Provided by: iperf3_3.9-1+deb11u1build0.22.04.1_amd64 
NAME
iperf3 - perform network throughput tests
SYNOPSIS
iperf3 -s [ options ]
iperf3 -c server [ options ]
DESCRIPTION
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 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.example.com
iperf3 -c 192.0.2.1
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 iperf3.example.com -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
client.
iperf3 -c iperf3.example.com -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.
GENERAL OPTIONS
-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.
-V, --verbose
give more detailed output
-J, --json
output in JSON format
--logfile file
send output to a log file.
--forceflush
force flushing output at every interval. Used to avoid buffering when sending
output to pipe.
--timestamps [format]
prepend a timestamp at the start of each output line. By default, timestamps have
the format emitted by ctime(1). Optionally, a format specification can be passed
to customize the timestamps, see strftime(3).
-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
SERVER SPECIFIC OPTIONS
-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.
--server-bitrate-limit n[KMGT]
set a limit on the server side, which will cause a test to abort if the client
specifies a test of more than n bits per second, or if the average data sent or
received by the client (including all data streams) is greater than n bits per
second. The default limit is zero, which implies no limit. The interval over
which to average the data rate is 5 seconds by default, but can be specified by
adding a '/' and a number to the bitrate specifier.
--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.
CLIENT SPECIFIC OPTIONS
-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 operating system's timeout for TCP
connection establishment. Providing a shorter value may speed up detection of a
down iperf3 server.
-b, --bitrate n[KMGT]
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[KMGT]
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[KMGT]
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.
--no-fq-socket-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[KMGT]
number of bytes to transmit (instead of -t)
-k, --blockcount n[KMGT]
number of blocks (packets) to transmit (instead of -t or -n)
-l, --length n[KMGT]
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
--bidir
test in both directions (normal and reverse), with both the client and server
sending and receiving data simultaneously
-w, --window n[KMGT]
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
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.
--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-server-output
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.
--udp-counters-64bit
Use 64-bit counters in UDP test packets. The use of this option can help prevent
counter overflows during long or high-bitrate UDP tests. Both client and server
need to be running at least version 3.1 for this option to work. It may become the
default behavior at some point in the future.
--repeating-payload
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.
Note, the password to use can also be specified via the IPERF3_PASSWORD environment
variable. If this variable is present, the password prompt will be skipped.
--rsa-public-key-path file
path to the RSA public key used to encrypt authentication credentials (if built
with OpenSSL support)
EXAMPLES
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
mario,bf7a49a846d44b454a5d11e7acfaf13d138bbe0b7483aa3e050879700572709b
AUTHORS
A list of the contributors to iperf3 can be found within the documentation located at
https://software.es.net/iperf/dev.html#authors.
SEE ALSO
libiperf(3), https://software.es.net/iperf