Applies To:
  • CitectSCADA 4.xx, 5.xx

How to set up two independent, redundant LANs with TCP/IP in Windows NT 4.0

The scenario is this - a group of machines that need to be networked using NT 4.0, with cable redundant networking. Two network cards per machine, and cables for each, and TCP/IP as the protocol for both (no other protocols).

Note that you must have an IP address for EACH card on the network. Install as per usual for NT networking, just note that you have to set up your IP addresses for BOTH cards. Make sure IP forwarding/routing is turned off in the "Protocols|TCP/IP|Routing" tab, otherwise packets on one network can be routed through the machine to the other network (very messy).

OK, so far so good, you should have two independent networks. HOWEVER - the IP addresses for one network must have a different subnet to the other ! Eg 203.19.130.XXX for one LAN, 203.19.222.XXX for the other. You can also try using different subnet masks instead, but this depends on the customer's networking requirements. This can be really annoying if you are using DHCP to allocate IP addresses, so bear this in mind when setting up the network.