Now - many months later I have run into a dilemma with VirtualBox. I want to have two virtual machines running (simultaneously) which can both access the network using IP addresses which they have obtained through DHCP. Setting up a single workstation proved to be quite a challenge, and two required a lot of reading and digging. VMWare definitely makes virtual networking easier - at least on the Windows side of things. I am, of course, running Ubuntu Linux natively and virtualizing all my Windows Operating Systems with VirtualBox.
Here is the script, which made this all possible for me - with comments to follow. In this example, I have TWO physical network cards. eth0, and eth1. eth0 connects my host (the Linux box) to one network for Internet connectivity, etc. in Linux. eth1 is connected to our production network, and will be used solely for my virtual guests.
Note: You will need to install uml-utilities and bridge-utils first. Do that with: sudo apt-get install uml-utilities bridge-utils.
modprobe tun
tunctl -t tap0 -u ballantynesd
brctl addbr br0
ifconfig eth1 0.0.0.0 promisc
brctl addif br0 eth1
ifconfig eth1 up
dhclient br0
brctl addif br0 tap0
ifconfig tap0 up
chmod 0666 /dev/net/tun
# This was added Apr 22 2008
tunctl -t tap1 -u ballantynesd
brctl addif br0 tap1
ifconfig tap1 up
echo 1 > /proc/sys/net/ipv4/conf/tap0/proxy_arp
echo 1 > /proc/sys/net/ipv4/conf/tap1/proxy_arpThe above was saved into a file, which should be run as root *before* starting VirtualBox. You can do this with a 'sudo vboxup.sh', or similar. Exchange 'ballantynesd' with the user name that you are running with on your Linux box. Exchange eth1 for your production NIC, whatever that happens to be.
To complete setting up your virtual guests, you will need to shut them down, open up the settings for them, browse to network settings. Change from "NAT" to "Host", and in the lower area set the network card to tap0 or tap1. Leave the rest alone!
With luck, and prayer - you should be able to boot up your virtual machine and obtain an IP with DHCP (or assign one statically if you like).
Good luck! Give me a shout if this should help you out.
-Steve Ballantyne
EDIT: 05/08/2008
It seems that an upgrade to Ubuntu 8.04 LTS, and an upgrade to the new "Sun" branded VirtualBox 1.6.0 ... is not a good idea. I have tried for the past two days to make things work as documented. Namely, the nice little bridge that I had going on. Following the prescribed documentation got me nowhere, so I reverted back to configuring my interfaces "the old fashioned way" and used the above script. My new script is for a single Virtual Box, and it looks a little something like this ...
As stated earlier - this script must be run with 'sudo'.
# Don't need these, so they die
ifconfig vbox0 down
ifconfig eth1 down
# Throw up a bridge
brctl addbr br0
# Add my main card to the bridge
brctl addif br0 eth0
ifconfig eth0 0.0.0.0 promisc
# Bridge goes up
ifconfig br0 up
# Bridge obtains an IP address
dhclient br0
# Give me a virtual adapter
modprobe tun
tunctl -t tap0 -u ballantynesd
# Add the adapter to the bridge
brctl addif br0 tap0
chmod 0666 /dev/net/tun
ifconfig tap0 up
Good luck!!
