S7 400H CP443-1 comms issue

2 CPU's Fiber connected on same rack etc out to a number of ET200s. Set up and running, happily falls over to the other PLC if one switched or th eother switched off.

One port on each CP connected to a separate switch via the X1 P1 R ports and then on to Third party OPC and own HMI.

If I disconnect the Switch on the Eth port on CP connected to PLC A, PLC A continues to work and the Heartbeat can be seen in OPC, (via connection on second CP) if I reconnect and then disconnect the Eth on the second CP I lose all visibility????

I can connect to the PLC using the second port on the second CP with the Laptop but if the first port on this second CP is disconnected as above I lose connection to the PLC as well. It's as if the comms is via our switches and not the fiber or backplane. Do the two CPs need to be connected on the second ports to maintain connection?

Hope that explanation is fairly clear!

Not sure exactly how your system is supposed to work.
If you have two S7-400H CPUs in a redundant configuration, then you probably need your OPC server to connect to the CPU that is the one that has the control, and not the standby CPU. The only OPC server I know that can handle that is Simatic Net Redconnect. I havent used Redconnect myself, so that is all I know.
Pretty sure that a 3rd party OPC server for Siemens S7 cannot handle redundancy.

THank you for the response. We are using Kepware and it falls over quite nicely in the event of a PLC failure, the issue is not being able to see PLC A except via our switch connected to CP1, I thought the connection went through CP2 ->CP1 and then to PLCA. I was wondering if we need to have duplicate connections to each port on the CP's to each switch?