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FCS/Dup Ack/Retransmit

asked 2019-01-31 15:54:25 +0000

euscada gravatar image

Hi all,

My first post here and hope I can get some insight to an issue we are having at one of our facilities.

We recently upgraded all of our un-managed 10M/HD switches to 10/100M/FD managed switches and encountered an issue that has stumped others and an integrator we had on site.

The communicating equipment is a Modicon M340 and an Eaton VFD drive with a Modbus TCP adapter (OPTCI card).

There are 12 devices in this comm path and 6 are having issues talking back to our PLC (all on the same switch, the local switch is a N-TRON 7900 series managed switch 10/100 / non Gb)

Previously, all 12 Eaton drives had a similar issue, although we were able to force a duplex mode on 6 of the Eaton drives (Using a different model Modbus TCP card) and the issue stopped (we forced a 10M/FD mode).

With the other 6 drives, we are unable to force the duplex modes (appears to be an issue with a software revision or firmware) and those 6 are the ones giving us trouble.

Eaton claims the auto-negotiation should work fine, although I have read that there is a possibility some manufacturers have different implementations of "auto-negotiation".

It appears the 6 drives are in "auto negotiate mode", but when we set both sides to auto-negotiate (we can set this in the switch and we assume the drive is auto-negotiate/we can not see or change this setting) the drive fails to communicate and the switch claims a 100M/FD mode.

I am assuming I am seeing a Duplex Mismatch (in my wireshark capture), although I can not confirm this.

Is there any chance someone can take a look at my capture and provide some feedback?

Thanks all and if more info is needed I can provide it asap.


*It appears I can not attach a file -- here is a link to my capture --

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answered 2019-01-31 21:05:40 +0000

Christian_R gravatar image

updated 2019-01-31 21:45:14 +0000

For debugging a Duplex there are mostly 2 ways

-1st way: If your switch has some port counter you would see CRC error on a duplex mismatch port

-2nd way: If you have a tap you can bring it in between the switch port and the device, and then you should see corrupted ethernet CRCs - a mirror port is not enough as a mirror port eliminates the frames with corrupted CRC errors.

But maybe your issue is on the uplink of the switch, where the devices with the problem are located.

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Thank you for the reply.

It turns out the speed and duplex settings for the Eaton Modbus card was not accepting the changed settings values (on the switch side) until a power cycle of the comm card takes place.

After finding this out with much trial and error, we have cleaned up comms on our local subnet...

Thanks again

euscada gravatar imageeuscada ( 2019-02-05 14:06:18 +0000 )edit

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Asked: 2019-01-31 15:54:25 +0000

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Last updated: Feb 05 '19