Ethernet comms PLC5 SLC5/05

Ran into an issue the other day where a network of PLC's (3 PLC5's with ethernet sidecars and a single SLC 5/05) all faulted at the same time. The PLC5's showed coprocessor faults, which I believe is an issue with the ethernet modules attached to the processor. The SLC 5/05 showed a hard fault on the ethernet comm port, and even went as far as to disable this port while it was faulted. I was able to connect with a DF1 driver and see this before resetting this.
Has anyone else seen this type of behavior where all the processors on an ethernet network fault like this? This also happened about 4 months ago when we only had the three PLC5's on the network.

something is either shorting or overloading the network. fun part is that it intermittent

What else is on the network?
Obviously there is a switch at least.
That behavior sounds almost like a broadcast storm, or someone plugging a patch cord in to two ports on the same network.

All PLC's are plugged into managed switches. Part of the problem is that the IT dept. manages these switches, and they may be carrying traffic from up to three different LAN's. The LAN we use only has maybe ten computers/PLC's on it, but I can't tell if it is something on "our" side of the network or theirs.

Realized I never posted the resolution on this thread...Turns out the corporate IT guys were searching the LAN every once in a while (from a different country). When they found an IP address they couldn't identify, they would hammer it with data requests. This overloaded the comms cards on the PLC's and caused them to fault. Once they were notified to stay away from certain addresses, the problem went away.

"We're here from corporate...We're here to help."

It guys must be away from plcs.

Thanks for the follow-up !

I had something similar once, when all the A-B devices would "lose their IP addresses and go to DHCP".

Turns out that the IT department had installed a "DHCP Enforcer" tool and had opened up all the routers so it could go around into all the automation workcells and force everything to DHCP mode. We caught it doing its dirty work via Wireshark, after a few months of the customer chewing on RA Tech Support.