Modbus TCP with [RST] Flags

asked 2022-12-04 04:30:54 +0000

HPC gravatar image

Hi, I have few controllers (one main and 6 auxiliaries) communicating on Modbus TCP. The main controller is on and the auxiliaries are in the range One of the auxiliaries can not communicate with master. On Wireshark, I am getting [TCP Out-Of-Order] followed by [TCP Dup Ack], [TCP Retransmission], and finally [RST] flags at the end of some streams. This issue is only happen for one of the controllers. In this case, the one on ip: The timeout is set to 1000 ms on controllers.

If I reupload the code on the main, one randomly selected auxiliary will have the above issue. If I reupload the program on auxiliaries, the controller which is updated the last will have this issue. For example, If I re-upload on auxiliaries #1,2,3,4,5,6 in order then #6 will have the error. If reupload on auxiliaries in order #5,3,4,6,1,2 then #2 will have the error.

Any idea what could cause this issue?

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Could be a buffer overrun somewhere. In what topology are these nodes connected? Is there, and if so what kind of switch is between them? What about the link speed between the nodes and the switch (if any)?

Jaap gravatar imageJaap ( 2022-12-04 07:59:35 +0000 )edit

There is a Hirschmann unmanaged switch where all nodes are connected to it.

HPC gravatar imageHPC ( 2022-12-04 08:05:32 +0000 )edit

Possible duplicate IP address?

Chuckc gravatar imageChuckc ( 2022-12-04 12:40:02 +0000 )edit

There is no ip conflict or duplication.

HPC gravatar imageHPC ( 2022-12-04 12:50:15 +0000 )edit

We'll need a capture otherwise we're just guessing.

As it's Modbus you're not leaking any "secret" info by sharing a capture with us, post it on to a public share and add a link to it back here.

grahamb gravatar imagegrahamb ( 2022-12-05 08:59:37 +0000 )edit