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Old 02-11-2010, 06:08 PM   #1
m4rtin
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Question analyzing iperf output


I did iperf test from one Linux server to another. One server is in Helsinki, other is in London and they are connected with a VPN tunnel(should be 100Mbps/100Mbps connection). I started iperf server in London(192.168.1.2) and iperf client in Helsinki(192.168.1.1). I started server with iperf -s -u -fm command and client with iperf -c 192.168.1.2 -fm -d -t600 -u -b 100m command. Output was fallowing:

Code:
#iperf -c 192.168.1.2 -fm -d -t600 -u -b 100m
Server listening on UDP port 5001
Receiving 1470 byte datagrams
UDP buffer size: 0.10 MByte (default)
------------------------------------------------------------
------------------------------------------------------------
Client connecting to 192.168.1.2, UDP port 5001
Sending 1470 byte datagrams
UDP buffer size: 0.10 MByte (default)
------------------------------------------------------------
[  4] local 192.168.1.1 port 44456 connected with 192.168.1.2 port 5001
[  3] local 192.168.1.1 port 5001 connected with 192.168.1.2 port 31435

[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-600.0 sec  7189 MBytes    101 Mbits/sec
[  4] Sent 5128207 datagrams
[ ID] Interval       Transfer     Bandwidth       Jitter   Lost/Total Datagrams
[  3]  0.0-600.2 sec  2396 MBytes  33.5 Mbits/sec  0.244 ms
3419123/5128199 (67%)
[  4] Server Report:
[ ID] Interval       Transfer     Bandwidth       Jitter   Lost/Total Datagrams
[  4]  0.0-600.1 sec  2411 MBytes  33.7 Mbits/sec  0.199 ms
3408321/5128207 (66%)
[  4]  0.0-600.1 sec  299 datagrams received out-of-order
How can there be bandwidth from Helsinki to London 101 Mbits/sec when Iperf server from London raports 33.7 Mbits/sec? How can there be such a huge packet loss(67% from London to Helsinki and 66% from Helsinki to London)? I would appriciate any comments about inner workings of Iperf or explanations about Iperf output
 
Old 02-12-2010, 01:07 AM   #2
kbp
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I suppose the simplest question is - what else was using the link at the time ? ... do you have access to the networking gear to see what was flowing through the link when you were testing ?

You're also performing the tests simultaneously ('-d'), try one at a time ('-r') and see if it makes a difference

cheers
 
Old 02-14-2010, 08:15 AM   #3
m4rtin
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Quote:
Originally Posted by kbp View Post
I suppose the simplest question is - what else was using the link at the time ? ... do you have access to the networking gear to see what was flowing through the link when you were testing ?

You're also performing the tests simultaneously ('-d'), try one at a time ('-r') and see if it makes a difference

cheers
Iperf was the only application/service using the bandwidth at the time. I have access only to my Helsinki ISP side, which clearly indicates bandwidth 100Mbps/100Mbps. There are several ISP's involved from Helsinki to London(5 if my Iperf test uses the same path as my traceroute ).

However, I did a fallowing test between two computers in my home LAN: http://img52.imageshack.us/img52/3162/iperftest.png which produced very similar results as the Helsinki <--> London link. As I understand, there has to be some sort of slower connection somewhere between my Helsinki side ISP and London Any other ideas?

Last edited by m4rtin; 02-14-2010 at 08:18 AM.
 
Old 02-14-2010, 06:58 PM   #4
kbp
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No.. that sounds about right, but the path between the two endpoints could vary due to routing, maybe check it over several days.

cheers
 
  


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