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Re: Throughput riddle

On Sun, 20 Mar 2016 16:22:58 +0100
arian <debian@semioptimal.net> wrote:

> > No - I've been using the default: 'iperf -c hostxxxx' on laptop, 'iperf
> > -sD' on router, NAS.
> > 
> > Actually, this morning I've been getting about 17-20 Mbps between the
> > laptop and NAS. I tried bidirectional testing ('iperf -d -c hostxxxx',
> > and the results actually remained constant.
> That sound weird. Can you check by means of tcpdump, wireshark or similar wether packages are actually only hitting the air once?

I'm not very skilled with wireshark, but I tried it. I see lots of
packets with frame length 1514 (data length 1448) between the source
and destination, interspersed with many 66 byte frame length packets
between the dest and source (with no data). I suppose the former is the
iperf payload data, and the latter is just TCP/IP acknowledgments. What
should I be looking for, exactly?

Okay. More tests - currently the iperf tests are showing 17-20 Mbps
laptop - NAS, 14-16 Mbps laptop - router (even with '-d').

> another simple bandwidth check:
> # host1: nc -l 8090 > /dev/zero
> # host2: dd if=/dev/zero | nc host1 8090

2.0, 2.3, 2.4 and 2.5 Mbps laptop - NAS. Pretty much in line with the
ones above.

> bidirectional version:
> # host1: nc -l 8090 > /dev/zero
> # host2: nc -l 8090 | nc host1 8090
> # host1: dd if=/dev/zero | nc host2 8090
> kill the last after a while
> with that I get very consistent 2.7 MB/s unidirectional, 1.4 MB/s bidirectional

I must be doing something wrong with the last - it just exists
immediately, no error and no output. I think I understand the command
syntax, and it makes sense to me, but it just doesn't work. I feel like
I'm missing something obvious.

Sorry if I'm being dense, thanks for the help,


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