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<span style="color: rgb(0, 0, 0); font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;">Hi All, </span><br>
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On TCP sender side, "ss -imnHoe 'dst *:55064'" shows that "retrans" keep rising. </div>
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After decrypt IPSec .pcap file captured on TCP reader side, I saw reader side really get the TCP packet. But kernel in read side sends back multiple TCP duplicated ACK. It indicate that kernel in reader side missed that packet.</div>
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<span style="font-family:Calibri,Helvetica,sans-serif; background-color:rgb(255,255,255); display:inline!important">My machine is HP Chassis Gen 10 with 10Gbps NIC, and 3.6GHz CPU. </span><br>
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<span style="font-family:Calibri,Helvetica,sans-serif; background-color:rgb(255,255,255); display:inline!important">Libreswan is v3.25. Kernel is "3.10.0-957.43.1.el7.x86_64" . </span></div>
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<span style="color:rgb(0,0,0); font-family:Calibri,Helvetica,sans-serif; font-size:12pt">"</span><span style="color:rgb(0,0,0); font-family:Calibri,Helvetica,sans-serif; font-size:12pt">ethtool -S eth0 | grep rx_discards" shows that no packet drop by NIC. </span><br>
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<span style="font-family:Calibri,Helvetica,sans-serif; background-color:rgb(255,255,255); display:inline!important">The "</span><span style="font-family:Calibri,Helvetica,sans-serif; background-color:rgb(255,255,255); display:inline!important">net.ipv4.tcp_rmem
= 1048576 8388608 16777216". </span><br>
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<span style="font-family:Calibri,Helvetica,sans-serif; background-color:rgb(255,255,255); display:inline!important">I already "echo 300000 > /proc/sys/net/core/netdev_max_backlog". </span></div>
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<span style="font-family:Calibri,Helvetica,sans-serif">"netstat -na | grep 55064" shows that "Recv-Q" is 0 during test. </span><br>
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<span style="color:rgb(0,0,0); font-family:Calibri,Helvetica,sans-serif; font-size:12pt">CPU usage of "ksoftirqd" and my plain TCP-Reader program is 10%.</span><br>
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<span style="color:rgb(0,0,0); font-family:Calibri,Helvetica,sans-serif; font-size:12pt">Except above configuration, where I can tweak kernel? </span></div>
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<span style="color:rgb(0,0,0); font-family:Calibri,Helvetica,sans-serif; font-size:12pt">Thanks</span></div>
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