Installation guide

Network Infrastructure for EtherNet/IP™
A-5
Appendix A Recommendations for Ethernet Switches in EtherNet/IP Systems
This simplifies network configuration and improves fault tolerance. Engineers can enable or
disable the protocol as needed. Both of these standards support ring and tree/mesh topologies,
integrate with existing office switches, and are well known by IT personnel. Network
recovery times range from a few seconds for the Rapid Spanning Tree Protocol, to 30
seconds to 60 seconds for Spanning Tree Protocol.
3. IEEE Std 802.1p frame prioritization (QoS): This function allows control traffic to have a
higher priority (serviced first by the switch) then non-time critical traffic. There are two basic
levels of implementation common in industrial switches:
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Industrial switch recognition of pre-tagged packets: Common in managed
switches, emerging in unmanaged switches, this level of functionality is where the switch
receives, reads, and places the packets in two or more (eight maximum) priority queues.
The packets are prioritized via a managed switch or a router located in the system.
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Industrial switch both assigns tags and recognizes pre-tagged packets: The
managed switch typically assigns priorities by the port to which a particular device is
connected. Routers can also assign priorities by device MAC or IP address. Other, more
sophisticated options may include the ability to also set a CoS (Class of Service) that is
configurable for I/O traffic (i.e., UDP, port 0x8AE) on EtherNet/IP and the support of
configurable algorithms to manage multiple priority levels.
4. Port aggregation: In multi-switch applications, port aggregation allows traffic between
switches to be shared between two or more physical connections, essentially increasing the
bandwidth of the backbone connections. In this case, two 100-Mbps ports can be combined
using IEEE Std 802.1ad link aggregation protocol to form a single 200-Mbps connection that
supports load balancing.
5. One Gigabit or higher port data rates: For large-scale, enterprise-connected and
enterprise-integrated systems, larger 1-Gbps backbone capacity may be desired. These
connections are used for switch-to-switch uplink or backbone connections, not control
connections to EtherNet/IP devices. EtherNet/IP industrial control devices support 10 Mbps
and 100 Mbps data rates. The decentralized architecture of industrial Ethernet reduces the
need for large concentrations of devices and higher than 100-Mbps connections.
6. Broadcast or multicast threshold filters: Switches may have a fixed or user-variable
option for restricting the maximum allowed level of broadcast or multicast traffic. Once the
threshold is exceeded, the port may turn itself off until the traffic falls below the threshold
level or shut down the port completely based on the vendor’s implementation. This feature
can help lessen the effects of abnormal traffic conditions. For high-speed control applications,
the threshold level must be checked to confirm it does not interfere with normal traffic.
Vendor-specific operation of this function, such as operation on ingress/egress, types of
messages filtered (unicast, multicast, or broadcast), and action of the ports when the limit is
reached (clipping versus a shutdown that requires manual reset) must be considered.
Attention to the overall network design will reduce the need for these filtering functions.