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On 10/02/2013 02:14 AM, James Page wrote:

>
> I tcpdump'ed the traffic and I see alot of duplicate acks which makes
> me suspect some sort of packet fragmentation but its got me puzzled.
>
> Anyone have any ideas about how to debug this further? or has anyone
> seen anything like this before?

Duplicate ACKs can be triggered by missing or out-of-order TCP segments. 
  Presumably that would show-up in the tcpdump trace though it might be 
easier to see if you run the .pcap file through tcptrace -G.

Iperf may have a similar option, but if there are actual TCP 
retransmissions during the run, netperf can be told to tell you about 
them (when running under Linux):

netperf -H <remote> -t TCP_STREAM -- -o 
throughput,local_transport_retrans,remote_transport_retrans

will give to <remote>

and

netperf -H <remote> -t TCP_MAERTS -- -o 
throughput,local_transport_retrans,remote_transport_retrans

will give from <remote>.  Or you can take snapshots of netstat -s output 
from before and after your iperf run(s) and do the math by hand.

rick jones
if the netperf in multiverse isn't new enough to grok the -o option, you 
can grab the top-of-trunk from http://www.netperf.org/svn/netperf2/trunk 
via svn.