From: sjpark@xxxxxxxxxx > Sent: 31 January 2020 12:24 ... > The acks in lines 6 and 8 are the acks. If the line 8 packet is > processed before the line 6 packet, it will be just ignored as it is not > a expected packet, and the later process of the line 6 packet will > change the status of Process A to FIN_WAIT_2, but as it has already > handled line 8 packet, it will not go to TIME_WAIT and thus will not > send the line 10 packet to Process B. Thus, Process B will left in > CLOSE_WAIT status, as below. > > 00 (Process A) (Process B) > 01 ESTABLISHED ESTABLISHED > 02 close() > 03 FIN_WAIT_1 > 04 ---FIN--> > 05 CLOSE_WAIT > 06 (<--ACK---) > 07 (<--FIN/ACK---) > 08 (fired in right order) > 09 <--FIN/ACK--- > 10 <--ACK--- > 11 (processed in reverse order) > 12 FIN_WAIT_2 Why doesn't A treat the FIN/ACK (09) as valid (as if the ACK had got lost) and then ignore the ACK (10) because it refers to a closed socket? I presume that B sends two ACKs (06 and 07) because it can sit in an intermediate state and the first ACK stops the FIN being resent? I've implemented lots of protocols in my time, but not TCP. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
