User manual
Publication ENET-UM001I-EN-P - January 2010 157
Troubleshoot an EtherNet/IP Module Chapter 11
Switch Considerations
To help troubleshoot your EtherNet/IP network, you must use a managed
switch. Some of the important features in a managed switch include:
• Internet Group Multicast Protocol (IGMP) snooping.
• support for Virtual Local Area Networks (VLAN).
• port mirroring.
Internet Group Multicast Protocol
EtherNet/IP implicit (I/O) messaging mostly uses IP multicasting to
distribute I/O control data, which is consistent with the CIP
produced/consumer model. Most switches retransmit multicast packets and
broadcast packets to all ports.
IGMP snooping constrains the flooding of multicast traffic by dynamically
config
uring switch ports so that multicast traffic is forwarded only to ports
associated with a particular IP multicast group. This also helps minimize the
CPU utilization rate.
Switches that support IGMP snooping learn which ports have devices that are
pa
rt of a particular multicast group and only forward the multicast packets to
the ports that are part of the multicast group.
IGMP snooping cannot control unicast or broadcast traffic. To learn how to
c
ont
rol unicast or broadcast traffic, see Virtual Local Area Networks on
page 158
.
IMPORTANT
Use a switch equipped with wire-speed switching fabric. The
switch fabric is a measure of the maximum traffic that a switch
can handle without dropping a packet and without storing a
packet in memory. Wire-speed switching fabric refers to a
switch that can handle the maximum data rate of the network
on each of its ports.
Switches are typically rated in Gbps. For a 10-port switch
connected to EtherNet/IP products, the maximum data rate
needed is typically 100...200 MB/s. Therefore, a 10-port-switch
rated at least 1 GB/s should be adequate for an EtherNet/IP
application.
IMPORTANT
Not all switches support the IGMP snooping querier function,
that is, snooping. Those that do not support IGMP snooping
querier require a router. For switches that do support IGMP
snooping, you can configure them to conduct the polling.