Checking for Network packet Retransmission , troubleshooting network card & switches

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So, you might want to test whether the NIC of your box is ‘bad’, one way to do this is looking at the retransmissions.

netstat -s | grep retransmits
   3535665 fast retransmits
   3920918 forward retransmits
   122319 retransmits in slow start
   3652 sack retransmits failed

netstat -s | grep transmit
    10512472 segments retransmited
    733 times recovered from packet loss due to fast retransmit
    Detected reordering 73 times using reno fast retransmit
    TCPLostRetransmit: 196
    400 timeouts after reno fast retransmit
    3535665 fast retransmits
    3920918 forward retransmits
    122319 retransmits in slow start
    13652 sack retransmits failed

This isn’t much use though, because you need to see how many total packets come in:

netstat -s | grep total
    23799703342 total packets received

It’s possible to get the full details with netstat -s , naturally.