Redundant Ethernet


Rayno Powell

What you want to do???? Windows 2000 Advanced Server allows you to install a windows component called netwrok load ballance. This allows you to have one pc with two network cards on the same network witch will share the load of the network and provide redundancy. If one card fails, the other will immedietely take over the load.

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Yeasir Rahul

Add more NICs in the PC. We've successfully run Linux machines with four NICs. I've heard that in Windows, multiple NICs cause problems. It is painless and simple under Linux, that I can say.


Hitendra Uppal


It is important to know the scheme. You can have 2 options.
1. Have 2 LAN cards with different IP add. on a PC & write a Redn. algorithm.
2. Bring the 2 LAN inputs to a Hardware based Ethernet Redn. switch, designating one input as a Primary Master & the other, Secondary.

Let the switch pass to the Primary to the output (to the PC) & in case of its failure, the Redn. automatically switches to the secondry input & continues the transmission.

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Syncrude Engineer

Either FTE or Cisco HSBY protocol. FTE will only apply to flat network, HSBY would be used segregated network through router.

Fabio Mielli

Suggestion: Remember that a right Ethernet redundancy has to have a self ring topology, so, if you have two PC ports with different IP addresses, you can create a ring topology with your PLC (other 2 Eth ports) - you have to consider appropriate switchs or hubs that accept ring topoligies.

You will have a ring with 4 nodes and 4 switches.
Do you mean redundant network? just add one more network card (PCI, ISA). The IP for both Port must have different network ID. eq:port 1= and Port 2 Subnet Mask=
There are vendors that make redundant ethernet cards for PCs. Just do a search on google, etc.
I use a Trunking software package called NIC Express. It creates an array of NICs similar to a RAID array for hard drives. It has load balancing and full fail over. I have used it with NT and W2K the web site is
Up to 4 Ethernet cards in a Windows machine is no problems. We use 2 Ethernet cards in most systems.

Make sure that your OPC server (or other communication driver) automatically handles the switching between the Ethernet cards.

Another alternative to using dual Ethernet cards mention by some is to use a ring topology. This has some advantages over a single star topology but still has some single points of failure. Really using dual Ethernet cards is best, but requires that the devices such as controllers and PLC also have dual Ethernet ports. We (SMAR) make such controllers for Modbus/TCP and FoundationT Ethernet (HSE).

To lean more about Ethernet redundancy and availability, check out chapters 3 and 10 of the book "Fieldbuses for Process Control: Engineering, Operation, and Maintenance" (buy online in hardcopy or download immediately in softcopy):

If you can't buy the book now, you can download chapter 1 (overview) for free in softcopy form. It's free, but you must register an account. If your email does not support this hyperlink feature correctly, please copy the entire link and paste it into your Internet browser. Mind the line wrap, make sure to get the complete path all the way to the 4585: Display.cfm&ProductID=4585

Jonas Berge SMAR
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Learn fieldbus at your own pace:
Jonas makes a good point of making sure your OPC server allows you to do on the fly switching of which Ethernet card is used. For an example of one that does this see - this utility when used with OPC servers from Software Toolbox ( and KEPware automates the switching between redundant NICs based on user specified configuration and notifies the user via email/pager/phone when a switch has occurred. The utility also switches between redundant PLCs (i.e different IPs) if required.