Iperf User Documentation

Command line option	Environment variable option	Description
Client and Server options
`-f, --format [bkmaBKMA]`	`$IPERF_FORMAT`	A letter specifying the format to print bandwidth numbers in. Supported formats are 'b' = bits/sec 'B' = Bytes/sec 'k' = Kbits/sec 'K' = KBytes/sec 'm' = Mbits/sec 'M' = MBytes/sec 'g' = Gbits/sec 'G' = GBytes/sec 'a' = adaptive bits/sec 'A' = adaptive Bytes/sec The adaptive formats choose between kilo- and mega- as appropriate. Fields other than bandwidth always print bytes, but otherwise follow the requested format. Default is 'a'. NOTE: here Kilo = 1024, Mega = 1024^2 and Giga = 1024^3 when dealing with bytes. Commonly in networking, Kilo = 1000, Mega = 1000^2, and Giga = 1000^3 so we use this when dealing with bits. If this really bothers you, use -f b and do the math.
`-i, --interval #`	`$IPERF_INTERVAL`	Sets the interval time in seconds between periodic bandwidth, jitter, and loss reports. If non-zero, a report is made every interval seconds of the bandwidth since the last report. If zero, no periodic reports are printed. Default is zero.
`-l, --len #[KM]`	`$IPERF_LEN`	The length of buffers to read or write. Iperf works by writing an array of len bytes a number of times. Default is 8 KB for TCP, 1470 bytes for UDP. Note for UDP, this is the datagram size and needs to be lowered when using IPv6 addressing to 1450 or less to avoid fragmentation. See also the -n and -t options.
`-m, --print_mss`	`$IPERF_PRINT_MSS`	Print the reported TCP MSS size (via the TCP_MAXSEG option) and the observed read sizes which often correlate with the MSS. The MSS is usually the MTU - 40 bytes for the TCP/IP header. Often a slightly smaller MSS is reported because of extra header space from IP options. The interface type corresponding to the MTU is also printed (ethernet, FDDI, etc.). This option is not implemented on many OSes, but the read sizes may still indicate the MSS.
`-p, --port #`	`$IPERF_PORT`	The server port for the server to listen on and the client to connect to. This should be the same in both client and server. Default is 5001, the same as ttcp.
`-u, --udp`	`$IPERF_UDP`	Use UDP rather than TCP. See also the -b option.
`-w, --window #[KM]`	`$TCP_WINDOW_SIZE`	Sets the socket buffer sizes to the specified value. For TCP, this sets the TCP window size. For UDP it is just the buffer which datagrams are received in, and so limits the largest receivable datagram size.
`-B, --bind host`	`$IPERF_BIND`	Bind to host, one of this machine's addresses. For the client this sets the outbound interface. For a server this sets the incoming interface. This is only useful on multihomed hosts, which have multiple network interfaces. For Iperf in UDP server mode, this is also used to bind and join to a multicast group. Use addresses in the range 224.0.0.0 to 239.255.255.255 for multicast. See also the -T option.
`-C, --compatibility`	`$IPERF_COMPAT`	Compatibility mode allows for use with older version of iperf. This mode is not required for interoperability but it is highly recommended. In some cases when using representative streaming you could cause a 1.7 server to crash or cause undesired connection attempts.
`-M, --mss #[KM}`	`$IPERF_MSS`	Attempt to set the TCP maximum segment size (MSS) via the TCP_MAXSEG option. The MSS is usually the MTU - 40 bytes for the TCP/IP header. For ethernet, the MSS is 1460 bytes (1500 byte MTU). This option is not implemented on many OSes.
`-N, --nodelay`	`$IPERF_NODELAY`	Set the TCP no delay option, disabling Nagle's algorithm. Normally this is only disabled for interactive applications like telnet.
