Hello!
> Server decides to retransmit a packet.
>
> 10:35:46.021434 server > client: P 2288418825:2288420285(1460) ack 2282978624 win
>32120
> 10:35:46.301434 server > client: P 2288418825:2288420285(1460) ack 2282978624 win
>32120
It is not retransmit, because congestion window is not reduced (seen from
the following dump). If you add "-v" option to tcpdump you will see
IP identifier and I am ready to bet that it coincides in these two lines.
It is possible, if server's output device has broken flow control.
The first packet does not appear on wire really, it is deferred by device.
> And every packet from here on down is duplicated. No idea why, the
> ACKs are ticking over nicely. The rest of the transmission has these
> repeated packet sends and it sends almost double the file size.
See above. Did you look at throughput? I think, no packets were lost
and server saturated link speed in this example.
Your following dump shows the same behaviour, complicated by
the fact that server overflowed device queue size (packet disappears).
If it is harmful, you have no choice but limiting receiver window
or sender congestion window. Vegas also can help.
Alexey
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