic. If data sharing
between controllers (i.e., implicit messaging) or the use of produce-consume tags is required,infrastructure requirements are the same as those for an isolated network with a single controller. The
same is true when controllers share remote inputs.

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6.4 Enterprise-Connected and Integrated Control Systems
There are often requirements for enterprise or plant-wide networks to selectively access control systemdata. Higher level plant systems often contain servers used to download the control programs necessary toreconfigure flexible manufacturing systems. Plant-wide systems may also carry video monitoring, MRP,
and other production data that needs to be processed separately from real-time critical control traffic on
the plant floor. There are two approaches to allowing this selected access to occur while isolating theplant-floor network from the plant backbone.

6.4.1 Networks Connected via CIP Gateways
An EtherNet/IP network can be connected to the enterprise network via a gateway. A typical example of agateway is a programmable logic controller with multiple EtherNet/IP ports acting as a CIP gateway as
shown in Figure 6-10. In such a network, all of the implicit real-time control traffic is isolated to one ormore separate EtherNet/IP ports. Since EtherNet/IP and enterprise networks are connected via a CIP
gateway, there is no propagation of unwanted traffic from the EtherNet/IP network into the enterprisenetwork and vise versa. Therefore, there is no difference, from the EtherNet/IP infrastructure point ofview, between enterprise-connected and isolated EtherNet/IP networks. This approach requires that any
data transfer between networks be done through PLC programming or setup.
Enterprise
Backbone

Enterprise layer 2 switch, layer 3
switchor router
PLC Module 1 has
IP address A
PLC acting as CIP
Gateway
PLC Module 2 has
IP address B
Industrial Ethernet
SwitchI/O

Figure 6-10

I/O

I/O

EtherNet/IP and Enterprise Networks Connected via a CIP Gateway.

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6.4.2 Networks Integrated with Routers (or Layer 3 Switches)
An enterprise-integrated EtherNet/IP network is fully integrated into the enterprise network infrastructure.
This type of interconnection results in a single, integrated network. The addressing practices, security
policies, network management techniques, and “change control” procedures of the enterprise network andthe control system portions of that network must be harmonized.

6.4.3 Two Types of Integration
The type of integration—non-interlock connected or interlock connected—used depends on whether or
not implicit message traffic will traverse the corporate backbone network. These two integration types are
representative of large corporate installations where the corporate backbone and the plant-floor
environments span a large area. Non-interlock is quite common as it allows selected data transfers, but
keeps the real-time data isolated to a particular area of the plant floor and isolated from other plant trafficthat may affect control system performance.
6.4.3.1 Non-Interlock Connections
A non-interlock connection is used if there is no implicit message traffic traversing the backbone network.
As shown in Figure 6-11, the only traffic being passed is supervisory, programming, monitoring, and soforth. There is no real-time data being passed. There is no CIP gateway in use; the backbone is connected
directly to the plant-floor network infrastructure. There may be implicit messaging within the local
network zone, but it is not meant to pass into the backbone network. Protection may be needed to prevent
multicast traffic from adversely affecting the backbone environment. Connection points to the backbone
may be a Layer 2 switch (VLANs, Layer 2 filtering), a Layer 3 switch (Access Control Lists, Layer 2/3
filtering), or a router (ACLs, Layer 2/3 filtering, firewall function).
Corporate
Backbone

Layer2switch,Layer3 switch
or routerEnterprise
Network
Plant Floor

Supervisory andnon-implicit
control traffic
Industrial
switchPLC
Industrial
switchI/O

Figure 6-11

I/O

I/O

Example of a Non-interlocked Integrated Network.

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6.4.3.2 Interlock Connections
An interlock connection is used if there is implicit message traffic traversing the backbone network. As
shown in Figure 6-12, the traffic being passed is real-time implicit, supervisory, programming,monitoring, and so forth. There is real-time data being passed. There is no CIP gateway in use. The
backbone is connected directly to the plant-floor network infrastructure. There will be implicit messaging
within the local network zone and some will be passed across the backbone network to another zone.
Protection (firewall, ACL, VLAN, etc.) may be needed to prevent unwanted multicast traffic fromadversely affecting the backbone environment or the plant floor. The recommended connection point is a
Layer 3 switch or router.
Interlocking Across Corporate Backbones

Interlocking across corporate backbone systems should be only considered by expert users. There
are baseline requirements for the backbone that must be met, such as multicast routing protocols,
spanning VLANs, redundancy protocol interaction, etc. that must be extensively tested, and timing
characteristics must be confirmed before deployment. The impact on control system throughput(determinism, control data latency) must be extensively tested and evaluated for a successful
deployment.

Corporate
Backbone

Enterprise
Network

Layer3 switch
or router

Plant
Floor

Layer3switchor routerEnterprise
Network
Plant
Floor

Industrial
switchPLC

Industrial
switchPLC

Industrial
switchI/O

I/O

Figure 6-12

I/O

Industrial

switch

I/O

I/O

I/O

Example of an Interlocked Integrated Network.

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6.5 Application Summary
Characterizing network traffic on EtherNet/IP helps determine which type of network will provide thebest balance of performance and installed cost. The recommendations provided here are aimed at
optimizing network—and ultimately control system—performance. They are based on the use of switcheswith the increasing levels of functionality needed to handle more devices with more traffic and short,
implicit I/O control response times. Routers are used to selectively link these systems with enterprise orplant networks without disrupting any of the networks. Table 6-1 summarizes the relative degree that theapplication considerations discussed here are factors in the four general system types.
Table 6-1

Application Factors for System Types
System Type

Application Factors

Isolation of control
system vs. plant
network traffic andprevention ofmulticast traffic
overload of control
devices

Isolated System
Single Controller

Isolated System
Multiple Controllers

Enterprise
Network
Connected

Enterprise
Network
Integrated

Use of lower-cost
unmanaged switches
possible.

Requires managed(IGMP snooping)switches.

PC with 2 NICs
possible; use of a
CIP gateway
preferred.

Requires managed
switches with
IGMP snooping
and VLAN
functionality.

Added traffic design
calculations if
unmanaged switches
are used.

VLAN functionality
may optionally beneeded.

Requires managed(IGMP snooping)switches.

Will likely require
Layer 3 switches orrouters at the join
points.

VLAN functionality
may optionally beneeded.

Appendix A Recommendations for Ethernet Switches in EtherNet/IP Systems summarizes the required anddesirable switch features for the various system types described here.

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7 Selecting Components
This detailed look at the component features behind successful EtherNet/IP networks canbe used as a checklist to help ensure the chosen components can provide the rightfunctionality and withstand their industrial environments. Included here are connectors,
wire and fiber-optic cabling, switches, routers, and equipment housings.

7.1 Sealed Connectors: Key to Successful Operation
Standard RJ-45 connectors, also called 8-way modular connectors, are not designed to operate in manyindustrial environments. Lower Common Mode Rejection Ratio (CMRR) cable types, also calledbalanced cables, may not provide adequate protection from industrial electrical noise levels and thepotentially high amount of cross-talk. In high-vibration applications, additional mechanical securingmeans may also be required. For “outside the panel” connections, commercial-off-the-shelf RJ-45
connectors are not sealed to meet the IP65 and IP67 specifications for EtherNet/IP. Therefore, The
EtherNet/IP™ Specification22 includes an industrial version of the RJ-45 connector rated to meet IP65 andIP67. An M12 4-pin “D”-coded connector also is included to provide a smaller connector form factor.
Connectors play an important role in any EtherNet/IP network, and if they are going to be used in harshindustrial environments, they need to be sealed to keep out moisture and chemicals, and they have to beable to withstand high vibration. While EtherNet/IP uses standard RJ-45 connector technology, about the
only locations in which these connectors can be used is inside sealed equipment cabinets where they areprotected from plant-floor environments or in the relatively safe environments of control rooms.

