Rockwell Automation Ethernet Design Considerations Reference Manual - Manual (Page 34)

34 Rockwell Automation Publication ENET-RM002C-EN-P - May 2013
Chapter 3 Ethernet Infrastructure Features
Frames
Use multicast frames in these situations:
• Redundancy applications
• Communication with more than one destination
Multicast is more efficient than sending multiple, unicast streams to
multiple nodes.
• Video streaming
You must use unicast communication if the transmission routes through a Layer 3
device.
I/O devices generally produce at very fast rates, such as 10 ms, so it is easy to
flood the network with multicast traffic and force each end device to spend time
deciding whether to discard numerous multicast frames. If there are a lot of I/O
devices, they can easily use up a significant part of a router’s CPU time.
You must consider control network traffic propagating onto the plant
information network, as well as, plant information network traffic propagating
onto the control network. Some best practices include the following:
• Minimize device load due to unwanted IP multicast traffic
• Minimize switch load due to unwanted IP multicast traffic
• Minimize network load due to unwanted incoming IP multicast or
broadcast traffic
• Block IP multicast traffic generated within the EtherNet/IP subnet from
propagating onto the plant network
• Implement standard network troubleshooting tools
For more information, see Virtual LANs and Segmentation on page 42 and
Internet Group Management Protocol (IGMP) on page 55 .
Layer 2
Switch
Layer 2
Switch
I/O
(producer)
Controller
(consumer)
Switch or
Router
To Plant Network