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, iperf3 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). iperf3 does also have flags for “extreme best case” optimizations but they must be explicitly activated. These flags include the -Z (--zerocopy) and -A (--affinity) options.

iperf3 Manual Page

This section contains a plaintext rendering of the iperf3 manual page. It is presented here only for convenience; the text here might not correspond to the current version of iperf3. The authoritative iperf3 manual page is included in the source tree and installed along with the executable.

IPERF3(1)                        User Manuals                        IPERF3(1)

       iperf3 - perform network throughput tests

       iperf3 -s [ options ]
       iperf3 -c server [ options ]

       iperf3  is  a  tool for performing network throughput measurements.  It
       can test TCP, UDP, or SCTP throughput.  To perform an iperf3  test  the
       user must establish both a server and a client.

       The  iperf3  executable  contains both client and server functionality.
       An iperf3 server can be started using either of the -s or --server com-
       mand-line parameters, for example:

              iperf3 -s

              iperf3 --server

       Note  that  many  iperf3  parameters  have  both  short  (-s)  and long
       (--server) forms.  In this section we will generally use the short form
       of  command-line  flags,  unless only the long form of a flag is avail-

       By default, the iperf3 server listens on TCP port 5201 for  connections
       from  an iperf3 client.  A custom port can be specified by using the -p
       flag, for example:

              iperf3 -s -p 5002

       After the server is started, it will listen for connections from iperf3
       clients  (in  other words, the iperf3 program run in client mode).  The
       client mode can be started using the -c command-line option, which also
       requires a host to which iperf3 should connect.  The host can by speci-
       fied by hostname, IPv4 literal, or IPv6 literal:

              iperf3 -c

              iperf3 -c

              iperf3 -c 2001:db8::1

       If the iperf3 server is running on a non-default TCP  port,  that  port
       number needs to be specified on the client as well:

              iperf3 -c -p 5002

       The initial TCP connection is used to exchange test parameters, control
       the start and end of the test, and to exchange test results.   This  is
       sometimes  referred  to  as  the "control connection".  The actual test
       data is sent over a separate TCP connection, as a separate flow of  UDP
       packets, or as an independent SCTP connection, depending on what proto-
       col was specified by the client.

       Normally, the test data is sent from the client to the server, and mea-
       sures  the  upload  speed  of the client.  Measuring the download speed
       from the server can be done by specifying the -R flag  on  the  client.
       This causes data to be sent from the server to the client.

              iperf3 -c -p 5202 -R

       Results  are displayed on both the client and server.  There will be at
       least one line of output per measurement interval (by  default  a  mea-
       surement  interval lasts for one second, but this can be changed by the
       -i option).  Each line of output includes (at least) the time since the
       start  of  the test, amount of data transfered during the interval, and
       the average bitrate over that interval.  Note that the values for  each
       measurement  interval  are taken from the point of view of the endpoint
       process emitting that output (in other words, the output on the  client
       shows the measurement interval data for the client.

       At  the  end of the test is a set of statistics that shows (at least as
       much as possible) a summary of the test as seen by both the sender  and
       the  receiver,  with  lines tagged accordingly.  Recall that by default
       the client is the sender and the server is the  receiver,  although  as
       indicated above, use of the -R flag will reverse these roles.

       The  client  can be made to retrieve the server-side output for a given
       test by specifying the --get-server-output flag.

       Either the client or the server can produce its output in a JSON struc-
       ture,  useful for integration with other programs, by passing it the -J
       flag.  Because the contents of the JSON structure  are  only  competely
       known after the test has finished, no JSON output will be emitted until
       the end of the test.

       iperf3 has a (overly) large set of command-line  options  that  can  be
       used  to  set the parameters of a test.  They are given in the "GENERAL
       OPTIONS" section of the manual page below, as  well  as  summarized  in
       iperf3's help output, which can be viewed by running iperf3 with the -h

       -p, --port n
              set server port to listen on/connect to to n (default 5201)

       -f, --format
              [kmgtKMGT]   format to report: Kbits/Mbits/Gbits/Tbits

       -i, --interval n
              pause n seconds between periodic throughput reports; default  is
              1, use 0 to disable

       -F, --file name
              Use  a  file  as  the  source  (on  the  sender) or sink (on the
              receiver) of data, rather than just generating  random  data  or
              throwing  it  away.  This feature is used for finding whether or
              not the storage subsystem is the bottleneck for file  transfers.
              It  does not turn iperf3 into a file transfer tool.  The length,
              attributes, and in some cases contents of the received file  may
              not match those of the original file.

