tree: 2783b413c36e93075de9fecad72e2d1a8b11a773 [path history] [tgz]
  1. config/
  2. examples/
  3. src/
  4. .gitignore
  5. .travis.yml
  6. aclocal.m4
  9. configure
  14. make_release

iperf3: A TCP, UDP, and SCTP network bandwidth measurement tool


iperf is a tool for active measurements of the maximum achievable bandwidth on IP networks. It supports tuning of various parameters related to timing, protocols, and buffers. For each test it reports the bandwidth, loss, and other parameters.

This version, sometimes referred to as iperf3, is a redesign of an original version developed at NLANR/DAST. iperf3 is a new implementation from scratch, with the goal of a smaller, simpler code base, and a library version of the functionality that can be used in other programs. iperf3 also a number of features found in other tools such as nuttcp and netperf, but were missing from the original iperf. These include, for example, a zero-copy mode and optional JSON output. Note that iperf3 is NOT backwards compatible with the original iperf.

Primary development for iperf3 takes place on CentOS Linux, FreeBSD, and MacOS X. At this time, these are the only officially supported platforms, however there have been some reports of success with OpenBSD, Android, other Linux distributions.

iperf3 is principally developed by ESnet / Lawrence Berkeley National Laboratory. It is released under a three-clause BSD license.

For more information see:

Source code and issue tracker:

Obtaining iperf3

Downloads of iperf3 are available at:

To check out the most recent code, do:

git clone

Building iperf3


  • libuuid: this is not installed by default for Debian/Ubuntu Systems to install: apt-get install uuid-dev


./configure; make; make install

(Note: If configure fails, try running ./ first)

Invoking iperf3

iperf3 includes a manual page listing all of the command-line options. The manual page is the most up-to-date reference to the various flags and parameters.

For sample command line usage, see:

Using the default options, iperf is meant to show typical well designed application performance. ‘Typical well designed application’ means avoiding artificial enhancements that work only for testing (such as splice()'ing the data to /dev/null). iperf does also have flags for ‘extreme best case’ optimizations but they must be explicitly activated.

These flags include:

-Z, --zerocopy            use a 'zero copy' sendfile() method of sending data
-A, --affinity n/n,m      set CPU affinity

Bug Reports

Before submitting a bug report, try checking out the latest version of the code, and confirm that its not already fixed. Then submit to:

Changes from iperf 2.x

New options:

-V, --verbose             more detailed output than before
-J, --json                output in JSON format
-Z, --zerocopy            use a 'zero copy' sendfile() method of sending data
-O, --omit N              omit the first n seconds (to ignore slowstart)
-T, --title str           prefix every output line with this string
-F, --file name           xmit/recv the specified file
-A, --affinity n/n,m      set CPU affinity (Linux only)
-k, --blockcount #[KMG]   number of blocks (packets) to transmit (instead 
                          of -t or -n)
-L, --flowlabel           set IPv6 flow label (Linux only)

Changed flags:

-C, --linux-congestion    set congestion control algorithm (Linux only)
                          (-Z in iperf2)

Deprecated options:

Not planning to support these iperf2 flags. If you really miss these options, please submit a request in the issue tracker:

-d, --dualtest           Do a bidirectional test simultaneously
-r, --tradeoff           Do a bidirectional test individually
-T, --ttl                time-to-live, for multicast (default 1)
-x, --reportexclude [CDMSV]   exclude C(connection) D(data) M(multicast) 
                              S(settings) V(server) reports
-y, --reportstyle C      report as a Comma-Separated Values

Also deprecated is the ability to set the options via environment variables.

Known Issues

  • UDP performance: Some problems have been noticed with iperf3 on the ESnet 100G testbed at high UDP rates (above 10Gbps). The symptom is that on any particular run of iperf3 the receiver reports a loss rate of about 20%, regardless of the -b option used on the client side. This problem appears not to be iperf3-specific, and may be due to the placement of the iperf3 process on a CPU and its relation to the inbound NIC. In some cases this problem can be mitigated by an appropriate use of the CPU affinity (-A) option. (Issue #55)

  • The -Z flag sometimes causes the iperf3 client to hang on OSX. (Issue #129)

  • When specifying the TCP buffer size using the “-w” flag on Linux, Linux doubles the value you pass in. (You can see this using iperf3's debug flag). But then the CWND does not actually ramp up to the doubled value, but only to about 75% of the doubled value. This appears to be by design.

  • On some platforms, it might be necessary to invoke “ldconfig” manually after doing a “make install” before the iperf3 executable can find its shared library. (Issue #153)


This section lists links to user-contributed Web pages regarding iperf3. ESnet and Lawrence Berkeley National Laboratory bear no responsibility for the content of these pages.


iperf, Copyright (c) 2014-2015, The Regents of the University of California, through Lawrence Berkeley National Laboratory (subject to receipt of any required approvals from the U.S. Dept. of Energy). All rights reserved.

If you have questions about your rights to use or distribute this software, please contact Berkeley Lab's Technology Transfer Department at

NOTICE. This software is owned by the U.S. Department of Energy. As such, the U.S. Government has been granted for itself and others acting on its behalf a paid-up, nonexclusive, irrevocable, worldwide license in the Software to reproduce, prepare derivative works, and perform publicly and display publicly. Beginning five (5) years after the date permission to assert copyright is obtained from the U.S. Department of Energy, and subject to any subsequent five (5) year renewals, the U.S. Government is granted for itself and others acting on its behalf a paid-up, nonexclusive, irrevocable, worldwide license in the Software to reproduce, prepare derivative works, distribute copies to the public, perform publicly and display publicly, and to permit others to do so.

This code is distributed under a BSD style license, see the LICENSE file for complete information.