Sometimes (*) during connection initiated from W5500 I got following sequence:
For me it looks that Wiznet chip reports to server (using RST,ACK packet) that port is closed.
Interesting is that before I start sending “POST …” request the socket reports its state as ESTABLISHED.
Why can be reason for this?
Another mysterious (for me) fact is sending of TCP retries with POST request.
Because to my SW socket looks like in state ESTABLISHED then I try to send POST request and after 1.5 s socket is explicitely disconnected (see: FIN, ACK packet) and closed because of (application) timeout.
But why in such case it still tries to resend TCP packet?
Additional info: there is only one socket used during this test.
(*) Sometimes means that few times per hour when there is established a few tens of connections per hour.
For this internet connection most of TCP connections have to resend packets but usually it is does not cause problem like above.