Network Issue with Wire Fault

Obviously the wire faults have to be corrected, additionally there are a lot of other communications problems that can be caused by poor cable management. I recommend putting managed switches in so you can have better port diagnostics.

With a managed switch you will be able to see Ethernet errors on individual ports such as CRC, FCS, and others. This error data will help you do network repairs based on the severity and type of errors, as well as provide a baseline to improve against. I have unfortunately been through this a few times on I/O networks with up to 30 nodes on them.

It's important to follow good Ethernet cabling practices, observing all specs. Bend radius, pull tension, separation from EMI sources, proper connector installation, I recommend shielded Ethernet cabling. A poor network install/design can result in a network that will eat your lunch daily.
 
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Thanks for those Wireshark captures and diagrams !

I'm not convinced that the ARP 0.0.0.0 is a cause of a connection drop, rather than a symptom.

You can see the low-level Ethernet packets for the N-Tron ring protocol (they're labeled Red Lion) still flowing rapidly after the interruption.

I wonder what kind of diagnostics the 708TX is logging when this event occurs.

What kind of tap are you using between the PLC and the switch ? I see all the Magelis HMI requests to the PLC, but none of the PLC replies to those requests, so I don't think we're seeing everything in Wireshark.


You really need a managed switch to get good information from Wireshark logs. Normally we have to clone ports to whatever port the Wireshark computer is connected to, otherwise Wireshark will only log broadcast traffic.

For example; Connect the Wireshark computer to port 6 on a managed switch, say you want to capture all the communication to and from devices on ports 1 and 2. Port 1 and 2 should be cloned to port 6, so every packet that is transmitted/received on port 1 and 2 is cloned and sent to port 6 for Wireshark to log.
 
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If you are stuck with the festoon wireway maybe look into some tougher Ethernet cable. I am thinking for example something like Allen Bradley 1585 cable or possibly something along the lines of Belden MarineTuff Offshore and Marine cable. The Belden would even be available with a bronze braid armor.
I work in the oil and gas industry, doing service work on onshore drilling rigs and the marine shipboard cable is usually holding up really well in this harsh environment.
 
Because your unmanaged switch is unmanaged, you're probably only seeing the broadcast packets.

"ARP for address 0.0.0.0" is a duplicate address check packet called an ARP Probe, which is totally normal when a device is first connected to a network.

Are you saying that when you get a short circuit on one of your "droplines", that all of the ControlLogix and HMIs connected to other unmanaged switches on the network have their connections fail, not just the one whose cable was damaged ?

It does sound like a Layer 2 loop to me. Hmm.

This was my first thought as well.
 
You really need a managed switch to get good information from Wireshark logs. Normally we have to clone ports to whatever port the Wireshark computer is connected to, otherwise Wireshark will only log broadcast traffic.

For example; Connect the Wireshark computer to port 6 on a managed switch, say you want to capture all the communication to and from devices on ports 1 and 2. Port 1 and 2 should be cloned to port 6, so every packet that is transmitted/received on port 1 and 2 is cloned and sent to port 6 for Wireshark to log.

This is what I did with the N-Trons, mirrored the ports.

I do have managed switches if you look at the diagram the unmanaged is just tying the PLC and HMI together running back to the managed switch. To monitor traffic on the unmanaged switch I have to use a passive tap to capture the packets.

The Stratix switch sees the wire fault as a loop back and will block the port, but this is only if the wire is plugged directly into the Stratix, if it happens somewhere else in the network it won’t block the port.
 

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