Modbus parallel connection

[elvir.brkic@bstelecom.ba]

We are using Modbus TCP driver (3.14 P004) to connect to Remote I/O module over Ethernet.
What we noticed in Wireshark is that WinCC OA opens two connections (two TCP source ports) upon connecting and that each polling request is mix of requests using both connections.
So I would like to know if this is by design or is it bug?

The thing is that Remote I/O module stops responding after some time, so I wondered if this could be cause.

[Gertjan van Schijndel]

The Modbus driver only establishes a single connection. But in a redundant system both servers poll Modbus devices.

Do the connections have the same ip address? Or are you using multiple Modbus drivers?

[elvir.brkic@bstelecom.ba]

You are right, we are using multiple Modbus drivers.
Apparently some addresses got mixed up between two drivers, so that's why we were seeing two connections.

Thanks for your help.