7.1.1 Approved Sealed Version of RJ-45 Connectors
If an application requires cable and connectors to be exposed to liquid or dust contaminates, then theconnectors need to be protected from chemicals, dust, solvents, oil, etc. RJ-45 (8-way modular)
connectors and bulkheads sealed to meet IP65 and IP67 standards ratings are used to protect the wiringand plug connector pins from these contaminants. The IP65 and IP67 ratings specify that the connectors
can withstand immersion in water at a depth of 1 meter (3.28 ft) for 30 minutes without incursion. IP65
and IP67 sealed RJ-45 (8 way modular) connectors are shown in Figure 7-1 and Figure 7-2 and have thefollowing features:
•
•
•
•

22

Bayonet-style flangeStandard RJ-45 jackSeal at face of jackAccommodation for PCB mount, flange mount, or bulkhead mount

ODVA, The CIP Networks Library, Vol. 1 and 2, The EtherNet/IP™ Specification. Ann Arbor: ODVA, Inc., 2006.

www.odva.org. CD-ROM.
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Figure 7-1

Figure 7-2

Infrastructurefor

EtherNet/IP™

RJ-45 Sealed Connector.

RJ-45 Sealed Plug.

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7.1.2 M12 “D”-Coded Connector for EtherNet/IP
The EtherNet/IP™ Specification also allows the use of the four-pin, “D”-coded M12 connector for IP65and IP67-rated environments. This device is shown on the left in Figure 7-3 and is the pin-and-socket
style connector for EtherNet/IP. It will be familiar to many engineers from its standard version, which isin widespread use in industrial applications, such as with sensors and actuators. The connectors are notquite the same, however, and for good reason. The “D-coding” keying is different from the standard M12connector to prevent accidental connection of other devices that may have high enough voltages todamage Ethernet circuits. The connector provides for two-pair shielded cables, and a variety of cables canbe used to withstand most industrial conditions.

2
3

1
4

M12 (D-coding)Figure 7-3

Standard M12

Comparison of “D”-Coded and Standard M12 Connectors.

7.1.3 Fiber-Optic Connectors
For fiber optics, there are three types of approved connectors: the quarter-turn LC, ST and the SC
connectors. The ST (for straight-through) is shown on the left in Figure 7-4, and the SC (for standard
connector) is shown on the right. The LC connector is a smaller version of the SC. A pair of fibers areused for each link to support separate receive and transmit paths. Therefore, like twisted-pair connections,
receivers must be tied to transmitters. Ports on both the DTE and DCE are marked as TX (transmit) andRX (receive) to guide connections.

Figure 7-4

ST (left) and SC (right) Fiber-Optic Connectors.

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7.2 Cabling Considerations: Twisted-Pair vs. Fiber-Optic Cable
Deciding whether to use fiber-optic cable or twisted-pair copper cable depends on specific application andenvironmental requirements. Users need to compare capabilities to find the right match for theirrequirements.
•

Fiber-optic cable is inherently impervious to noise from electrical and magnetic fields.

•

Fiber-optic cable may cost more per foot than standard, twisted-pair cable; however,users should consider the cost of installation for either type of cable.

•

Fiber-optic cable has fairly stringent requirements regarding bend radiuses. (See 7.2.5
Bend Radius / Pull Force of Fiber.)•Shielded twisted-pair cable has been found to be resistant to some types of electricalnoise; however, ground loops must be avoided. (See 7.2.1 When to Use Shielded TwistedPair Cabling.)•

Fiber-optic cable can provide immunity to lightning and is a good choice between
buildings or in other outdoor areas.

•

Fiber-optic cable is a good option within hazardous areas. If it is necessary to mix
communications cabling with high-voltage runs, fiber optics is superior to twisted-paircabling due to the limited breakdown voltage rating of twisted-pair cable and potential
noise coupling.

•

Although not completely immune to security breaches, fiber-optic cable is much moredifficult to tap into and access unauthorized data.

•

Twisted-pair runs are limited to 100 meters (328 ft); fiber-optic cable can provide much
longer transmission distances. Typical multi-mode installations allow distances up to 2
kilometers (1.24 mi), but single-mode installations can be 30 kilometers (18.64 mi) or
greater.

•With both fiber-optic and copper cables, the cable jacket specifications for weld splatter,
moisture, and UV (sunlight) resistance must be considered.

7.2.1 When to Use Shielded Twisted-Pair Cabling
Engineers need to select the correct cable for the environment. Cable selection is dependent on theplanned cable route. Shielded cable may perform better than unshielded cable in high-noise industrial
environments. In particular, if an application is in a high-noise environment or a cable must be run inclose proximity to noise-radiating sources, shielded or fiber-optic cables should be used.
Shielded cables are appropriate if an application includes one or more of the following:•

Motor-control centers•

Induction-welding processes•

Proximity to high-power RF radiation
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Electrostatic processes•

High-current devices (greater than 100 amps)for

EtherNet/IP™

7.2.2 Terminating Copper Cable
Termination of copper cables is a simple process. Copper cable termination tools and supplies areavailable from many convenient sources. Figure 7-5 shows a typical RJ-45 Ethernet connector. Studies
have shown, however, when communicating at 100 Mbps, poor cable terminations can increase thenumber of retransmissions. This will reduce system throughput.
Attention also must be paid to the selection of wire pairs used when terminating a copper Ethernet cable.
The proper wire pairs as defined in Table 7-1 must be used to preserve the cable’s ability to reject noise
and achieve the proper impedance.

Figure 7-5

Views of an RJ-45 Ethernet Connector.

Table 7-1

Pinouts for RJ-45 Ethernet Connectors
Color
Color
EIA/TIA 568B EIA/TIA 568A

Pin No.

Function

1

TX +White/Orange

White/Green

2

TX -

Orange

Green

3

RX +

White/GreenWhite/Orange

4

Blue

Blue

5

White/BlueWhite/BlueGreen

Orange7

White/Brown

White/Brown

8

Brown

Brown

6

RX -

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7.2.3 When to Use Fiber-Optic Cabling
Fiber should be considered when the required length is greater than 100 meters (328 ft) between two
devices. If an application creates high magnetic and electric fields, fiber should be considered.
Applications such as magnetic galvanizing annealing furnaces and high-power RF cross-linking machines
are ideally suited to the use of fiber-optic cabling.

7.2.4 Types of Optical Fiber
Optical fiber consists of five basic elements: core, cladding, strength members, coating, and outer jacket.
The core, constructed of either glass or plastic, provides the basic means for transmitting the light energy
down the cable. The cladding prevents the light from exiting the core and being absorbed by the cable
itself. The coating protects the core while providing strength. An overall jacket provides final protection
and may consist of other strengthening and protective elements. Strength members provide protection
when pulling the cable and for securing the connector.
Classification of Optical Fibers

Optical fibers are classified by their diameter in microns. A micron is a millionth of a meter and isdesignated by the symbol µm. The core, cladding, and coating frequently are specified using slashes(/) to separate the values. For example, 50/125/250 means that the core is 50 µm, the cladding is 125µm, and the coating is 250 µm. Since the cable dimensions all pertain to the concentric diameters ofthe various elements, a concise way of specifying the fiber is to list only the core and cladding sizes.
In the above example, this fiber would be classified as 50/125. Core sizes range from as small as 5
µm to as large as 1000 µm.

