I've encountered an force termination by a host, even after a successful (at least it seems to be successful; correct me if I'm wrong) FIN ACK close of connection. Packet trace at the moment is attached below. I've left the last digit of hosts unmasked to identify them separately.
My analysis is this: Despite the out of order packet, the connection termination handshake went well, but after that, one party calls an RST.
Window update, FIN termination went well right? How an RST is possible if connection is closed by the FIN already?
Best Answer
The RST is in response to receiving something on a connection that no longer exists. The connection was closed by FIN, and it was acknowledged, so the connection no longer exists, and then something was received on the closed connection, so a RST was sent. This is actually covered in RFC 793, Transmission Control Protocol: