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VirtualBox, Virtual Networking

VirtualBox provides up to four virtual PCI Ethernet cards for each virtual machine.
Each of these adapters can be separately configured in one of the following four
modes:
• Not attached
• Network Address Translation (NAT)
• Host Interface Networking
• Internal Networking
By default, virtual network cards are set up to use network address translation, which
is well suited to standard networking needs (accessing the Internet from programs
running in the guest and providing network services for machines in a local intranet).
In particular, if all you want is to browse the Web, download files and view e-mail
inside the guest then the default configuration of the NAT network should be sufficient
for you, and you can safely skip the rest of this section.

Please note that the ping utility does not work over NAT, and that there are certain limitations when using Windows file sharing.


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For advanced networking needs such as network simulations, host interface networking can be used to set up an additional, software based network interface on the host to which the virtual machine is connected. Finally, VirtualBox internal networking can be used to create a virtual network which is visible to selected virtual machines, but not to applications running on the host or to the outside world. The following sections describe the available network modes in more detail.

“Not attached” mode
When a virtual network card’s mode is set to “Not attached”, VirtualBox reports to the guest that a network card is present, but that there is no connection – as if no Ethernet cable was plugged into the card. This way it is possible to “pull” the virtual Ethernet cable and disrupt the connection, which can be useful to inform a guest operating system that no network connection is available and enforce a reconfiguration.

Network Address Translation (NAT).
Network Address Translation is the simplest way of accessing an external network from a virtual machine. Usually, it does not require any configuration on the host network and guest system. For this reason, it is the default networking mode in VirtualBox.

A virtual machine with NAT networking enabled acts much like a real computer that connects to the Internet through a router. The “router”, in this case, is the VirtualBox networking engine, which maps traffic from and to the virtual machine transparently.
The disadvantage of NAT mode is that, much like a private network behind a router, the virtual machine is invisible and unreachable from the outside internet; you cannot run a server this way unless you set up port forwarding (described below).

The virtual machine receives its network address and configuration on the private network from a DHCP server that is integrated into VirtualBox. The address which the virtual machine receives is usually on a completely different network to the host. As more than one card of a virtual machine can be set up to use NAT networking, the first card is connected to the private network 10.0.2.0, the second card to the network 10.0.3.0 and so on.

The network frames sent out by the guest operating system are received by VirtualBox’s NAT engine, which extracts the TCP/IP data, and resends it using the host operating system. To an application on the host, or to another computer on the same network as the host, it looks like the data was sent by the VirtualBox application on the host, using an IP address belonging to the host. VirtualBox listens for replies to the packages sent, and repacks and resends them to the guest machine on its private network.

As the virtual machine is connected to a private network internal to VirtualBox and invisible to the host, network services on the guest are not accessible to the host machine or to other computers on the same network. However, VirtualBox can make given services available outside of the guest by using port forwarding. This means that VirtualBox listens to certain ports on the host and resends all packages which arrive on them to the guest on the ports used by the services being forwarded.

To an application on the host or other physical (or virtual) machines on the network, it looks as though the service being proxied is actually running on the host (note that this also means that you cannot run the same service on the same ports on the host). However, you still gain the advantages of running the service in a virtual machine – for example, services on the host machine or on other virtual machines cannot be compromised or crashed by a vulnerability or a bug in the service, and the service can run in a different operating system to the host system.

