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.