Why take risks with your control network?
August 2006
Fieldbus & Industrial Networking
Contemporary Controls offers three new managed features to safeguard against risks to control networks. "The reason being," says R&D manager Bennett Levine, "that the popularity of Ethernet employed in the control system is gaining strength every day. Most users are of the opinion that you can simply connect your devices to the office network. The logic behind this viewpoint is that both the control devices and the office devices communicate via Ethernet, and they can simply be connected together. However, there are considerations to keep in mind."
After discussion with the company's customers, engineers designed three new features associated with their EISX_M, EICP_M and EISB_M managed switches. These features - rate limiting, port locking and overlapping VLANs - prevent risks when interconnecting office and factory networks, says Levine.
The rate limiting feature lets the individual select a maximum traffic level (from 64 Kbps to 100 Mbps) so varied communications operate properly - even allowing the control network to function in the event the office network has a catastrophic problem. "For example," says Levine, "an individual can use this feature to limit the amount of traffic your office network can send to your control network." One related feature of rate limiting is broadcast storm control which the company's switches also support.
The second feature is port locking. This is another method of controlling the traffic that comes from the office network. Port locking limits what devices can communicate through a specific port of the switch.
"For example," Levin explains, "you can employ this port locking to only allow certain computers in the office network to communicate with the control network. This can help restrict your problems to a few office devices and not the entire office network."
The third feature is known as overlapping VLANs. It allows a few devices to be shared between the office and the control network. Office traffic is eliminated from the portion of the control network that does not need to communicate with the office network. Levine says if a scada system needs to communicate with both the office network and the control network, an 'overlapping VLAN' could be used to keep office traffic from all control devices except for the scada system. "Any problems in the office network will not affect the rest of the control network," he adds.
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