You can set up a guest service which you wish to proxy using the command line tool VBoxManage. You will need to know which ports on the guest the service uses and to decide which ports to use on the host (often but not always you will want to use the same ports on the guest and on the host). You can use any ports on the host which are not already in use by a service. An example of how to set up incoming NAT connections to a ssh server on the guest requires the following three commands:
VBoxManage setextradata "Linux Guest"
"VBoxInternal/Devices/pcnet/0/LUN#0/Config/guestssh/Protocol" TCP
VBoxManage setextradata "Linux Guest"
"VBoxInternal/Devices/pcnet/0/LUN#0/Config/guestssh/GuestPort" 22
VBoxManage setextradata "Linux Guest"
"VBoxInternal/Devices/pcnet/0/LUN#0/Config/guestssh/HostPort" 2222
The name guestssh is an arbitrary one chosen for this particular forwarding config-
uration. With that configuration in place, all TCP connections to port 2222 on the host
will be forwarded to port 22 on the guest. Protocol can be either of TCP or UDP
(these are case insensitive). To remove a mapping again, use the same commands, but
leaving out the values (in this case TCP, 22 and 2222).

It is not possible to configure incoming NAT connections while the VM is running.

However you can change the settings for a VM which is currently saved (or powered off at a snapshot).

Two limitations of NAT networking are that finding Windows shares by browsing is not possible in the default configuration (although they can still be accessed if you know the name or the IP address of the machine that is sharing them) and that the ping utility will not get a response from the host or other machines outside of the private network. Browsing Windows shares requires the guest to receive incoming TCP and UDP connections on ports 135, 137 and 139, so you can enable this by forwarding those ports to the guest, but this will then prevent the host from using them to browse shares. And the ping utility uses ICMP network packages, which can
only be sent by an application with administrator privileges. Since VirtualBox runs as a user application it can not proxy these in NAT mode.
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Introduction to host interface networking.
With Host Interface Networking, VirtualBox creates a new networking interface in software on the host computer. When you connect a guest to it, the host can see the guest through the new network interface as though the interface were connected to the guest’s network card with a network cable. As a result, the guest then behaves like a real computer connected to the network: the host can send data to the guest through that interface and receive data from it. This means that you can set up routing or bridging between the host and the guest.

You can create several VirtualBox host interfaces on the host system (see the following subsections for instructions on how to do so), but each of them can only be connected to a single virtual network card in a single guest at one time. In other words, for each virtual network card that is supposed to use Host Interface Networking, you will need to set up a new interface on the host.

Warning: Please be aware that setting up host interface networking always involves making changes to your host’s network configuration, which can cause the host to lose its network connection. Do not change network settings on remote or production systems unless you know what you are doing.

As there are few limits on the number of setups which can be created using host networking, we will only describe Ethernet bridging for the different host operating system that VirtualBox supports. For more advanced networking needs, we recommend that you consult general documentation about networking on your host operating system.

Ethernet bridging is a way of connecting several network devices together in software, effectively “splitting” a network card into several. With VirtualBox, you will then use the same networking card for your host operating system and your virtual machines. Other computers on your network will then see your guests as though they had their own physical network cards. You will need Ethernet hardware for this as most current wireless network devices do not support bridging.

In some network environments (often company networks), measures are taken to prevent several MAC addresses being used on a single network interface by temporarily blocking communication to that interface. This is intended to prevent certain types of network attacks, but will also prevent bridging setups from working correctly.

Host interface networking on Windows hosts.
When you install VirtualBox on the Windows host, the setup program installs a special networking driver on your system. This driver, the VirtualBox Host Interface NDIS driver, can be used to create additional host interfaces. These must be created explicitly before they can be attached to a virtual machine.

Use the VBoxManage tool to create new host interfaces on your Windows system:
VBoxManage createhostif "VM1 external"
Alternatively you can use the network configuration in the VirtualBox GUI to create and delete host interfaces.
Each new host interface thus created appears as an additional network card in your standard “Network Connections” properties. After you have created your new host interface this way, you can select “Host Interface” as the networking mode in a virtual machine’s Settings window and select the new interface in the “Interface name” dropdown list. With the above example, this drop-down list would contain “VM1 external”.

