This page provides an introduction to the network XML format. For background information on the concepts referred to here, consult the relevant wiki page.
The root element required for all virtual networks is
named network and has no configurable attributes
(although since 0.10.0 there is one
optional read-only attribute - when examining the live
configuration of a network, the
attribute connections, if present, specifies the
number of guest interfaces currently connected via this
network). The network XML format is
available since 0.3.0
The first elements provide basic metadata about the virtual network.
<network ipv6='yes' trustGuestRxFilters='no'>
<name>default</name>
<uuid>3e3fce45-4f53-4fa7-bb32-11f34168b82b</uuid>
<metadata>
<app1:foo xmlns:app1="http://app1.org/app1/">..</app1:foo>
<app2:bar xmlns:app2="http://app1.org/app2/">..</app2:bar>
</metadata>
...
namename element provides
a short name for the virtual network. This name should
consist only of alphanumeric 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 0.3.0metadata node can be used by applications to
store custom metadata in the form of XML nodes/trees. Applications
must use custom namespaces on their XML nodes/trees, with only
one top-level element per namespace (if the application needs
structure, they should have sub-elements to their namespace
element). Since 2.1.0ipv6yes, the optional parameter
ipv6 enables
a network definition with no IPv6 gateway addresses specified
to have guest-to-guest communications. For further information,
see the example below for the example with no gateway addresses.
Since 1.0.1trustGuestRxFilterstrustGuestRxFilters can
be used to set that attribute of the same name for each domain
interface connected to this network (since
1.2.10). See
the Network
interfaces section of the domain XML documentation for
more details. Note that an explicit setting of this attribute
in a portgroup or the individual domain interface will
override the setting in the network.The 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" macTableManager="libvirt"/> <mtu size="9000"/> <domain name="example.com" localOnly="no"/> <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. When defining
a new network with a <forward> mode of
"nat", "route", or "open" (or an isolated network with
no <forward> element), libvirt will
automatically generate a unique name for the bridge device if
none is given, and this name will be permanently stored in the
network configuration so that that the same name will be used
every time the network is started. For these types of networks
(nat, route, open, and isolated), a bridge name beginning with the
prefix "virbr" is recommended (and that is what is
auto-generated), but not enforced.
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
The macTableManager attribute of the bridge
element is used to tell libvirt how the bridge's MAC address
table (used to determine the correct egress port for packets
based on destination MAC address) will be managed. In the
default kernel setting, the kernel
automatically adds and removes entries, typically using
learning, flooding, and promiscuous mode on the bridge's
ports in order to determine the proper egress port for
packets. When macTableManager is set
to libvirt, libvirt disables kernel management
of the MAC table (in the case of the Linux host bridge, this
means enabling vlan_filtering on the bridge, and disabling
learning and unicast_filter for all bridge ports), and
explicitly adds/removes entries to the table according to
the MAC addresses in the domain interface configurations.
Allowing libvirt to manage the MAC table can improve
performance - with a Linux host bridge, for example, turning
off learning and unicast_flood on ports has its own
performance advantage, and can also lead to an additional
boost by permitting the kernel to automatically turn off
promiscuous mode on some ports of the bridge (in particular,
the port attaching the bridge to the physical
network). However, it can also cause some networking setups
to stop working (e.g. vlan tagging, multicast,
guest-initiated changes to MAC address) and is not supported
by older kernels.
Since 1.2.11, requires kernel 3.17 or
newer
The optional zone attribute of
the bridge element is used to specify
the firewalld
zone for the bridge of a network with forward
mode of "nat", "route", "open", or one with
no forward specified. By default, the bridges
of all virtual networks with these forward modes are placed
in the firewalld zone named "libvirt", which permits
incoming DNS, DHCP, TFTP, and SSH to the host from guests on
the network. This behavior can be changed either by
modifying the libvirt zone (using firewalld management
tools), or by placing the network in a different zone (which
will also be managed using firewalld tools).
Since 5.1.0
mtusize attribute of the mtu>
element specifies the Maximum Transmission Unit (MTU) for the
network. Since 3.1.0. In the case
of a libvirt-managed network (one with forward mode
of nat, route, open, or
no forward element (i.e. an isolated network),
this will be the MTU assigned to the bridge device when
libvirt creates it, and thereafter also assigned to all tap
devices created to connect guest interfaces. Network types not
specifically mentioned here don't support having an MTU set in
the libvirt network config. If mtu size is unspecified, the
default setting for the type of device being used is assumed
(usually 1500).
