Publication 1756-UM001G-EN-P - January 2007
Configure Redundancy 115
EtherNet/IP Considerations
in Redundant Systems
You can have as many as two EtherNet/IP modules in the redundant
chassis. You can use 1756-ENBT EtherNet/IP and 1756-EWEB
EtherNet/IP Web Server modules.
In a redundant system, use EtherNet/IP for HMI communication or
inter-controller messaging only. HMI can talk directly to the primary
controller. You no longer need RSLinx Alias Topics. Redundancy does
not support EtherNet/IP for I/O control or producing and consuming
data.
IP Address Swapping
Firmware version 13 supports IP address swapping in redundant
systems. Configure the primary and secondary EtherNet/IP modules
with the same IP address. The primary EtherNet/IP module takes the
IP address; the secondary module takes that address plus one in the
last address segment.
On switchover, the EtherNet/IP modules swap IP addresses. HMI
devices automatically continue to communicate with the primary
controller. Because of the way EtherNet/IP modules work, during a
switchover, communication between the controller and an HMI device
halts for several seconds, typically less than a minute, while the IP
address propagates.
Use a dedicated ControlNet network instead of an EtherNet/IP
network if you need a bumpless HMI connection.
Primary Chassis
IP Address
Secondary Chassis
IP Address
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