There are many cool options you can use with iperf but I think it’s important to use multiple simultaneous streams. I’ve seen people use this tool without the -P option which will only utilize 1 stream and doesn’t really tell you much when it comes to speed and throughput. You’ll see what I mean when you run the commands.
#Defaults (these can be changed):
default run time 10 seconds
port 5001
window size of 64k :Windows max size is 1024k.
Below I’m going to do multiple streams while changing the windows sizes. I find this the best way to see if you have speed or throughput issues.
iperf3 -c 172.16.10.100 -P 20 -w 128K -T 20Streams iperf3 -c 172.16.10.100 -P 30 -w 512K -T 30Streams iperf3 -c 172.16.10.100 -P 40 -w 1024K -T 40Streams
-c is the end device running in server mode
-P is the amount of streams
-w is the windows size
-T is the label for the test
So lets say you want to run the same tests above but in the other direction. Add a -R to the end of the command:
iperf3 -c 172.16.10.100 -P 40 -w 1024K -T 40Streams -R
Now there may be times where you need to run more than one instance at a time. This is usually the case when troubleshooting 40G+ links. In this situation, you can actually start up multiple server and client instances of iperf using different ports:
Start multiple server instances of iperf with different port numbers:
iperf3 -s -p 5101 iperf3 -s -p 5102 iperf3 -s -p 5103
Then run multiple clients instances using the different port numbers from above:
iperf3 -c hostname -T test1 -p 5101 iperf3 -c hostname -T test2 -p 5102 iperf3 -c hostname -T test3 -p 5103
Again, this tool has so many options and you should play around with them. Below are all the options:
iperf3: parameter error - must either be a client (-c) or server (-s)
Usage: iperf [-s|-c host] [options]
iperf [-h|--help] [-v|--version]
Server or Client:
-p, --port # server port to listen on/connect to
-f, --format [kmgKMG] format to report: Kbits, Mbits, KBytes, MBytes
-i, --interval # seconds between periodic bandwidth reports
-F, --file name xmit/recv the specified file
-B, --bind bind to a specific interface
-V, --verbose more detailed output
-J, --json output in JSON format
--logfile f send output to a log file
-d, --debug emit debugging output
-v, --version show version information and quit
-h, --help show this message and quit
Server specific:
-s, --server run in server mode
-D, --daemon run the server as a daemon
-I, --pidfile file write PID file
-1, --one-off handle one client connection then exit
Client specific:
-c, --client run in client mode, connecting to
-u, --udp use UDP rather than TCP
-b, --bandwidth #[KMG][/#] target bandwidth in bits/sec (0 for unlimited)
(default 1 Mbit/sec for UDP, unlimited for TCP)
(optional slash and packet count for burst mode)
-t, --time # time in seconds to transmit for (default 10 secs)
-n, --bytes #[KMG] number of bytes to transmit (instead of -t)
-k, --blockcount #[KMG] number of blocks (packets) to transmit (instead of -t or -n)
-l, --len #[KMG] length of buffer to read or write
(default 128 KB for TCP, 8 KB for UDP)
--cport bind to a specific client port (TCP and UDP, default: ephemeral port)
-P, --parallel # number of parallel client streams to run
-R, --reverse run in reverse mode (server sends, client receives)
-w, --window #[KMG] set window size / socket buffer size
-M, --set-mss # 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'
-Z, --zerocopy use a 'zero copy' method of sending data
-O, --omit N omit the first n seconds
-T, --title str prefix every output line with this string
--get-server-output get results from server
--udp-counters-64bit use 64-bit counters in UDP test packets
[KMG] indicates options that support a K/M/G suffix for kilo-, mega-, or giga-
EXAMPLES:
1. Basic client command:
iperf -c server
2. Basic server command:
iperf -s
3. UDP test:
iperf -c server -u
4. Reverse mode (server sends, client receives):
iperf -c server -R
5. Set bandwidth for UDP:
iperf -c server -u -b 100M
6. Use specific interface:
iperf -c server -B local_IP_address
7. Set window size:
iperf -c server -w 256K
8. Set test duration:
iperf -c server -t 60
9. Run in daemon mode:
iperf -s -D
10. Use multiple parallel connections:
iperf -c server -P 4