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
If the optional localOnly attribute on the
domain element is "yes", then DNS requests under
this domain will only be resolved by the virtual network's own
DNS server - they will not be forwarded to the host's upstream
DNS server. If localOnly is "no", and by
default, unresolved requests will be forwarded.
Since 1.2.12
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
Since 1.0.3 it is possible to
specify a public IPv4 address and port range to be used for
the NAT by using the <nat> subelement.
Note that all addresses from the range are used, not just those
that are in use on the host.
The address range is set with the <address>
subelements and start and stop
attributes:
...
<forward mode='nat'>
<nat>
<address start='1.2.3.4' end='1.2.3.10'/>
</nat>
</forward>
...
A single IPv4 address can be set by setting
start and end attributes to
the same value.
The port range to be used for the <nat> can
be set via the subelement <port>:
...
<forward mode='nat'>
<nat>
<port start='500' end='1000'/>
</nat>
</forward>
...
Since 6.5.0 it is possible to enable NAT with IPv6 networking. As noted above, IPv6 has historically done plain forwarding and thus to avoid breaking historical compatibility, IPv6 NAT must be explicitly requested.
...
<forward mode='nat'>
<nat ipv6='yes'/>
</forward>
...
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. All incoming and outgoing sessions
to guest on these networks are unrestricted. (To restrict
incoming traffic to a guest on a routed network, you can
configure nwfilter rules
on the guest's interfaces.)
Since 0.4.2
opendev attribute
cannot be set (because the forward dev is enforced with
firewall rules, and the purpose of forward='open' is to
have a forwarding mode where libvirt doesn't add any
firewall rules). This mode presumes that the local LAN
router has suitable routing table entries to return
traffic to this host, and that some other management
system has been used to put in place any necessary
firewall rules. Although no firewall rules will be added
for the network, it is of course still possible to add
restrictions for specific guests using
nwfilter rules on the
guests' interfaces.)
Since 2.2.0
bridge<bridge name='xyz'/> element has been
specified, Since 0.9.4), 2) an
existing Open vSwitch bridge that was configured outside of
libvirt (if both a <bridge name='xyz'/>
element and a <virtualport
type='openvswitch'/> have been
specified Since 0.10.0) 3) 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, Since 0.9.4)
(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
hostdev<virtualport>
element. Note that - due to limitations in standard
single-port PCI ethernet card driver design - only SR-IOV
(Single Root I/O Virtualization) virtual function (VF)
devices can be assigned in this manner; to assign a
standard single-port PCI or PCIe ethernet card to a guest,
use the traditional <hostdev> device
definition. Since 0.10.0
To force use of a particular type of device assignment,
a <forward type='hostdev'> interface can have an
optional driver sub-element with
a name attribute set to either "vfio" (VFIO
is a new method of device assignment that is compatible
with UEFI Secure Boot) or "kvm" (the legacy device
assignment handled directly by the KVM kernel module)
Since 1.0.5 (QEMU and KVM only,
requires kernel 3.6 or newer). When specified,
device assignment will fail if the requested method of
device assignment isn't available on the host. When not
specified, the default is "vfio" on systems where the
VFIO driver is available and loaded, and "kvm" on older
systems, or those where the VFIO driver hasn't been
loaded Since 1.1.3 (prior to
that the default was always "kvm").
Note that this "intelligent passthrough" of network
devices is very similar to the functionality of a
standard <hostdev> device, the
difference being that this method allows specifying a MAC
address, vlan tag, and <virtualport>
for the passed-through device. If these capabilities are
not required, if you have a standard single-port PCI,
PCIe, or USB network card that doesn't support SR-IOV (and
hence would anyway lose the configured MAC address during
reset after being assigned to the guest domain), or if you
are using a version of libvirt older than 0.10.0, you
should use a standard
<hostdev> device definition in the
domain's configuration to assign the device to the guest
instead of defining an <interface
type='network'> pointing to a network
with <forward mode='hostdev'/>.
<forward> element can
have multiple <interface> subelements, each
one giving the name of a physical interface that can be used
for this network Since 0.9.4:
...
