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.
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