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 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.
- -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.
- --forceflush
- 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 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[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 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[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 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.
- --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.
- --rsa-public-key-path file
- path to the RSA public key used to encrypt authentication credentials (if
built with OpenSSL support)
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.
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
A list of the contributors to iperf3 can be found within the documentation
located at https://software.es.net/iperf/dev.html#authors.
libiperf(3), https://software.es.net/iperf