different results from iperf 1.7.0 to 2.0.1.

[Garcia M. M. <mar...@iw...>]

My name is Marc Garcia and I am doing my Diploma-Thesis in the 
Forschungszentrum Karlsruhe in the field of Networking in the Gridka 
project (www.gridka.de). Some days ago I sent you an Email explaining you 
some strange results within our Gigabit ethernet network and your software 
(iperf) but we received no answere. 

Using a Tyan  motherboard chipset  E7501 dual Pentium, Intel Corp. 82546EB 
Gigabit Ethernet Controller and iperf version 2.0.1 (lastest one) we 
obtained strange results in a back to back UDP test, iperf gave us around 
500Mbps with a high packet loss but under the same conditions, the 
behaviour of an TCP test was stable and close to 1Gbps. We tried the same 
test in other equipment (IBM) and both test succeeded with preety and 
stable results; no errors and both protocols were close to 1Gbps. We 
thought it was a hardware problem and after analising the device driver of 
the first group of equipments the problems still persisted; far from the 
good IBM results. Connecting the nodes back to back or via a switch did not 
change the results at all.

We also observed that when using -l parameter and a bigger value than the 
default one (1700 and upper), it worked perfectly; no errors, very good 
throughput...  As I told you in my last email, for us it didn't make sense 
(and still it doesn't) because the MTU of the GEthernet is set to its 
default (1500 bytes) so the TCP/IP must fragment the packet before sending 
it and then the 2 second packed won't be fullfilled so in principle the 
performance should be lower but it was not. 

On the other hand, we have decided to install the previous version of 
iperf (1.7.0) and it works simply great. I attach you the results we 
gathered with the hope it may clarify. We intended to use Iperf till 
version 1.7.0 as a network quality measurement tool. Since result of version 
2.0.1 is so different, could you please explain.


Thanks a lot in advance for your time, 
 
Best Regards, 
 
Marc Garcia Marti                       mar...@iw... 
Forschungszentrum Karlsruhe               Tel.: +497247828601 
Institute for Scientific Computing / Inst. f. Wissenschaftliches Rechnen 
Hermann-von-Helmholtz-Platz 1,  76344 Eggenstein-Leopoldshafen,  Germany