[libvirt-users] What's the meaning of sub-element <ip address='X.X.X.X'> in <interface type='bridge'> of domain xml?

Hi guys, I saw this sub-element in http://libvirt.org/firewall.html, there is some confusion, what's the meaning of sub-element <ip address='X.X.X.X'> in <interface type='bridge'> of domain xml? The detail <interface> in domain xml as below: <interface type='bridge'> <mac address='52:54:00:56:44:32'/> <source bridge='br1'/> <ip address='10.X.X.X'/> <===it's my question <target dev='vnet0'/> <model type='virtio'/> <filterref filter='clean-traffic'/> </interface> Is it static IP(specified by customer) in guest OS? or a IP of interface(e.g. eno1) in "br1" on host machine? what's definition about it? [root@localhost src]# brctl show bridge name bridge id STP enabled interfaces br1 8000.24be051881ce no eno1 If you know how to use it, please show me a detail scenario. Thanks, Jianwei