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I ran iperf on Windows and Linux machine to check bandwidth speed.

Windows bandwidht speed, I explicitly set to 10Mbps/Full and Linux's BW speed is 100Mbps/Full.

Following is the strange output I got: Client Side ( Linux Box ):

iperf -c 192.168.1.72 -r
Server listening on TCP port 5001
TCP window size: 85.3 KByte (default)
Client connecting to 192.168.1.72, TCP port 5001
TCP window size: 16.0 KByte (default)
[  5] local 192.168.1.70 port 52358 connected with 192.168.1.72 port 5001
[ ID] Interval       Transfer     Bandwidth
[  5]  0.0-10.2 sec  11.6 MBytes  **9.60 Mbits/sec**
[  4] local 192.168.1.70 port 5001 connected with 192.168.1.72 port 1334
[  4]  0.0-10.1 sec  11.2 MBytes  **9.34 Mbits/sec**

And on server side ( Windows Box ):

iperf.exe -s
Server listening on TCP port 5001
TCP window size: 64.0 KByte (default)
[  4] local 192.168.1.72 port 5001 connected to 192.168.1.70 port 52358
[ ID] Interval Transfer Bandwidth
[  4] 0.0-10.4 sec 11.6 MBytes **9.40 Mbits/sec**
Client connecting to 192.168.1.70 port 5001
TCP window size: 64.0 KByte (default)
[  4] local 192.168.1.72 port 1334 connected with 192.168.1.70 port 5001
Waiting for server threads to complete. Interrupt again to force quit.
[  4] 0.0-10.1 sec 11.2 MBytes **9.35 Mbits/sec**

I don't understand this difference between output

share|improve this question
Could you elaborate on what specific concern you have? – Mike Pennington Jun 15 '12 at 14:26
If the bandwidth is between Linux-windows is 100Mbps, then why it is showing just ~9Mbits. Output need to be around 90+Mbps – SHW Jun 15 '12 at 14:27
If your windows machine is at 10/full how could it possibly handle 90Mbps? – Mike Pennington Jun 15 '12 at 14:29
But If I do vice versa, means making windows as client and Linux as server, then still I am getting the same result – SHW Jun 15 '12 at 14:43
please see my answer below – Mike Pennington Jun 15 '12 at 15:24

2 Answers

up vote 2 down vote accepted

You are confusing NIC transmit speed (100M vs 10M) and throughput. iperf measures throughput.

I'm going on the assumption you have a network set up like this:

Windows---------[Ethernet Switch]-----------Linux
       10M/full                    100M/full

It does not matter whether your server or client is the 100M side. TCP throughput is constrained by the lowest bandwidth in the path, which means that you cannot exceed 10Mbps in this topology.

If you want more throughput, ensure that windows links up at 100M.

share|improve this answer
Look like, there was some confusion. Thnx for clearing the thing – SHW Jun 16 '12 at 6:29
up vote 0 down vote

I believe you are getting Mbits output opposed to Mbytes output that you expect. You can use the --format or -f switch to change the output format.

Use these client commands:

For KBytes: iperf -f K -c 192.168.1.72 -r

For MBytes: iperf -f M -c 192.168.1.72 -r

For more info man iperf

share|improve this answer
If the bandwidth is between Linux-windows is 100Mbps, then why it is showing just ~9Mbits ??? – SHW Jun 15 '12 at 13:38

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