virtualbox.org

I was using libvirt till now, and there you just specify the bridge name, br0, on the vm conf file and, when vm boots, a vnetx interface is automatically created.

Now I'd like to pass to virtualbox, because libvirt isn't suited to my needs, but looking at tutorials they all convey that vnetx interfaces have to be created prior to vbox booting and this trounbles me,

I explain you my problem: I need to migrate VMs. So, if a VM is attached to vnet0 on the first host I would need to find a vnet0 interface on the host2 too...and I don't like that because I would need to create interfaces just because *maybe* a VM will be migrated to me.

I'm not certain what libvirt is, and why there's a need to make "vnet" interfaces with it. But there's command-line VBoxManage commands for doing just about everything one can do to Virtualbox and the guests. And one could make a batch file to run a series of Vboxmanage commands then start the guest. That might do what you need.