If your host is running Windows XP or newer, you can also use the built-in bridging feature to connect your host interfaces to your physical network card. After creating the desired host interfaces, select your physical network adapter in the Network Connections folder and the desired host interface adapters and select “Bridge connections” from the popup menu. Note that you have to transfer your network configuration from your physical network adapter to the network bridge as mentioned above, because your physical network adapter will only function as a transport medium in your bridge setup. When more than one connection is active on a bridge, Windows will automatically put your physical Ethernet adapter into promiscuous mode so that it will receive network data for all bridged connections.

Host interface networking on Linux hosts.
Note: There were some changes to the way dynamic host interface configuration is done in VirtualBox 1.4.0, due to changes in Linux kernel versions 2.6.18 and later. Also, this entire section of the manual was rewritten for Virtual 1.4.0. Please reread these sections if you used dynamic interfaces on earlier versions.

Since the Linux kernel has built-in support for virtual network devices (so-called TAP interfaces), VirtualBox on Linux makes use of these instead of providing custom host networking drivers. The TAP interfaces behave like physical network interfaces on your host and will work with any networking tools installed on your host system.

From the point of view of the host, it looks like the guest’s network card is connected to the TAP interface with a network cable. In order to use Host Interface Networking in VirtualBox, you must have access to the device /dev/net/tun. Check which group this device belongs to and make sure that any users who need access to VirtualBox Host Networking are members of this group. In most cases, this device will belong to the vboxusers group.

On Linux hosts, you have a choice of creating permanent networking interfaces which guests can attach to when they are created or having VirtualBox create a dynamic interface for a guest when the guest is started and remove it when the guest is stopped. Permanent interfaces are more suitable for hosts which run a known set of guests which does not change often (such as some server setups), and they are easier to set up. Having VirtualBox create the interfaces dynamically when a virtual machine is started provides more exibility, but will normally require you to enter an administrator password when the interfaces are created and removed.

Since not all popular Linux distributions provide their own methods of creating permanent TAP interfaces, we provide utilities which will do this on most distributions.
If your distribution does provide its own method, we recommend that you use that instead (we provide instructions below for doing this on current Debian and Ubuntu systems). We also provide instructions for setting up a network bridge on Debian, Ubuntu, openSUSE, Fedora and Redhat hosts. If you use a different distribution, please consult the documentation provided with it to find out how to do this.

Permanent host interfaces and bridging.
On Linux hosts, setting up a permanent host interface typically consists of three steps:
1. In most cases, you will want to create a bridge for one of your physical network interfaces, e.g. eth0. This will allow for sharing the same physical interface between the “real” host and the “virtual” host interfaces that you will create for your virtual machines.

The bridging step is not strictly required; you can create a host interface and make a virtual machine use it without having created a bridge (and without having added the host interface to the bridge) first. This may be useful for testing scenarios, or if you have more complex networking setups where you would prefer routing to briding. However, in most cases, you will want to allow a virtual machine to share your physical networking interface, for which bridging
is the most practical way, which is why we describe bridging in the following sections.

Also, keep in mind that briding is an Ethernet concept and therefore unrelated to TCP/IP. In physical networks, bridging is typically used to reduce collisions between many Ethernet hosts. A bridge thus connects two previously unrelated subnetworks.1
2. For each guest network card that uses host interface networking, you must create a new “virtual” host interface (called tap0 or vbox0 or something similar) and add this interface to the bridge.
3. Finally, specify the new host interface in the settings for the virtual network card of a virtual machine.

Unfortunately, Linux distributions differ substantially in their networking configuration. The exact steps how to do this therefore vary depending on the distribution of your host. Below, we will describe the setup procedures for Debian, Ubuntu, Fedora/Red Hat and openSUSE; in addition, we offer some generic instructions for advanced users.
Some distributions – such as Debian and Ubuntu – have build-in tools to create host interfaces; we recommend those built-in tools on those distributions.
For use with other distributions, VirtualBox ships with two utilities, VBoxAddIF and VBoxDeleteIF, which are explained in chapter 6.5.1.5, The VBoxAddIF and VBoxDeleteIF utilities, page 64. These tools allow you to create and delete host interfaces and optionally add them to an existing bridge.
Note: While we have made any attempt to ensure that the below distributionspecific instructions work, we strongly recommend that you look up your distribution’s own documentation about how to set up briding in addition to the below instructions.
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Debian and Ubuntu hosts
To set up a permanent host interface on a Debian or Ubuntu host, follow these steps:
1. On modern Debian and Ubuntu based hosts, you must first install the User Mode Linux utilities package (uml-utilities), which contains tools to create TAP interfaces, as well as the bridge utilities (bridge-utils). package. You can do this from the command line using.

