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" stp="on" delay="5"/>
<domain name="example"/>
<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 with a <forward> mode of
"nat" or "route" (or an isolated network with
no <forward> element).
Attribute stp specifies if Spanning Tree Protocol
is 'on' or 'off' (default is
'on'). Attribute delay sets the bridge's forward
delay value in seconds (default is 0).
Since 0.3.0
domainname attribute on the domain
element defines the DNS domain of the DHCP server. This
element is optional, and is only used for those networks with
a <forward> mode of "nat" or "route" (or an
isolated network with no <forward>
element). Since 0.4.5
forwardforward element indicates that
the virtual network is to be connected to the physical
LAN.Since 0.3.0.
The mode attribute determines the method of
forwarding. If there is no forward element, the
network will be isolated from any other network (unless a
guest connected to that network is acting as a router, of
course). The following are valid settings
for mode (if there is a forward
element but mode is not specified, mode='nat' is
assumed):
natdev attribute is set, the
firewall rules will restrict forwarding to the named
device only. Inbound connections from other networks are
all prohibited; all connections between guests on the same
network, and to/from the host to the guests, are
unrestricted and not NATed.Since
0.4.2
routedev
attribute is set, firewall rules will restrict forwarding
to the named device only. This presumes that the local LAN
router has suitable routing table entries to return
traffic to this host. Firewall rules are also installed
that prevent incoming sessions from the physical network
to the guests, but outgoing sessions are unrestricted (as
are sessions from the host to the guests, and between
guests on the same network.)Since
0.4.2
bridge<bridge name='xyz'/> element has been
specified), or 2) an interface or group of interfaces to
be used for a "direct" connection via macvtap using
macvtap's "bridge" mode (if the forward element has one or
more <interface> subelements)
(see Direct
attachment to physical interface for descriptions of
the various macvtap modes). libvirt doesn't attempt to
manage the bridge interface at all, thus
the <bridge> element's stp
and delay attributes are not allowed; no
iptables rules, IP addresses, or DHCP/DNS services are
added; at the IP level, the guest interface appears to be
directly connected to the physical
interface.Since 0.9.4
private<interface> subelements
of the <forward> element; when using
802.1Qbh mode (as indicated by
the <virtualport> type attribute - note
that this requires an 802.1Qbh-capable hardware switch),
each physical interface can only be in use by a single
guest interface at a time; in modes other than 802.1Qbh,
multiple guest interfaces can share each physical
interface (libvirt will attempt to balance usage between
all available interfaces).Since
0.9.4
vepa<interface> subelements of
the <forward> element; multiple guest
interfaces can share each physical interface (libvirt will
attempt to balance usage between all available
interfaces).Since 0.9.4
passthrough<interface> subelements of
the <forward> element. Each physical
interface can only be in use by a single guest interface
at a time, so libvirt will keep track of which interfaces
are currently in use, and only assign unused interfaces
(if there are no available physical interfaces when a
domain interface is being attached, an error will be
logged, and the operation causing the attach will fail
(usually either a domain start, or a hotplug interface
attach to a domain).Since 0.9.4
<forward> element can
have multiple <interface> subelements, each
one giving the name of a physical interface that can be used
for this networkSince 0.9.4:
...
<forward mode='passthrough'>
<interface dev='eth10'/>
<interface dev='eth11'/>
<interface dev='eth12'/>
<interface dev='eth13'/>
<interface dev='eth14'/>
</forward>
...
When a guest interface is being constructed, libvirt will pick
an interface from this list to use for the connection. In
modes where physical interfaces can be shared by multiple
guest interfaces, libvirt will choose the interface that
currently has the least number of connections. For those modes
that do not allow sharing of the physical device (in
particular, 'passthrough' mode, and 'private' mode when using
802.1Qbh), libvirt will choose an unused physical interface
or, if it can't find an unused interface, fail the operation.
...
<forward mode='nat' dev='eth0'/>
<bandwidth>
<inbound average='1000' peak='5000' burst='5120'/>
<outbound average='128' peak='256' burst='256'/>
</bandwidth>
...
This part of network XML provides setting quality of service. Incoming
and outgoing traffic can be shaped independently. The
bandwidth element can have at most one inbound
and at most one outbound child elements. Leaving any of these
children element out result in no QoS applied on that traffic direction.
So, when you want to shape only network's incoming traffic, use
inbound only, and vice versa. Each of these elements have one
mandatory attribute average. It specifies average bit rate on
interface being shaped. Then there are two optional attributes:
peak, which specifies maximum rate at which bridge can send
data, and burst, amount of bytes that can be burst at
peak speed. Accepted values for attributes are integer
numbers, The units for average and peak attributes
are kilobytes per second, and for the burst just kilobytes.
The rate is shared equally within domains connected to the network.
Moreover, bandwidth element can be included in
portgroup element.
Since 0.9.4
...
<forward mode='private'/>
<interface dev="eth20"/>
<interface dev="eth21"/>
<interface dev="eth22"/>
<interface dev="eth23"/>
<interface dev="eth24"/>
</forward>
<portgroup name='engineering' default='yes'>
<virtualport type='802.1Qbh'>
<parameters profileid='test'/>
</virtualport>
<bandwidth>
<inbound average='1000' peak='5000' burst='5120'/>
<outbound average='1000' peak='5000' burst='5120'/>
</bandwidth>
</portgroup>
<portgroup name='sales'>
<virtualport type='802.1Qbh'>
<parameters profileid='salestest'/>
</virtualport>
<bandwidth>
<inbound average='500' peak='2000' burst='2560'/>
<outbound average='128' peak='256' burst='256'/>
</bandwidth>
</portgroup>
...
