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 IPERF3(1)                          ESnet                          IPERF3(1)
 User Manuals                                                   User Manuals

                                  June 2017

      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
      command-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

      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 specified 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

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 IPERF3(1)                          ESnet                          IPERF3(1)
 User Manuals                                                   User Manuals

                                  June 2017

      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 protocol was specified by the client.

      Normally, the test data is sent from the client to the server, and
      measures 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
      measurement 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

      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
      structure, 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 flag.

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

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 IPERF3(1)                          ESnet                          IPERF3(1)
 User Manuals                                                   User Manuals

                                  June 2017

      -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
           multiple CPUs).

      -B, --bind host
           bind to a specific interface. If the host has multiple
           interfaces, 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 buffering
           when sending output to pipe.

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

      -v, --version
           show version information and quit

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 IPERF3(1)                          ESnet                          IPERF3(1)
 User Manuals                                                   User Manuals

                                  June 2017

      -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
           credentials 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.

           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
           operating system's timeout for TCP connection establishment.
           Providing a shorter value may speed up detection of a down iperf3

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 IPERF3(1)                          ESnet                          IPERF3(1)
 User Manuals                                                   User Manuals

                                  June 2017

      -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

      --fq-rate n[KM]
           Set a rate to be used with fair-queueing based socket-level
           pacing, in bits per second.  This pacing (if specified) will be
           in addition to any pacing due to iperf3's internal throughput
           pacing (-b/--bitrate flag), and both can be specified for the
           same test.  Only available on platforms supporting the
           SO_MAX_PACING_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

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 IPERF3(1)                          ESnet                          IPERF3(1)
 User Manuals                                                   User Manuals

                                  June 2017

           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
           association. Specifying at least one --X name will disable this
           behaviour.  This flag must be specified for each link to be

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 IPERF3(1)                          ESnet                          IPERF3(1)
 User Manuals                                                   User Manuals

                                  June 2017

           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
           arguments 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; otherwise 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
           interactively when the test is run.

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

    Authentication - RSA Keypair
      The authentication feature of requires an RSA public keypair.  The
      public key is used to encrypt the authentication token containing the
      user credentials, while the private key is used to decrypt the

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 IPERF3(1)                          ESnet                          IPERF3(1)
 User Manuals                                                   User Manuals

                                  June 2017

      authentication 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
           > openssl rsa -in private.pem -out private_not_protected.pem
           -outform PEM

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

    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
      "{$user}$password".  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
      documentation located at


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