       -A, --affinity n/n,m
              Set  the CPU affinity, if possible (Linux and FreeBSD only).  On
              both the client and server you can set  the  local  affinity  by
              using the n form of this argument (where n is a CPU number).  In
              addition, on the client  side  you  can  override  the  server's
              affinity for just that one test, using the n,m form of argument.
              Note that when using this feature, a process will only be  bound
              to  a single CPU (as opposed to a set containing potentialy mul-
              tiple CPUs).

       -B, --bind host
              bind to a specific interface. If the host  has  multiple  inter-
              faces, it will use the first interface by default.

       -V, --verbose
              give more detailed output

       -J, --json
              output in JSON format

       --logfile file
              send output to a log file.

              force  flushing output at every interval.  Used to avoid buffer-
              ing when sending output to pipe.

       -d, --debug
              emit debugging output.  Primarily (perhaps exclusively)  of  use
              to developers.

       -v, --version
              show version information and quit

       -h, --help
              show a help synopsis

       -s, --server
              run in server mode

       -D, --daemon
              run the server in background as a daemon

       -I, --pidfile file
              write  a file with the process ID, most useful when running as a

       -1, --one-off
              handle one client connection, then exit.

       --rsa-private-key-path file
              path to the RSA private key  (not  password-protected)  used  to
              decrypt  authentication  credentials  from  the client (if built
              with OpenSSL support).

       --authorized-users-path file
              path to the configuration file containing authorized users  cre-
              dentials  to  run  iperf  tests (if built with OpenSSL support).
              The file is a comma separated list  of  usernames  and  password
              hashes;  more  information  on  the structure of the file can be
              found in the EXAMPLES section.

       -c, --client host
              run in client mode, connecting  to  the  specified  server.   By
              default,  a test consists of sending data from the client to the
              server, unless the -R flag is specified.

       --sctp use SCTP rather than TCP (FreeBSD and Linux)

       -u, --udp
              use UDP rather than TCP

       --connect-timeout n
              set timeout for establishing the initial control  connection  to
              the  server, in milliseconds.  The default behavior is the oper-
              ating system's timeout for TCP connection  establishment.   Pro-
              viding  a  shorter value may speed up detection of a down iperf3

       -b, --bitrate n[KM]
              set target bitrate to n bits/sec (default 1  Mbit/sec  for  UDP,
              unlimited  for  TCP/SCTP).   If  there  are multiple streams (-P
              flag), the  throughput  limit  is  applied  separately  to  each
              stream.   You  can  also  add  a '/' and a number to the bitrate
              specifier.  This is called "burst mode".  It will send the given
              number  of  packets  without  pausing,  even if that temporarily
              exceeds the specified  throughput  limit.   Setting  the  target
              bitrate  to  0  will disable bitrate limits (particularly useful
              for UDP tests).  This throughput limit is implemented internally
              inside  iperf3, and is available on all platforms.  Compare with
              the --fq-rate flag.  This option replaces the --bandwidth  flag,
              which is now deprecated but (at least for now) still accepted.

       --pacing-timer n[KMG]
              set   pacing   timer  interval  in  microseconds  (default  1000
              microseconds, or 1 ms).  This controls iperf3's internal  pacing
              timer  for  the  -b/--bitrate  option.   The  timer fires at the
              interval set by this parameter.  Smaller values  of  the  pacing
              timer  parameter  smooth  out the traffic emitted by iperf3, but
              potentially at the cost of  performance  due  to  more  frequent
              timer processing.

       --fq-rate n[KM]
              Set a rate to be used with fair-queueing based socket-level pac-
              ing, in bits per second.  This pacing (if specified) will be  in
              addition  to any pacing due to iperf3's internal throughput pac-
              ing (-b/--bitrate flag), and both can be specified for the  same
              test.   Only  available  on platforms supporting the SO_MAX_PAC-
              ING_RATE socket option (currently only Linux).  The  default  is
              no fair-queueing based pacing.

              This option is deprecated and will be removed.  It is equivalent
              to specifying --fq-rate=0.

       -t, --time n
              time in seconds to transmit for (default 10 secs)

       -n, --bytes n[KM]
              number of bytes to transmit (instead of -t)

       -k, --blockcount n[KM]
              number of blocks (packets) to transmit (instead of -t or -n)

       -l, --length n[KM]
              length of buffer to read or write.  For TCP tests,  the  default
              value is 128KB.  In the case of UDP, iperf3 tries to dynamically
              determine a reasonable sending size based on the  path  MTU;  if
              that  cannot be determined it uses 1460 bytes as a sending size.
              For SCTP tests, the default size is 64KB.

