# virsh net-autostart default --desable
# virsh net-destroy default

If you want to use default bridge, do follow commands

# virsh net-start default
# virsh net-autostart default

/etc/virnet/virnet1.xml

<network>
	<name>vnet01</name>
	<bridge name="virbr1" />
	<ip address="192.168.123.1" netmask="255.255.255.0">
	</ip>
</network>

# virsh net-define /etc/virnet/virnet1.xml 
# virsh net-start virnet1

If you want to destroy, do follow commands.

# virsh net-destroy virnet1
# virsh net-undefine virnet1

# virsh net-list
# brctl show

# cat /etc/libvirt/qemu/networks/virnet1.xml
# cat /etc/librt/qemu/networks/autostart/virnet1.xml