Depending on the core size, the cable transmits light in either one or two modes: single-mode or multimode. For each fiber-optic link, a pair of fibers is required. Usually several fibers are pulled to provide
spares. The most popular multi-mode fiber-optic cables are 62.5/125 µm and 50/125 µm. A single-mode
fiber-optic cable will have an inner core diameter of 10 µm or less.

7.2.5 Bend Radius / Pull Force of Fiber
Bend radius is defined as the radius of curvature that a fiber-optic cable can bend without causing any
adverse effects. Each manufacturer will have different ratings for each of its products. It’s important torefer to the fiber-optic cable manufacturer’s data sheet for specific pulling force and bend radius
recommendations when installing fiber-optic cable.
In the absence of this data, the pulling force should be limited to no more than 222 N (50 lbs) and thebend radius under load generally should be limited to 20 times the outside diameter of the cable and to 10
times the outside diameter under static conditions. For more information on fiber-optic bend radius, see
the BICSI (a telecommunications association) Telecommunications Distribution Methods Manual.23

23

BICSI, Inc., Telecommunications Distribution Methods Manual, 11th Edition, BICSI, Inc., Tampa: 2006. www.bicsi.org
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7.2.6 Terminating Fiber-Optic Cable
Proper termination of fiber-optic cable can be a difficult process. If not performed properly, poorconnections can reduce the distance capability of the system. Tools are available to help judge the qualityof the termination and the fiber-optic cables.
Fiber connectors should only be installed by trained personnel. The channel performance can beseverely degraded by improper connector installation.
In some cases, field splices may be required. Fusion splices should always be considered over amechanical type of splice. Fusion splices should be performed by trained installers.

7.3 Key Switch Selection Issues
The additional functions offered by managed switches can facilitate faster start-ups, allow more devices
to be connected without overloading the network, and add other capabilities often attributed to routers.
Managed infrastructure devices, such as switches and routers, are “intelligent” plant-floor devices. Usersof managed infrastructure devices can enable or disable different functions—just like PLCs. Downloading
the configuration parameters of a managed device, such as for a replacement switch, is no different fromreloading a replacement PLC with the correct program. Also like PLCs, if multiple switches havedifferent configurations, the engineer must maintain a library of configurations for specific switches.
Table 7-2 summarizes the types of functions that may be found in a managed versus an unmanaged
switch.
Table 7-2

Managed Switch versus Unmanaged Switch Functions

Switch Function

Managed Switch

Unmanaged Switch

Switched Ethernet: Eliminate collisions

Yes

Yes

10 Mbps to 100 Mbps data rates: Auto negotiation

Yes

Yes

10 Mbps to 100 Mbps data rates: Manual setting

Optional

Not available

Multicast message handling

Optional

Not available

Quality Of Service options

Optional

Optional

Security options

Optional

Not available

Virtual LAN: Forward messages

Yes

Yes

Virtual LAN: Configure/assign devices to a VLAN

Optional

Not available

Diagnostics: LED-based

Yes

Yes

Diagnostics: Software accessed (remote monitoring, web- Optional
based, set trap addresses)

Not available

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7.3.1 Address Table Size Limits Control Device Quantity
Switches learn what devices are connected to each port by noting the address of each device that transmits(is the source of) a message. These addresses are stored in a look-up table in the switch’s memory. Eachswitch has a finite capacity for stored addresses—usually several thousand. A switch updates its list using
a process termed aging by periodically (ranging from tenths of seconds to minutes) removing addresses
from which it has not received a message. If it receives a subsequent message from the device, the switch
restores the device address to the table.
If a factory-floor system has thousands of connected devices, and it interconnects other systems that
regularly broadcast messages that may pass through part of the control system, it is possible for a switch
to run out of address table memory. Routers can block undesired broadcasts. Undesired broadcasts canalso be contained through use of VLANs.

7.3.2 Auto-negotiation vs. Manual Setting of Switched Port Data Rates
The ports on most switches support both 10 Mbps and 100 Mbps—and many, 1 Gbps—data rates andhalf- or full-duplex operation. The capability of switches to automatically configure to the data rate (andhalf- versus full-duplex operation) of another auto-negotiation device that is connected can be a drawbackin certain cases. When two auto-configuration devices are connected, they will first attempt to connect at
the highest data rate, usually 100 Mbps. This can be undesirable in two cases:•

High electrical noise environments with twisted-pair cable. Manually setting theports to 10 Mbps can provide a higher degree of noise immunity when using twisted-paircable.
•

Fiber-optic cable runs. Auto-negotiation is only offered for twisted-pair cabling and
10-Mbps fiber segments. The 100 Mbps data rates for fiber cables must be set manually.

7.3.3 Multicast Messaging Handling Option
EtherNet/IP can use multicast Ethernet frames for real-time communications. A typical switch will
receive multicast (and broadcast) messages, and then rebroadcast them to the remaining switch’s ports.
Layer 2 and Layer 3 switches with IGMP snooping or equivalent functions learn which multicast
messages to send to which ports.

7.3.4 Quality of Service Options
Switches can prioritize traffic based on MAC addresses, IP addresses, switch port numbers, and protocol
identification information. This ability to prioritize and provide a different QoS based on the message
type can help improve real-time performance. It requires the user to enter QoS configuration information
into the Layer 2 or Layer 3 switch.

7.3.5 Security Options
Switches can maintain port-based Access Control Lists (ACL). This capability prevents unauthorizedaccess into the control network based on the user entering a MAC address or a port-number-based ACL.
This approach is also used to disable unused ports, so they cannot be used for unauthorized network
access.

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7.3.6 Broadcast or Multicast Threshold Filters
Switches may have a fixed or user-variable option for restricting the maximum allowed level of broadcast
or multicast traffic. Once the threshold is exceeded, it may turn off the port until the traffic falls below thethreshold level or shut down the port completely based on the vendor’s implementation. This feature canhelp lessen the effects of abnormal traffic conditions. For high-speed control applications, the thresholdlevel must be checked to confirm that it does not interfere with normal traffic.

7.3.7 Additional Functions
The switch functions described above provide an overview of basic capabilities. Appendix A
Recommendations for Ethernet Switches in EtherNet/IP Systems contains descriptions of additional
industrial switch functions, and how they relate to the various types of application scenarios described in
6 Infrastructure Application Scenarios.

7.4 Distributed Enclosures and Environmental Considerations
Commercial switches, routers, and other equipment are fine for the office closet. If, however, commercial
network equipment is to be located on the plant floor, it must be housed in industrial enclosures that arecapable of protecting it from plant-floor environments. Industrial-grade equipment is the better option as
it is designed to withstand harsh conditions. In either case, environmental factors can be critical to reliable
operation, and all equipment should be protected accordingly. Lost or corrupted data is bad enough, but
harsh conditions—especially heat and vibration—can slowly destroy unprotected equipment.

7.4.1 Environmental Specification Considerations
The required specifications for Ethernet devices used in industrial applications are dependent on where
and how the devices are to be mounted. DIN-rail versus rack mounting and the use of 120 Vac versus 24
Vdc power need to be considered. Some additional considerations follow.

7.4.2 TemperatureIndustrial manufacturing facilities can contain a wide range of environments, even within the samefacility. The environment outside the enclosure, as well as heat-generating devices within the enclosure,needs to be considered. Without added environmental conditioning equipment, traditional (commercial)
infrastructure components with 40o C to 45o C (104o F to 113o F) ratings should be used in control rooms
or lighter industrial environments away from heat-producing machines or processes.
Cabinet fans or air conditioners may be needed for hot environments or where heat-producing PCs or
motion control devices are mounted in the same enclosure. When mounted near or on heat-producing
machines or processes, and where space, maintenance or other considerations prevent the use of air
conditioners or fans, infrastructure components with PLC ratings of 55o C (131o F) or higher are available.
Operating humidity specifications of 85% to 95% RH (non-condensing) should be considered forprocessing applications where water is present (wood, paper, food, etc.) and in non-air-conditioned plants
in high-humidity locations. In corrosive atmospheres, electronics should be sealed completely to protect
circuits from caustic or acidic vapors that can strip away conductors on printed circuits.