A useful introduction to bridging can be found here: http://gentoo-iki.com/HOWTO_setup_a_
gentoo_bridge. While this is targeted at a Gentoo system, it contains some general introductions.

sudo apt-get install uml-utilities
sudo apt-get install bridge-utils
In order for VirtualBox to be able to access the interface, the user who will be running the virtual machine must be added to the group uml-net, for example with the following command (replace vboxuser with your user name):

sudo gpasswd -a vboxuser uml-net

You may have to log out and log in again for the change to take effect.

2. To describe the TAP interface to your Debian or Ubuntu system, add an entry to the file /etc/network/interfaces. This names the the interface and must also specify the user who will be running the virtual machine using the interface.

The following sample entry creates the interface tap0 for the user vboxuser (again, replace with your user name):

auto tap0
iface tap0 inet manual
up ifconfig $IFACE 0.0.0.0 up
down ifconfig $IFACE down
tunctl_user vboxuser

You will probably want to change the entry based on your networking needs. On the host, you will find more documentation in these files:
a) /usr/share/doc/uml-utilities/README.Debian and
b) /usr/share/doc/ifupdown/examples/network-interfaces.gz.
3. The first time it is used, activate the new interface and the bridge with these two commands:
sudo /sbin/ifup tap0
sudo /sbin/ifup br0

This is only needed once, however; the next time the host is restarted, the interface and the bridge should be activated automatically.
4. Another entry must be added to the file /etc/network/interfaces to describe the bridge. The following sample entry creates a bridge called br0, adds to it all ethernet interfaces on the host as well as the TAP interface created above and tells it to obtain an IP address using DHCP so that the host remains able to access the network.

auto br0
iface br0 inet dhcp
bridge_ports all tap0

Again, you will probably want to change this to suit your own networking needs.
In particular, you may want to assign a static IP address to the bridge, or if you are using TAP interfaces created by VirtualBox (these are described later), you will want to remove tap0 from the last line. On the host, you will find more
documentation in the files

a) /usr/share/doc/bridge-utilities/README.Debian.gz and
b) /usr/share/doc/ifupdown/examples/network-interfaces.gz.

5. To tell VirtualBox to use the interface, select the virtual machine which is to use it in the main window of the VirtualBox application, configure one of its network adaptors to use Host Interface Networking (using “Settings”, “Network”, “Attached to”) and enter “tap0” into the “Interface name” field.

Alternatively, you can use the VBoxManage command line tool (in this example we are attaching the interface to the first network card of the virtual machine “My VM”):

VBoxManage modifyvm "My VM" -hostifdev1 tap0

Bridging on openSUSE hosts.
On openSUSE hosts, we recommend to use the VBoxAddIF utility to create a TAP interface and add it to a bridge.

That leaves open the question how to create bridge on openSUSE; for this, please follow the below instructions. Note that bridging on openSUSE hosts may not work properly if you are using NetworkManager to manage your network connections. To create a bridge on a recent openSUSE host, you must first install the bridge utilities (bridge-utils) package. If you are working from the command line this can be done as follows:

sudo /sbin/yast -i bridge-utils

Then you must create a text file describing the bridge to be created. The name of the file must correspond to the name of the bridge you wish to create. To create the bridge br0, you should call the file /etc/sysconfig/network/ifcfg-br0. Below we have given an example of a file which creates a bridge including the network device eth0, obtains an IP address by DHCP (through the network device) and is started automatically when openSUSE starts. You will probably want to adjust this to match your networking requirements.

