How to restrict internet access in VirtualBox and only allow to a specific IP?

Question

VPN

VPN installed on VirtualBox.
How to allow access only to the VPN so that when the connection is broken, the traffic does not go past the VPN?

Answer 1

Exit outside through a virtual machine?
Primary system with hypervisor - Windows? Maybe also Windows 10? If that's the case, then it's all over-the-top. Do the opposite. The hypervisor on Linux on it also raises VPN and DNS, and only inside the virtual machine it is better to run Linux, but you can also Windows. Configure the firewall on the host system so that by default it blocks all incoming and outgoing traffic. Then slowly let go. In this case, the traffic is filtered out very simply.
There are specially sharpened Linux distributions for such purposes. For example WHONIX.
There are two virtual machines, one client another serves as a gate. But all this can be done independently on any full-fledged Linux distribution.
Another possibility is to take a router that can flash OpenWRT on it to raise a VPN computer to connect to it. This option is the most reliable. The router, of course, also needs to be configured so that when the VPN crashes, it does not throw out the packet in the clear.
On Linux, in order for traffic not to bypass VPN, you need to write rules for interfaces. We block all outgoing traffic except for the address to the VPN server and even register the port in the rule. And the rest of the traffic, including DNS, is allowed through the TUNx interface. All this is very simple. But I don’t know how to do this on Windows, especially using OpenSource firewalls, I’m looking for an answer myself.
But the question is too general. There will be specific questions and there will be specific answers.