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: https://fasterdata.es.net/performance-testing/network-troubleshooting-tools/iperf/ 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) 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 com- mand-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 avail- able. 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 speci- fied 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 proto- col was specified by the client. Normally, the test data is sent from the client to the server, and mea- sures 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 mea- surement 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 struc- ture, 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. If the host has multiple interfaces, it will use the first inter- face 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 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 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. --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. 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 oper- ating system's timeout for TCP connection establishment. Pro- viding 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 pac- ing, in bits per second. This pacing (if specified) will be in addition to any pacing due to iperf3's internal throughput pac- ing (-b/--bitrate flag), and both can be specified for the same test. Only available on platforms supporting the SO_MAX_PAC- ING_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 associa- tion. Specifying at least one --X name will disable this behav- iour. 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 argu- ment 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-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; 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) EXAMPLES 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- vate_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 "{$user}$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 mario,bf7a49a846d44b454a5d11e7acfaf13d138bbe0b7483aa3e050879700572709b AUTHORS A list of the contributors to iperf3 can be found within the documenta- tion located at http://software.es.net/iperf/dev.html#authors. SEE ALSO libiperf(3), http://software.es.net/iperf ESnet March 2018 IPERF3(1) The iperf3 manual page will typically be installed in manual section 1.