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 either TCP or UDP throughput.  To perform an iperf3  test  the
       user must establish both a server and a client.

       -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
              client-side: read from  the  file  and  write  to  the  network,
              instead of using random data; server-side: read from the network
              and write to the file, instead of throwing the data away

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

       --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/--bandwidth  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 bandwidth pacing
              (-b 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
              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                              May 2017                          IPERF3(1)

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