BOOTPROTO=’dhcp’
NETMASK=’255.255.255.0’
STARTMODE=’auto’
USERCONTROL=’no’
DHCLIENT_TIMEOUT=30
BRIDGE=’yes’
BRIDGE_PORTS=’eth0’

For this example to work, you will also need to change the configuration for the network interface eth0 to a static IP address of 0.0.0.0, as openSUSE does not do this automatically when the interface is added to the bridge. You can do this using the graphical interface or by changing the following settings in the file /etc/sysconfig/network/ifcfg-eth-xx:xx:xx:xx:xx:xx, where the last part should be replaced with the hardware address of the network card.

BOOTPROTO=’static’
IPADDR=’0.0.0.0’
You can activate the bridge immediately after creating it with the command:

sudo /sbin/ifdown eth0
sudo /sbin/ifup br0

The bridge will be activated automatically from now on when the host is restarted.
Now, to create a permanent host interface called vbox0 (all host interfaces created in this way must be called vbox followed by a number) and add it to the network bridge created above, use the following command:

sudo VBoxAddIF vbox0 vboxuser br0
Replace vboxuser with the name of the user who is supposed to be able to use the
new interface.
To tell VirtualBox to use this interface (vbox0) for a virtual machine, select the
VM in the main window, configure one of its network adaptors to use Host Interface
Networking (using “Settings”, “Network”, “Attached to”) and enter “vbox0” into the
“Interface name” field.
Alternatively, you can use the VBoxManage command line tool (in this example we
are attaching the interface to the first network card of the virtual machine “My VM”:
VBoxManage modifyvm "My VM" -hostifdev1 vbox0


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Bridging on Redhat and Fedora hosts.
On Redhat and Fedora hosts, we recommend to use the VBoxAddIF utility (shipped with VirtualBox; see chapter 6.5.1.5, The VBoxAddIF and VBoxDeleteIF utilities).

As with openSUSE, this leaves open the question how to create bridge on Redhat and Fedora. For this, you must first install the bridge utilities (bridge-utils)
package. Then you must create a configuration file describing the bridge you wish to create. The following is the contents of an example configuration file /etc/sysconfig/network-scripts/ifcfg-br0, which sets the bridge br0 to get its IP address using DHCP and to start automatically when the system is started.

You will probably want to adjust this to match your networking requirements.
DEVICE=br0
TYPE=Bridge
BOOTPROTO=dhcp
ONBOOT=yes
To add the network card eth0 to the bridge, add the following line to the end of
the file /etc/sysconfig/network-scripts/ifcfg-eth0:
BRIDGE=br0

You can activate the bridge immediately after creating it with the command:

sudo /sbin/service network restart

The bridge will be activated automatically from now on when the host is restarted.
Now, to create a permanent host interface called vbox0 (all host interfaces created in this way must be called vbox followed by a number) and add it to the network bridge created above, use the following command:

sudo VBoxAddIF vbox0 vboxuser br0

Replace vboxuser with the name of the user who is supposed to be able to use the new interface.
To tell VirtualBox to use this interface (vbox0) for a virtual machine, select the VM in the main window, configure one of its network adaptors to use Host Interface Networking (using “Settings”, “Network”, “Attached to”) and enter “vbox0” into the “Interface name” field.
Alternatively, you can use the VBoxManage command line tool (in this example we
are attaching the interface to the first network card of the virtual machine “My VM”:
VBoxManage modifyvm "My VM" -hostifdev1 vbox0

Bridging with other distributions.
Most modern Linux distributions provide their own way of setting up ethernet bridges.
We recommend that you follow the instructions provided by your distribution to create the bridge, and the instructions in chapter 6.5.1.5, The VBoxAddIF and VBoxDeleteIF utilities, page 64 to create the host interface if your distribution does not provide its own method.

