Network Redundancy

If the computers in your Plant SCADA system support dual networks interface cards (NICs) or multiple network interface capabilities, you can configure redundant end-to-end network connections between clients and servers.

Consider the following diagram:

The above example shows two levels of redundancy:

• Network redundancy

  Each of the system components in the cluster are connected to two networks (LAN 1 and LAN 2). This is achieved by using the dual end points of each server. This provides LAN redundancy as follows:

  • If LAN 1 is suddenly inoperative, each component in the cluster can easily maintain connection by using LAN 2.

  • In turn, if LAN 2 becomes inoperative, LAN 1 remains in operation.

    For this type of redundancy to work, each system component needs to have two NICs to support two parallel LANs. On every computer, each NIC needs to use a separate IP network or subnet.

    Note: Currently Plant SCADA does not support dynamic port binding.

• Server redundancy

  This is achieved by adding standby servers, within a defined cluster, to provide redundant system components.

  For information about server redundancy, see Reports and Trends Server Redundancy and Alarm Server Redundancy.

When Plant SCADA runtime starts on a computer, it compares the server topology configuration with the computer's network addresses to determine the role or roles assigned to that computer. For example, it may identify the computer as an I/O server, trend server, or alarm server. Plant SCADA performs this configuration check only once during runtime startup. If no match is found, runtime assumes the role of a client.

This means that a computer's network identity must be available when runtime starts to ensure the correct roles are established for communication. For this reason, it is recommended that you assign static IP addresses to all Plant SCADA computers. This ensures that Plant SCADA always has a known and valid IP address for sending and receiving communications. If network connectivity is temporarily lost and later restored, Plant SCADA can resume communications without requiring IP address reassignment.

Assigning a DNS Name (hostname) to a computer will allow Plant SCADA to assign the correct role. However, if runtime starts before the computer receives an IP address (for example, due to a DHCP server outage or a slow-starting network switch), communication with other computers will not occur because Plant SCADA resolves IP addresses only once during startup.

See Also

Configuring Network Redundancy