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Setting up a wireless virtualisation host with Debian Squeeze and KVM

At the moment, I have two 'servers' on my attic. A file server, which is an old laptop running Freenas 8, and a server for printing, scanning and backups, which is a 10 year old PC running Ubuntu Server 10.04.

Since I don't have ethernet cables to the attic, the print server is accessable via wifi. I connected the print server to the file server with a cable, and to access the file server, I just route the traffic through the print server.

Now I want to replace those two servers on the attic by one virtualization host, which will at first just run a virtual copy of the servers I have right now.

For this virtual host, I have a 6 year old PC with 64-bit AMD processor, 1 GB ram and 150 GB disk space. This should be enough for my needs atm. I can always add more ram over time if needed.

UPDATE:Freenas used to be a lightweight file server. It isn't any more since version 8. Certainly don't use zfs as file system on your low end machine. Open Media Vault is probably a better file server solution.

UPDATE: I have upgraded to a 3.2-kernel, which makes adding a non-access-point wireless interface to a bridge impossible. So I created another subnet for the virtual machines, as described in the remarks below. Which makes the ebtables thing irrelevant.

UPDATE: Although it worked quite well (at last), I connected my virtual host to the wired network some day ago. Which makes things a lot easier and more stable. See comment below.

I'm not sure wheter it will work. Right now I have one virtual server ready to use, I'm still experiencing some network problems, and I am not sure whether what I am trying will actually work. But I'll keep you updated. This is what I did so far:

Setting up the Debian server

I set up a very basic Debian installation for the virtualization host. I used the 64-bit netinstall CD, to install only the basic system tools. No graphical environment, since the resources of my 'server' are limited. I created a large partition for virtual disk files, which I mounted under /vdisks.

My server has no space for PCI-cards (only mini-PCI), I don't have a mini-PCI wireless card, so I will be using a Linksys WUSB54GC usb wireless adapter I had lying around.

(Note: I will have to search for something else, because after some time the wireless card just stops working.)

To enable wireless networking, I had to install wireless-tools and wpasupplicant, because my network is secured with WPA-PSK authentication. I also needed a driver for the network card, so I had to enable the non-free repositories, and after that I could install firmware-ralink. With all those packages installed, enabling the wireless networking was a piece of cake.

Then I installed the tools for running and managing virtual machines on the command line: qemu-kvm, libvirt-bin and virtinst. Because the virtual hosts will be accessed using the wireless network, we will also need ebtables.

Setting up the bridge

Because the virtual machines will have to be accessible from my wireless lan, I need to configure a network bridge on the host, which will bridge the wireless card on the host to the virtual network interfaces of the guests. Configuring a bridge on a Debian system is very easy, but not if one of the interfaces has to use WPA-PSK. After a lot of trial and error, I got it working with this /etc/network/interfaces:

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
#allow-hotplug eth0
iface eth0 inet dhcp

auto wlan0
iface wlan0 inet static
      wpa-ssid **MySsid**
      wpa-psk **MyPsk**

iface br0 inet static
      bridge_ports wlan0
      bridge-stp off
      bridge-maxwait 5

As you can see, I used static IP-addresses, I think I had troubles when using dhcp. I had to start wlan0 first, and then br0, probably because the network card has to associate to the access point. The configuration above only starts wlan0, but I start br0 in /etc/rc.local, by adding the following line:

ifup br0

Installing a virtual FreeNAS server

To set up the virtual file server, I used this command:

virt-install --connect qemu:///system -n gobelijn -r 256 --disk path=/vdisks/gobelijn/gobelijn01.img,size=2 --disk path=/vdisks/gobelijn/gobelijn02.img,size=40 -c /vdisks/iso/FreeNAS-8.0.3-RELEASE-x64.iso --vnc --noautoconsole --os-type unix --os-variant freebsd7 --network=bridge:br0 --hvm

This creates a system with 256 MB ram, a disk of 2 GB for the OS and a disk of 40 GB for the data. It boots from the FreeNAS-iso, which I placed on /vdisks/iso/FreeNAS-8.0.3-RELEASE-x64.iso. The virtual server is called ‘Gobelijn’, I tend to choose characters of comic strips as server names at home. I ran the command as root, because it didn't work with a user in the kvm-group.

Now the new virtual server is booted, but of course I couldn't see what was happening. Since there is no graphical environment installed on the server, I needed another computer to connect to it. I installed virt-viewer on there, and connected as follows:

virt-viewer --connect qemu+ssh://root@ gobelijn

For some or another reason, I had to enter the password twice. It should probably work with a non-root user as well, still have to try it out.

After the installation, instead of rebooting, the system just shuts down. I restarted it by issuing these commands on the virtual machine host:

virsh --connect qemu:///system
start gobelijn

... and it didn't work. The virtual guests didn't recognize it's virtual network card. Luckily, this is a known problem, you can fix it by changing the network device type in the appropriate configuration file in /etc/libvirt/qemu. I had to replace the line <model type='ne2k_pci'/> in the xml (under devices, interface), and change it to <model type='rtl8139'/>.

After rebooting the virtual machine, it had a network interface.


... but it still didn't work. I could connect from the virtual guest to the virtual host and vice versa, but I couldn't connect the virtual host from other machines in the same subnet. The cause seems to be that wireless routers reject network packages with source mac-addresses that didn't authenticate.

This can be fixed with ebtables, as described in the Debian wiki. I just did what's described in there: I entered

ebtables -t nat -A POSTROUTING -o wlan0 -j snat --to-src $MAC_OF_BRIDGE --snat-arp --snat-target ACCEPT

and used the script

# addcomputer
# Will Orr - 2009


function add_ebtables () {

  ebtables -t nat -A PREROUTING -i $INIF -p IPv4 --ip-dst $COMPIP -j \
dnat --to-dst $COMPMAC --dnat-target ACCEPT
  ebtables -t nat -A PREROUTING -i $INIF -p ARP --arp-ip-dst $COMPIP \
-j dnat --to-dst $COMPMAC --dnat-target ACCEPT

if [[ $# -ne 2 ]]; then
  echo "Usage: $0 ip mac"
elif [[ $(whoami) != "root" ]]; then
  echo "Error: must be root"
  add_ebtables $1 $2

to change the source mac address from source packages from the virtual guest. I saved the rules using

EBTABLES_ATOMIC_FILE=/root/ebtables-atomic ebtables -t nat --atomic-save

and load them at boot time by adding this to /etc/rc.local:

EBTABLES_ATOMIC_FILE=/root/ebtables-atomic ebtables -t nat --atomic-commit


Now I still want to start the guest automatically when the host boots. Normally this can be done with virsh autostart gobelijn, but that doesn't work, probably because the hack of starting the bridge in /etc/rc.local. So I just start the virtual guest in /etc/rc.local as well, by adding

sleep 4
virsh start gobelijn



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