This page provides an introduction to the network XML format. For background information on the concepts referred to here, consult the network driver architecture page.
The root element required for all virtual networks is
named network and has no attributes.
The network XML format is available since 0.3.0
The first elements provide basic metadata about the virtual network.
<network>
<name>default</name>
<uuid>3e3fce45-4f53-4fa7-bb32-11f34168b82b</uuid>
...
namename element provides
a short name for the virtual network. This name should
consist only of alpha-numeric characters and is required
to be unique within the scope of a single host. It is
used to form the filename for storing the persistent
configuration file. Since 0.3.0uuiduuid element provides
a globally unique identifier for the virtual network.
The format must be RFC 4122 compliant, eg 3e3fce45-4f53-4fa7-bb32-11f34168b82b.
If omitted when defining/creating a new network, a random
UUID is generated. Since 0.3.0The next set of elements control how a virtual network is provided connectivity to the physical LAN (if at all).
...
<bridge name="virbr0" />
<forward mode="nat" dev="eth0"/>
...
bridgename attribute on the bridge element
defines the name of a bridge device which will be used to construct
the virtual network. The virtual machines will be connected to this
bridge device allowing them to talk to each other. The bridge device
may also be connected to the LAN. It is recommended that bridge
device names started with the prefix vir, but the name
virbr0 is reserved for the "default" virtual network.
This element should always be provided when defining a new network.
Since 0.3.0
forwardforward element indicates that
the virtual network is to be connected to the physical LAN. If
no attributes are set, NAT forwarding will be used for connectivity.
Firewall rules will allow forwarding to any other network device whether
ethernet, wireless, dialup, or VPN. If the dev attribute
is set, the firewall rules will restrict forwarding to the named
device only. If the mode attribute is set to route
then the traffic will not have NAT applied. This presumes that the
local LAN router has suitable routing table entries to return traffic
to this host. Since 0.3.0; 'mode' attribute since
0.4.2The final set of elements define the IPv4 address range available, and optionally enable DHCP sevices.
...
<ip address="192.168.122.1" netmask="255.255.255.0">
<dhcp>
<range start="192.168.122.100" end="192.168.122.254" />
<host mac="00:16:3e:77:e2:ed" name="foo.example.com" ip="192.168.122.10" />
<host mac="00:16:3e:3e:a9:1a" name="bar.example.com" ip="192.168.122.11" />
</dhcp>
</ip>
</network>
ipaddress attribute defines an IPv4 address in
dotted-decimal format, that will be configured on the bridge
device associated with the virtual network. To the guests this
address will be their default route. The netmask
attribute defines the significant bits of the network address,
again specified in dotted-decimal format. Since 0.3.0
dhcpip element there is an
optional dhcp element. The presence of this element
enables DHCP services on the virtual network. It will further
contain one or more range elements.
Since 0.3.0
rangestart and end attributes on the
range element specify the boundaries of a pool of
IPv4 addresses to be provided to DHCP clients. These two addresses
must lie within the scope of the network defined on the parent
ip element. Since 0.3.0
hostdhcp element there may be zero or more
host elements; these specify hosts which will be given
names and predefined IP addresses by the built-in DHCP server. Any
such element must specify the MAC address of the host to be assigned
a given name (via the mac attribute), the IP to be
assigned to that host (via the ip attribute), and the
name to be given that host by the DHCP server (via the
name attribute). Since 0.4.5
This example is the so called "default" virtual network. It is provided and enabled out-of-the-box for all libvirt installations. This is a configuration that allows guest OS to get outbound connectivity regardless of whether the host uses ethernet, wireless, dialup, or VPN networking without requiring any specific admin configuration. In the absence of host networking, it at least allows guests to talk directly to each other.
<network>
<name>default</name>
<bridge name="virbr0" />
<forward mode="nat"/>
<ip address="192.168.122.1" netmask="255.255.255.0">
<dhcp>
<range start="192.168.122.2" end="192.168.122.254" />
</dhcp>
</ip>
</network>
This is a variant on the default network which routes traffic
from the virtual network to the LAN without applying any NAT.
It requires that the IP address range be pre-configured in the
routing tables of the router on the host network. This example
further specifies that guest traffic may only go out via the
eth1 host network device.
<network>
<name>local</name>
<bridge name="virbr1" />
<forward mode="route" dev="eth1"/>
<ip address="192.168.122.1" netmask="255.255.255.0">
<dhcp>
<range start="192.168.122.2" end="192.168.122.254" />
</dhcp>
</ip>
</network>
This variant provides a completely isolated private network
for guests. The guests can talk to each other, and the host
OS, but cannot reach any other machines on the LAN, due to
the omission of the forward element in the XML
description.
<network>
<name>private</name>
<bridge name="virbr2" />
<ip address="192.168.152.1" netmask="255.255.255.0">
<dhcp>
<range start="192.168.152.2" end="192.168.152.254" />
</dhcp>
</ip>
</network>