1. Ethernet Switch Features Important to EtherNet/IP
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2. Switch Features are Important
The proper selection of switches to be used in real-time (I/O) EtherNet/IP networks is critical. There are several features that are very important and can provide the appropriate infrastructure for your application. The following features need to be considered:
Required:
Full-duplex capability on all ports
IGMP Snooping
Port Mirroring
Recommended:
VLAN
Auto-negotiation and manually configurable speed/duplex
Wire-speed switching fabric
SNMP for switch management
IEEE 802.1D Spanning Tree Protocol
Desirable: see last slide
Copyright © 2005 Rockwell Automation, Inc. All rights reserved.

3. Copyright © 2005 Rockwell Automation, Inc. All rights reserved.
Full-duplex
Full-duplex capability on all ports:
Full duplex capability eliminates collisions on the wire due to the separate transmit and receive channels for each device. Combined with the speed of switches available today, delays related to collisions or traffic in the switch can be made negligible. The end result is you can achieve a high degree of determinism with an EtherNet/IP network and it works well for I/O control.
Copyright © 2005 Rockwell Automation, Inc. All rights reserved.

4. Internet Group Multicast Protocol (IGMP) Snooping
IGMP snooping constrains the flooding of multicast traffic by dynamically configuring switch ports so that multicast traffic is forwarded only to ports associated with a particular IP multicast group.
Switches that support IGMP snooping “learn” which ports have devices that are part of a particular multicast group and only forward the multicast packets to the ports that are part of the multicast group.
Sends out IGMP polls to determine who is in a multicast group
to plant network
Listens to the polls and responses to determine who is in each multicast group
Layer 3 Switch or Router
Layer 2 Switch
Layer 2 Switch
Controller
I/O
(Multicast
Producer)
(Consumer)
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5. IGMP Snooping - continued
Normally, a commercial layer 2 switch that “supports” IGMP snooping needs a router (which could be a layer 3 switch) to send out the IGMP polls in order to learn what devices are part of the multicast group.
*** IMPORTANT ***
Some industrial layer 2 switches support IGMP snooping without the requirement for a router or layer 3 switch to be present to send out the IGMP polls.
to plant network
Note that none of the multicast traffic hits the router
Layer 3 Switch or Router
Layer 2 Switch
Layer 2 Switch
Controller
I/O
(Multicast
Producer)
(Consumer)
Copyright © 2005 Rockwell Automation, Inc. All rights reserved.

6. Copyright © 2005 Rockwell Automation, Inc. All rights reserved.
Port Mirroring
Port Mirroring:
Port mirroring refers to the ability to direct a duplicate of the frames being transmitted on one port to another port. This allows a traffic analyzer to be connected to a switch and have the ability to monitor the traffic on a given port. Without port mirroring, an analyzer is not able to see frames on other ports.
Traffic analyzers are used extensively by people who support Ethernet networks. Therefore, it is critical that a switch is selected that supports port mirroring so that a traffic analyzer will function correctly on the network.
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7. Virtual Local Area Networks (VLANs)
The benefits of VLANs are that a switch can be configured to handle two isolated networks without the traffic from one network burdening the other. IP multicast traffic from VLAN 1 will not reach VLAN 2. For multicast traffic, you could accomplish the same thing with IGMP snooping. However, a VLAN will also block unicast and broadcast traffic, and adds a measure of security between networks.
I/O
Controller1 PC
Controller2 1 2 3 4 5 6 7 8
VLAN 1
VLAN 2
Switch
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8. Auto-negotiation / Manually Configurable Speed/Duplex
Auto-negotiation and manually configurable speed/duplex:
Auto-negotiation allows devices to select the most optimal way to communicate without the user having to configure the devices. If a manually configured device is attached to an auto-negotiation device there can be problems which result in a high rate of CRC errors. While all 100 Mbps devices are required to support auto-negotiation, most existing 10 Mbps devices do not.
Two other areas where this switch feature can be helpful include when fibers converters are used in a system (auto-negotiation is not supported by fiber links) and to eliminate potential incompatibilities in the implementation of the auto-negotiation by different device vendors.
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9. Wire-speed Switching Fabic
Wire-speed switching fabric:
The switch fabric capacity is a measure of the maximum traffic that a switch can handle without dropping a packet. Wire speed switching fabric refers to a switch that can handle the maximum data rate of the network on each of its ports.
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10. Simple Network Management Protocol (SNMP)
SNMP, Simple Network Management Protocol, is a TCP/IP protocol used to obtain statistical information about a device. SNMP software is very popular with network managers. It allows a network manager to view and modify a wide variety of network parameters, and also provides a common way to manage many diverse vendor products utilizing a single Network Management Tool.
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11. IEEE 802.1D Spanning Tree Protocol
Ethernet infrastructures can be designed to provide redundant backbone connections for improved fault tolerances. The Spanning Tree Protocol is to ensure that although multiple paths may exist between two devices connected to the infrastructure, only a single path will be used for communications at any one time.
The switch should have the ability to enable and disable this feature on a per port basis.
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12. Desirable Switch Features
IEEE 802.1p Frame Prioritization
IP address blocking
Restricts traffic to IP Addresses in specific range (down to one)
DHCP Option 82
Limited DHCP Server (for small systems)
Auto-restore of switch config on replacement
Per port broadcast and multicast storm control
Port Trunking for applications with many switches
Various security functions
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