A portgroup provides a method of easily putting guest
connections to the network into different classes, with each
class potentially having a different level/type of service. Each
network can have multiple portgroup elements (and one of those
can optionally be designated as the 'default' portgroup for the
network), and each portgroup has a name, as well as various
subelements associated with it. The currently supported
subelements are <bandwidth>
(documented here)
and <virtualport>
(documented here).
If a domain interface definition specifies a portgroup (by
adding a portgroup attribute to
the <source> subelement), that portgroup's
info will be merged into the interface's configuration. If no
portgroup is given in the interface definition, and one of the
network's portgroups has default='yes', that
default portgroup will be used. If no portgroup is given in the
interface definition, and there is no default portgroup, then
none will be used. Any <bandwidth>
or <virtualport> specified directly in the
domain XML will take precedence over any setting in the chosen
portgroup.
The final set of elements define the addresses (IPv4 and/or
IPv6, as well as MAC) to be assigned to the bridge device
associated with the virtual network, and optionally enable DHCP
services. These elements are only valid for isolated networks
(no forward element specified), and for those with
a forward mode of 'route' or 'nat'.
...
<mac address='00:16:3E:5D:C7:9E'/>
<dns>
<txt name="example" value="example value" />
</dns>
<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>
<ip family="ipv6" address="2001:db8:ca2:2::1" prefix="64" />
</network>
macaddress attribute defines a MAC
(hardware) address formatted as 6 groups of 2-digit
hexadecimal numbers, the groups separated by colons
(eg, "52:54:00:1C:DA:2F"). This MAC address is
assigned to the bridge device when it is created. Generally
it is best to not specify a MAC address when creating a
network - in this case, if a defined MAC address is needed for
proper operation, libvirt will automatically generate a random
MAC address and save it in the config. Allowing libvirt to
generate the MAC address will assure that it is compatible
with the idiosyncrasies of the platform where libvirt is
running. Since 0.8.8
dnstxtdns element can have 0 or more txt elements.
Each txt element defines a DNS TXT record and has two attributes, both
required: a name that can be queried via dns, and a value that will be
returned when that name is queried. names cannot contain embedded spaces
or commas. value is a single string that can contain multiple values
separated by commas. Since 0.9.3
hosthost element within dns is the
definition of DNS hosts to be passed to the DNS service. The IP
address is identified by the ip attribute and the names
for that IP address are identified in the hostname
sub-elements of the host element.
Since 0.9.3
ipaddress attribute defines an IPv4 address in
dotted-decimal format, or an IPv6 address in standard
colon-separated hexadecimal format, that will be configured on
the bridge
device associated with the virtual network. To the guests this
address will be their default route. For IPv4 addresses, the netmask
attribute defines the significant bits of the network address,
again specified in dotted-decimal format. For IPv6 addresses,
and as an alternate method for IPv4 addresses, you can specify
the significant bits of the network address with the prefix
attribute, which is an integer (for example, netmask='255.255.255.0'
could also be given as prefix='24'. The family
attribute is used to specify the type of address - 'ipv4' or 'ipv6'; if no
family is given, 'ipv4' is assumed. A network can have more than
one of each family of address defined, but only a single address can have a
dhcp or tftp element. Since 0.3.0;
IPv6, multiple addresses on a single network, family, and
prefix since 0.8.7
tftpip element there is an optional tftp
element. The presence of this element and of its attribute
root enables TFTP services. The attribute specifies
the path to the root directory served via TFTP. tftp is not
supported for IPv6 addresses, and can only be specified on a single IPv4 address
per network.
Since 0.7.1
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. The
dhcp element is not supported for IPv6, and
is only supported on a single IP address per network for IPv4.
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
bootpbootp
element specifies BOOTP options to be provided by the DHCP server.
Two attributes are supported: file is mandatory and
gives the file to be used for the boot image; server is
optional and gives the address of the TFTP server from which the boot
image will be fetched. server defaults to the same host
that runs the DHCP server, as is the case when the tftp
element is used. The BOOTP options currently have to be the same
for all address ranges and statically assigned addresses.Since 0.7.1 (server since 0.7.3).
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>
<ip family="ipv6" address="2001:db8:ca2:2::1" prefix="64" />
</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>
<ip family="ipv6" address="2001:db8:ca2:2::1" prefix="64" />
</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>
<ip family="ipv6" address="2001:db8:ca2:3::1" prefix="64" />
</network>
This shows how to use a pre-existing host bridge "br0". The guests will effectively be directly connected to the physical network (i.e. their IP addresses will all be on the subnet of the physical network, and there will be no restrictions on inbound or outbound connections).
<network>
<name>host-bridge</name>
<forward mode="bridge"/>
<bridge name="br0"/>
</network>
This shows how to use macvtap to connect to the physical network directly through one of a group of physical devices (without using a host bridge device). As with the host bridge network, the guests will effectively be directly connected to the physical network so their IP addresses will all be on the subnet of the physical network, and there will be no restrictions on inbound or outbound connections. Note that, due to a limitation in the implementation of macvtap, these connections do not allow communication directly between the host and the guests - if you require this you will either need the attached physical switch to be operating in a mirroring mode (so that all traffic coming to the switch is reflected back to the host's interface), or provide alternate means for this communication (e.g. a second interface on each guest that is connected to an isolated network). The other forward modes that use macvtap (private, vepa, and passthrough) would be used in a similar fashion.
<network>
<name>direct-macvtap</name>
<forward mode="bridge">
<interface dev="eth20"/>
<interface dev="eth21"/>
<interface dev="eth22"/>
<interface dev="eth23"/>
<interface dev="eth24"/>
</forward>
</network>