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Overview

Iperf is a commonly used network testing tool to help measure network throughput
Iperf is an open source tool. There are clients for Mac, Linux, BSD, etc. There is a port for Windows; however, in our testing we found it to lack certain features and to lag in performance.
Iperf operates where one end is the client, the other is the server.

WiscNet Server Details

WiscNet runs an Iperf version 2 server in Eau Claire, WI
The server is restricted to WiscNet IP addresses
Iperf2 and iperf3 are incompatible
iperf.wiscnet.net runs a TCP Iperf server on the default port 5001
iperf.wiscnet.net runs a UDP Iperf server on port 5001
iperf.ipv6.wiscnet.net runs a v6 TCP Iperf server on port 5001
iperf.ipv6.wiscnet.net runs a v6 UDP Iperf server on port 5001

TCP vs UDP Testing

Iperf uses TCP by default. TCP has built in congestion avoidance. If TCP detects any packet loss, it assumes that the link capacity has been reached, and it slows down. This works very well, unless there is packet loss caused by something other than congestion. If there is packet loss due to errors, TCP will back off even if there is plenty of capacity. iperf allows TCP to send as fast as it can, which generally works to fill a clean, low latency link with packets. If a path is not clean/error free or has high latency, TCP will have a difficult time filling it. For testing higher capacity links and for links with higher latency, you will want to adjust the window size (-w option).
By using the -u option, you have told iperf to use UDP packets, rather than TCP. UDP has no built in congestion avoidance, and iperf doesn't implement it either. When doing a UDP test, iperf requires that the bandwidth of the test be specified. If it isn't, it defaults to 1Mb/s. You can use the -b option to specify bandwidth to test. iperf will then send packets at the request rate for the requested period of time. The other end measures how many packets are received vs how many were sent and reports its results.

Note

Please note:

The hardware performance of the client running this test has a significant impact on results

WiscNet has noticed that the Iperf clients for Linux, Unix, and macOS perform better than the ports for Windows

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Some Common Iperf Flags

Enter iperf -h or man iperf depending on your operating system. Here are some common flags:

Flag	Details	Example
-c	Client mode	-c
-t	Time to run the test in seconds	-t 30
-P	Number of parallel connections	-P 2
-u	UDP (default is TCP)	-u
-b	Bandwidth per thread	-b 250m
-i	Interval between bandwidth reports in seconds	-i 1
-L	Listen on port	-L 5001
-r	bidirectional test (individually)	-r
-d	bidirectional test (simultaneously)	-d

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Note

Please note:

The hardware performance of the client running this test has a significant impact on results

WiscNet has noticed that the Iperf clients for Linux, Unix, and macOS perform better than the ports for Windows

Unidirectional UDP 1Gbps circuit test

Command

Confluence

Code Block
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iperf -c iperf.wiscnet.net -t 10 -P 4 -u -b 250m -i1

Results

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When runing multiple threads you must look at

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the SUM

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lines for total throughput. Output below shows successfully getting 953Mbits/sec through

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Click here to expand results...

