[Mashiro]

Neither the staff nor the VPS owner have access to vzctl because this is a administrative tool that is only available to the hosting provider with access to the physical host node.

So my point stands. If you break the network by installing a network manager (either on purpose or by accident through other packages) and you don't have control panel access: only staff can fix the issue by applying simple commands to either stop, disable or remove the network manager. If you have control panel access you can fix it yourself using the emergency SSH access that is provided in the control panel.

A OpenVZ VPS gets its network adapters configured at boot by the host node settings for that VPS. The network manager starts afterwards and breaks the configuration that was applied by OpenVZ. Therefore the VPS network simply stops working until the network manager is disable or removed. After that you have to reboot the VPS once so that OpenVZ can apply the correct network adapter settings again.

OpenVZ is limited in many regards and network is one part. You can't do much more advanced stuff because the way the OpenVZ networking stack works is too limited to support necessary features and the kernel is simply too old. The other part is a limited firewall where a lot of modules are disable (fortunately a part can be enable by the hosting provider if they feel like it).