Well, if you ask me if you should use these commands, you probably won't solve it yourself :-/.
These tools are for basic Linux network diagnostics only.
You need to find more information about them yourself about their use (there are a lot of these manuals on the internet - they are also known as "man-pages").
Ok thank you, I will be near the box on weekend and I will use those commands and come back with feedback.
But I'm also wondering if I stop to use OpenVPN and keep only ZeroTier, if is it possible to use ZeroTier as a VPN and have it changing my external IP of all the devices connected to his network...