iPerf is a tool designed to test the bandwidth between two hosts using the network. It is a really simple, powerful CLI which allows generating traffic / load TCP or UDP between 2 hosts. You could use to measure the maximum bandwidth of the network between a client and a server. It can be used to do stress tests of the Ethernet, Wi-Fi or of your ISP.
iPerf2 vs iPerf3, what is the difference?
There has been different versions of this tool in the last years. It started ttcp from the National Laboratory for Applied Network Research (NLANR), and then it was developed iPerf (iPerf 2). iPerf3 is a new implementation from scratch, with the goal of a smaller, simpler code base, and a library version of the functionality that can be used in other programs. The functionality between iPerf2 and iPerf3 are mostly compatible, however you should know they use different ports by default. In iPerf2, the default port is 5001, and in iPerf3, 5201.
iPerf3 adds additional features, such as reports of TCP retransmit info, and the verbose mode gives a lot of useful information on CPU usage…etc. Also, it has a better implementation to perform UDP tests. Finally, the code of iPerf3 is smaller, and it is optimized.
In the tests done in this post, we are going to use iPerf3.
Testing the network bandwidth with TCP
To run a quick bandwidth test, first you have to identify the server node, and the client node.
Server Node
The server node is listening for new connections. In our case, using iPerf3, the listening port is 5201.
To leave the iPerf server running:
iperf3 -s
Client Node
Now you can start a client in which you are going to test the Upload performance from the client to the server (Client -> Server).
iperf3 -c <SERVER IP> -i 1 -t 20
In this case, I have added the -i option, to have report information each 1 seconds, and the -t parameter to establish the length of the test, in our case 20 seconds.
root|lavrea:~$ iperf3 -c 159.65.5.190 -i 1 -t 20
Connecting to host 159.65.5.190, port 5201
[ 5] local 167.172.3.43 port 49756 connected to 159.65.5.190 port 5201
[ ID] Interval Transfer Bitrate Retr Cwnd
[ 5] 0.00-1.00 sec 214 MBytes 1.80 Gbits/sec 13018 55.1 KBytes
[ 5] 1.00-2.00 sec 196 MBytes 1.65 Gbits/sec 13665 250 KBytes
[ 5] 2.00-3.00 sec 254 MBytes 2.13 Gbits/sec 19770 42.4 KBytes
[ 5] 3.00-4.00 sec 184 MBytes 1.54 Gbits/sec 11308 188 KBytes
[ 5] 4.00-5.00 sec 241 MBytes 2.02 Gbits/sec 18500 48.1 KBytes
[ 5] 5.00-6.00 sec 188 MBytes 1.57 Gbits/sec 13761 56.6 KBytes
[ 5] 6.00-7.00 sec 235 MBytes 1.97 Gbits/sec 12436 245 KBytes
[ 5] 7.00-8.00 sec 205 MBytes 1.72 Gbits/sec 13587 318 KBytes
[ 5] 8.00-9.00 sec 229 MBytes 1.92 Gbits/sec 14720 191 KBytes
[ 5] 9.00-10.00 sec 229 MBytes 1.92 Gbits/sec 12992 188 KBytes
[ 5] 10.00-11.00 sec 241 MBytes 2.02 Gbits/sec 15559 19.8 KBytes
[ 5] 11.00-12.00 sec 238 MBytes 1.99 Gbits/sec 13002 69.3 KBytes
[ 5] 12.00-13.00 sec 211 MBytes 1.77 Gbits/sec 18426 31.1 KBytes
[ 5] 13.00-14.00 sec 212 MBytes 1.78 Gbits/sec 12496 33.9 KBytes
[ 5] 14.00-15.00 sec 200 MBytes 1.68 Gbits/sec 16435 191 KBytes
[ 5] 15.00-16.00 sec 225 MBytes 1.89 Gbits/sec 12645 35.4 KBytes
[ 5] 16.00-17.00 sec 212 MBytes 1.78 Gbits/sec 17291 53.7 KBytes
[ 5] 17.00-18.00 sec 212 MBytes 1.78 Gbits/sec 13723 48.1 KBytes
[ 5] 18.00-19.00 sec 238 MBytes 1.99 Gbits/sec 11413 70.7 KBytes
[ 5] 19.00-20.00 sec 212 MBytes 1.78 Gbits/sec 13865 46.7 KBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-20.00 sec 4.27 GBytes 1.84 Gbits/sec 288612 sender
[ 5] 0.00-20.01 sec 4.27 GBytes 1.83 Gbits/sec receiver
iperf Done.
In the client report, we can see in this case our TCP bandwidth is 1.84 Gbits/sec.
