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Old June 23rd, 2022, 02:02 AM   #1

moistcat is offline
Join Date: Jun 2020
Location: Melbourne
Posts: 13
Industrial Network Inspection / Analysis?

Hi All,

I'm doing mainly PLC programming but dabbling in industrial networking.

I am investigating an intermittent communication fault between a AB 1756-L82E (v33) and a RTU. PLC executes EthernetI/P Explicit messaging instructions. I have enabled logging on the RTU, is there any way to capture message logs from the PLC side?

Question part 2:
The issue has occurred once in the last month, so I doubt i'm going to find anything, and my hunch is the RTU Ethernet port has frozen up, as this has happened at other sites. However I have an order to do some on site investigation, what are some valuable documents / findings I can produce as part of the exercise / report?

I'm sure this is an exercise network ppl go though all the time:
-Wireshark capture?
-Average traffic throughput?
-Scan with fluke cat6 tester?

Basically wanting to show I properly investigated the issue..

Interested to see what comes back!
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Old June 23rd, 2022, 02:13 AM   #2
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AlfredoQuintero is offline
Join Date: Feb 2015
Location: Yokohama
Posts: 1,055
You can use Wireshark but you need a managed switch with mirror port function to get the traffic between the PLC and the remote IO device. The Wireshark dissector for EtherNet/IP is great and usually provides a lot of good information, including decoding of error responses, so in many cases you do not need to check the specification to figure out the meaning.
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Old June 23rd, 2022, 06:33 AM   #3
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TurpoUrpo is offline
Join Date: May 2008
Location: Switzerland
Posts: 1,552
Check if any new machinery was installed lately and if was where their power supply is wired from. Once had a network probs cos of new installations going too near of network cables. The thing was that the errors showed up only when the machine was started (startup current peak was much higher and thus also interference was much higher), not that often as it was normally running all the time.
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Old June 23rd, 2022, 08:37 AM   #4
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mk42 is offline
Join Date: Jun 2013
Location: MI
Posts: 2,841
Wireshark will show you WHAT happened, but it won't always show you why. Managed switches with port mirroring are one good way to get a trace; there are also dedicated ethernet taps you can use that provide everything going across one cable.

I'd strongly recommend checking all cables with a tester. Some switches have one built in, otherwise you might need to buy one or hire an IT firm. It's also important to check the configuration. If some devices are fixed at 100mbps instead of autonegotiate, you can have instances where there is a mismatch and they don't communicate well, especially if it's because of a bad cable.
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Old June 23rd, 2022, 07:29 PM   #5

moistcat is offline
Join Date: Jun 2020
Location: Melbourne
Posts: 13

Thanks @AlfredoQuintero, @TurpoUrpo, @mk42.

I'm sure its a rack mounted greyhound switch between them so ill be sure to bring my Hirschman cable and set up a mirror port.

All else fails i have some code where the RTU can reboot itself if the heartbeat isn't seen for x seconds..
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