libvirtd can't create virtual network if sys-apps/iproute2 is not installed. When libvirtd create virtual network interface (virbr0), it called /sbin/ip command. But sys-apps/iproute2 is not mandatory for app-emulation/libvirt. Maybe it is a mistake in ebuild: virt-network? ( net-dns/dnsmasq >=net-firewall/iptables-1.4.10 net-firewall/ebtables sys-apps/iproute2 )" All this packages are mandatory for libvirt virtual networks. Reproducible: Always Steps to Reproduce: 1.install app-emulation/libvirt (if sys-apps/iproute2 is not installed) 2. /etc/init.d/libvirtd start 3. virsh net-start default at this step libvirt fails
"net-start default" is the exactly network that the USE=virt-network setting is for. Enable the USE flag if you want to use that type of setup.