How to create "internal network" using libvirt/QEMU/KVM stack

In Virtual Box there is a network type "Internal Network", which is where two or more VMs can communicate with each other only. No network connection to the host or other machines. This is the kind of network I need. Using libvirt I was able to set up an "Isolated Network". According to the libvirt docs "In this mode, guests connected to the virtual switch can communicate with each other, and with the host". This doesn't quite work for me as I need network isolation from the host. Does anyone know how to accomplish this using libvirt? I tried following along with this link and creating a virtual private bridge but couldn't get it to work. https://www.linux-kvm.org/page/Networking