[c-nsp] Performance issue on link

Saku Ytti saku at ytti.fi
Wed Apr 3 02:39:54 EDT 2013

On (2013-04-03 16:54 +1100), CiscoNSP List wrote:

> Thanks Mikael - I have captured a wget with tcpdump, but Im not exactly sure what I should be looking for in wireshark....I see a LOT of "TCP segment of a reassembled PDU", a LOT of "Dup ACK's" and graph shows peaks of 25Mb...

For typical TCP stack, if you've received TCP segment 42 previously then
you'll receive TCP segment 43, you'll duplicate ACK 42, in order to signal
to sender that you believe you're experiencing packet loss (which might not
be packet loss, it might be just reordering, but modern TCP stack does not
cope with reordering, because it copes aggressively well with packet loss)

So you're experiencing packet loss, which shouldn't be surprising I think
Mikael was also interested in hearing your TCP window size, preferably when
it was highest.
(You need to capture session from the start to know TCP window scale


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