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Ethernet Troubleshooting

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I am having an issue with a ControlLogix PLC installation which I am relatively sure will be a network issue, but I don't want to overlook something.

The system was originally a 1756-ENBT\A with a 1756-L61 CPU which we upgraded today with a 1756-EN2T\C.

We are chasing a problem where the FCS errors are occurring at the rate of 1-8 per minute.  The 1756-EN2T has been running for 4 hours (240 minutes) and accumulated 685 FCS. {See EthernetStatistics.png}  Now my IT counterpart swore he saw no issue at his switch ports and the issue should have been the 1756-ENBT\A.  Todays results would dispute that.

Now looking at connection counts I noticed that both CIP and TCP connections cycle from a low value 7/8 respectively to a high value 13/25 and then back to the low value count.  Not sure if there is a way short of wireshark at the switch to ferret out the source of these connections.

I did notice that the TCP Connections list shows three connections from the same IP address {A Scada HMi Node} having the same serial number and very low uptimes.  And they never seem to age much before they close and are reopened.  I'm wondering if I have a configuration error on some SCADA hooks that I need to find and address?

I'm open to any suggestions as to where to look next.  Has anyone had issues like this between their PLC and their SCADA.



Connections Counts.PNG

Ethernet Statistics.PNG

TCP Connections.PNG

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