Always wanted to now how to add interfaces (VLANs or bridges) to your Linux hypervisor without dealing with the distribution specific network configuration to serve guest networks ?

Just use libvirt or its command line tool virsh to accomplish this tutorial.

First create a XML file containing your physical network layout. In this example I have a bonded Ethernet interface (bond0) and create a new Ethernet interface bond0.10 which tags the Ethernet traffic to VLAN ID 10. It is just a arbitrary number in this example but I always suggest to tag all VM guest traffic using a bridge. Ideally those bridges are running on top a bonding interface which is sometimes called teaming. Using the Linux bonding driver you can aggregate multiple interfaces to a logical interfaces which can enhance bandwidth. Your switch should support IEEE 802.3AD aggregation protocols like LACP otherwise I recommend to use active-passive bonding to enhance reliability against NIC or switch failures.

<interface type='bridge' name='br10'> 
  <start mode='onboot'/> 
  <bridge> 
    <interface type='vlan' name='bond0.10'> 
      <vlan tag='10'> 
        <interface name='bond0'/> 
      </vlan> 
    </interface> 
  </bridge> 
</interface>

Finally create your libvirt/Linux interface

sudo virsh iface-define br10.xml
sudo virsh iface-start br10


Now adding a libvirt network using this XML file. I just create a network called vlan10 and connect it to the previous created bridge.

<network connections='1'>
 <name>vlan10</name>
 <forward mode='bridge'/>
 <bridge name='br10' />
</network>
 

Time to assemble your libvirt network.

sudo virsh net-define vlan10.xml
sudo virsh net-start vlan10
sudo virsh net-autostart vlan10


If everything is done right just check it using virsh again :

virsh # iface-list
Name State MAC Address
--------------------------------------------
bond0 active 00:1d:09:70:a5:a2
br10 active 00:1d:09:70:a5:a2
lo active 00:00:00:00:00:00

virsh # net-list

Name State Autostart Persistent
-------------------------------------------------
default active yes yes
vlan10 active yes yes

virsh # net-info vlan10
Name vlan10
UUID a19fa2be-161a-f7cc-a776-e645a990eee2
Active: yes
Persistent: yes
Autostart: yes
Bridge: br10

For the RedHat or CentOS guys who want to know how bonding interfaces can be created, just add the file  ifcfg-bond0 (the number must be incremented with every new interface)

DEVICE=bond0
TYPE=Ethernet
BOOTPROTO=none
ONBOOT=yes
BONDING_OPTS="mode=1 miimon=100"

Finally assign multiple Ethernet interfaces, at least one for mode 1 (active-passive), to this bonding device by adding the following lines in each ifcfg-ethX file:

SLAVE="yes"
MASTER="bond0"