It depends on the distribution you are using how to configure these, below you'll find examples for RHEL/CentOS and Ubuntu.
The required packages were installed when libvirt was installed, we can proceed to configuring the network.
First we configure eth0
vi /etc/sysconfig/network-scripts/ifcfg-eth0
Make sure it looks similair to:
DEVICE=eth0
HWADDR=00:04:xx:xx:xx:xx
ONBOOT=yes
HOTPLUG=no
BOOTPROTO=none
TYPE=Ethernet
We now have to configure the three VLAN interfaces:
vi /etc/sysconfig/network-scripts/ifcfg-eth0.100
DEVICE=eth0.100
HWADDR=00:04:xx:xx:xx:xx
ONBOOT=yes
HOTPLUG=no
BOOTPROTO=none
TYPE=Ethernet
VLAN=yes
IPADDR=192.168.42.11
GATEWAY=192.168.42.1
NETMASK=255.255.255.0
vi /etc/sysconfig/network-scripts/ifcfg-eth0.200
DEVICE=eth0.200
HWADDR=00:04:xx:xx:xx:xx
ONBOOT=yes
HOTPLUG=no
BOOTPROTO=none
TYPE=Ethernet
VLAN=yes
BRIDGE=cloudbr0
vi /etc/sysconfig/network-scripts/ifcfg-eth0.300
DEVICE=eth0.300
HWADDR=00:04:xx:xx:xx:xx
ONBOOT=yes
HOTPLUG=no
BOOTPROTO=none
TYPE=Ethernet
VLAN=yes
BRIDGE=cloudbr1
Now we have the VLAN interfaces configured we can add the bridges on top of them.
vi /etc/sysconfig/network-scripts/ifcfg-cloudbr0
Now we just configure it is a plain bridge without an IP-Adress
DEVICE=cloudbr0
TYPE=Bridge
ONBOOT=yes
BOOTPROTO=none
IPV6INIT=no
IPV6_AUTOCONF=no
DELAY=5
STP=yes
We do the same for cloudbr1
vi /etc/sysconfig/network-scripts/ifcfg-cloudbr1
DEVICE=cloudbr1
TYPE=Bridge
ONBOOT=yes
BOOTPROTO=none
IPV6INIT=no
IPV6_AUTOCONF=no
DELAY=5
STP=yes
With this configuration you should be able to restart the network, although a reboot is recommended to see if everything works properly.
Make sure you have an alternative way like IPMI or ILO to reach the machine in case you made a configuration error and the network stops functioning!