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7.4.3 Electrical noiseElectrical noise is produced by motors, welders, and power-switching control devices, such as drives andservo controls, RF wireless transmitters, incoming power lines, and a variety of other sources. The higher
data rates of Ethernet, especially fast Ethernet (100 Mbps), require greater attention to cabling issues andequipment noise specifications. Equipment rated under the following standards should be considered forelectrically noisy environments:•

IEC 61000 (electromagnetic interference)•

IEC 61000-4-2 (electrostatic discharge)•

IEC 61000-4-3 (radiated noise immunity)•

IEC 61000-4-4 (noise burst)•

IEC 61000-4-5 (surge)•

IEC 61000-4-6 (conducted noise immunity)•

IEC 61000-4-8 (magnetic field immunity)•

IEC 61000-4-11 (voltage dips and interruptions)

It is important to remember when comparing specifications, that many of the above mentioned standards
specify different immunity levels or criteria ratings. Vendors are a good source for any additional criteriathat may apply.

7.4.4 Shock and Vibration
When mounting infrastructure components on or near vibrating machinery, such as punch or stamping
presses, etc., it is important to carefully review all shock and vibration specifications for all thecomponents. Equipment rated under the following standards should be considered for higher shock andvibration environments:•

IEC 61131-2, IEC 60068-2-27 (shock)•IEC 60068-2-6 (vibration)

7.4.4.1 Certifications
Typical certifications for industrial applications include CE, EN 60950, UL/cUL1950, and UL/cUL 508.
For use in potentially explosive environments in the United States, added certifications such as UL/cUL
1604 Class 1, Div. 2 (A, B, C, D) or FM 3611 Class 1, Div. 2 may be required. In Canada or Europe,
certification to a zone rating system may be required.

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Appendix A Recommendations for Ethernet Switches
in EtherNet/IP Systems
In industrial applications, infrastructure devices are mounted in the same enclosures as the control
devices, as opposed to the dedicated switch cabinets used in the office world. Therefore, the infrastructuredevices used in an EtherNet/IP system must withstand the same environmental conditions as the control
devices and be compatible with their voltage and mounting conventions.

Personnel for System Start-Up and Maintenance
While a facility may have an Information Technology Department staffed to support hundreds of PCs, thesame facility can have over a thousand control devices with the potential for Ethernet connectivity. The
basic startup, maintenance diagnostics, and configuration of industrial infrastructure devices must be
supported by existing plant and control engineering staffs. Equally important, the infrastructure devices
need to be compatible with IT tools and network standards.
The recommendations presented here are consistent with these objectives:•

Consider the impact of system cost while providing switch functionality adequate forsuccessful initial I/O control applications and expansions.

•

Use only industry standards (i.e., IEEE, IEC, TIA, etc.)—not company-owned
proprietary functions.

•

Include common functions available from three or more industrial infrastructure vendors.

•

Use the application-based system types described in 6 Infrastructure Application
Scenarios to accommodate EtherNet/IP applications that range from small initial
applications to large enterprise-integrated systems.

This appendix categorizes certain switch features as REQUIRED, RECOMMENDED, or APPLICATIONSPECIFIC.
•REQUIRED = functions that are the minimum required for typical performance in the
majority of installations of the application type described in 6 Infrastructure Application
Scenarios. When in doubt, use the next higher application section’s recommendations. In
addition to performance factors, the most likely required plant-floor installation andmaintenance functions are included. Each section’s requirements build on the previous
section’s requirements.

•

RECOMMENDED = functions that are not necessarily needed for all application scenariosof this type, but typically improve or simplify maintenance or provide added performancein certain situations.
•

APPLICATION SPECIFIC = functions that may be significant based on the specificapplication, but not necessarily for the particular type of system architecture (scenario).
These functions typically cross several application categories. The more features a switch
has, the broader the application range, and potentially, the higher the cost.
A-1
Appendix A Recommendations for Ethernet Switches in EtherNet/IP Systems

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Isolated Systems: Small Scale
Application Range: Isolated control network with a single controller and a low device count
REQUIRED:1.

Speeds are 10 Mbps through 100 Mbps with full-duplex operation on all ports. Full-

duplex operation eliminates collisions, a key requirement for deterministic control.
2.

LED diagnostics have a Link LED per port (a physical cable connection is
acceptable) and a network traffic activity indication per port. The traffic indication

allows the user to differentiate between no traffic, intermittent traffic, and high traffic.
RECOMMENDED:

3.

The switch auto-negotiates the data rate, the duplex settings, and provides autocrossover (MDI/MDX) functionality to reduce device set-up requirements and cable

compatibility problems.
4.

The switch supports a maximum operating temperature of 55° C (131° F) or higher.

5.

The switch meets the IEC Std 61000-4 or equivalent standards for noise immunityand emission.

Application Notes:

The primary use of these types of switches is for small applications (less than10 devices) with a small
number of CIP connections and slower RPIs, or applications that are lower cost extensions to IGMPenabled switches.
The above specifications relate to switches without IGMP snooping (unmanaged switches). Due to themulticast operation of EtherNet/IP, one must either calculate the total multicast traffic to which eachconnected unmanaged switch will be exposed or test the configuration in advance. Failure to do this may
result in devices overloaded with unwanted multicast traffic, which may cause communications to stop.

Isolated Systems: General Use
Application Range: Isolated control network with a single controller and a high (more than 10) device

count, or an isolated network with multiple, interlocked controllers
REQUIRED:1.

All specifications included in Isolated Systems: Small Scale.

2.

IGMP snooping: This provides for proper management of IP multicast traffic. Morespecifically, it provides for fast consumer joins and leaves of multicast streams (reducing
memory use) and limits bandwidth-intensive IP multicast traffic to only those ports that are
intended to consume it.
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Lack of IGMP snooping function may result in flooding of the subnet with multicast traffic,
potentially overloading devices on the subnet. This is because the default operation of switches
treats multicast packets the same as broadcast packets, while much I/O messaging with
EtherNet/IP uses IP multicast to distribute I/O data, which is consistent with the CIP producerconsumer model.
3.

IGMP query: Each application must have at least one switch or router that can generate theperiodic IGMP query commands used to determine which devices are members of which
multicast groups.

RECOMMENDED:

4.

Manual port settings: The switch should allow manual configuration of both port mode

(full- or half-duplex) and speed selection (10 Mbps, 100 Mbps, or 1000 Mbps). Legacy
devices may have auto-negotiation compatibility problems. In addition, in some exceptionallyhigh electrical noise environments, manually reducing the 100-Mbps data rate to 10 Mbps
provides higher noise immunity.
5.

Web- and SNMP-accessible port status and diagnostics: A managed switch, which has

its own IP address, should support SNMP and web server as means for remote monitoring
and configuration. As switches are applied in larger scale or faster, time-critical applications,the need for diagnostics increases. Web interfaces allow diagnostic access by plant-floor
personnel. SNMP diagnostics are needed to interface with network management (plant-flooror IT Department-based) and IT Department support tools. Port status information, typically a
web page, allows fast determination of which ports are connected and their operating status.
This is often required for basic cabling troubleshooting. RMON diagnostics provide statistics
regarding the types and sizes of packets being received by any port, as well as port utilization.
This provides basic network traffic statistics to optimize response times and locate noiseinduced disruptions without a sophisticated traffic analyzer.
6.

