ubuntu add default network(nat) to libvirt

Every standard libvirt installation provides NAT based connectivity to virtual machines out of the box. This is the so called 'default virtual network'. You can verify that it is available with:

# virsh net-list --all

Name                 State      Autostart 

-----------------------------------------

default              active     yes

If it is missing, then the example XML config can be reloaded & activated:

If there is not networks folder in the path /usr/share/libvirt create it:

sudo mkdir /usr/share/libvirt/networks

then create a file which name is defalt.xml and change its mod:

cd /usr/share/libvirt/networks

sudo touch default.xml

sudo chmod 777 default.xml

edit the default.xml,add default network:

<network>

   <name>default</name>

   <bridge name="virbr0" />

   <forward/>

<ip address="192.168.122.1" netmask="255.255.255.0">

     <dhcp>

       <range start="192.168.122.2" end="192.168.122.254" />

     </dhcp>

   </ip>

</network>

Now that the xml file has been created, we can use virsh net-define to define it.

# virsh net-define /usr/share/libvirt/networks/default.xml

Network default defined from /usr/share/libvirt/networks/default.xml

And we can see the network show up in virsh net-list:

# virsh net-list --all

Name                 State      Autostart

-----------------------------------------

default              inactive     no             

But as can be seen above, the network is not active, nor set to autostart. So let’s do that:

# virsh net-autostart default

Network default marked as autostarted

# virsh net-start default

Network default started

see it:

# virsh net-list

Name                 State      Autostart

-----------------------------------------

default              active     yes       

references:

Adding networks to libvirt: http://serverascode.com/2014/04/26/adding-networks-libvirt.html

wiki libvirt using QEMU/KVM with libvirt on Ubuntu: http://wiki.libvirt.org/page/UbuntuKVMWalkthrough

wiki libvirt Networking: http://wiki.libvirt.org/page/Networking