Network XML format
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.
Element and attribute overview
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
General metadata
The first elements provide basic metadata about the virtual network.
<network>
<name>default</name>
<uuid>3e3fce45-4f53-4fa7-bb32-11f34168b82b</uuid>
...
name- The content of the
nameelement 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 0.3.0 uuid- The content of the
uuidelement provides a globally unique identifier for the virtual network. The format must be RFC 4122 compliant, eg3e3fce45-4f53-4fa7-bb32-11f34168b82b. If omitted when defining/creating a new network, a random UUID is generated. Since 0.3.0
Connectivity
The 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"/>
...
bridge- The
nameattribute on thebridgeelement 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 prefixvir, but the namevirbr0is reserved for the "default" virtual network. This element should always be provided when defining a new network. Since 0.3.0 forward- Inclusion of the
forwardelement 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 thedevattribute is set, the firewall rules will restrict forwarding to the named device only. If themodeattribute is set toroutethen 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 0.4.2
Addressing
The 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>
ip- The
addressattribute 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. Thenetmaskattribute defines the significant bits of the network address, again specified in dotted-decimal format. Since 0.3.0 tftp- Immediately within
the
ipelement there is an optionaltftpelement. The presence of this element and of its attributerootenables TFTP services. The attribute specifies the path to the root directory served via TFTP. Since 0.7.1 dhcp- Also within the
ipelement there is an optionaldhcpelement. The presence of this element enables DHCP services on the virtual network. It will further contain one or morerangeelements. Since 0.3.0 range- The
startandendattributes on therangeelement 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 parentipelement. Since 0.3.0 host- Within the
dhcpelement there may be zero or morehostelements; 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 themacattribute), the IP to be assigned to that host (via theipattribute), and the name to be given that host by the DHCP server (via thenameattribute). Since 0.4.5 bootp- The optional
bootpelement specifies BOOTP options to be provided by the DHCP server. Two attributes are supported:fileis mandatory and gives the file to be used for the boot image;serveris optional and gives the address of the TFTP server from which the boot image will be fetched.serverdefaults to the same host that runs the DHCP server, as is the case when thetftpelement is used. The BOOTP options currently have to be the same for all address ranges and statically assigned addresses.Since 0.7.1 (serversince 0.7.3).
Example configuration
NAT based network
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>
Routed network config
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>
Isolated network config
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>