Port mirroring: This function allows traffic from any port on a switch to be duplicated on aspare port for advanced network diagnostic monitoring and troubleshooting. Port mirroring is
the function that provides compatibility with IT-level personnel and network troubleshooting
tools.
Application Notes:

The primary use of these types of switches is, in general, isolated system applications where all thedevices need to interoperate within a single system. The use of IGMP snooping reduces traffic and allows
larger systems and faster response times. While low-cost unmanaged switches may be used as an
expansion to unmanaged switches, precautions must be taken to prevent the multicast overload of devices.
For the highest performance systems with the fewest start-up or future expansion concerns, it isrecommended that all switches have IGMP snooping functionality.
When connecting multiple controllers over EtherNet/IP, if controller-to-controller communications isneeded (i.e., for interlocking or other peer-to-peer communications) on the same network, then IGMP
snooping is required. If the multiple controllers are independent systems (no peer-to-peer
communications), then they are either a collection of general, small isolated systems, or they connect to asupervisory network and are classified as an enterprise-connected system.

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Large-scale Control and Enterprise Networking
Application Range: Enterprise-connected control system or enterprise-integrated control system
REQUIRED:1.

All specifications included in Isolated Systems: General Use.

2.

Web- or SNMP-accessible port utilization and bandwidth diagnostics: In systems

where enterprise connectivity and real-time control performance needs must be balanced, theability to see the percent of bandwidth utilization of each port allows a faster means oflocating traffic overload points. The RMON diagnostics can then be used to further dissect
the nature of the high traffic, and corrective action can be taken by changing VLAN, routing,or other parameters.
RECOMMENDED:

3.

For enterprise-connected applications without gateways, the use of industrial
switches with VLAN capability is recommended. In this case, existing office (non-industrial) routers may be used to manage the selected data transfer between the control
system and the plant network systems.
4.

For enterprise-integrated applications, additional Layer 3 switches or routers arerecommended to provide the real-time transfer of data while isolating disruptive traffic fromthe control system and enterprise networks.
Application Notes:

See 6.4 Enterprise-Connected and Integrated Control Systems.
APPLICATION-SPECIFIC OPTIONS:

The functions noted here provide added performance or ease of maintenance. The actual need for theseand any associated cost versus functionality tradeoffs need to be evaluated for each application. Some of
the functions are still emerging in the industrial application range and may not yet have widespread multivendor support. Generally speaking, the more of these functions a given switch has, the greater the rangeof EtherNet/IP applications that can be addressed. Unless otherwise noted, the functions noted here relate
to applications using managed switches (isolated, general use systems and higher).
System Performance:

1.

IEEE Std 1588 functionality for motion control applications coordinated with CIP
Sync: In order to implement CIP Sync applications, switches must support IEEE 1588

functionality. See 6.4.1 Networks Connected via CIP Gateways and The EtherNet/IP
Specification24 for more information.
2.

IEEE-based redundancy: IEEE Std 802.1D (Spanning Tree) and IEEE Std 802.1w (Rapid

Spanning Tree) provide redundant backbone connections and loop-free networks. Thesepreviously separate standards have now been combined under the single IEEE Std 802.1D.

24

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www.odva.org. CD-ROM.
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This simplifies network configuration and improves fault tolerance. Engineers can enable ordisable the protocol as needed. Both of these standards support ring and tree/mesh topologies,
integrate with existing office switches, and are well known by IT personnel. Network
recovery times range from a few seconds for the Rapid Spanning Tree Protocol, to 30
seconds to 60 seconds for Spanning Tree Protocol.
3.

IEEE Std 802.1p frame prioritization (QoS): This function allows control traffic to have ahigher priority (serviced first by the switch) then non-time critical traffic. There are two basic
levels of implementation common in industrial switches:•

Industrial switch recognition of pre-tagged packets: Common in managed

switches, emerging in unmanaged switches, this level of functionality is where the switch
receives, reads, and places the packets in two or more (eight maximum) priority queues.
The packets are prioritized via a managed switch or a router located in the system.
•

Industrial switch both assigns tags and recognizes pre-tagged packets: The

managed switch typically assigns priorities by the port to which a particular device isconnected. Routers can also assign priorities by device MAC or IP address. Other, moresophisticated options may include the ability to also set a CoS (Class of Service) that isconfigurable for I/O traffic (i.e., UDP, port 0x8AE) on EtherNet/IP and the support ofconfigurable algorithms to manage multiple priority levels.
4.

Port aggregation: In multi-switch applications, port aggregation allows traffic between
switches to be shared between two or more physical connections, essentially increasing the
bandwidth of the backbone connections. In this case, two 100-Mbps ports can be combinedusing IEEE Std 802.1ad link aggregation protocol to form a single 200-Mbps connection that
supports load balancing.

5.

One Gigabit or higher port data rates: For large-scale, enterprise-connected andenterprise-integrated systems, larger 1-Gbps backbone capacity may be desired. These
connections are used for switch-to-switch uplink or backbone connections, not control
connections to EtherNet/IP devices. EtherNet/IP industrial control devices support 10 Mbps
and 100 Mbps data rates. The decentralized architecture of industrial Ethernet reduces theneed for large concentrations of devices and higher than 100-Mbps connections.

6.

Broadcast or multicast threshold filters: Switches may have a fixed or user-variableoption for restricting the maximum allowed level of broadcast or multicast traffic. Once thethreshold is exceeded, the port may turn itself off until the traffic falls below the thresholdlevel or shut down the port completely based on the vendor’s implementation. This feature
can help lessen the effects of abnormal traffic conditions. For high-speed control applications,the threshold level must be checked to confirm it does not interfere with normal traffic.
Vendor-specific operation of this function, such as operation on ingress/egress, types ofmessages filtered (unicast, multicast, or broadcast), and action of the ports when the limit isreached (clipping versus a shutdown that requires manual reset) must be considered.
Attention to the overall network design will reduce the need for these filtering functions.

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Industrial System Maintainability

In addition to infrastructure-embedded functions, the use of plant-floor network management software
provides added plant maintainability, and compliments the IT-based network management software
already installed in many facilities. This type of software provides a simplified “PLC look” interface tothe entire EtherNet/IP industrial system. The system-wide view allows quick identification of noncommunicating devices, the centralized viewing of SNMP diagnostic “trap” messages, and the ability to“zoom” into detailed device-specific diagnostics using network management screens or the device’s
embedded web pages. These packages also allow easy upload/download (via open Trivial File Transfer
Protocol [TFTP]) of switch/device configurations and upgrades. Because these packages use the industry
standards, such as SNMP protocol, network management software from one vendor can work with othervendor’s switches.
The functions below relate to infrastructure (switch or router) embedded functions.
1.

Alarm contact: The addition of a physical relay-out allows annunciation of power outages
and/or disabling of key links (cable cut, device powered down, etc). The alarm contact isconnected to either physical alarms, lights, etc., or to automation inputs (i.e., spare PLC
inputs) for operator intervention. This provides added cabling and power supply diagnostics
for non-IT or engineering trained personnel.

2.

Serial configuration port for managed switches: A serial configuration port allows the
IP addressing of managed switches or the confirmation of an IP address by plant personnel(using Hyper Terminal with a laptop) without special software, training, or network access.

3.

Automatic re-addressing of replacement devices with DHCP Option 82: DHCP Option

82 allows dynamic IP address assignment for the attached nodes to either be fixed, based on
the port they are plugged into (instead of their MAC_ID), or centrally managed (typically
based in the IT Department) in a server that contains the master IP address list. This function
eliminates the need to manually assign the same IP address to a replacement device’s new
MAC address.
4.

