After shutting down sys-net, I can no longer connect to the internet

[apparatus]

Be aware that permissive=true option has a downside:

NOTE: The permissive flag increases attack surface and possibility of side channel attacks. While using the no-strict-reset flag, do not require PCI device to be reset before attaching it to another VM. This may leak usage data even without malicious intent. Both permissive and no-strict-reset options may not be necessary and you should try one first, then the other, before using both.

PCI troubleshooting

I’d suggest you to first try to use just no-strict-reset=true option:
Get your network card DEVID from the output of this command in dom0 terminal:

qvm-pci ls | grep sys-net

Then run the commands below in dom0 terminal but replace xx_xx.x with DEVID of your network card:

qvm-pci detach sys-net dom0:xx_xx.x
qvm-pci attach -o no-strict-reset=True --persistent sys-net dom0:xx_xx.x

If it won’t work then try to use pci=nomsi kernel option for sys-net:

4.2-RC4: WiFi stopped working in sys-net

Probably worth explaining: qvm-prefs -- sys-net kernelopts displays the current kernel options used by sys-net some-name=$(some-command) stores the output of some-command in a variable named some-name. The content of that variable can later be recalled as $some-name. && allows to chain two commands. The second will run once the first succeeds. qvm-prefs -- sys-net kernelopts "option1=some-value option2=some-other-value" is different from the first item in this list, because there is a list of…

And only use permissive=true as your last resort if nothing else works.