Re: Reason to drop packets
When encountering reported "packet loss" by iperf, I have had good results by running iperf at a higher priority on a unix box using the nice command. It is also worthwhile shutting down extraneous services and graphical user interfaces if the CPU load is maxed out when iperf is being run.
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Laurence Kirchmeier
Senior Systems Engineer, Merit Network Inc.
Email: laurie --at-- merit.edu
Tel. 734 936 9703 Fax. 734 647 3185
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On Feb 23, 2004, at 4:01 PM, Jon Dugan wrote:
On Mon, Feb 23, 2004 at 06:46:30PM +0100, onorati_m --at-- virgilio.it wrote:
Hi all!
Could someone explain why Iperf really starts dropping packets?
I mean, selecting the UDP mode, setting a UDP bandwidth value and the
number of bytes to be transmitted, why does Iperf show losses for higher
values of the UDP bandwdith rate?
Is it a matter of CPU load or something related with the buffer sizes?
Iperf using UDP doesn't drop packets per se, rather it will blindly transmit
at the specified rate and if there is contention for resources somewhere in
the system the data will be lost. Often it is CPU utilization that is the
culprit. What is the CPU utilization you see during the test? Using larger
buffers may help this since there will be less overhead.
The other common cause of lost data with a UDP test is loss somewhere in the
network. How are the two systems interconnected?
Jon
--
Jon Dugan | Senior Network Engineer, NCSA Network Research
jdugan --at-- ncsa.uiuc.edu | 269 CAB, 605 E Springfield, Champaign, IL 61820
217-244-7715 | http://www.ncsa.uiuc.edu/~jdugan/