How to do a speed test
Quick answer
Use iperf3 from your server to Worldstream's public test host (iperf.worldstream.nl) to measure real throughput. Browser-based tools like speedtest.net use a single thread and a single nearby server, which understates the capacity of a 1G or 10G connection.
Speedtest.net and similar browser tools are fine for a rough check on a home connection, but they don't give you a reliable read on server-grade bandwidth. They open one transfer thread to whichever server happens to be nearest, and you have no way of knowing how loaded that server is at the time. iperf3 gives you a controlled, repeatable test of bandwidth, latency, and packet loss directly between your server and Worldstream's public iperf host, so it's the better tool for verifying throughput on a 1G or 10G port.
Linux (CentOS, AlmaLinux, Rocky Linux, Ubuntu)
Install iperf3
On RHEL-based distributions (AlmaLinux, Rocky Linux, CentOS Stream):
sudo yum install iperf3On Ubuntu and other Debian-based distributions:
sudo apt-get install iperf3Run a test
Run a basic test from your Worldstream server against Worldstream's public iperf host, iperf.worldstream.nl:
iperf3 -c iperf.worldstream.nl -p 5201For a more accurate reading, run several parallel streams over a longer window:
iperf3 -c iperf.worldstream.nl -p 5201 -P 8 -t 60 -i 0Add the -R flag to reverse the test and measure download speed instead of upload:
iperf3 -c iperf.worldstream.nl -p 5201 -P 8 -t 60 -i 0 -Riperf3 listens on port 5201 by default; ports 5201 to 5205 give you room to run several tests without clashing. Results appear at the end of the output, showing total transferred data and average bandwidth for the run.
VMware ESXi
This section applies to a VMware ESXi host you run yourself on a dedicated server, testing the host itself rather than a guest VM.
Enable SSH on the host
In the ESXi web interface, go to Host → Actions → Services → Enable Secure Shell (SSH), then connect to the host over SSH on port 22.
Allow the test through the host firewall
ESXi blocks the iperf3 port by default, and esxcli cannot create a rule for an arbitrary port. Many guides tell you to switch the whole firewall off. Do not start there: it exposes every service on the host for as long as the test runs, and it stays off if your session drops before step 4.
Narrow the opening instead. List the existing rulesets, run iperf3 on a port one of them already covers, and restrict that ruleset to the test host only:
esxcli network firewall ruleset list
esxcli network firewall ruleset allowedip add --ruleset-id=[ruleset] --ip-address=iperf.worldstream.nl
esxcli network firewall ruleset set --ruleset-id=[ruleset] --allowed-all falseAlternatively, add a custom ruleset for the iperf3 port by placing a firewall XML file in /etc/vmware/firewall/ and reloading with esxcli network firewall refresh.
Only if neither option is workable, disable the firewall for the duration of the test. The host is completely unprotected while it is off, so do this only when the management interface is not reachable from the internet, stay connected, and re-enable it the moment you finish.
esxcli network firewall set --enabled falseRun the test
ESXi does not put iperf3 on your PATH. Use the binary that ships with vSAN:
Upload test:
/usr/lib/vmware/vsan/bin/iperf3 -c iperf.worldstream.nl -p 5201 -t 60 -P 8 -i 0 -4Download test:
/usr/lib/vmware/vsan/bin/iperf3 -c iperf.worldstream.nl -p 5201 -t 60 -P 8 -i 0 -4 -RPut the firewall back
If you disabled the firewall, turn it back on immediately:
esxcli network firewall set --enabled trueIf you widened a ruleset instead, remove the allowed IP you added and restore its previous setting. Turn SSH access back off from the web interface once you're done.
Windows
Download and install iPerf
Download the Windows build from iperf.fr and extract the archive to a folder of its own, for example C:\Tools\iperf3. Keep cygwin1.dll next to iperf3.exe in that folder. Do not copy either file into C:\Windows\System32: putting an unsigned third-party DLL on the system search path can shadow or break other software, and it is not needed here.
If you want to run iperf3 from any directory, add the folder to your PATH rather than moving the files.
Run the test
Open a command prompt in that folder and run:
cd C:\Tools\iperf3
iperf3.exe -c iperf.worldstream.nl -p 5201Useful parameters
| Parameter | Function |
|---|---|
-p | Server port to listen on or connect to |
-P | Number of parallel client streams to run |
-t | Test duration in seconds (default: 10) |
-i | Interval between periodic bandwidth reports |
-R | Reverse the test to measure download instead of upload |