I would like to test my VPN for leaking but don't want to be limited to testing it in a small time window like some of those VPN leak testing websites do.

Can I just turn on my VPN, then also run iftop on the CLI (Ubuntu), and then use my computer normally all day and see if shows anything other than the VPN and network IPs? Or is there something I'm missing?

1 Answer 1


If you have a local e.g. Wi-Fi router and devices connected to it, e.g. smartphones, you will definitely see some local "leaked" traffic except it's not leaking, it's just local and it should belong to your local net, e.g. Your ISP shouldn't see this traffic as it shouldn't leave the confines of your LAN.

VPN leaking primarily concerns your DNS requests - in order to avoid this you have several options:

  • Set-up DoT (DNS over TLS) for your DNS resolver - this can be trivially done for systemd-resolved. Do not use network/DHCP provided DNS servers in this case. For Network Manager that would be "IPv4 Settings" -> Method -> "Automatic DHCP addresses only" and set DNS servers to
  • Enable DoH (DNS over HTTPS) for your web browser - Firefox has this in "Network Settings" -> "Configure how Firefox connects to the internet" -> "Enable DNS over HTTPS". For Google Chrome that would be chrome://settings/security -> "Use Secure DNS".
  • This is a very helpful answer, thank you. I was more concerned about being able to monitor traffic and wondering if the simple "iftop" command would suffice. However, it sounds like if I did what you suggested, it would be foolproof enough that monitoring would not be needed? (Similar to how if i shut off my home's water main, it would not make sense to watch my faucet to see if it leaks) @artem
    – TkqiQvGx
    Nov 30, 2022 at 16:22

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