4. Setting Up the iperf3 Server¶

Before running the full certification test or any test run that involves network tests, you should ensure that your iperf3 Target is properly configured. To do so, follow these steps:

On the iperf3 Target, install the certification-tools package from the certification PPA. (This package should be installed by default when you install maas-cert-server version 0.3.7 or later; but you may need to install it manually if you’re using another computer as your iperf3 Target.)
On the iperf3 Target, ensure that jumbo frames are configured on high-speed network interfaces (25 Gbps and faster). You can do this either temporarily or permanently:
- To make a temporary change, type sudo ip link set ens1f1 mtu 9000, changing ens1f1 to your high-speed network interface’s name.
- With recent versions of Ubuntu, a permanent change is done by editing the configuration file in /etc/netplan (such as /etc/netplan/01-netcfg.yaml, although the exact name may differ). Locate the section for the high-speed network interface and add the line mtu: 9000. The result might look something like this, although several options may be different depending on your network configuration:
```
ens1f1:
  match:
    macaddress: 24:8a:07:a3:18:fc
  addresses: [ 172.24.124.1/22 ]
  dhcp4: false
  mtu: 9000
  optional: true
```
- Note that setting jumbo frames is not normally necessary on low-speed network interfaces, and in some cases jumbo frames can cause problems. Specifically, some EFI-based computers can’t PXE-boot from a MAAS server’s interface that’s configured to use jumbo frames, and switches that don’t support jumbo frames can cause problems, too, as described shortly. Thus, you should restrict this procedure to interfaces from which servers do not PXE-boot, if possible. If this is not possible and if you have problems PXE-booting computers, you may need to enable jumbo frames manually only when performing network tests that require this feature.
- It’s possible to configure the MAAS server to enable jumbo frames automatically on all nodes deployed on a particular network. Appendix B: Network Testing Options describes how to configure MAAS in this way.
If iperf3 is already running on the iperf3 server, kill it.
On the iperf3 server, type start-iperf3 -a 172.24.124.1 -n 20, changing the IP address to the interface you want to bring up on the iperf3 Target system and setting the -n option to the number of iperf3 instances you want to run. The network test in Checkbox defaults to using one instance for every 10 Gbps of network throughput being tested, but it may use up to twice that number if conditions warrant, so you’ll need at least -n 8 to test a 40 Gbps NIC and -n 20 to test a 100 Gbps NIC. You may find you’ll need another value, though, as described in Appendix D - Network Performance Tuning. If in doubt, run more iperf3 instances than you think you’ll need; the cost of running too many instances is very low. You can configure iperf3 to start automatically by editing a startup script, such as /etc/rc.local. (The generic /etc/rc.local startup script is not enabled by default in recent versions of Ubuntu. Numerous online tutorials, such as this blog post, describe how to enable it.)
Repeat the preceding step for every other network interface that may be receiving iperf3 connections.
You may need to enable jumbo frames on any switch(es) between the iperf3 Target and the SUT. How to do this varies from one switch to another, so you must consult the switch’s documentation. If a switch drops jumbo-frame traffic, the result can be a complete failure of communication between two computers configured to use jumbo frames.
If the SUT has high-speed network cards (faster than 10 Gbps), repeat steps 1 and 2 on the SUT.

You don’t need to run all of these steps prior to each test run. Once an iperf3 Target is properly configured, it should remain configured at least until it’s rebooted; and if you set an MTU of 9000 in the NetPlan configuration and set the computer to automatically launch iperf3 on reboot, then everything should come up properly after a reboot.

In some cases, additional network configuration steps may be required to further optimize performance. Appendix D - Network Performance Tuning describes these steps. If you run your tests and your network ports all pass, though, there’s no need to consult this Appendix.