GE PACSystems RX7i, User Manual

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Chapter 1. Introduction
GFK-2224Q January 2017 11
1.4
Ethernet Redundancy Operation
2
Note: Ethernet Redundancy Operation is not supported on the RX3i CPE305/CPE310 embedded
Ethernet Interface.
The Redundant IP feature of the Ethernet Interface allows a single IP address called the Redundant IP address to
be assigned to two Ethernet modules. The two modules are in two different PLCs that are configured as a
redundant system.
Note: The CPE400 does not support Redundant IP at this time.
The Redundant IP Address is configured
in addition
to the normal unique (direct) IP address of each interface.
Only one of the two Ethernet interfaces that share the Redundant IP address may use the Redundant IP address
at any time; this is the “active” unit. When commanded by its PLC CPU, this Ethernet interface activates the
Redundant IP address and starts responding to the Redundant IP address in addition to its direct IP address. The
active unit continues responding to the Redundant IP address until it is commanded to deactivate the
Redundant IP or until the Ethernet interface determines that it has lost communications with the PLC CPU.
The other unit (the “backup” unit) does not initiate communications or respond on the network using the
Redundant IP address. It can only use the Redundant IP address if it is commanded by its CPU to become the
active unit.
Both the active and backup unit may continue to use their individual direct IP addresses, permitting programmer
connection to the active or backup PLC at any time.
PLC A
PLC B
Redundant System
Programmer
Remote host
(HMI, PLC, etc.)
Redundant
IP Address
Direct IP
Addresses
Figure 2: Ethernet Operation in Redundancy Mode
The Redundant IP feature is supported by Hot Standby (HSB) CPUs and non-HSB CPUs.
HSB CPU Redundancy
An HSB system uses redundancy CPUs that provide the coordination between the PLC units in the system and
determine which is the active unit and which is the backup unit. HSB redundancy requires dedicated links to
provide communications between the units in a redundancy system. Redundancy CPUs that include an
embedded Ethernet Interface have a “CRE” designation, for example IC698CRE040. For information about HSB
architectures, refer to the
PACSystems Hot Standby CPU Redundancy User’s Guide,
GFK-2308.
2
Not supported on the RX3i CPE305/CPE310 embedded Ethernet Interface.