Testing the network bandwidth with UDP
TCP is a protocol which automatically do rate-limiting to adapt to the available bandwidth a connection can handle, so it’s difficult to truly stress a connection using TCP. For a more stress test, you can use the UDP protocol instead.
Server Node
With iPerf3, it is not needed to change anything in the server side from the TCP test.
iperf3 -s
Client Node
In the client side, it is needed to add the option -u to use UDP. Besides, it is needed to define the bandwidth with the parameter -b (by default it is 1 Mbps). In our case, I am going to set 10G (10 Gbps).
iperf3 -c <SERVER IP> -u -i 1 -t 20 -b 10G
And here is the test:
root|lavrea:~$ iperf3 -c 159.65.5.190 -u -i 1 -t 20 -b 10G
Connecting to host 159.65.5.190, port 5201
[ 5] local 167.172.3.43 port 47554 connected to 159.65.5.190 port 5201
[ ID] Interval Transfer Bitrate Total Datagrams
[ 5] 0.00-1.00 sec 198 MBytes 1.66 Gbits/sec 143338
[ 5] 1.00-2.00 sec 175 MBytes 1.47 Gbits/sec 126975
[ 5] 2.00-3.00 sec 189 MBytes 1.59 Gbits/sec 137109
[ 5] 3.00-4.00 sec 147 MBytes 1.24 Gbits/sec 106805
[ 5] 4.00-5.00 sec 170 MBytes 1.43 Gbits/sec 123358
[ 5] 5.00-6.00 sec 218 MBytes 1.83 Gbits/sec 158036
[ 5] 6.00-7.00 sec 150 MBytes 1.26 Gbits/sec 108566
[ 5] 7.00-8.00 sec 190 MBytes 1.60 Gbits/sec 137854
[ 5] 8.00-9.00 sec 185 MBytes 1.55 Gbits/sec 133897
[ 5] 9.00-10.00 sec 203 MBytes 1.70 Gbits/sec 146706
[ 5] 10.00-11.00 sec 223 MBytes 1.87 Gbits/sec 161391
[ 5] 11.00-12.00 sec 203 MBytes 1.70 Gbits/sec 146963
[ 5] 12.00-13.00 sec 201 MBytes 1.69 Gbits/sec 145463
[ 5] 13.00-14.00 sec 188 MBytes 1.57 Gbits/sec 135785
[ 5] 14.00-15.00 sec 218 MBytes 1.83 Gbits/sec 158091
[ 5] 15.00-16.00 sec 195 MBytes 1.64 Gbits/sec 141318
[ 5] 16.00-17.00 sec 192 MBytes 1.61 Gbits/sec 139124
[ 5] 17.00-18.00 sec 199 MBytes 1.67 Gbits/sec 144444
[ 5] 18.00-19.00 sec 192 MBytes 1.61 Gbits/sec 139256
[ 5] 19.00-20.00 sec 203 MBytes 1.71 Gbits/sec 147310
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bitrate Jitter Lost/Total Datagrams
[ 5] 0.00-20.00 sec 3.75 GBytes 1.61 Gbits/sec 0.000 ms 0/2781789 (0%) sender
[ 5] 0.00-20.00 sec 3.74 GBytes 1.61 Gbits/sec 0.003 ms 4889/2781789 (0.18%) receiver
iperf Done.
In this case, the UDP bandwidth has a bitrate of 1.61 Gbits/sec.
Testing with public iPerf servers
In order to check an Internet connection, you could use a public iPerf server. In the official iPerf website, there is a list of available servers.
Basic commands you should know
Server Node
Start the server in Daemon mode
iperf3 -s -D
Define a different port
iperf3 -s -p 5003
Add a log file with timestamps
iperf3 -s -D --logfile /var/log/iperf.log --timestamps
Add the verbose option
iperf3 -s -V
Client Node
Set the interval reports
Run a 30 seconds test, giving results each 2 seconds
iperf3 -c <SERVER IP> -i 2 -t 30
Reverse direction
Run a test in the direction SERVER -> CLIENT. By default, iPerf sends the traffic in the other direction (CLIENT -> SERVER). Specially interesting to compare uplink vs downlink.
iperf3 -c <SERVER IP> -r -i 1 -t 30
Parallel Streams and change of TCP window size
Run a test with 4 parallel streams, and with a TCP window size of 32768K.
iperf3 -c <SERVER IP> -i 1 -t 20 -w 32768 -P 4
Conclusion
iPerf3 is a very interesting tool with a lot of different options of configuration which can help us to measure the bandwidth of our nodes.