EXTENDED VLAN

Network Topology, Configuration and Hardware: Industrial VLAN Best Practices

Industrial VLANs use a wide variety of configurations and equipment. Part of the attraction of Ethernet VLANs is that legacy devices, wiring and topology can be used as part of a full system of VLANs.

Managed switches make it possible to create and manage VLANs, and the right industrial switch can save a lot of trouble. An industrial managed switch should have the right number and kind of ports, strength, dependability and ultra fast recovery for the real needs of the industrial settings*. The need for reliable ruggedness typically exceeds that of commercial installations. Data flow rates can be controlled to avoid problems. The fastest ports available on each switch should be used for network trunk links, as these carry the most traffic.

Switch and router placement makes a difference. Inefficiencies may arise if they aren’t located the shortest physical distance to the maximum number of nodes on the VLAN. Longer paths increase the likelihood of failures and
complicate problem diagnosis.

Unshielded twisted pair (UTP) cable is the most commonly used wiring. At many plants is this is already in place, often making a VLAN possible without running new cable. Fiber optic cable carries more data over greater distances, and is useful for network trunk links.

Management Software for industrial VLANs should be graphic oriented. In non-industrial settings it’s presumed that everyone dealing with the network went to IT school. But industrial automation is very visual, and plant personnel are often the first responders to VLAN issues. They’re much more used to dealing with colors and check boxes than a command line interface.

Packet Filtering – Tag VLAN headers may cause trouble on industrial networks. It’s OK to leave the tag data on packets going to tag-aware devices. But if all devices aren’t tag-aware, the switch must strip tags from packets before they go out to the VLAN. This is very important in dealing with the legacy equipment found in many industrial settings.

Redundancy is a key to reliable operation. Though industrial equipment typically withstands far more abuse than commercial, the nature of many industrial networks makes back-up systems necessary. A degree of redundancy is often the best way to ensure network stability. And in some situations full redundancy is both needed and available.

*Equipment capability - The best equipment is “tuned” to the needs of the specific industrial situation. An outstanding example of how to do this is B&B Electronics’ robust line of Elinx 500/600 Managed Industrial Switches.