W5500 Sends RST after FIN, ACK

Question

Our W5500 configured as a client randomly sends an RST message after receiving the FIN, ACK response from the server when closing a socket. The socket was opened successfully, data was sent to the server and acknowledged, and then our application tells the W5500 to close the socket. The W5500 sends FIN, ACK to the server, and the server sends FIN, ACK back to the W5500 about 72ms later. The W5500 then instantly (2us later) sends an RST, ACK message back to the server. This only happens on random occasions - perhaps once every few hours. What would cause it to send this RST message? Wiznet RST Trace2986×1152 131 KB

Eugeny · Answer

This is normal behavior and means that W5500 has closed the socket and communication through it is not possible any more - and therefore W5500 asks remote node not to send anything for it.