6.6. Internal Networking

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

Even though technically, everything that can be done using
internal networking can also be done using bridged networking,
there are security advantages with internal networking. In bridged
networking mode, all traffic goes through a physical interface of
the host system. It is therefore possible to attach a packet
sniffer such as Wireshark to the host interface and log all
traffic that goes over it. 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, bridged
networking therefore is not an option.

Internal networks are created automatically as needed. There is no
central configuration. Every internal network is identified simply
by its name. Once there is more than one active virtual network
card with the same internal network ID, the Oracle VM VirtualBox support
driver will automatically wire the cards and
act as a network switch. The Oracle VM VirtualBox support driver
implements a complete Ethernet switch and supports both
broadcast/multicast frames and promiscuous mode.

In order to attach a VM’s network card to an internal network, set
its networking mode to Internal Networking. There are two ways to
accomplish this:

Use the VM’s Settings dialog
in the Oracle VM VirtualBox graphical user interface. In the
Networking category of the
settings dialog, select Internal
Networking from the drop-down list of networking
modes. Select the name of an existing internal network from
the drop-down list below, or enter a new name into the
Name field.
Use the command line, for example:
```
VBoxManage modifyvm "VM name" --nic<x> intnet
```
Optionally, you can specify a network name with the command:
```
VBoxManage modifyvm "VM name" --intnet<x> "network name"
```
If you do not specify a network name, the network card will be
attached to the network intnet by default.

Unless you configure the virtual network cards in the guest
operating systems that are participating in the internal network
to use static IP addresses, you may want to use the DHCP server
that is built into Oracle VM VirtualBox to manage IP addresses for the
internal network. See Section 7.42, “VBoxManage dhcpserver”.

As a security measure, by default, the Linux implementation of
internal networking only allows VMs running under the same user ID
to establish an internal network. However, it is possible to
create a shared internal networking interface, accessible by users
with different user IDs.