KVM Linux guest cannot get network address

I use libvirt-manager to manager my VMs. I create a new VM, and a default virtual network, which uses NAT. **virsh net-edit default** gives me: default ec2b5979-dd0c-43db-ab16-99f2e48ef0dd I have configured my Linux guest to use this network, and the device is set to **rtl8139**. After I started the VM, it can see the device, but it cannot get network address. **brctl show** gives me: bridge name bridge id STP enabled interfaces virbr0 8000.5254000eb14f yes virbr0-nic **ip link show** gives me: 1: lo: mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1 link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 2: wlan0: mtu 1500 qdisc pfifo_fast state UP mode DORMANT group default qlen 1000 link/ether c8:ff:28:78:44:01 brd ff:ff:ff:ff:ff:ff 3: virbr0: mtu 1500 qdisc noqueue state DOWN mode DEFAULT group default qlen 1000 link/ether 52:54:00:0e:b1:4f brd ff:ff:ff:ff:ff:ff 4: virbr0-nic: mtu 1500 qdisc pfifo_fast master virbr0 state DOWN mode DEFAULT group default qlen 1000 link/ether 52:54:00:0e:b1:4f brd ff:ff:ff:ff:ff:ff One odd thing I found is that in "Connection Details"/"Network Interfaces" page, the virbr0 is shown as **inactive**, and I cannot activate it. Trying to activate it gives me: > libvirtError: this function is not supported by the connection driver: virInterfaceCreate