The sever send SYN/ACK after receive SYN from client immediately
The sever send SYN/ACK after receive SYN from client immediately I found the request from client timeout sometimes. And I use tcpdump on the server side to catch some special tcp packet as follows. It seems no packet was lost. Why the server doesn't reply to client after receiving the first SYN? enter image description here netstat -n | awk '/^tcp/ {++S[$NF]} END {for(a in S) print a, S[a]}' SYN_RECV 220 CLOSE_WAIT 1 ESTABLISHED 496 FIN_WAIT1 42 FIN_WAIT2 2 TIME_WAIT 72588 sysctl -a | grep tcp net.ipv4.tcp_abort_on_overflow = 0 net.ipv4.tcp_adv_win_scale = 1 net.ipv4.tcp_allowed_congestion_control = cubic reno net.ipv4.tcp_app_win = 31 net.ipv4.tcp_available_congestion_control = cubic reno net.ipv4.tcp_base_mss = 512 net.ipv4.tcp_challenge_ack_limit = 100 net.ipv4.tcp_congestion_control = cubic net.ipv4.tcp_dsack = 1 net.ipv4.tcp_early_retrans = 3 net.ipv4.tcp_ecn = 2 net.ipv4.tcp_fack = 1 net.ipv4.tcp_fastopen = 0 net.ipv4.tcp_fastopen_key = fc1980cc-2a3369bf-91223671-bb8e...