Solved

Iperf output question

Posted on 2014-10-20
7
219 Views
Last Modified: 2014-11-13
I am running iperf across a few different type of links. I have a server setup on the other end and I am getting varying values depending on the line. I'm finding the output very up and down. e.g iperf -c myserver -I 1 can produce speeds of anywhere from 30Mbps - 85mbps.
I am a little confused on the transfer figure. Why does the amount being transferred keep changing. I have looked at a number of videos but they don't seem to give specifics on the actual output. Sorry for the stupid question but I'm guessing that the bandwidth figure being presented is relative to the amount of data being transferred e.g I can't say my network has a 44Mbit/sec throughput to server X, I have to say when transferring 7.25MBytes per second my network has a throughput of 44Mbit/sec to the server..
0
Comment
Question by:Sid_F
7 Comments
 
LVL 32

Expert Comment

by:aleghart
ID: 40393580
Speed can vary based on connection type (wireless, wired), congestion, resource contention, and network (Layer 2 or routed) + the number of hops.

If both end points are not loaded with any other services, and the network is stable, then the reading should be close.

If it's wireless in a busy environment, then all bets are off.  In a wireless environment I can get 5Mbps, then 15Mbps only a few seconds later.  Or by taking one step around a corner, or by standing instead of sitting...many variables.

What kind of environment are you testing in?
0
 
LVL 38

Expert Comment

by:Aaron Tomosky
ID: 40393588
Instead of -I 1 do -I 60
That will give you the average bandwidth over 60 seconds
0
 
LVL 22

Expert Comment

by:eeRoot
ID: 40393623
Network congestion, QOS, server utilization...  There are many things that can affect performance.  If you are testing across a network that others are using, and testing a server that others are using, then you have to share resources with them.  If this is a local network, and a dedicated test server, something else may be going on.  What is the server's NIC, CPU, & Mem utilization when you are NOT running iperf?
0
Give your grad a cloud of their own!

With up to 8TB of storage, give your favorite graduate their own personal cloud to centralize all their photos, videos and music in one safe place. They can save, sync and share all their stuff, and automatic photo backup helps free up space on their smartphone and tablet.

 
LVL 32

Expert Comment

by:aleghart
ID: 40393636
Good catch, Aaron Tomosky.  Why are you changing the sampling time?  The default is 10 seconds, and should be good enough for a snapshot of a network without tying up the line for other people.
0
 
LVL 5

Author Comment

by:Sid_F
ID: 40393789
Thanks all, It's a wired network, I'm using iperf to get familiar with my network benchmarks but with such a huge difference in speed its difficult to know what through put I have. If for a minute I suppose that a third party has indicated my network is the reason there application is slow, if I ran the throughput test I couldn't say hey I'm getting 72Mbits throughput as some of the below indicates as low as 26Mbits?.
As mentioned in my OP I am still confused on the transfer amounts, why does it transfer 8MBytes and then jump to transferring 72MBytes?

[ ID] Interval       Transfer     Bandwidth
[  3]  0.0- 1.0 sec  8.62 MBytes  72.4 Mbits/sec
[  3]  1.0- 2.0 sec  8.88 MBytes  74.4 Mbits/sec
[  3]  2.0- 3.0 sec  8.12 MBytes  68.2 Mbits/sec
[  3]  3.0- 4.0 sec  8.62 MBytes  72.4 Mbits/sec
[  3]  4.0- 5.0 sec  8.50 MBytes  71.3 Mbits/sec
[  3]  5.0- 6.0 sec  6.75 MBytes  56.6 Mbits/sec
[  3]  6.0- 7.0 sec  8.50 MBytes  71.3 Mbits/sec
[  3]  7.0- 8.0 sec  3.12 MBytes  26.2 Mbits/sec
[  3]  8.0- 9.0 sec  5.25 MBytes  44.0 Mbits/sec
[  3]  9.0-10.0 sec  5.75 MBytes  48.2 Mbits/sec
[  3]  0.0-10.0 sec  72.2 MBytes  60.5 Mbits/sec
0
 
LVL 32

Accepted Solution

by:
aleghart earned 500 total points
ID: 40394288
Look at the interval.  You're seeing 1 second intervals, then the total size and average bandwidth for all 0-10 seconds.

The last figure is for the entire 10 second test.  It should be the total of the size transferred for all of the preceding intervals.

The drops in speed are congestion at a choke point (uplink or router) and/or resource contention at either the server or client doing the iperf test.

It could be a random file write, anti-virus kicking off, update downloading, Outlook syncing because you forgot to close it...etc.  Try to kill as many programs and services as possible while you're using iperf.
0
 
LVL 5

Author Closing Comment

by:Sid_F
ID: 40441345
Thanks sorry for delay
0

Featured Post

VMware Disaster Recovery and Data Protection

In this expert guide, you’ll learn about the components of a Modern Data Center. You will use cases for the value-added capabilities of Veeam®, including combining backup and replication for VMware disaster recovery and using replication for data center migration.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

So, you're experiencing issues on your network and you've decided that you need to perform some tests to determine whether your cabling is good.  You're likely thinking that you may need to spend money which you probably don't have on hiring/purchas…
David Varnum recently wrote up his impressions of PRTG, based on a presentation by my colleague Christian at Tech Field Day at VMworld in Barcelona. Thanks David, for your detailed and honest evaluation!
Get a first impression of how PRTG looks and learn how it works.   This video is a short introduction to PRTG, as an initial overview or as a quick start for new PRTG users.
This video gives you a great overview about bandwidth monitoring with SNMP and WMI with our network monitoring solution PRTG Network Monitor (https://www.paessler.com/prtg). If you're looking for how to monitor bandwidth using netflow or packet s…

863 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

19 Experts available now in Live!

Get 1:1 Help Now