I am observing an overwhelming flow of TCP retransmissions on the loopback interface. It seems that the application is not reading fast enough, causing repeated retransmissions, even though the receiver’s advertised window (Win=24349) is larger than the segment size (Len=10367).
Here is an example from the capture:
39821 3.761904 ::1 → ::1 TLSv1.2 10453 Application Data
39822 -1774530056.844555 ::1 → ::1 TCP 10453 [TCP Retransmission] 298 → 40404 [PSH, ACK] Seq=35900922 Ack=166663 Win=512 Len=10367 TSval=3985282601 TSecr=3985282600
39825 3.762127 ::1 → ::1 TLSv1.2 10453 Application Data
39826 -1774530056.844332 ::1 → ::1 TCP 10453 [TCP Retransmission] 298 → 40404 [PSH, ACK] Seq=35911289 Ack=166663 Win=512 Len=10367 TSval=3985282602 TSecr=3985282600
39829 3.762379 ::1 → ::1 TLSv1.2 10453 Application Data
39830 -1774530056.844081 ::1 → ::1 TCP 10453 [TCP Retransmission] 298 → 40404 [PSH, ACK] Seq=35921656 Ack=166663 Win=512 Len=10367 TSval=3985282602 TSecr=3985282600
39833 3.762747 ::1 → ::1 TLSv1.2 184 Application Data
39834 -1774530056.843713 ::1 → ::1 TCP 184 [TCP Retransmission] 40404 → 298 [PSH, ACK] Seq=166663 Ack=35932023 Win=24258 Len=98 TSval=3985282602 TSecr=3985282600
39837 3.762842 ::1 → ::1 TLSv1.2 184 Application Data
39838 -1774530056.843617 ::1 → ::1 TCP 184 [TCP Retransmission] 40404 → 298 [PSH, ACK] Seq=166761 Ack=35932023 Win=24258 Len=98 TSval=3985282602 TSecr=3985282600
39839 3.762868 ::1 → ::1 TLSv1.2 184 Application Data
39840 -1774530056.843590 ::1 → ::1 TCP 184 [TCP Retransmission] 40404 → 298 [PSH, ACK] Seq=166859 Ack=35932023 Win=24258 Len=98 TSval=3985282602 TSecr=3985282600