Modbus TCP source IP in CPU redundancy configuration

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1

Hello,

I have a question about Modbus communication in a CPU redundancy configuration.

Modbus is activated on the POWERLINK port of a CP3685 (on every CPU). The Modbus Master configuration is intrinsically imposed by the CPU redundancy configuration, as described in the manual.

When testing the Modbus frames with a simulator, I noticed that the requests are sent from the IP address of the active CPU (in the redundant configuration there is an active CPU and a standby CPU), rather than from the cluster (virtual) IP address as I expected.

With a standard Modbus slave this isn’t a significant issue, but when the communication is being monitored (e.g. a PC running a Kepware driver), a change of source IP after a failover could cause problems, since the monitoring system may not recognize the new source as the same device.

Is there a way to force the Modbus requests to originate from the cluster IP instead of the active CPU’s IP?

Thank you for your help

2

Hello,

this is little bit strange because the communication should run through cluster IP address because it doesn’t make any sense that IP address of the PLC is used. When there is switchover that IP address will change and in this case the communication will have to be established again. Please create a ticket for this issue for the local support. Thank you

3

Hello, local support reply me that the situation described is correct. So i made same question : could i be fixed it ? I’m waiting an answer.

Best regards

4

So issue was moved ti official support, right? please update us with final findings.