Installation guide

Network Infrastructure for EtherNet/IP™
A-3
Appendix A Recommendations for Ethernet Switches in EtherNet/IP Systems
Lack of IGMP snooping function may result in flooding of the subnet with multicast traffic,
potentially overloading devices on the subnet. This is because the default operation of switches
treats multicast packets the same as broadcast packets, while much I/O messaging with
EtherNet/IP uses IP multicast to distribute I/O data, which is consistent with the CIP producer-
consumer model.
3. IGMP query: Each application must have at least one switch or router that can generate the
periodic IGMP query commands used to determine which devices are members of which
multicast groups.
RECOMMENDED:
4. Manual port settings: The switch should allow manual configuration of both port mode
(full- or half-duplex) and speed selection (10 Mbps, 100 Mbps, or 1000 Mbps). Legacy
devices may have auto-negotiation compatibility problems. In addition, in some exceptionally
high electrical noise environments, manually reducing the 100-Mbps data rate to 10 Mbps
provides higher noise immunity.
5. Web- and SNMP-accessible port status and diagnostics: A managed switch, which has
its own IP address, should support SNMP and web server as means for remote monitoring
and configuration. As switches are applied in larger scale or faster, time-critical applications,
the need for diagnostics increases. Web interfaces allow diagnostic access by plant-floor
personnel. SNMP diagnostics are needed to interface with network management (plant-floor
or IT Department-based) and IT Department support tools. Port status information, typically a
web page, allows fast determination of which ports are connected and their operating status.
This is often required for basic cabling troubleshooting. RMON diagnostics provide statistics
regarding the types and sizes of packets being received by any port, as well as port utilization.
This provides basic network traffic statistics to optimize response times and locate noise-
induced disruptions without a sophisticated traffic analyzer.
6. Port mirroring: This function allows traffic from any port on a switch to be duplicated on a
spare port for advanced network diagnostic monitoring and troubleshooting. Port mirroring is
the function that provides compatibility with IT-level personnel and network troubleshooting
tools.
Application Notes:
The primary use of these types of switches is, in general, isolated system applications where all the
devices need to interoperate within a single system. The use of IGMP snooping reduces traffic and allows
larger systems and faster response times. While low-cost unmanaged switches may be used as an
expansion to unmanaged switches, precautions must be taken to prevent the multicast overload of devices.
For the highest performance systems with the fewest start-up or future expansion concerns, it is
recommended that all switches have IGMP snooping functionality.
When connecting multiple controllers over EtherNet/IP, if controller-to-controller communications is
needed (i.e., for interlocking or other peer-to-peer communications) on the same network, then IGMP
snooping is required. If the multiple controllers are independent systems (no peer-to-peer
communications), then they are either a collection of general, small isolated systems, or they connect to a
supervisory network and are classified as an enterprise-connected system.