`-V` (from v1.6 or higher)	.	Bind to an IPv6 address Server side: $ iperf -s -V Client side: $ iperf -c <Server IPv6 Address> -V Note: On version 1.6.3 and later a specific IPv6 Address does not need to be bound with the -B option, previous 1.6 versions do. Also on most OSes using this option will also respond to IPv4 clients using IPv4 mapped addresses.
Server specific options
`-s, --server`	`$IPERF_SERVER`	Run Iperf in server mode.
`-D` (from v1.2 or higher)	.	Run the server as a daemon (Unix platforms) On Win32 platforms where services are available, Iperf will start running as a service.
`-R` (only for Windows, from v1.2 or higher)	.	Remove the Iperf service (if it's running).
`-o` (only for Windows, from v1.2 or higher)	.	Redirect output to given file.
`-c, --client host`	`$IPERF_CLIENT`	If Iperf is in server mode, then specifying a host with -c will limit the connections that Iperf will accept to the host specified. Does not work well for UDP.
`-P, --parallel #`	`$IPERF_PARALLEL`	The number of connections to handle by the server before closing. Default is 0 (which means to accept connections forever).
Client specific options
`-b, --bandwidth #[KM]`	`$IPERF_BANDWIDTH`	The UDP bandwidth to send at, in bits/sec. This implies the -u option. Default is 1 Mbit/sec.
`-c, --client host`	`$IPERF_CLIENT`	Run Iperf in client mode, connecting to an Iperf server running on host.
`-d, --dualtest`	`$IPERF_DUALTEST`	Run Iperf in dual testing mode. This will cause the server to connect back to the client on the port specified in the -L option (or defaults to the port the client connected to the server on). This is done immediately therefore running the tests simultaneously. If you want an alternating test try -r.
`-n, --num #[KM]`	`$IPERF_NUM`	The number of buffers to transmit. Normally, Iperf sends for 10 seconds. The -n option overrides this and sends an array of len bytes num times, no matter how long that takes. See also the -l and -t options.
`-r, --tradeoff`	`$IPERF_TRADEOFF`	Run Iperf in tradeoff testing mode. This will cause the server to connect back to the client on the port specified in the -L option (or defaults to the port the client connected to the server on). This is done following the client connection termination, therefore running the tests alternating. If you want an simultaneous test try -d.
`-t, --time #`	`$IPERF_TIME`	The time in seconds to transmit for. Iperf normally works by repeatedly sending an array of len bytes for time seconds. Default is 10 seconds. See also the -l and -n options.
`-L, --listenport #`	`$IPERF_LISTENPORT`	This specifies the port that the server will connect back to the client on. It defaults to the port used to connect to the server from the client.
`-P, --parallel #`	`$IPERF_PARALLEL`	The number of simultaneous connections to make to the server. Default is 1. Requires thread support on both the client and server.
`-S, --tos #`	`$IPERF_TOS`	The type-of-service for outgoing packets. (Many routers ignore the TOS field.) You may specify the value in hex with a '0x' prefix, in octal with a '0' prefix, or in decimal. For example, '0x10' hex = '020' octal = '16' decimal. The TOS numbers specified in RFC 1349 are: IPTOS_LOWDELAY minimize delay 0x10 IPTOS_THROUGHPUT maximize throughput 0x08 IPTOS_RELIABILITY maximize reliability 0x04 IPTOS_LOWCOST minimize cost 0x02
`-T, --ttl #`	`$IPERF_TTL`	The time-to-live for outgoing multicast packets. This is essentially the number of router hops to go through, and is also used for scoping. Default is 1, link-local.
`-F` (from v1.2 or higher)	.	Use a representative stream to measure bandwidth, e.g. :- $ iperf -c <server address> -F <file-name>
`-I` (from v1.2 or higher)	.	Same as -F, input from stdin.
Miscellaneous options
`-h, --help`		Print out a summary of commands and quit.
`-v, --version`		Print version information and quit. Prints 'pthreads' if compiled with POSIX threads, 'win32 threads' if compiled with Microsoft Win32 threads, or 'single threaded' if compiled without threads.