Comment 5 for bug 1724441

I managed to get this working in the end. Turns out that despite using the libvirt/qemu user session for the VMs, gnome-boxes actually uses the *system* libvirt network named "default" for networking so it works "out of the box". In reality, I had to delete that network and re-create it using virt-manager before it actually started bridging traffic to my physical connection.

See this blog post and the comments: http://blog.wikichoon.com/2016/01/qemusystem-vs-qemusession.html for more information.

So to fix this, at a minimum gnome-boxes should depend on libvirt-daemon-system so that the "default" network is running and attendent virbr0 interface is created at startup, and whichever libvirt package is responsible for creating that network needs to ensure it bridges to all physical devices by default.