Complete web access to all switch parameters: If the EtherNet/IP system is to be
primarily maintained by plant and control engineering personnel, there is a greater need tohave all switch configuration parameters accessible from standard laptop browsers.
Parameters that can only be accessed via SNMP network management software require thepurchase of network management software or reliance on IT Department tools and personnel.
If the control network is to be primarily maintained by IT personnel, this is not as great arequirement.

5.

Port mirroring: This function allows traffic from any port on a switch to be duplicated on aspare port for advanced network diagnostic monitoring and troubleshooting. Port mirroring is
the function that provides compatibility with IT-level network troubleshooting tools.
6.

Physical storage/retrieval of switch configuration: As an alternative to network-based
auto-addressing and auto-reconfiguration, memory cards or modules may be used to store aswitch’s configuration. If replacement of a switch becomes necessary, plant personnel canremove the card or module from the previous switch, insert it into the new switch, and have
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the configuration read-in automatically. This allows switch maintenance and replacementwith non-engineering personnel or where access to switch configuration data is restricted.
7.

Security functionality: Security appropriate for Ethernet-based control systems is currently

being evaluated. Most managed switches support at least port disable functions. Current
security measures that are becoming more common in managed switches include thefollowing:•

Port disable: The ability to disable/enable spare maintenance ports to prevent casual

access.
•Port security: The ability to enter a list of one or more authorized devices’ MAC or IP

addresses. Connected devices that do not match the list are prevented from
communicating and typically also generate an SNMP alarm message.
•

VLANs: VLANs can be used to restrict traffic and network access. Unauthorized accessin one area can be restricted to that section of the application instead of the entire
EtherNet/IP application.

•

Radius authentication: This includes IEEE Std 802.1X for plant-floor based
programming stations and PCs. It prevents the non-authorized laptop or PC that is new tothe area from being attached to and used on the network without being authenticated by acentral server.

•

SSL/SSH: These security measures allow the secure remote monitoring and configurationof devices via the web or command line (CLI) Telnet.
•

Firewalls and VPNs: These allow the secure movement of data across unsecured lines
and keep access to sensitive areas secure from unauthorized personnel.

More information related to various encryption techniques will be added in future revisions of thisdocument.

Summary
The minimum functional switch requirements related to EtherNet/IP vary based on the size, performance,
functionality and network connectivity requirements of the application. (See 6 Infrastructure Application
Scenarios for more information.) For EtherNet/IP applications, these are summarized with three levels of
required functionality:•••

Isolated systems, small scale
Isolated systems, general use
Large-scale control and enterprise networking

In any specific application, there are additional optional functions that can increase performance andmaintainability of the system. The following represent current widely available or quickly emerging
functions.

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APPLICATION-SPECIFIC FUNCTIONS
Overall System Performance

•
•
•
•
•
•
•

IEEE Std 1588
IEEE redundancy
IEEE Std 802.1p frame prioritization
Port trunking
Routing
One Gbps (and higher) data rates for the uplinks
Broadcast or multicast threshold filters

Added Industrial System Maintainability

•
•
•
•
•
•
•

Alarm contact
Serial configuration port for managed switches
Automatic re-addressing of replacement devices with DHCP Option 82
Complete web access to all switch parameters
Port mirroring
Physical storage/retrieval of switch configuration
Security functionality

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Appendix B Overview of the OSI Model, EtherNet/IP
and CIPThe Open System Interconnection (OSI) Reference Model describes how information from asoftware application in one computer moves through a network medium to a software application inanother computer. The OSI Reference Model is a conceptual model composed of seven layers, eachspecifying particular network functions as shown in Figure B-1. The International Organization forStandardization (ISO) developed the model in 1984, which is now considered the primary architecturalmodel for inter-computer communications.
The OSI Model divides the tasks involved in moving information between networked computers into
seven smaller, more manageable task groups. A task or group of tasks is then assigned to each of theseven OSI layers. Each layer is reasonably self-contained so that the tasks assigned to each layer can be
implemented independently. This enables the solutions offered by one layer to be updated without
adversely affecting the other layers.

Figure B-1

The OSI Reference Model’s Seven Independent Layers.

Characteristics of the OSI Layers
The seven layers of the OSI Reference Model can be divided into two categories: upper layers and lower
layers as shown in Figure B-2.

Figure B-2

The OSI Model’s Two Sets of Layers.

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The upper layers deal with application issues and generally are implemented only in software. The
highest layer, the application layer, is closest to the end user. Both users and application layer processes
interact with software applications that contain a communications component. The term “upper layer” issometimes used to refer to any layer above another layer in the OSI Model.
The lower layers handle data transport issues. The physical layer and the data link layer are implemented
in hardware and software. The lowest layer, the physical layer, is closest to the physical network medium(the network cabling, for example) and is responsible for actually placing information on the medium.

Communication between Systems
Information being transferred from a software application in one computer system to a software
application in another must pass through the OSI layers. For example, if a software application in System
A has information to transmit to a software application in System B, the application program in System A
will pass its information to the application layer (Layer 7) of System A. The application layer then passes
the information to the presentation layer (Layer 6), which relays the data to the session layer (Layer 5),
and so on—down to the physical layer (Layer 1). At the physical layer, the information is placed on thephysical network medium and is sent across the medium to System B.
The physical layer of System B removes the information from the physical medium, and then its physicallayer passes the information up to the data link layer (Layer 2), which passes it to the network layer(Layer 3), and so on, until it reaches the application layer (Layer 7) of System B. Finally, the application
layer of System B passes the information to the recipient application program to complete thecommunication process.
Interaction between OSI Model Layers

A given layer in the OSI model generally communicates with three other OSI layers: the layer
directly above it, the layer directly below it, and its peer layer in other networked computer systems.

The data link layer in System A, for example, communicates with the network layer of System A, thephysical layer of System A, and the data link layer in System B as shown in Figure B-3.

Figure B-3

How OSI Layers Communicate.

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OSI Layer Services
One OSI layer communicates with another layer to make use of the services provided by the second layer.
The services provided by adjacent layers help a given OSI layer communicate with its peer layer in othercomputer systems.
Basic Elements of Layer Services

Three basic elements are involved in layer services: the service user, the service provider, and theservice access point (SAP).
In this context, the service user is the OSI layer that requests services from an adjacent OSI layer. The
service provider is the OSI layer that provides services to service users. OSI layers can provide services
to multiple service users. The service access point (SAP) is a conceptual location at which one OSI
layer can request the services of another OSI layer. Figure B-4 shows how these three elements interact at
the network and data link layers.

Figure B-4

Service Users, Providers, and SAPs Interact at the Network and Data Link Layers.

OSI Model Layers and Information Exchange
In one computer, the seven OSI layers use various forms of control information to communicate with
their peer layers in other computer systems. This control information consists of specific requests andinstructions that are exchanged between peer OSI layers.
Control information typically takes one of two forms: headers and trailers. Headers are prepended todata that has been passed down from upper layers. Trailers are appended to data that has been passed
down from upper layers. An OSI layer is not required to attach a header or a trailer to data from upper
layers.
Headers, trailers, and data are relative concepts, depending on the layer that analyzes the information unit.
At the network layer, for example, an information unit consists of a Layer 3 header and data. At the datalink layer, however, all the information passed down by the network layer (the Layer 3 header and thedata) is treated as data.
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In other words, the data portion of an information unit at a given OSI layer potentially can containheaders, trailers, and data from all the higher layers. This is known as encapsulation. Figure B-5 shows
how the header and data from one layer are encapsulated into the header of the next lowest layer.

Figure B-5

Headers and Data Can Be Encapsulated during Information Exchange.

