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<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE topic PUBLIC "-//OASIS//DTD DITA Topic//EN" "topic.dtd">
<topic xml:lang="en-us" id="network_hostonly">
<title>Host-Only Networking</title>
<body>
<p>
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.
</p>
<p>
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
<i>loopback</i> 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.
</p>
<note>
<p>
Hosts running recent macOS versions do not support host-only
adapters. These adapters are replaced by host-only networks,
which define a network mask and an IP address range, where the
host network interface receives the lowest address in the range.
</p>
<p>
The host network interface gets added and removed dynamically by
the operating system, whenever a host-only network is used by
virtual machines.
</p>
<p>
On macOS hosts, choose the <b outputclass="bold">Host-Only
Network</b> option when configuring a network adapter.
The <b outputclass="bold">Host-Only Adapter</b> option is
provided for legacy support.
</p>
</note>
<p>
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.
</p>
<p>
To enable a host-only network interface for a virtual machine, do
either of the following:
</p>
<ul>
<li>
<p>
Go to the <b outputclass="bold">Network</b> page in the
virtual machine's <b outputclass="bold">Settings</b>
dialog and select an <b outputclass="bold">Adapter</b>
tab. Ensure that the <b outputclass="bold">Enable Network
Adapter</b> check box is selected and choose
<b outputclass="bold">Host-Only Adapter</b> for the
<b outputclass="bold">Attached To</b> field.
</p>
</li>
<li>
<p>
On the command line, use <userinput>VBoxManage modifyvm
vmname --nic <varname>x</varname> hostonly</userinput>. See
<xref href="man_VBoxManage-modifyvm.dita#vboxmanage-modifyvm"/>.
</p>
</li>
</ul>
<p>
For host-only networking, as with internal networking, you may
find the DHCP server useful that is built into Oracle VM VirtualBox.
This is enabled by default and manages the IP addresses in the
host-only network. Without the DHCP server you would need to
configure all IP addresses statically.
</p>
<ul>
<li>
<p>
In VirtualBox Manager you can configure the DHCP server by choosing
<b outputclass="bold">File</b>,
<b outputclass="bold">Tools</b>,
<b outputclass="bold">Network Manager</b>. The Network
Manager window lists all host-only networks which are
presently in use. Select the network name and then use the
<b outputclass="bold">DHCP Server</b> tab to configure
DHCP server settings. See <xref href="network-manager.dita#network-manager"/>.
</p>
</li>
<li>
<p>
Alternatively, you can use the <userinput>VBoxManage
dhcpserver</userinput> command. See
<xref href="man_VBoxManage-dhcpserver.dita#vboxmanage-dhcpserver"/>.
</p>
</li>
</ul>
<note>
<p>
On Linux and macOS hosts the number of host-only interfaces is
limited to 128. There is no such limit for Oracle Solaris and
Windows hosts.
</p>
</note>
<p>
On Linux, macOS and Solaris Oracle VM VirtualBox will only allow IP
addresses in 192.168.56.0/21 range to be assigned to host-only
adapters. For IPv6 only link-local addresses are allowed. If other
ranges are desired, they can be enabled by creating
<filepath>/etc/vbox/networks.conf</filepath> and specifying
allowed ranges there. For example, to allow 10.0.0.0/8 and
192.168.0.0/16 IPv4 ranges as well as 2001::/64 range put the
following lines into <filepath>/etc/vbox/networks.conf</filepath>:
</p>
<pre xml:space="preserve"> * 10.0.0.0/8 192.168.0.0/16
* 2001::/64
</pre>
<p>
Lines starting with the hash <userinput>#</userinput> are ignored. The
following example allows any addresses, effectively disabling
range control:
</p>
<pre xml:space="preserve"> * 0.0.0.0/0 ::/0
</pre>
<p>
If the file exists, but no ranges are specified in it, no
addresses will be assigned to host-only adapters. The following
example effectively disables all ranges:
</p>
<pre xml:space="preserve"> # No addresses are allowed for host-only adapters
</pre>
</body>
</topic>
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