wiki:netmon2017iperfw

iperf

Linux systems administrators and network administrators often find diagnosing network speed degradation complicated, as there are very few tools available to diagnose these issues. iperf is a command-line tool used in the diagnostics of network speed issues. iperf measures the maximum network throughput a server can handle. It is particularly useful when experiencing network speed issues, as you can use iperf to determine which server is unable to reach maximum throughput.

Installation

You can use apt-get to install iperf on Debian and Ubuntu:

apt-get install iperf

Note: Installation of perfsonar gives you iperf3 by default. Therefore you do not have to install iperf.

How to Use iperf

iperf must be installed on both computers between which you are testing the connection. If you are using a Unix or Linux-based operating system on your personal computer, you may be able to install iperf on your local machine. If you are testing the throughput of your Linode, however, it’s better to use another server as the end point, as your local ISP may impose network restrictions that can affect the results of your test.

TCP Clients & Servers

iperf requires two systems because one system must act as a server, while the other acts as a client. The client connects to the server you’re testing the speed of.

  • On the Linode you wish to test, launch iperf3 in server mode:
    iperf -s
    

You should see output similar to:

------------------------------------------------------------
Server listening on TCP port 5001
TCP window size:  128 KByte (default)
------------------------------------------------------------
  • On your second Linode, connect to the first. Replace 192.168.1.1 with the first Linode’s IP address.
iperf -c 192.168.1.1

The output should be similar to:

------------------------------------------------------------
Client connecting to 192.168.1.1, TCP port 5001
TCP window size: 85.0 KByte (default)
------------------------------------------------------------
[  3] local 192.168.1.2 port 45448 connected with 192.168.1.1 port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec   524 MBytes   439 Mbits/sec

You will also see the connection and results on your iperf server. This will look similar to:

------------------------------------------------------------
Server listening on TCP port 5001
TCP window size:  128 KByte (default)
------------------------------------------------------------
[  4] local 192.168.1.1 port 5001 connected with 192.168.1.2 port 45448
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-10.1 sec   524 MBytes   437 Mbits/sec
  • To stop the iperf server process, press CTRL + c.

UDP Clients & Servers

Using iPerf, you can also test the maximum throughput achieved via UDP connections.

  • Start a UDP iperf server:
    iperf -s -u
    

The output will be similar to:

------------------------------------------------------------
Server listening on TCP port 5001
Receiving 1470 byte datagrams
UDP buffer size:  192 KByte (default)
------------------------------------------------------------
  • -u Connect your client to your iperf UDP server. Replace 192.168.1.1 with your IP address:
    iperf -c 198.168.1.1 -u
    

The -u option we’ve passed tells iperf3 that we are connecting via UDP. This is important, because we want to see the maximum throughput achieved via UDP. The output should be similar to:

------------------------------------------------------------
Client connecting to 192.168.1.1, UDP port 5001
Sending 1470 byte datagrams
UDP buffer size:  208 KByte (default)
------------------------------------------------------------
[  3] local 192.168.1.2 port 35650 connected with 192.168.1.1 port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec  1.25 MBytes  1.05 Mbits/sec
[  3] Sent 893 datagrams
[  3] Server Report:
[  3]  0.0-10.0 sec  1.25 MBytes  1.05 Mbits/sec   0.408 ms    0/  893 (0%)

  • Looking at the output we have received, 1.05 Mbits/sec is considerably less than what we received on the TCP tests. It is also considerably less than the maximum outbound bandwidth cap provided by the 1GB Linode. This is because iperf limits the bandwidth for UDP clients to 1 Mbit per second by default.

You can change this with the -b flag, replacing the number after with the maximum bandwidth rate you wish to test against. If you are testing for network speed, we recommend setting this number above the maximum bandwidth cap provided by Linode. For example, this test was run on a 1GB Linode:

iperf -c 192.168.1.1 -u -b 100m

This tells the client that we want to achieve a maximum of 100 Mbits per second if possible.

------------------------------------------------------------
Client connecting to 192.168.1.1, UDP port 5001
Sending 1470 byte datagrams
UDP buffer size:  208 KByte (default)
------------------------------------------------------------
[  3] local 192.168.1.29 port 57998 connected with 192.168.1.1 port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec   120 MBytes   101 Mbits/sec
[  3] Sent 85471 datagrams
[  3] Server Report:
[  3]  0.0-10.0 sec   120 MBytes   101 Mbits/sec   0.147 ms    1/85470 (0.0012%)
[  3]  0.0-10.0 sec  1 datagrams received out-of-order

Now that is considerably better than the 1.05 Mbits/sec we were seeing earlier!

Bidirectional Tests

In some cases, you may want to test both servers for the maximum amount of throughput. This can easily be done using the built-in bidirectional testing feature iperf offers.

Run the following command to test both connections:

iperf -c 192.168.1.1 -d

The result is that iperf will start a server and a client connection on the original client server (192.168.1.2). Once this has been done, iPerf will connect the original iperf server to the client connection, which is now acting as both a server connection and a client connection. This will look similar

------------------------------------------------------------
Server listening on TCP port 5001
TCP window size: 85.3 KByte (default)
------------------------------------------------------------
------------------------------------------------------------
Client connecting to 192.168.1.1, TCP port 5001
TCP window size:  170 KByte (default)
------------------------------------------------------------
[  5] local 192.168.1.2 port 45544 connected with 192.168.1.1 port 5001
[  4] local 192.168.1.2 port 5001 connected with 192.168.1.1 port 50048
[ ID] Interval       Transfer     Bandwidth
[  5]  0.0-10.0 sec   304 MBytes   255 Mbits/sec
[  4]  0.0-10.0 sec   236 MBytes   197 Mbits/sec

On the original iPerf server, you will see:

------------------------------------------------------------
Client connecting to 192.168.1.2, TCP port 5001
TCP window size:  129 KByte (default)
------------------------------------------------------------
[  6] local 192.168.1.1 port 50048 connected with 192.168.1.2 port 5001
Waiting for server threads to complete. Interrupt again to force quit.
[ ID] Interval       Transfer     Bandwidth
[  6]  0.0-10.0 sec   236 MBytes   198 Mbits/sec
[  4]  0.0-10.1 sec   304 MBytes   253 Mbits/sec
Last modified 2 years ago Last modified on Nov 20, 2017, 1:40:55 PM