Hi All,
We have an S7-1200 system consisting of the following:
-3 S7-1200 PLCs with associated cards
-2 HMIs
-1 Remote I/O module

When not connected to anything, the system works correctly. All PLCs communicate, all HMIs get information, and no errors occur. When I do connect to our client's network however, issues start cropping up. HMIs temporarily lose connections to PLCs, and monitored values are intermittently lost on the HMI.

If I disconnect the client network, and power cycle the system, everything goes back to normal. If I leave the client network connected, and power cycle the system, I get all sorts of communications errors, and no PLC values show up on either of the HMIs. And when I try to ping the devices from the first HMI (cmd program), I can only get a response from the second HMI, no PLC responds.

The network setup is as follows: we have two Siemens switches that the devices go through, and then out to the client's switch on site. We were given an address range from the client to use on our devices, with a gateway address as well. I confirmed that the address range is not used by any other device. The HMIs seem to be able to be pinged by the client's IT guy after a power cycle, but no PLC is able to be pinged. Yet when I disconnect the client's network, and power cycle, everything seems to go back to normal.

Any idea what could be happening?

Thanks for any help!

Hello,

I would check how many broadcasts?multicasts the "client network" generates and if these frames can be detected on the PLC network. I my opinion the rate of these packets is too high and affects the good working of the PLC network. These frames may show up in bursts depending on the activity on the client network.

Can be easaly detected with the free tool wireshark
Connect a PC on the PLC side, start the tool, monitor the traffic, and go to the statistics.

A way to get rid of that type of problems is to separate both networks via a router/firewall.
A scalance S602 or S615 is an example of device playing that role.
Here an application example with more details.

Such a device will block unwanted traffic and protect the PLC network, even to illegimate access to the PLCs by unauthorized people on the client side.