Information Exchange Process
The information exchange process occurs between peer OSI layers. Each layer in the source system adds
control information to the data, and each layer in the destination system analyzes and removes the control
information from that data.
If System A has data from a software application to send to System B, the data is passed to the application
layer. The application layer in System A then communicates any control information required by theapplication layer in System B by prepending a header to the data. The resulting information unit (a header
and the data) is passed to the presentation layer, which prepends its own header containing control
information intended for the presentation layer in System B. The information unit grows in size as eachlayer prepends its own header (and, in some cases, a trailer) that contains control information to be usedby its peer layer in System B. At the physical layer, the entire information unit is placed onto the network
medium.
The physical layer in System B receives the information unit and passes it to the data link layer. The datalink layer in System B then reads the control information contained in the header prepended by the datalink layer in System A. The header is then removed, and the remainder of the information unit is passed to
the network layer.
Each Layer Performs the Same Actions

The layer reads the header from its peer layer, strips it off, and passes the remaining information unit
to the next highest layer. After the application layer performs these actions, the data is passed to therecipient software application in System B, in exactly the form in which it was transmitted by theapplication in System A.

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Physical Layer
The physical layer defines the electrical, mechanical, procedural, and functional specifications for
activating, maintaining, and deactivating the physical link between communicating network systems.
Physical layer specifications define characteristics, such as voltage levels, timing of voltage changes,
physical data rates, maximum transmission distances, and physical connectors. Physical layer
implementations can be categorized as either LAN or WAN specifications. Figure B-6 illustrates somecommon LAN and WAN physical layer implementations.

Figure B-6

Physical Layer Implementations Can Be LAN or WAN Specifications.

Data Link Layer
The data link layer provides reliable transit of data across a physical network link. Different data link
layer specifications define different network and protocol characteristics, including physical addressing,
network topology, error notification, sequencing of frames, and flow control. Physical addressing (asopposed to network addressing) defines how devices are addressed at the data link layer.
Network topology consists of the data link layer specifications that often define how devices are to bephysically connected, such as in a bus or a ring topology. Error notification alerts upper-layer protocols
that a transmission error has occurred, and the sequencing of data frames reorders frames that weretransmitted out of sequence. Finally, flow control moderates the transmission of data such that thereceiving device is not overwhelmed with more traffic than it can handle at one time.
IEEE has subdivided the data link layer into two sub-layers: Logical Link Control (LLC) and Media
Access Control (MAC). Figure B-7 illustrates the IEEE sub-layers of the data link layer.

Figure B-7

The Data link layer Contains Two Sub-layers.

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The Logical Link Control (LLC) sublayer of the data link layer manages communications between
devices over a single link of a network. Defined in IEEE Std 802.2, LLC supports both connectionlessand connection-oriented services used by higher-layer protocols. IEEE Std 802.2 defines a number offields in data link layer frames that enable multiple higher-layer protocols to share a single physical datalink.
The Media Access Control (MAC) sub-layer of the data link layer manages protocol access to thephysical network medium. The IEEE MAC specification defines MAC addresses, which enable multiple
devices to uniquely identify one another at the data link layer.

Network Layer
The network layer defines the network address, which differs from the MAC address. Some network layer
implementations, such as the Internet Protocol (IP), define network addresses in a way that route selection
can be determined systematically by comparing the source network address with the destination network
address and applying the subnet mask. Because this layer defines the logical network layout, routers canuse this layer to determine how to forward packets. Because of this, much of the design and configuration
work for inter-networks happens at Layer 3, the network layer.

Transport Layer
The transport layer accepts data from the session layer and segments the data for transport across the
network. Generally, the transport layer is responsible for making sure that the data is delivered error-free
and in the proper sequence. Flow control generally occurs at the transport layer.
Flow control manages data transmission between devices so that the transmitting device does not sendmore data than the receiving device can process. Multiplexing enables data from several applications tobe transmitted onto a single physical link. Virtual circuits are established, maintained, and terminated by
the transport layer. Error checking involves creating various mechanisms for detecting transmission
errors, while error recovery involves acting, such as requesting that data be retransmitted, to resolve any

errors that occur. The transport protocols used on the Internet are TCP and UDP.

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Appendix C EtherNet/IP and International Standards
EtherNet/IP is not just an open network based on the CIP specification. Its lower layers are based on
Internet and Ethernet standards. In addition, The EtherNet/IP™ Specification25 is rapidly being
incorporated into international standards. This high degree of standardization assures users that
EtherNet/IP systems will work with Commercial Off-The-Shelf (COTS) Ethernet infrastructure devices
and Internet protocols, and be accepted in manufacturing systems around the world. Listed here are otherinternational standards related to EtherNet/IP.

Internet and Ethernet Standards
The Internet Engineering Task Force (IETF) publishes its standards under a series called Request For
Change documents (RFCs). EtherNet/IP is based on the following Ethernet and Internet standards:
RFC 768 User Datagram Protocol
RFC 791 Internet Protocol
RFC 792 Internet Control Message Protocol
RFC 793 Transmission Control Protocol
RFC 826 Ethernet Address Resolution Protocol
RFC 894 Transmission of IP Datagrams over Ethernet Networks
RFC 1112 Host Extensions for IP Multicasting
RFC 2236 Internet Group Management Protocol, Version 2
ISO/IEC 8802-3:1996 Information Technology, Telecommunications and informationexchange between systems, Local and metropolitan area networks,
Specific requirements, Part 3: Carrier sense multiple access withcollision detection (CSMA/CDD) access method and physical layer
specifications.

Protocols and Profiles
EtherNet/IP is a part of the following IEC and CENELEC standards:
IEC 61158:2003 (Type 2) Covers a wide range of application requirements from discrete
manufacturing automation to process control. It includes the CIP
application layer used by EtherNet/IP and other CIP-based networks,
and the mapping protocol for putting CIP on TCP/IP/UDP
IEC 61784-1:2003 CP 2/2 Type 2 Includes the communication profile defining how to extract therelevant EtherNet/IP specifications from IEC 61158 documents
EN 61158:2003 (Type 2) European equivalent of the corresponding IEC standard

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www.odva.org. CD-ROM.
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EN 61784-1:2003 CP 2/2 Type 2 European equivalent of the corresponding IEC standard

Electronic Data Sheets (EDS)
The definitions contained in the Electronic Data Sheet (EDS) as defined in The EtherNet/IP™
Specification are in compliance with ISO 15745-Parts 1 and 4:2003. ISO 15745 is applicable to a wide
range of application requirements from discrete manufacturing automation to process control. It defines
an application integration framework, i.e., a set of elements and rules for describing integration models
and application interoperability profiles.

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Appendix D Glossary of Terms
Some of the terms defined below have been copied from [1] and [2] with some tailoring to EtherNet/IP
terminology where appropriate.
Term

Definition

Address Resolution Protocol (ARP)

A protocol used to dynamically bind a high-level IP address to alow–level physical hardware address. Within the scope of thisdocument it means a protocol that converts an IP address into an
Ethernet address. ARP is used across a single physical network
and is limited to networks, like Ethernet, which support
broadcast.

BOOTstrap Protocol (BOOTP)

A protocol a node uses to obtain its IP Address, Subnet Mask
and Gateway Address from a server.

broadcast

A transmission method, by which a packet is sent to multiple,
unspecified recipients. Broadcast transmission is supported by
Ethernet and IP protocols.

Dynamic Host Configuration Protocol (DHCP)

A protocol a node uses to obtain its IP Address, Subnet Mask
and Gateway Address from a server. A superset of the BOOTP.

explicit messaging

Explicit messages can be sent as connected or unconnected
messages. CIP defines an explicit messaging protocol that states
the meaning of the message. This messaging protocol is
contained in the message data. Explicit messages provide a onetime transport of a data item. Explicit messaging provides themeans by which typical request/response oriented functions are
performed (e.g., module configuration). These messages are
typically point-to-point.

