Excerpts from Vasanthy Kolluri (vkolluri)'s message of Mon Mar 21 13:49:45 
-0500 2011:
> I have two iperf clients sending UDP packets to a iperf server. Once the
> test is completed, the Server side results for only one of the streams
> is reported both on the client and server.
> 
>  
> 
> Iperf client:
> 
>  
> 
> # iperf -c 10.0.50.100 -B 10.0.50.1 -u -b1G -t100 &
> 
> # iperf -c 10.0.50.100 -B 10.0.50.2 -u -b1G -t100 &

This isn't the common way to do multiple streams with Iperf and I suspect the
code won't deal with this gracefully.  In this case I believe Iperf is
silently failing.  Iperf3 handles this case by only allowing one client at a
time and rejects other clients until tests are complete.  

Are you running the two client processes on different machines or the same
machine?  I see that you're binding (-B) to two different IP addresses but
that could be two NICs on the same machine or could be on different machines.

If you are running on two machines you'll be best off starting two Iperf
servers on the server end, eg:

iperf -u -s -p 5001
iperf -u -s -p 5002

and then on each of the client machines doing:

iperf -c 10.0.50.100 -u -b1G -t100 -p 5001
iperf -c 10.0.50.100 -u -b1G -t100 -p 5002

If both clients are on the same machine you can do:

iperf -c 10.0.50.100 -u -b1G -t100 -P2

(just use your original Iperf invocation on the server side)

The -P flag spawns 2 threads each trying to send at 1G/s.

Modern hardware should have no trouble doing 2 x 1G UDP streams on a 10G NIC.
It's often hard to get UDP working faster than 8-9G/s for a variety of
reasons as you usually end up buring a lot of CPU to receive them.

Hope that helps,

Jon

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