For distributions which do not provide their own method of creating bridges, we provide generic instructions below. Please ensure that you thoroughly understand how your distribution’s networking scripts work before following these instructions, as they involve making changes to your host network configuration in ways normally only done by the networking scripts, and as such may interfere with your network setup.

First of all, you will need to install the bridge utilities (usually named bridge-utils or similar). Once installed, as root, follow these instructions to create and configure a bridge:

1. Create a new bridge with this command:
brctl addbr br0
2. If you are not using DHCP, run ifconfig and note down the network configuration of your existing network interface (e.g. eth0), which we will need to copy to the bridge in a minute.
3. Switch your physical network adapter to “promiscuous” mode so that it will ac-
cept Ethernet frames for MAC addresses other than its own:

ifconfig eth0 0.0.0.0 promisc

Warning: You will lose network connectivity on eth0 at this point.
4. Add your network adapter to the bridge:
brctl addif br0 eth0
5. Transfer the network configuration previously used with your physical ethernet adapter to the new bridge. If you are using DHCP, this should work:
dhclient br0
Otherwise, run ifconfig br0 x.x.x.x netmask x.x.x.x and use the
values that you noted down previously.
6. To create a permanent host interface called vbox0 (all host interfaces created in this way must be called vbox followed by a number) and add it to the network bridge created above, use the following command:
VBoxAddIF vbox0 vboxuser br0
Replace vboxuser with the name of the user who is supposed to be able to use the new interface.

The VBoxAddIF and VBoxDeleteIF utilities.
The VBoxAddIF and VBoxDeleteIF utilities used in the above instructions (except for Debian and Ubuntu, where we recommend to use the networking configuration that is native to those distributions) are shipped with VirtualBox to make the creation of TAP interfaces easier.

VBoxAddIF creates a permanent TAP interface which does not go away when the host system is restarted and, if a bridge parameter is specified, adds the new interface to the given bridge. This command replaces the tunctl sequences that were described in earlier versions of this manual.

To remove an interface which you have created with VBoxCreateIF previously (vbox0 in the above examples), you can use the following command:

sudo VBoxDeleteIF vbox0

As an alternative to VBoxAddIF and VBoxDeleteIF, you can still use tunctl if you want. We now supply our own version of this command, called VBoxTunctl. To create a new interface, use VBoxTunctl -t tap1 -u vboxuser (with vboxuser being the user name who will be using the interface). You can then add this new interface to a bridge using brctl addif br0 tap1. Don’t forget to bring up the new interface with ifconfig tap1 up.


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Creating interfaces dynamically on VM startup.
As an alternative to the permanent interfaces described previously, you can tell VirtualBox to execute commands (usually scripts) to set up your network dynamically, every time a virtual machine starts or stops. This is normally done in order to create the TAP interfaces at VM startup time, although you can also use this feature to configure existing interfaces. If you are not using permanent interfaces then the startup command should write the name of the interface which it has created, typically something like tap0 or tap2, to its standard output (the VBoxTunctl -b command does exactly this) and the command executed when the machine stops should remove the interface again.

The commands and scripts used will depend on the networking configuration that you want to set up. Both commands are given a file descriptor to the Linux TAP device as their first argument (this is only valid if the virtual machine is using previously created interfaces) and the name of the interface, if it is known, as the second argument.

