virsh net-edit default
<ip address='192.168.122.1' netmask='255.255.255.0'>
<tftp root='/livenet/boot'/>
<dhcp>
<range start='192.168.122.2' end='192.168.122.254'/>
<bootp file='/pxelinux.0'>
</dhcp>
</ip>
virsh net-destroy default virsh net-start default