Provided by: iperf3_3.6-2_amd64 bug


       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

       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 available.

       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

       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

              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 transferred 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  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)

       -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, FreeBSD, and Windows 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  the  specific  interface  associated  with address host.  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 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 daemon.

       -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

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

       -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 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

              This option is deprecated and will be removed.   It  is  equivalent  to  specifying

       -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. The usual prefixes for octal and hex can be used, i.e.
              52, 064 and 0x34 all specify the same value.

       --dscp dscp
              set the IP DSCP bits.  Both numeric  and  symbolic  values  are  accepted.  Numeric
              values can be specified in decimal, octal and hex (see --tos above).

       -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 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

       -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.

       --extra-data str
              Specify an extra data string field to be included in JSON output.

       -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.

              Use  repeating  pattern  in  payload, instead of random bytes.  The same payload is
              used in iperf2 (ASCII '0..9' repeating).  It might help to test and reveal problems
              in  networking  gear with hardware compression (including some WiFi access points),
              where iperf2 and iperf3 perform differently, just based on payload entropy.

       --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 iperf3 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  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 public.pem
            > 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 private_not_protected.pem.

   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