If a network adapter is enabled in your Virtual Machine configuration, you can connect/disconnect it when running guest OS.
Note: If the guest OS is started with network adapter disabled, you should shut down the OS first, then enable network adapter in the Configuration Editor (select the Enabled checkbox in the Network Adapter Options tab) and restart the guest OS.
To connect or disconnect network adapter, do the following:
Note: There is another way to connect/disconnect network adapter. Right-click network adapter icon
on the status bar to display context menu and select the required command.