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How to Test Network Throughput with iPerf on Debian and Ubuntu

Posted on February 21, 2023 by nexonhost

How to Test Network Throughput with iPerf on Debian and Ubuntu

 

Install iPerf

The iperf package is included in most Linux distribution’s repositories.

 

Debian and Ubuntu

apt-get install iperf

 

How to Use iPerf

iPerf must be installed on the computers at both ends of the connection you’re testing. If you are using a Unix or Linux-based operating system on your personal computer, you can 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.

  1. On the Linode you plan to test, launch iPerf in server mode:
  2. iperf -s

You should see output similar to:

————————————————————

Server listening on TCP port 5001

TCP window size: 85.3 KByte (default)

————————————————————

  1. On your second Linode, connect to the first. Replace 198.51.100.5 with the first Linode’s IP address.
  2. iperf -c 198.51.100.5
  3. ————————————————————
  4. Client connecting to 198.51.100.5, TCP port 5001
  5. TCP window size: 45.0 KByte (default)
  6. ————————————————————
  7. [ 3] local 198.51.100.6 port 50616 connected with 198.51.100.5 port 5001
  8. [ ID] Interval Transfer Bandwidth

[ 3] 0.0-10.1 sec 1.27 GBytes 1.08 Gbits/sec

  1. You will also see the connection and results on your iPerf server:
  2. ————————————————————
  3. Server listening on TCP port 5001
  4. TCP window size: 85.3 KByte (default)
  5. ————————————————————
  6. [ 4] local 198.51.100.5 port 5001 connected with 198.51.100.6 port 50616
  7. [ ID] Interval Transfer Bandwidth

[ 4] 0.0-10.1 sec 1.27 GBytes 1.08 Gbits/sec

  1. 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.

  1. Start a UDP iPerf server:
  2. iperf -s -u
  3. ————————————————————
  4. Server listening on UDP port 5001
  5. Receiving 1470 byte datagrams
  6. UDP buffer size: 208 KByte (default)

————————————————————

  1. Connect your client to your iPerf UDP server. Replace 198.51.100.5 with your IP address:
  2. iperf -c 198.51.100.5 -u
  3. ————————————————————
  4. Client connecting to 198.51.100.5, UDP port 5001
  5. Sending 1470 byte datagrams
  6. UDP buffer size: 208 KByte (default)
  7. ————————————————————
  8. [ 3] local 198.51.100.6 port 58070 connected with 198.51.100.5 port 5001
  9. [ ID] Interval Transfer Bandwidth
  10. [ 3] 0.0-10.0 sec 1.25 MBytes 1.05 Mbits/sec
  11. [ 3] Sent 893 datagrams
  12. [ 3] Server Report:

[ 3] 0.0-10.0 sec 1.25 MBytes 1.05 Mbits/sec 0.084 ms 0/ 893 (0%)

1.05 Mbits/sec is considerably less than what was observed 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.

  1. 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, set this number above the maximum bandwidth cap provided by Linode:
  2. iperf -c 198.51.100.5 -u -b 1000m

This tells the client that we want to achieve a maximum of 1000 Mbits per second if possible. The -b flag only works when using UDP connections, since iPerf does not set a bandwidth limit on the TCP clients.

————————————————————

Client connecting to 198.51.100.5, UDP port 5001

Sending 1470 byte datagrams

UDP buffer size: 208 KByte (default)

————————————————————

[ 3] local 198.51.100.5 port 52308 connected with 198.51.100.5 port 5001

[ ID] Interval Transfer Bandwidth

[ 3] 0.0-10.0 sec 966 MBytes 810 Mbits/sec

[ 3] Sent 688897 datagrams

[ 3] Server Report:

[ 3] 0.0-10.0 sec 966 MBytes 810 Mbits/sec 0.001 ms 0/688896 (0%)

[ 3] 0.0-10.0 sec 1 datagrams received out-of-order

This time the results are considerably higher.

 

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.

to test both connections, run the following command from the client:

iperf -c 198.51.100.5 -d

The result is that iPerf will start a server and a client connection on the client server (198.51.100.6). Once this has been done, iPerf will connect the iPerf server to the client connection, which is now acting as both a server connection and a client connection.

————————————————————

Server listening on TCP port 5001

TCP window size: 85.3 KByte (default)

————————————————————

————————————————————

Client connecting to 198.51.100.5, TCP port 5001

TCP window size: 351 KByte (default)

————————————————————

[ 3] local 198.51.100.6 port 50618 connected with 198.51.100.5 port 5001

[ 5] local 198.51.100.6 port 5001 connected with 198.51.100.5 port 58650

[ ID] Interval Transfer Bandwidth

[ 5] 0.0-10.1 sec 1.27 GBytes 1.08 Gbits/sec

[ 3] 0.0-10.2 sec 1.28 GBytes 1.08 Gbits/sec

On the server, you will see:

————————————————————

Client connecting to 198.51.100.6, TCP port 5001

TCP window size: 153 KByte (default)

————————————————————

[ 6] local 198.51.100.5 port 58650 connected with 198.51.100.6 port 5001

[ 6] 0.0-10.1 sec 1.27 GBytes 1.08 Gbits/sec

[ 5] 0.0-10.2 sec 1.28 GBytes 1.08 Gbits/sec