I/O client

The IEEE standard for bridging 802.3 local area networks(LANs).

I/O messaging

The IEEE standard for Ethernet.

I/O server

A function that constrains flooding of multicast traffic through
Layer 2 switch ports by dynamically configuring them such thatmulticast traffic is forwarded only to those ports associated withnodes belonging to a specific IP multicast group.

IEEE 802.1

Implicit messages are exchanged across I/O connections with anassociated Connection ID (CID). The CID defines the meaningof the data and establishes the regular/repeated transport rate andtransport class. No messaging protocol is contained within themessage data (as with explicit messaging). Implicit messages
can be point-to-point or multicast and are used to transmit
application-specific I/O data. This term is used interchangeably
with the term I/O messaging.
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Definition

IEEE 802.3

A function that uses the I/O messaging services of another (I/O
server) device to perform a task. It initiates a request for an I/Omessage to the server module.

IGMP snooping

See implicit messaging.

implicit messaging

A function that provides I/O messaging services to another (I/O
client) device. It responds to a request from the I/O client.

Internet Group Management Protocol (IGMP)

A protocol that nodes use to keep local switches apprised of
their membership in multicast groups. When all nodes leave agroup, switches (and routers) no longer forward packets that
arrive for the group.

Layer 2 (data link layer or level)

A reference to the data link layer communication (e.g., frame
formats) or data link layer connections derived from the OSI
Reference Model. For local area networks, Layer 2 refers tophysical frame format and addressing. Thus, for an EtherNet/IP
network, a Layer 2 address is an Ethernet address.

Layer 3 (network layer or level)

A reference to the network layer communication derived fromthe OSI Reference Model. For TCP/IP networks, Layer 3 refers
to IP and the IP packet format. Thus, a Layer 3 address is an IP
address.

linkCollection of nodes with unique MAC IDs. Segments connectedby repeaters make up a link; links connected by routers make up
a network.

message client

A function that uses the explicit messaging services of another(Message Server) device to perform a task. It initiates an explicit
message request to the server device.

message router

The object within a node that distributes messaging requests tothe appropriate application objects.

message server

A function that provides explicit messaging services to another(Message Client) device. It responds to an explicit message
request from the Message Client.

multicast

A transmission method by which a packet is sent to a selected
subset of all possible recipients. A node can belong to one ormore multicast groups. Multicast transmission is supported by
Ethernet and IP protocols. Approximately half of the UDP
packets on EtherNet/IP are sent via multicast.

multicast connection

A connection from one node to many. Multicast connections
allow a single producer to be received by many consumer nodes.

network

A collection of one or more subnets where each node’s MAC ID
is unique on the network. The series of nodes are connected bysome type of communication medium. The connection paths
between any pair of nodes can include repeaters, routers andgateways.

network address or node address

An identification value assigned to each node on the CIP
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Definition
network. This value distinguishes a node among all other nodes
on the same link. The format is network specific.

node

A collection of objects that communicate over a subnet andarbitrate using a single MAC ID. A physical device may containone or more nodes.

node address

See network address.

object(1) An abstract representation of a particular component within a
product. Objects can be composed of any or all of the following
components:a) data (information which changes with time);b) configuration (parameters for behavior);c) methods (things that can be done using data andconfiguration).
(2) A collection of related data (in the form of variables) andmethods (procedures) for operating on that data that have clearly
defined interface and behavior.

object-specific service

A service defined by a particular object class to perform arequired function that is not performed by a common service.
An object specific service is unique to the object class thatdefines it.

octet

An octet is 8 bits that indicate no particular data type.

off-link connection

A connection between two or more devices that are on
physically different networks.

originator

A node (client) that requests the creation of a connection to atarget.

ping

The sequence of messages that coordinates time between
consumers and producers

ping request

Request for the acknowledge of the reception of a message.

ping response

Response to a ping request.

point-to-point connection

A connection that exists between two nodes only. Connections
can be either point-to-point or multicast.

port

A CIP port is the abstraction for a physical network connection
to a CIP device. A CIP device has one port for each network
connection. Note: network specific definitions may include
additional definitions of this term within the context of the
network.

produce

Act of sending data to a consumer.

producerA node that is responsible for transmitting data.

redundant media

A system using more than one medium to help prevent
communication failures.

Requested Packet Interval (RPI)

The measure of how frequently the originating application
requires the transmission of data from the target application.
D-3
Appendix D Glossary of Terms

Network

Term

Infrastructurefor

EtherNet/IP™

Definition

segment

A collection of nodes connected to an uninterrupted section ofphysical media.

Simple Network Management Protocol (SNMP)

A standard protocol used to monitor nodes, switches, routers,
and networks to which they are attached.

Spanning Tree Protocol (STP)

A switch (or bridge) protocol that uses the spanning-tree
algorithm, enabling a switch to dynamically work around loops
in a network topology by creating a spanning tree. Switches
exchange special messages with other switches to detect loops,
and then remove the loops by shutting down selected switch
interfaces. Refers to both the IEEE 802.1D Spanning-TreeProtocol standard and the earlier Digital Equipment Corporation
Spanning-Tree Protocol on which it is based.

subnetA collection of nodes using a common protocol and shared
media access arbitration. Subnets may have multiple physicalsegments and contain repeaters.

systemContains one or more domains.

targetA destination for I/O connection or message requests. It can
only respond to a request (not initiate an I/O connection ormessage.)Time to Live (TTL)

A technique used in best-effort delivery systems to avoid
endlessly looping packets. For example, each IP packet is
assigned an integer TTL when it is created (TTL is a field in the
IP packet header). Each router decrements the TTL field when
the packet arrives. A router discards any packet when TTL
reaches zero.

unicastA transmission method by which a packet is sent to a single
destination. All TCP packets are sent via unicast on EtherNet/IP.

Virtual LAN (VLAN)

A group of devices on one or more LANs that is configured(using management software) such that the devices cancommunicate as if they were attached to the same wire, when infact they are located on a number of different LAN segments.
Because VLANs are based on logical as opposed to physicalconnections, they are extremely flexible.

References

1 Comer, Douglas E., Internetworking with TCP/IP, Volume 1: Principles, Protocol, and Architecture,
Prentice Hall, 1995.
2 Dictionary of Internetworking Terms and Acronyms, available on www.cisco.com

D-4
Appendix D Glossary of Terms

Network

Infrastructurefor

EtherNet/IP™

Appendix E Ingress Protection (IP) Codes
Ingress Protection (IP) Codes are environmental ratings for enclosures. The following table shows how
these ratings are designated.
IP Codes1st Digit

Protection Against Foreign
Objects

2nd Digit

Protection Against Moisture0

Not protected0

Not protected

1

Protected against objects greaterthan 50 mm

1

Protected against dripping water2

Protected against objects greaterthan 12 mm

2

Protected against dripping water whentilted up to 15 N

3

Protected against objects greaterthan 2.5 mm

3Protected against spraying water

4

Protected against objects greaterthan 1.0 mm

4Protected against splashing water

5

Dust protected

5

Protected against water jets

6

Dust tight6

Protected against heavy seas------

7

Protection against the effects ofimmersion------

8

Protection against submersion

Example marking: IP 68 would indicate a dust-tight (first digit 6) piece of equipment that is protectedagainst submersion in water (second digit 8).
Source: Underwriters Laboratories, Inc.

E-1
Appendix E Ingress Protection (IP) Codes