Installation guide

Network Infrastructure for EtherNet/IP™
Planning the Infrastructure
3-21
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, and
so 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 streaming
of 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 an
industrial 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 most
commonly 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 for
examples). 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 starting
up 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 encapsulating
these CIP messages inside the TCP/IP Ethernet protocols, EtherNet/IP is able to provide a powerful
control 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.