The ifconfig of a single server that servers for the whole Openstack looks like this:

br-ext, br-int , eth0, tap per instance (VM) and virbr0.

Q: what is the purpose of the virbr0 and the IP address that appears there , e.g :

virbr0: flags=4099<up,broadcast,multicast> mtu 1500

    inet 192.168.122.1  netmask 255.255.255.0  broadcast 192.168.122.255

    ether fe:4a:e2:35:97:63  txqueuelen 0  (Ethernet)

    RX packets 0  bytes 0 (0.0 B)

    RX errors 0  dropped 0  overruns 0  frame 0

    TX packets 0  bytes 0 (0.0 B)

    TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0