Applies To:
  • CitectSCADA 1.x 2.x 3.x 4.x

Citect supports LAN redundancy by allowing you to install more than 1 LAN adaptor in your computer. If Citect cannot communicate over one network adaptor Citect will try the second adaptor. This works fine for Citect, however this can cause problems for other applications you are running in the same computer. 

Problems can occur if you are using a Network File server (which you are most likely are with a LAN) and you have Citect and other applications installed on the file server. When a network fails Citect will switch across to the second network. If the second network is also failed then Citect will just keep retyring until one of the networks is available.

The connection to the network file server must also do the same change over as Citect. When the primary LAN is failed the Microsoft file redirector will time out the next time you try to access any data on the file server. The redirector will then try to re-establish communication to the file server by trying all network adaptors. This can take up to 1 minute to occur and during this time it may appear that applications have hung. During this time it may fail file service requests to any application. Citect is designed to handle this failure, however other applications may fail. Also if the application is installed on the file server it may cause the application to crash with a General Protection Fault (GPF) see Q1885 for details.

If you are using LAN redundancy you should try to install as much data as possible on the local hard disk. So that this data is always available in case of network failure. I would recommned you install Citect applications and other 3rd party applications on the local hard disk. You do not have to install the Citect project on the local hard disk as Citect can access the project over either network adapator. Moving the Citect project to the local hard disk will allow Citect to keep displaying new pages if both LAN fail, however it does require more maintance to make changes to your project.

See also Q1378, Q1195 and Q1121.