[Fwd: asymetric speeds over gigE link]

Andrew Gallatin gallatin at cs.duke.edu
Wed May 30 18:25:12 UTC 2007

security writes:
 > Sent this to -net and didn't get much info, so I'll try here since
 > there's some overlap
 > Summary:  Using iperf to measure TCP net speed between a linux (kubuntu edgy) and

Iperf is probably your problem, it tends to perform really poorly on
nearly any OS other than linux as it measures lots of things besides
network performance (like gettimeofday performance).  Try a network
benchmark that just benchmarks the network, like netperf.

For example, on an amd64x2 running -current, I see ~4.75Gb/s from
netperf (no options) and 2.85Gb/s from iperf (no options)


% netperf242 -H127.0.0.1
TCP STREAM TEST from ( port 0 AF_INET to
( port 0 AF_INET
Recv   Send    Send                          
Socket Socket  Message  Elapsed              
Size   Size    Size     Time     Throughput  
bytes  bytes   bytes    secs.    10^6bits/sec  

 65536  32768  32768    10.00    4757.03   
% iperf -c 
Client connecting to, TCP port 5001
TCP window size: 42.0 KByte (default)
[  3] local port 60961 connected with port 5001
[  3]  0.0-10.0 sec  3.31 GBytes  2.85 Gbits/sec

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