====== Open Virtual Switch ======

  * Install package
<WRAP prewrap center>
<code>
# apt-get install openvswitch-switch
</code>
</WRAP>
  * Use em2 for VM network 
<WRAP prewrap center>
<code>
# nano -w /etc/network/interfaces

+ auto em2
+ iface em2 inet manual
+         up ifconfig $IFACE 0.0.0.0 up
+         down ifconfig $IFACE down
</code>
</WRAP>
Reboot or to enable em2 without rebooting
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<code>
# ifconfig em2 up
</code>
</WRAP>

  * Configure virtual bridge
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<code>
# ovs-vsctl add-br br0
# ovs-vsctl add-port br0 em2
</code>
</WRAP>

  * Disable default KVM network
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<code>
# virsh net-destroy default
# virsh net-deactivate default
# virsh net-undefine default
</code>
</WRAP>

  * Define OVS networks for KVM
I.e. em2 network has untagged and tagged VLANs and we need one network for untagged VLAN and one network for tag 33 VLAN\\
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<code>
# nano -w ovs-network-V0.xml
</code>
</WRAP>
<WRAP prewrap center>
<code xml>
<network>
  <name>ovs-network-V0</name>
  <forward mode='bridge'/>
  <bridge name='br0'/>
  <virtualport type='openvswitch'/>
</network>
</code>
</WRAP>
<WRAP prewrap center>
<code>
# nano -w ovs-network-V33.xml
</code>
</WRAP>
<WRAP prewrap center>
<code xml>
<network>
  <name>ovs-network-V33</name>
  <forward mode='bridge'/>
  <bridge name='br0'/>
  <virtualport type='openvswitch'/>
  <vlan>
      <tag id='33'/>
  </vlan>
</network>
</code>
</WRAP>
  * Enable networks for KVM VMs
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<code>
# virsh net-define ovs-network-V0.xml
# virsh net-start ovs-network-V0
# virsh net-autostart ovs-network-V0

# virsh net-define ovs-network-V33.xml
# virsh net-start ovs-network-V33
# virsh net-autostart ovs-network-V33
</code>
</WRAP>
<WRAP prewrap center>
<code>
# virsh net-list

 Name                 State      Autostart     Persistent
----------------------------------------------------------
 ovs-network-V0       active     yes           yes
 ovs-network-V33      active     yes           yes

</code>
</WRAP>
You can use these networks in VM configuration from "Virtual Machine Manager" GUI.