Host-only networking can be thought of as a hybrid between the bridged and internal networking modes. As with bridged networking, the virtual machines can talk to each other and the host as if they were connected through a physical Ethernet switch. As with internal networking, a physical networking interface need not be present, and the virtual machines cannot talk to the world outside the host since they are not connected to a physical networking interface.
When host-only networking is used, Oracle VM VirtualBox creates a new software interface on the host which then appears next to your existing network interfaces. In other words, whereas with bridged networking an existing physical interface is used to attach virtual machines to, with host-only networking a new loopback interface is created on the host. And whereas with internal networking, the traffic between the virtual machines cannot be seen, the traffic on the loopback interface on the host can be intercepted.
Host-only networking is particularly useful for preconfigured virtual appliances, where multiple virtual machines are shipped together and designed to cooperate. For example, one virtual machine may contain a web server and a second one a database, and since they are intended to talk to each other, the appliance can instruct Oracle VM VirtualBox to set up a host-only network for the two. A second, bridged, network would then connect the web server to the outside world to serve data to, but the outside world cannot connect to the database.
To change a virtual machine's virtual network interface to Host Only mode, do either of the following:
Go to the Network page in the virtual machine's Settings dialog and select Host-Only Networking.
On the command line, enter VBoxManage modifyvm
"vmname--nicxhostonly. See Section 7.8, “VBoxManage modifyvm”.
Before you can attach a VM to a host-only network you have to create at least one host-only interface. You can use the VirtualBox Manager for this. Choose File, Preferences, Network, Host-Only Network, (+)Add Host-Only Network.
Alternatively, you can use the command line:
VBoxManage hostonlyif create
See Section 7.36, “VBoxManage hostonlyif”.
For host-only networking, as with internal networking, you may find the DHCP server useful that is built into Oracle VM VirtualBox. This can be enabled to then manage the IP addresses in the host-only network since otherwise you would need to configure all IP addresses statically.
In the Oracle VM VirtualBox graphical user interface, you can configure all these items in the global settings by choosing File, Preferences, Network. This lists all host-only networks which are presently in use. Click on the network name and then on Edit. You can then modify the adapter and DHCP settings.
Alternatively, you can use VBoxManage dhcpserver on the command line. See Section 7.42, “VBoxManage dhcpserver”.
On Linux and Mac OS X hosts the number of host-only interfaces is limited to 128. There is no such limit for Oracle Solaris and Windows hosts.