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Hi all, I have my own driver to communicate with a MicroLogix 1400. Please refer to the attached screenshot from Wireshark. 10.10.21.10 is my driver's host, and 192.168.1.192 is the ML1400. The startup sequence to establish a connection & session with the PLC is correct I believe: - In the grey highlight, client requests a connection to .192 via SYN and this is ack'd - A session is registered, and forward open is successful - There's a lot of stuff in green simply because I've also got an HTTP browser session open to the PLC to monitor its session table - In between, spaced 8 seconds apart, are my two attempts to keep the connection alive by sending a List Identity request (as a ping, if you like). These are highlighted in pale blue. - However, 16.5 seconds from the start of the grey highlight, and 16.4 seconds after sequence=115 ack=99, the controller sends back a [RST, ACK] and a callback from my socket code tells me that the session has been dropped. The connection timeout for the PLC is configured as either 30 or 60 seconds, so I don't see how that's relevant here when the reset is happening only 17 seconds after it was established ? However, presumably the PLC doesn't see the application-level "List Identity" request as a valid means of keeping the connection alive. What is the correct mechanism to use that the PLC will accept as a keep-alive ?