changing KVM network interface cause net issue

[peyoot]

My host PC's virt manager is 0.9.5.
I have a CentOS 6.7 installed as a KVM vm. When I was install it. I use default "virtual network 'default': NAT" as network interface.
After I finished installation. I need to change it to bridge as I have a public IP need to apply on it.
But when I use "Host device eth0:macvtap" as source device in bridge mode. I boot in and maualy configure the static IP address
ifconfig and ip addr will show the ipaddress, But it can't ping through to itself and other public IP. ie those ip address is unreachable and network is completely unaccessible.

I wonder what cause it and how to fix it? checking with /etc/udev/rules.d/70-persistent-net.rules don't seem anything dis-match and shoudn't it just affected by this file and the /etc/sysconfig/network-scripts/ifcfg-eth0?