Prosoft AN-X4 to Mettler Toledo IND570 Communication Problems

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 that the problem is likely originating from the Mettler Toledo IND570

Funny how the one vendor blames the other as if that wasn't predictable, whether true or not! In this case I think they are right based on the packet capture. Some straightforward correlation: when the TCP connection for the EIP protocol Forward Open gets closed (via TCP Reset), the MT device stops producing Class1 implicit messages; this is the likely disconnect described. Recovery happens automatically.

I have seen this before from a different vendor, but it has been a long time and the specifications could have changed. That being said, it used to be that there was no requirement in the spec that the TCP connection has to remain open for implicit messaging to continue - recall for EIP, some CIP messaging via TCP is used to setup the implicit (class1 cyclic) communication stream. I don't know why Prosoft is shutting down the TCP connection, but I would argue that per specification, it shouldn't matter and implicit communications should continue until the implicit connection is shutdown at application layer.

The ODVA specs are not free so I cannot check to see if behavior in this area has changed.

Aside: Packets are out-of-order in the pcap file. I would revisit your capture strategy to avoid this - it does not have any bearing on this issue as it is easy to spot and workaround, but could matter in the future.