I asked a similar question here but I messed up logging in with my SE account and so I can't edit it.
Here is what I would specifically like to achieve with libvirt under the "Internal Network" heading.
A comment in the previous question mentioned Isolated mode, but according to the libvirt wiki:
In this mode, guests connected to the virtual switch can communicate with each other, and with the host. However, their traffic will not pass outside of the host, nor can they receive traffic from outside the host.
The diagram shows the virtual switch between the host and guests, but I want to have a similar configuration to the virtualbox diagram linked above, with one VM1 having 2 NICs of an internal network and a bridge (NAT in the picture but bridged is preferable).
Does the first answer apply here still given my more specific explanation? It seems like a bridge of this sort would not exactly do what I want. Should I do a VLAN instead?