Install the lxc and the debootstrap packages:

# pacman -Sy lxc debootstrap 

I will install Ubuntu 14.04 LTS. Therfore, I will use the trusty release. If you want to install Ubuntu 12.04 LTS, use the precise release.

I create an LXC container named trusty with the release trusty:

# lxc-create --name=trusty --template=ubuntu -- --dist ubuntu --release trusty --arch amd64

Install the libvirt package because we need the virsh program.

# pacman -Sy libvirt

Start and enable the libvirtd daemon.

# systemctl start libvirtd
# systemctl enable libvirtd

Print the virtual network configuration default provided by libvirtd.

# virsh net-dumpxml default
<network>
  <name>default</name>
  <uuid>f9f9128b-8183-4c2c-af56-23cd52100d3a</uuid>
  <forward mode='nat'/>
  <bridge name='virbr0' stp='on' delay='0'/>
  <mac address='52:54:00:8d:ea:7f'/>
  <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>

Edit the file /var/lib/lxc/trusty/config to set-up the network configuration of the container:

lxc.network.type = veth
lxc.network.flags = up
lxc.network.name = eth0
lxc.network.link = virbr0

Setup the virb0 interface:

# virsh net-start default

Start the Ubuntu container as follow:

# lxc-start --name trusty

Get the IP of the Ubuntu container:

# lxc-ls -f trusty -F IPV4

You can stop the Ubuntu container as follow:

# lxc-stop --name trusty

Edit the default virtual network provided by libvirtd to restrict the DHCP range from 192.168.122.2-192.168.122.254 to 192.168.122.10-192.122.254.

# virsh net-edit default

as follow:

<network>
  <name>default</name>
  <uuid>bd881c3e-406f-40bb-84ed-b09e68f210e2</uuid>
  <forward mode='nat'/>
  <bridge name='virbr0' stp='on' delay='0'/>
  <mac address='52:54:00:2d:23:30'/>
  <ip address='192.168.122.1' netmask='255.255.255.0'>
    <dhcp>
      <range start='192.168.122.10' end='192.168.122.254'/>
    </dhcp>
  </ip>
</network>

Restart the libvirtd daemon:

# systemctl restart libvirtd

Stop the the trusty container:

# lxc-stop --name trusty

Add the following line in the file /var/lib/lxc/trusty/config:

lxc.network.ipv4 = 192.168.122.2

Restart the trusty container.

# ssh ubuntu@192.168.122.2

The password is ubuntu.