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Dual NIC, 1 Primary, 1 Backup

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by mbrush

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Installing a Process Control System (Allen-Bradley) and need network redundancy. We have two different physical networks, one specifically for the Process Control System (Primary) and our "plant" LAN (backup). All servers and workstations have dual NIC's for the new system. We'd like to connect each server and workstation to each physical network. We want the Process Control System to use the new network and only use the "plant" LAN as a backup. We do not have a router for the new LAN. How can we configure this system? We can't seem to get traffic to stay on the New LAN.

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by mbatty

Need a little more information about the protocols that is running. Assuming it IP this sounds like a routing issue. Also assume that the two LANs have different IP network ranges.

Given the above assumptions, te traffic will be routed depending on the destination address of the traffic. So, when device A wants to talk to device B, if the address is resloved to be on the primary LAN is should route out the Primary LAN NIC card. How is the address being resolved?

If your application uses DNS to resolve host addresses you can implement round robin DNS to provide an alternate IP address in the event of a failure of the primary LAN.

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by lrund

I don't know all of the particulars but I beleive you want to use GateD with RIP (Routing information Protocol) or the newer GateD with OSPF protocol.
GateD with OSPF uses a virtual IP address to access the server and the two NICs act as passthruinterfaces. The server using OSPF keeps in contact with routers and when a segment or route drops the data is automatically routed to the other NIC. As you can see there is some overhead on the network with broadcasts to keep the routers informed of the availablity of the two NICs. You would register the virtual IP address to your DNS.
These are the only two protocols that I know that will accomplish what you want.

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