Ip Gateway Redundancy; Redundant Ip Gateway Configurations - Motorola MOSCAD 68P02958C00-B User Manual

IP Gateway Redundancy

A redundant IP Gateway can be configured to minimize the risk of a SCADA control center
losing contact with sites, and to ensure high availability for its applications. Two IP Gateways
are set up with similar configurations, except that one is designated as the primary and the
other is designated as the secondary. When the primary IP Gateway becomes unavailable, the
secondary (similarly configured) IP Gateway takes over. To increase the availability of the
LAN network, dual Ethernet segments can be used, and each IP Gateway can be connected to a
different segment.
When the IP Gateway is configured for redundancy, the NFM application will not operate.
Initially, the IP Gateway Redundancy Mode is set to 'Secondary'. In this state:
The IP Gateway does not ack any frame received by the MDLC communication (except
local connection).
The requests queued in the IP Gateway will return errors once activated. (In most cases
this will be immediately. However, in some cases it could take as long as the longest
MDLC session timeout defined.)
The IP Gateway disconnects from all the Terminal Server ports defined in the Site
Configuration.
The SCADA driver is responsible for changing the IP Gateway Redundancy Mode to
'Primary'. In this state, the IP Gateway communicates properly over MDLC communication
and over the SCADA channels.
When the IP Gateway is configured for redundancy, it checks each of the channels to the unit.
If all the channels to the unit are disconnected or unavailable, the unit automatically switches
to 'Secondary' mode.
When the SCADA establishes connections to the IP Gateway, it should change the redundancy
mode of the IP Gateway to 'Primary'. Only one IP Gateway should be in 'Primary' mode at
any time. 'Primary' mode of the IP Gateway allows bi-directional transfer of both SCADA
application messages and IP Gateway management messages. 'Secondary' mode allows
transferring of IP Gateway management messages only. (It does not send or receive any
MDLC messages, since it is logically disconnected from the link.)

Redundant IP Gateway Configurations

There are several possible options for Redundant IP Gateway system configuration:
1. Both IP Gateways are connected to the MOSCAD system over the same many-to-many
media (i.e. RS485/Radio). In this configuration, when the secondary IP Gateway becomes
primary, the IP Gateway's mode changes take effect immediately.
2. Both IP Gateways are connected to the MOSCAD system over the same Terminal Sessions.
In this configuration, the 'old primary' IP Gateway must close all of the Terminal Server
connections, the terminal server must end its sessions with the 'old primary' IP Gateway and
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