Installation guide

Network Infrastructure for EtherNet/IP™
6-67
Infrastructure Application Scenarios
6.1.2.2 Varying Sensitivity by Device Type
Certain devices, such as Windows-based PCs/workstations, may have an extra sensitivity to multicast
traffic. There can be significant variance in sensitivity between the same devices from different vendors,
and between different devices from the same vendor. Direct connection of the sensitive devices to
separate Ethernet ports on controllers or to Ethernet connections via switches capable of IGMP snooping
may be mandatory.
6.1.3 Configurable Isolation of Enterprise and Control Traffic
One of the promises of Ethernet-based systems is shop-floor-to-top-floor connectivity. When connecting
control networks to enterprise networks (i.e., networks supporting mainly office traffic, MES, plant
management, manufacturing line efficiency, quality monitoring , etc.), unwanted enterprise traffic
(including multicast and broadcast) must be blocked from disrupting control traffic. Equally important is
the need to prevent EtherNet/IP multicast control traffic from flooding and bogging down the enterprise
network. The conventional method used to connect separate fieldbus networks is to use two network
interface cards in a PC. The enterprise and control networks are physically isolated with a PC-based
program used to selectively enable data transfers in both directions.
Of course, any change in the desired data flow requires each of these PCs with two network cards to be
manually reprogrammed. For single connections and relatively stable data flows, this may be a
completely acceptable approach. However, as the quantity of control-to-enterprise connection points grow
and the need to adapt data flow increases, reprogramming all the intermediate databases becomes
unwieldy. In these cases, industrial switches and routers with Virtual LAN (VLAN) capabilities allow
configurable traffic isolation without reprogramming PCs, rewiring network cables, or purchasing
additional network cards. VLAN-capable switches and routers isolate broadcast and multicast traffic,
preventing it from passing into other network areas. These same functions and devices are also used to
implement network security functions. See 4.10 Virtual Local Area Networks for more VLAN
information.
Once traffic is isolated using VLANs, routers (or Layer 3 switches with routing functions) are required to
allow data to be selectively transported from one VLAN to another. Other router mechanisms, such as
Time-to-Live (TTL) thresholds and Access Control List (ACL) filtering may be used in conjunction with
VLANs to provide further isolation and protection between plant-floor and enterprise environments.
6.2 Isolated Control Network with a Single Controller
Isolated EtherNet/IP networks are not connected to other plant or enterprise-level networks. Control
system examples built around these networks typically contain one programmable controller, one or more
workstations, and control devices, which may include I/O nodes and/or drives, etc. Two configurations
are typical: low (usually with 10 or fewer devices) and high (usually with more than 10 devices). The
major performance concerns relate to managing multicast traffic and preventing device overload from
unwanted multicast traffic, which would shut down device communications.