Designing and implementing high-availability Ethernet LAN topologies in networks can be challenging. Traditionally, the choices for redundancy for edge of the network devices were too limited, too expensive, and too complicated to be considered in several networks. Redundancy at the edge of the network is greatly simplified by the using dual-homing.
In Ethernet LANs, dual-homing is a network topology that adds reliability by allowing a device to be connected to the network by way of two independent connection points (points of attachment). One connection point is the operating connection, and the other is a standby or back-up connection that is activated in the event of a failure of the operating connection. A dual-homing switch (such as EDS42) offers two attachments into the network or two independent media paths and two upstream switch connections. In the case of the Magnum 6K family of switches, any two ports can be defined as dual-home ports to provide this level of redundancy. Loss of the Link signal on the operating port connected upstream indicates a fault in that path, and traffic is quickly moved to the standby connection to accomplish a fault recovery.
In those situations where the end device is a PoE device (for example, a video surveillance camera, as shown above) a Magnum 6K switch with MNS-6K can provide PoE to the end devices, as well as other advantages such as IGMP, managed configuration and more. To provide the managed reliability to the end devices, dual-homing can be used with MNS-6K devices.
Because it takes advantage of Ethernet standards, the dual-homing redundancy features of the ESD42, as well as those for MNS-6K work with any brands or models of Ethernet switches upstream. With MNS-6K, the user has to define the set of ports, which make up the dual-home ports.
The following points should be remembered for setting up dual-homing
Configure dual-homing before connecting the Ethernet connectors (cables) in the switch
Only one set of dual-homing ports can be defined per switch
Port types (Copper vs fibre) as well as speeds can be mixed and matched, both ports need not be identical
By default dual-homing is turned off, it has to be enabled after the ports are defined
Dual-homing ports can span different modules in a switch
There are two modes in which the dual-homing works. The first one is where the ports are equivalent i.e. if one port fails, the other one take over, however, if the first (failed) port recovers, the active port does not switch back.
The second mode of operation is primary-secondary mode. In this mode of operation, the primary port is explicitly defined and the secondary port is explicitly defined. In the primary-secondary mode of operation, if the primary fails, the secondary takes over. When the primary recovers, the secondary switches back from active state to passive state and the primary port is now the active port.
The primary-secondary mode has to be explicitly setup. The primary-secondary mode of operation is only possible on managed switches such as the Magnum 6K family of switches.
The primary-secondary mode of operation allows the network manager to determine on which path the packets will flow (as a default).
While managed Ethernet Switches for use in redundant LAN structures such as rings and meshes have become increasingly available and popular, redundancy provisions for edge devices in Industrial Ethernet networks has not previously been addressed. The new dual-homing edge switch fills that void and provides a new tool for designers of redundant LANs that is simple and dependable in operation.
A dual-homing Ethernet switch allows the dual-homing function to be moved from the node into a small switch. This enables designers of redundant LANs to increase the reliability and uptime of any industrial control device that has an Ethernet port (not just those few designed with dual NICs, typically at a cost premium). Redundancy at the edge is now cost-effective and easy.
Creating effective redundant Ethernet LANs is a matter of complex trade-off calculations among up-time, cost, and control device selection. GarrettCom’s Magnum ESD42 dual-homing switch provides a new plug-and-play redundancy tool that opens up LAN design options and expands device choices. Any industrial SCADA device can now be used creatively in redundant LANs to create an installation that is more robust and less complex, at a more affordable price.