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No Format

$ iperf -c iperf.wiscnet.net -t 10 -P 4 -u -b 250m -i1
------------------------------------------------------------
Client connecting to iperf.wiscnet.net, UDP port 5001
Sending 1470 byte datagrams
UDP buffer size:  208 KByte (default)
------------------------------------------------------------
[  5] local 10.0.10.105 port 44098 connected with 205.213.14.56 port 5001
[  3] local 10.0.10.105 port 46090 connected with 205.213.14.56 port 5001
[  4] local 10.0.10.105 port 38200 connected with 205.213.14.56 port 5001
[  6] local 10.0.10.105 port 59296 connected with 205.213.14.56 port 5001
[ ID] Interval       Transfer     Bandwidth
[  5]  0.0- 1.0 sec  28.4 MBytes   238 Mbits/sec
[  3]  0.0- 1.0 sec  28.5 MBytes   239 Mbits/sec
[  4]  0.0- 1.0 sec  28.6 MBytes   240 Mbits/sec
[  6]  0.0- 1.0 sec  28.6 MBytes   240 Mbits/sec
[SUM]  0.0- 1.0 sec   114 MBytes   957 Mbits/sec
[  5]  1.0- 2.0 sec  28.5 MBytes   239 Mbits/sec
[  3]  1.0- 2.0 sec  28.4 MBytes   238 Mbits/sec
[  4]  1.0- 2.0 sec  28.5 MBytes   239 Mbits/sec
[  6]  1.0- 2.0 sec  28.2 MBytes   236 Mbits/sec
[SUM]  1.0- 2.0 sec   114 MBytes   953 Mbits/sec
[  5]  2.0- 3.0 sec  28.4 MBytes   238 Mbits/sec
[  3]  2.0- 3.0 sec  28.2 MBytes   237 Mbits/sec
[  4]  2.0- 3.0 sec  28.6 MBytes   240 Mbits/sec
[  6]  2.0- 3.0 sec  28.5 MBytes   239 Mbits/sec
[SUM]  2.0- 3.0 sec   114 MBytes   953 Mbits/sec
[  5]  3.0- 4.0 sec  28.3 MBytes   238 Mbits/sec
[  3]  3.0- 4.0 sec  28.3 MBytes   238 Mbits/sec
[  4]  3.0- 4.0 sec  28.5 MBytes   239 Mbits/sec
[  6]  3.0- 4.0 sec  28.4 MBytes   239 Mbits/sec
[SUM]  3.0- 4.0 sec   114 MBytes   952 Mbits/sec
[  5]  4.0- 5.0 sec  28.3 MBytes   237 Mbits/sec
[  3]  4.0- 5.0 sec  28.3 MBytes   238 Mbits/sec
[  4]  4.0- 5.0 sec  28.3 MBytes   238 Mbits/sec
[  6]  4.0- 5.0 sec  28.7 MBytes   241 Mbits/sec
[SUM]  4.0- 5.0 sec   114 MBytes   954 Mbits/sec
[  5]  5.0- 6.0 sec  28.6 MBytes   240 Mbits/sec
[  3]  5.0- 6.0 sec  28.4 MBytes   238 Mbits/sec
[  4]  5.0- 6.0 sec  28.3 MBytes   238 Mbits/sec
[  6]  5.0- 6.0 sec  28.5 MBytes   239 Mbits/sec
[SUM]  5.0- 6.0 sec   114 MBytes   955 Mbits/sec
[  5]  6.0- 7.0 sec  28.5 MBytes   239 Mbits/sec
[  3]  6.0- 7.0 sec  28.3 MBytes   238 Mbits/sec
[  4]  6.0- 7.0 sec  28.5 MBytes   239 Mbits/sec
[  6]  6.0- 7.0 sec  28.3 MBytes   237 Mbits/sec
[SUM]  6.0- 7.0 sec   114 MBytes   953 Mbits/sec
[  5]  7.0- 8.0 sec  28.4 MBytes   238 Mbits/sec
[  3]  7.0- 8.0 sec  28.4 MBytes   238 Mbits/sec
[  4]  7.0- 8.0 sec  28.3 MBytes   238 Mbits/sec
[  6]  7.0- 8.0 sec  28.5 MBytes   239 Mbits/sec
[SUM]  7.0- 8.0 sec   114 MBytes   953 Mbits/sec
[  5]  8.0- 9.0 sec  28.5 MBytes   239 Mbits/sec
[  3]  8.0- 9.0 sec  28.3 MBytes   237 Mbits/sec
[  4]  8.0- 9.0 sec  28.4 MBytes   238 Mbits/sec
[  6]  8.0- 9.0 sec  28.4 MBytes   238 Mbits/sec
[SUM]  8.0- 9.0 sec   114 MBytes   953 Mbits/sec
read failed: Connection refused
[  3] WARNING: did not receive ack of last datagram after 1 tries.
[  5]  9.0-10.0 sec  28.5 MBytes   239 Mbits/sec
[  5]  0.0-10.0 sec   284 MBytes   239 Mbits/sec
[  5] Sent 202875 datagrams
[  3]  0.0-10.0 sec   284 MBytes   238 Mbits/sec
[  3] Sent 202276 datagrams
[  4]  0.0-10.0 sec   284 MBytes   239 Mbits/sec
[  4] Sent 202852 datagrams
[  6]  0.0-10.0 sec   285 MBytes   239 Mbits/sec
[  6] Sent 203078 datagrams
[SUM]  0.0-10.0 sec  1.11 GBytes   954 Mbits/sec
read failed: Connection refused
[  5] WARNING: did not receive ack of last datagram after 5 tries.
read failed: Connection refused
[  6] WARNING: did not receive ack of last datagram after 9 tries.
[  4] WARNING: did not receive ack of last datagram after 10 tries.

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Note
Check your firewall settings and NAT to ensure port 5001 is open to your host

Command

Confluence

Code Block
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iperf -c iperf.wiscnet.net -t 10 -P 4 -u -b 250m -i1 -r

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Expand

title	Click here to expand the Ubuntu example...

Many Lunix and Unix distros will have iperf in official repositories. Make sure to install iperf2 (iperf), not iperf3, to have compatability with WiscNet's iPerf server.

Ubuntu - Install

Code Block

theme	Confluence

$ apt-cache search iperf | grep -i iperf
iperf - Internet Protocol bandwidth measuring tool
iperf3 - Internet Protocol bandwidth measuring tool
$ sudo apt-get install iperf

Ubuntu - Example

Code Block

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user@Latitude-E7440:~$ iperf -c iperf.wiscnet.net -t 10 -P 4
------------------------------------------------------------
Client connecting to iperf.wiscnet.net, TCP port 5001
TCP window size: 85.0 KByte (default)
------------------------------------------------------------
[  4] local 10.0.10.168 port 37014 connected with 205.213.14.56 port 5001
[  3] local 10.0.10.168 port 37010 connected with 205.213.14.56 port 5001
[  6] local 10.0.10.168 port 37016 connected with 205.213.14.56 port 5001
[  5] local 10.0.10.168 port 37012 connected with 205.213.14.56 port 5001
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-10.0 sec   266 MBytes   222 Mbits/sec
[  5]  0.0-10.0 sec   264 MBytes   221 Mbits/sec
[  3]  0.0-10.0 sec   278 MBytes   233 Mbits/sec
[  6]  0.0-10.0 sec   310 MBytes   259 Mbits/sec
[SUM]  0.0-10.0 sec  1.09 GBytes   934 Mbits/sec
user@Latitude-E7440:~$

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Versions Compared

Old Version 48

New Version 49

Key

Unidirectional UDP 1Gbps circuit test

Command

Results