       --cport port
              bind data streams to a specific client port  (for  TCP  and  UDP
              only, default is to use an ephemeral port)

       -P, --parallel n
              number  of  parallel  client streams to run. Note that iperf3 is
              single threaded, so if you are CPU bound, this  will  not  yield
              higher throughput.

       -R, --reverse
              reverse  the  direction of a test, so that the server sends data
              to the client

       -w, --window n[KM]
              window size / socket buffer size (this gets sent to  the  server
              and used on that side too)

       -M, --set-mss n
              set TCP/SCTP maximum segment size (MTU - 40 bytes)

       -N, --no-delay
              set TCP/SCTP no delay, disabling Nagle's Algorithm

       -4, --version4
              only use IPv4

       -6, --version6
              only use IPv6

       -S, --tos n
              set the IP type of service

       --dscp dscp
              set  the  IP  DSCP  bits.   Both numeric and symbolic values are

       -L, --flowlabel n
              set the IPv6 flow label (currently only supported on Linux)

       -X, --xbind name
              Bind SCTP associations to  a  specific  subset  of  links  using
              sctp_bindx(3).   The  --B  flag  will be ignored if this flag is
              specified.  Normally SCTP will include the protocol addresses of
              all  active  links on the local host when setting up an associa-
              tion. Specifying  at  least  one  --X  name  will  disable  this
              behaviour.   This  flag  must  be  specified for each link to be
              included in the association, and is  supported  for  both  iperf
              servers  and  clients  (the  latter are supported by passing the
              first --X argument to bind(2)).  Hostnames are accepted as argu-
              ments  and are resolved using getaddrinfo(3).  If the --4 or --6
              flags are specified, names which do  not  resolve  to  addresses
              within the specified protocol family will be ignored.

       --nstreams n
              Set number of SCTP streams.

       -Z, --zerocopy
              Use  a  "zero copy" method of sending data, such as sendfile(2),
              instead of the usual write(2).

       -O, --omit n
              Omit the first n seconds of the test, to skip past the TCP slow-
              start period.

       -T, --title str
              Prefix every output line with this string.

       -C, --congestion algo
              Set  the  congestion control algorithm (Linux and FreeBSD only).
              An older --linux-congestion synonym for this  flag  is  accepted
              but is deprecated.

              Get the output from the server.  The output format is determined
              by the server (in particular, if the server was invoked with the
              --json  flag,  the  output  will be in JSON format, otherwise it
              will be in human-readable format).  If the client  is  run  with
              --json,  the  server output is included in a JSON object; other-
              wise it is appended at the bottom of the human-readable  output.

       --username username
              username to use for authentication to the iperf server (if built
              with OpenSSL support).  The password will be prompted for inter-
              actively when the test is run.

       --rsa-public-key-path file
              path  to  the RSA public key used to encrypt authentication cre-
              dentials (if built with OpenSSL support)

   Authentication - RSA Keypair
       The authentication feature of requires an RSA public keypair.  The pub-
       lic key is used to encrypt the authentication token containing the user
       credentials, while the private key is used to decrypt  the  authentica-
       tion  token.   An  example  of a set of UNIX/Linux commands to generate
       correct keypair follows:

            > openssl genrsa -des3 -out private.pem 2048
            > openssl rsa -in private.pem -outform PEM -pubout -out public.pem
            > openssl rsa -in private.pem -out private_not_protected.pem -out-
            form PEM

       After these commands, the public key will be contained in the file pub-
       lic.pem  and  the  private  key  will  be  contained  in  the file pri-

   Authentication - Authorized users configuration file
       A simple plaintext file must be provided to the iperf3 server in  order
       to  specify the authorized user credentials.  The file is a simple list
       of comma-separated pairs of a username  and  a  corresponding  password
       hash.   The password hash is a SHA256 hash of the string "{$user}$pass-
       word".  The file can also contain commented lines (starting with the  #
       character).   An example of commands to generate the password hash on a
       UNIX/Linux system is given below:

            > S_USER=mario S_PASSWD=rossi
            > echo -n "{$S_USER}$S_PASSWD" | sha256sum | awk '{ print $1 }'

       An example of a password file (with an entry corresponding to the above
       username and password) is given below:
            > cat credentials.csv
            # file format: username,sha256

       A list of the contributors to iperf3 can be found within the documenta-
       tion located at


ESnet                              June 2017                         IPERF3(1)

The iperf3 manual page will typically be installed in manual section 1.