Rockwell Automation 20-750-ENETR PowerFlexDual-Port EtherNet/IP Option Module - Manual (Page 18)

18 Rockwell Automation Publication 750COM-UM008A-EN-P - July 2012
Chapter 2 Installing the Option Module
Much of EtherNet/IP implicit (I/O) messaging uses IP multicast to
distribute I/O control data, which is consistent with the CIP producer/
consumer model. Historically, most switches have treated multicast
packets the same as broadcast packets. That is, all multicast packets are re-
transmitted to all ports.
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 (managed switches) ‘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.
Be careful as to what level of support a switch has of IGMP snooping.
Some layer 2 switches that support IGMP snooping require a router
(which could be a layer 3 switch) to send out IGMP polls to learn what
devices are part of the multicast group. Some layer 2 switches can use
IGMP snooping without a router sending polls. If your control system is a
standalone network or is required to continue performing if the router is
out of service, make sure the switch you are using supports IGMP
snooping without a router being present.
• See Appendix A for the number of CIP connections supported by the
option module.
• Verify that you have all required equipment. See Required Equipment on
page 13 .
ATTENTION: Risk of equipment damage exists. The option module contains
electrostatic discharge (ESD) sensitive parts that can be damaged if you do not
follow ESD control procedures. Static control precautions are required when
handling the option module. If you are unfamiliar with static control procedures,
see Guarding Against Electrostatic Damage, publication
8000-4.5.2 .
IMPORTANT The option module has EtherNet/IP embedded switch technology, and ENET1
and ENET2 network ports to connect to a linear or device-level ring (DLR)
network in a single subnet.
You cannot use ENET1 and ENET 2 network ports as two network interface
cards connected to two different subnets.