I find a weird behavior in my Linux system, when I curling a web page, the received TCP segments are significant larger THAN the MSS.
here is the output of tcpdump:
00:00:00.000000 IP 10.15.71.190.44503 > 115.239.210.27.80: Flags [S], seq 248491621, win 29200, options [mss 1460,sackOK,TS val 294137 ecr 0,nop,wscale 7], length 0 00:00:00.004210 IP 115.239.210.27.80 > 10.15.71.190.44503: Flags [S.], seq 1384820706, ack 248491622, win 29200, options [mss 1380,sackOK,nop,nop,nop,nop,nop,nop,nop,nop,nop,nop,nop,wscale 7], length 0 00:00:00.000063 IP 10.15.71.190.44503 > 115.239.210.27.80: Flags [.], ack 1, win 229, length 0 00:00:00.000082 IP 10.15.71.190.44503 > 115.239.210.27.80: Flags [P.], seq 1:78, ack 1, win 229, length 77 00:00:00.004187 IP 115.239.210.27.80 > 10.15.71.190.44503: Flags [.], ack 78, win 193, length 0 00:00:00.002929 IP 115.239.210.27.80 > 10.15.71.190.44503: Flags [P.], seq 1:819, ack 78, win 193, length 818 00:00:00.000032 IP 10.15.71.190.44503 > 115.239.210.27.80: Flags [.], ack 819, win 241, length 0 00:00:00.000075 IP 115.239.210.27.80 > 10.15.71.190.44503: Flags [P.], seq 819:16385, ack 78, win 193, length 15566 00:00:00.000016 IP 10.15.71.190.44503 > 115.239.210.27.80: Flags [.], ack 16385, win 485, length 0 00:00:00.000016 IP 115.239.210.27.80 > 10.15.71.190.44503: Flags [.], seq 16385:19105, ack 78, win 193, length 2720 00:00:00.000009 IP 10.15.71.190.44503 > 115.239.210.27.80: Flags [.], ack 19105, win 527, length 0 00:00:00.000086 IP 115.239.210.27.80 > 10.15.71.190.44503: Flags [.], seq 19105:20465, ack 78, win 193, length 1360 00:00:00.000009 IP 10.15.71.190.44503 > 115.239.210.27.80: Flags [.], ack 20465, win 548, length 0 00:00:00.001338 IP 115.239.210.27.80 > 10.15.71.190.44503: Flags [.], seq 20465:28625, ack 78, win 193, length 8160 00:00:00.000015 IP 10.15.71.190.44503 > 115.239.210.27.80: Flags [.], ack 28625, win 676, length 0 00:00:00.132259 IP 115.239.210.27.80 > 10.15.71.190.44503: Flags [.], seq 28625:42225, ack 78, win 193, length 13600 00:00:00.000027 IP 10.15.71.190.44503 > 115.239.210.27.80: Flags [.], ack 42225, win 888, length 0 00:00:00.003511 IP 115.239.210.27.80 > 10.15.71.190.44503: Flags [P.], seq 42225:55825, ack 78, win 193, length 13600 00:00:00.000035 IP 10.15.71.190.44503 > 115.239.210.27.80: Flags [.], ack 55825, win 1101, length 0 00:00:00.000041 IP 115.239.210.27.80 > 10.15.71.190.44503: Flags [.], seq 55825:58545, ack 78, win 193, length 2720 00:00:00.000033 IP 10.15.71.190.44503 > 115.239.210.27.80: Flags [.], ack 58545, win 1143, length 0 00:00:00.001683 IP 115.239.210.27.80 > 10.15.71.190.44503: Flags [.], seq 58545:61265, ack 78, win 193, length 2720 00:00:00.000012 IP 10.15.71.190.44503 > 115.239.210.27.80: Flags [.], ack 61265, win 1186, length 0 00:00:00.000027 IP 115.239.210.27.80 > 10.15.71.190.44503: Flags [.], seq 61265:63985, ack 78, win 193, length 2720 00:00:00.000007 IP 10.15.71.190.44503 > 115.239.210.27.80: Flags [.], ack 63985, win 1228, length 0 00:00:00.000034 IP 115.239.210.27.80 > 10.15.71.190.44503: Flags [.], seq 63985:69425, ack 78, win 193, length 5440 00:00:00.000008 IP 10.15.71.190.44503 > 115.239.210.27.80: Flags [.], ack 69425, win 1313, length 0 00:00:00.001476 IP 115.239.210.27.80 > 10.15.71.190.44503: Flags [.], seq 69425:83025, ack 78, win 193, length 13600 00:00:00.000033 IP 10.15.71.190.44503 > 115.239.210.27.80: Flags [.], ack 83025, win 1300, length 0 00:00:00.004061 IP 115.239.210.27.80 > 10.15.71.190.44503: Flags [P.], seq 83025:89274, ack 78, win 193, length 6249 00:00:00.000026 IP 10.15.71.190.44503 > 115.239.210.27.80: Flags [.], ack 89274, win 1380, length 0 00:00:00.000139 IP 10.15.71.190.44503 > 115.239.210.27.80: Flags [F.], seq 78, ack 89274, win 1411, length 0 00:00:00.004609 IP 115.239.210.27.80 > 10.15.71.190.44503: Flags [.], ack 79, win 193, length 0 00:00:00.000038 IP 115.239.210.27.80 > 10.15.71.190.44503: Flags [F.], seq 89274, ack 79, win 193, length 0 00:00:00.000018 IP 10.15.71.190.44503 > 115.239.210.27.80: Flags [.], ack 89275, win 1411, length 0
As you can see, in TCP handshake, the MSS is 1380.
I have no idea how can this happen, my local link have a MTU of 1500. And I have tried this in My Windows, in Windows it is OK.