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2.5.5. Configure the network bridges

Warning

This is a very important section, please make sure you read this thoroughly.
In order to forward traffic to your instances you will need at least two bridges: public and private.
By default these bridges are called cloudbr0 and cloudbr1, but you do have to make sure they are available on each hypervisor.
The most important factor is that you keep the configuration consistent on all your hypervisors.

2.5.5.1. Network example

There are many ways to configure your network. In the Basic networking mode you should have two (V)LAN's, one for your private network and one for the public network.
We assume that the hypervisor has one NIC (eth0) with three tagged VLAN's:
  1. VLAN 100 for management of the hypervisor
  2. VLAN 200 for public network of the instances (cloudbr0)
  3. VLAN 300 for private network of the instances (cloudbr1)
On VLAN 100 we give the Hypervisor the IP-Address 192.168.42.11/24 with the gateway 192.168.42.1

Note

The Hypervisor and Management server don't have to be in the same subnet!

2.5.5.2. Configuring the network bridges

It depends on the distribution you are using how to configure these, below you'll find examples for RHEL/CentOS and Ubuntu.

Note

The goal is to have two bridges called 'cloudbr0' and 'cloudbr1' after this section. This should be used as a guideline only. The exact configuration will depend on your network layout.
2.5.5.2.1. Configure in RHEL or CentOS
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.

Warning

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!
2.5.5.2.2. Configure in Ubuntu
All the required packages were installed when you installed libvirt, so we only have to configure the network.
vi /etc/network/interfaces
Modify the interfaces file to look like this:
auto lo
iface lo inet loopback

# The primary network interface
auto eth0.100
iface eth0.100 inet static
    address 192.168.42.11
    netmask 255.255.255.240
    gateway 192.168.42.1
    dns-nameservers 8.8.8.8 8.8.4.4
    dns-domain lab.example.org

# Public network
auto cloudbr0
iface cloudbr0 inet manual
    bridge_ports eth0.200
    bridge_fd 5
    bridge_stp off
    bridge_maxwait 1

# Private network
auto cloudbr1
iface cloudbr1 inet manual
    bridge_ports eth0.300
    bridge_fd 5
    bridge_stp off
    bridge_maxwait 1
With this configuration you should be able to restart the network, although a reboot is recommended to see if everything works properly.

Warning

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!