In most circumstances, you will only want to use the second argument.
Here is an example of a set up script which creates a TAP interface and adds it to the network bridge br0.
#!/bin/bash
# Create an new TAP interface for the user ’vbox’ and remember its name.
interface=‘VBoxTunctl -b -u vbox‘
# If for some reason the interface could not be created, return 1 to
# tell this to VirtualBox.
if [ -z "$interface" ]; then
exit 1
fi
# Write the name of the interface to the standard output.
echo $interface
# Bring up the interface.
/sbin/ifconfig $interface up
# And add it to the bridge.
/sbin/brctl addif br0 $interface

If this script is saved as /home/vbox/setuptap.sh and made executable, it can be used to create a TAP interface when a virtual machine is started, by configuring one of the machines network adapters to use Host Interface Networking (without specifying a device in the “Interface Name” field) and entering gtksudo /home/vbox/setuptap.sh into the “Setup Application” field (replace gtksudo by kdesu, or whatever is appropriate for your system). Alternatively you can use the
the VBoxManage command line tool (in the following example for a machine called
“Linux VM”):

VBoxManage modifyvm "Linux VM" -tapsetup1 "gtksudo /home/vbox/setuptap.sh"

An example of a matching script to remove the interface from the bridge and shut it down would be:
#!/bin/bash
# Remove the interface from the bridge. The second script parameter is
# the interface name.
/sbin/brctl delif br0 $2
# And use VBoxTunctl to remove the interface.
VBoxTunctl -d $2
If this is saved as /home/vbox/cleanuptap.sh and made executable, the virtual machine can be told to execute it when it shuts down by entering gtksudo /home/vbox/cleanuptap.sh, into the “Termination Application” field in VirtualBox’s network configuration settings, or by using VBoxManage:
VBoxManage modifyvm "Linux VM" -tapterminate1
"gtksudo /home/vbox/cleanuptap.sh"
Note: The VBoxSDL front end to VirtualBox (see chapter 7.3, VBoxSDL, the simplified VM displayer, page 70) allows for an additional way of configuring TAP interfaces if it is started from a custom parent process. This parent process can allocate the required TAP interfaces and let VirtualBox inherit the file handles. For this to work, the file descriptor has to be passed to VBoxSDL
using the option -tapfd . In this case, the setup and termination scripts will not be called.





Internal networking.
Internal Networking is similar to host interface networking in that the VM can directly communicate with the outside world. However, the “outside world” is limited to other VMs which connect to the same internal network.

Even though technically, everything that can be done using internal networking can also be done using host interface networking, there are two good reasons why this extra mode was implemented:
1. Security. In host interface networking mode, all traffic goes through an interface of the host system. It is therefore possible to attach a packet sniffer (such as Ethereal) to the host interface and log all traffic that goes over a given interface.

If, for any reason, you prefer two or more VMs on the same machine to communicate privately, hiding their data from both the host system and the user, Host Interface Networking therefore is not an option.

2. Speed. Internal networking is more efficient than host interface networking, as VirtualBox can directly transmit the data without having to send it through the host operating system’s networking stack.
Internal networks are created automatically as needed, i.e. there is no central configuration. Every internal network is identified simply by its name. In order to attach a VM’s network card to an internal network, set its networking mode to “internal networking” using VBoxManage modifyvm -nic intnet and specify a network name with the command VBoxManage modifyvm
intnet .

If you do not specify a network name, the network card will be attached to the network “intnet” by default. You will also have to manually assign an IP address to the network adaptors. Guests which need to communicate with one another should use IP addresses on the same subnet (e.g. 192.168.2.1 and 192.168.2.2). Please note that you may have to deactivate guest firewalls in order to allow guests to communicate with each other.

VBoxManage
Once there is more than one active virtual network card with the same internal network ID, the VirtualBox support driver will automatically “wire” the cards and act as a network switch. The VirtualBox support driver implements a complete Ethernet switch and supports both broadcast/multicast frames and promiscuous mode.

As a security measure, the Linux implementation of internal networking only allows VMs running under the same user ID to establish an internal network. If you require more information on how to lift this restriction, please contact innotek.


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About Hugo Repetto

Ubuntu is a Linux distribution that offers an operating system predominantly focused on desktop computers but also provides support for servers. Based on Debian GNU / Linux, Ubuntu focuses on ease of use, freedom in usage restriction, regular releases (every 6 months) and ease of installation.
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