First of all, you’ll have to check the permissions on the device /dev/net/tun . The user running VirtualBox with bridged networking needs to have access to this device. The easiest way to do this is by chown’ing the group vboxusers to it:

sudo chown :vboxusers /dev/net/tun
sudo chmod 0660 /dev/net/tun

You will also have to install the package bridge-utils and uml-utilities:

sudo apt-get install bridge-utils uml-utilities

Now we will create 2 scripts which are executed when the virtual machine starts/stops. I will create those scripts in my home dir. Here is the start script, I called it starttun.sh:

#!/bin/bash
brctl addbr br0
ifconfig eth0 0.0.0.0
brctl addif br0 eth0

#if you have a dhcp-server uncomment this line:
#dhclient3 br0

#If you have a static IP uncomment the following lines and

#change the IP accordingly to your subnet:
#ifconfig br0 192.168.178.5 up
#route add default gw 192.168.178.1

#Now we will create the tap device for the vm,!

# change your username accordingly
tunctl -t tap0 -u simon

#Now add the tap-device to the bridge:
ifconfig tap0 up
brctl addif br0 tap0

Now you’ll have to create the stop script, i called it stoptun.sh

#!/bin/bash
#bring the interfaces down
ifconfig tap0 down
ifconfig br0 down
brctl delif br0 tap0
brctl delbr br0

#now setup your network-interface again
#for dhcp uncomment the following line
#dhclient3 eth0

#For a static IP uncomment the following lines and change them accordingly:
#ifconfig eth0 192.168.178.5
#route add default gw 192.168.178.1 dev eth0

Finally you’ll have to make the scripts executable:

sudo chmod ug+x starttun.sh
sudo chmod ug+x stoptun.sh

It’s time to set up VirtualBox to use the interface. For this go to the SetUp of your Virtual Machine under Network and tell VirtualBox to start/stop thescripts, when the VM is started/stopped. To do this, select “Host Interface” under Attached To. As Interface Name you use “tap0″ and for the startscript you use:

“gksudo /home/YOURHOMEDIR/starttun.sh”

For the stopscript accordingly:

“gksudo /home/YOURHOMEDIR/stoptun.sh”

Note: If you use KDE, you’ll have to use kdesu instead of gksudo