aesis05401
September 9th, 2009, 08:41 PM
From experience, leaving your VM without any net connection will get tiresome quickly - especially if you are using network printing or programs that need bug fixes downloaded etc... This advice probably applies most to users who occasionally need to spend a couple days straight inside an MS environment, but don't want to be toggling adapters from within the environment (ie: you want your VM and programs within to act like they are online even when they are not... )
I use brctl and tunctl utilities to create a host bridge and VM client tap connections. I don't actually connect the taps to the bridges until I want the VM to see the rest of the network, but the VM behaves as if it is online because the virtual interface it uses is up the whole time (ie: both VBox and XP display cable connected, but any outbound signals time out because they don't actually go anywhere).
If you do not have brctl or tunctl you can find them through Synaptic.
# Create a fake interface for my VM using tunctl (I will use tap0 as
# the name for my fake interface as per a tutorial I read somewhere):
sudo tunctl -u <your-user-name> -t tap0
# Configure tap0 for operation on your real network for when you want to
# hook it up
sudo ifconfig tap0 <ip-address> ... <any-other-required-settings> up
# Ensure permissions are proper on the /dev/net/tun file
sudo chmod 666 /dev/net/tun
# Open VirtualBox and add tap0 as the network interface for your VM
# Boot Vm - you should see the network connection reported as present
# but you can't actually get out to anywhere.
Now you should set up your host bridge. The following example is just the fastest way to do this as far as set-up goes. You should research promiscuous mode as it has some security side-effects, side-effects on busy LANs, and of course, allows you to sniff and spoof responses to all traffic on your LAN which is what we want for our quick and dirty method:
# Prepare physical interface to join bridge
sudo ifconfig eth0 0.0.0.0 promisc
# Create bridge, add eth0 to bridge
sudo brctl addbr br0
sudo brctl addif br0 eth0
# Dhclient the bridge for host visibility
sudo dhclient br0
So now, unless you need to modify your firewall settings, you are exactly one step away from connecting your VM to the internet.
# Simply enter this command from the host to go online with your VM
sudo brctl addif br0 tap0
# Enter this command from the host to go back offline..
sudo brctl delif br0 tap0
Once you have played around with this I would recommend writing simple scripts to manage everything. I turn off network-manager and use the /etc/interfaces file to make sure my machine boots with no interfaces loaded. Then I use scripts to bring up different interfaces/modify firewall rules depending on what VM's I need to run and how concerned I am about exposure to the internet...
Provided you are not setting up new VM's every day, but only running a few for interop reasons, these scripts should serve you well for a long time. Just be sure to research the various methods of creating a host bridge/managing your physical interfaces, there are advantages and drawbacks to each.
Finally, if you are going to be running VM's and have concerns I would recommend learning about iptables firewall/NAT configuration and log reading. With these tools you can turn your computer into a really nice VM platform w/solid security.
Hope this helps.