Iperf

Christian Külker

0.1.3

2023-03-03

The iperf tool can be used to measure network performance. The current version is iperf3. Iperf is a cross-platform tool for active measurements of the maximum achievable bandwidth on the IP network protocols TCP, UDP and SCTP with IPv4 and IPv6. iperf3 is a new implementation from scratch, aiming for a smaller, simpler code base and a library version of the functionality that can be used in other programs.

Features

TCP and SCTP UDP
Bandwidth measurement Creation of dedicated bandwidth streams
Report MSS/MTU size Measure package loss
Observe MSS/MTU size Measure delay jitter
Support TCP window size Use multicast

iperf3 and especially iperf3.1 have additional features compared to iperf2. The following features are not available:

  • -d/-r: Bidirectional testing
  • -I: Data transmitted from stdin
  • -T: Time-to-live (TTL), for multicast
  • -x: Exclude C(connection) D(data) M(multicast) S(settings) V(server) reports
  • -y: Report as a Comma-Separated Values
  • -C: Compatibility mode allows for use with older version of iPerf

The iperf2 has a nice short comparison table comparing iperf2 and iperf3.

Debian Versions

Debian iperf iperf3
Bullseye 11 2.0.14a+dfsg1-1 3.9-1
Buster 10 2.0.12+dfsg1-2 3.6-2
Stretch 9 2.0.9+dfsg1-1 3.1.3-1

Installation of Iperf 2.x

aptitude install iperf

Installation of Iperf 3.x

aptitude install iperf3

Command Line Completion

For command line completion, bash can be used. If the file /usr/share/bash-completion/completions/iperf is available, the bash completion will most likely work.

Mailinglist

Usage Of Iperf

iperf is a client and server application and is used on two computers. One is the server and the other is the client. iperf then sends packets over the network and measures the connection(s) between the server and the client. Normally, one would limit the number of links between server and client to understand which link has what performance. Many operations are similar between iperf2 and iperf3.

Simple Iperf2 Example

This is a simple TCP client server bandwidth test.

Server:

iperf -s

Client:

iperf -c 192.168.168.32
------------------------------------------------------------
Client connecting to 192.168.168.32, TCP port 5001
TCP window size: 85.0 KByte (default)
------------------------------------------------------------
[  3] local 192.168.168.33 port 42152 connected with 192.168.168.32 port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec  1.09 GBytes   939 Mbits/sec

MSS Iperf2 Example

Maximum Segment Size (-m argument) display:

The Maximum Segment Size (MSS) is the largest amount of data (often measured in bytes) that a computer can transfer in a single, unfragmented TCP segment.

It can be calculated as follows:

  • MSS = MTU - TCP + IP headers
  • The TCP + IP headers are equal to 40 bytes.
  • The maximum transmission unit (MTU) is the greatest amount of data that can be transferred in a frame.

Some default MTU sizes for different network topologies:

  • Ethernet - 1500 bytes: used in a LAN
  • PPPoE - 1492 bytes: used on ADSL links

In general, higher MTU (and MSS) results in higher bandwidth efficiency.

Server:

iperf -s

Client side:

iperf -c 192.167.168.32 -m
------------------------------------------------------------
Client connecting to 192.168.168.32, TCP port 5001
TCP window size: 16.0 KByte (default)
------------------------------------------------------------
[ 3] local 192.168.168.33 port 42384 connected with 192.168.168.32 port 5001
[ 3]   0.0-10.2 sec   1.27 MBytes   1.04 Mbits/sec
[ 3] MSS size 1448 bytes (MTU 1500 bytes, ethernet)

Here the MSS is not equal to 1500 - 40, but to 1500 - 40 - 12 (Timestamps option) = 1448

Simple Iperf3 Example

This is a simple TCP client server bandwidth test.

Server:

iperf3 -s

Client:

iperf3 -c 192.168.168.32
Connecting to host 192.168.168.32, port 5201
[  5] local 192.168.168.33 port 53614 connected to 192.168.168.32 port 5201
[ ID] Interval           Transfer     Bitrate         Retr  Cwnd
[  5]   0.00-1.00   sec   113 MBytes   951 Mbits/sec    0    378 KBytes
[  5]   1.00-2.00   sec   111 MBytes   931 Mbits/sec    0    428 KBytes
[  5]   2.00-3.00   sec   112 MBytes   944 Mbits/sec    0    455 KBytes
[  5]   3.00-4.00   sec   112 MBytes   938 Mbits/sec    0    455 KBytes
[  5]   4.00-5.00   sec   112 MBytes   938 Mbits/sec    0    455 KBytes
[  5]   5.00-6.00   sec   111 MBytes   930 Mbits/sec    0    455 KBytes
[  5]   6.00-7.00   sec   112 MBytes   943 Mbits/sec    0    477 KBytes
[  5]   7.00-8.00   sec   112 MBytes   942 Mbits/sec    0    477 KBytes
[  5]   8.00-9.00   sec   111 MBytes   933 Mbits/sec    0    477 KBytes
[  5]   9.00-10.00  sec   111 MBytes   934 Mbits/sec    0    477 KBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-10.00  sec  1.09 GBytes   938 Mbits/sec    0             sender
[  5]   0.00-10.00  sec  1.09 GBytes   937 Mbits/sec                  receiver

History

Version Date Notes
0.1.2 2023-03-03 Improve writing
0.1.2 2022-06-17 Shell->bash, add Bullseye version, Typo
0.1.1 2021-06-06 Add comparison table link, MSS example
0.1.0 2021-06-05 Initial release
  • Iperf