<forward mode='passthrough'>
<interface dev='eth10'/>
<interface dev='eth11'/>
<interface dev='eth12'/>
<interface dev='eth13'/>
<interface dev='eth14'/>
</forward>
...
since 0.10.0,
<interface> also has an optional read-only
attribute - when examining the live configuration of a
network, the attribute connections, if present,
specifies the number of guest interfaces currently connected
via this physical interface.
Additionally, since 0.9.10, libvirt
allows a shorthand for specifying all virtual interfaces
associated with a single physical function, by using
the <pf> subelement to call out the
corresponding physical interface associated with multiple
virtual interfaces:
...
<forward mode='passthrough'>
<pf dev='eth0'/>
</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.
since 0.10.0 When using forward
mode 'hostdev', the interface pool is specified with a list
of <address> elements, each of which has
<type> (must always be 'pci'),
<domain>, <bus>,
<slot>and <function>
attributes.
...
<forward mode='hostdev' managed='yes'>
<driver name='vfio'/>
<address type='pci' domain='0' bus='4' slot='0' function='1'/>
<address type='pci' domain='0' bus='4' slot='0' function='2'/>
<address type='pci' domain='0' bus='4' slot='0' function='3'/>
</forward>
...
Alternatively the interface pool can also be defined using a
single physical function <pf> subelement to
call out the corresponding physical interface associated with
multiple virtual interfaces (similar to passthrough mode):
...
<forward mode='hostdev' managed='yes'>
<pf dev='eth0'/>
</forward>
...
...
<forward mode='nat' dev='eth0'/>
<bandwidth>
<inbound average='1000' peak='5000' burst='5120'/>
<outbound average='128' peak='256' burst='256'/>
</bandwidth>
...
The <bandwidth> element allows setting
quality of service for a particular network
(since 0.9.4). Setting
bandwidth for a network is supported only
for networks with a <forward> mode
of route, nat, bridge,
or no mode at all (i.e. an "isolated" network). Setting
bandwidth is not supported for forward modes
passthrough, private,
or hostdev. Attempts to do this will lead to
a failure to define the network or to create a transient network.
The <bandwidth> element can only be a
subelement of a domain's <interface>, a
subelement of a <network>, or a subelement of
a <portgroup> in a <network>.
As a subelement of a domain's <interface>,
the bandwidth only applies to that one interface of the domain.
As a subelement of a <network>, the bandwidth
is a total aggregate bandwidth to/from all guest interfaces attached
to that network, not to each guest interface individually.
If a domain's <interface> has
<bandwidth> element values higher
than the aggregate for the entire network, then the aggregate
bandwidth for the <network> takes precedence.
This is because the two choke points are independent of each other
where the domain's <interface> bandwidth control
is applied on the interface's tap device, while the
<network> bandwidth control is applied on the
interface part of the bridge device created for that network.
As a subelement of a
<portgroup> in a <network>,
if a domain's <interface> has a
portgroup attribute in its
<source> element and if the
<interface>
itself has no <bandwidth> element, then the
<bandwidth> element of the portgroup will be
applied individually to each guest interface defined to be a
member of that portgroup. Any <bandwidth>
element in the domain's <interface> definition
will override the setting in the portgroup
(since 1.0.1).
Incoming and outgoing traffic can be shaped independently. The
bandwidth element can have at most one
inbound and at most one outbound
child element. Leaving either of these children elements out
results in no QoS applied for that traffic direction. So,
when you want to shape only incoming traffic, use
inbound only, and vice versa. Each of these
elements have one mandatory attribute - average (or
floor as described below). The attributes are as follows,
where accepted values for each attribute is an integer number.
averagepeakoutbound element is ignored (as Linux ingress
filters don't know it yet).
burstpeak speed.
floorinbound
element. This attribute guarantees minimal throughput for
shaped interfaces. This, however, requires that all traffic
goes through one point where QoS decisions can take place, hence
why this attribute works only for virtual networks for now
(that is <interface type='network'/> with a
forward type of route, nat, open or no forward at all). Moreover, the
virtual network the interface is connected to is required to have
at least inbound QoS set (average at least). If
using the floor attribute users don't need to specify
average. However, peak and
burst attributes still require average.
Currently, the Linux kernel doesn't allow ingress qdiscs to have
any classes therefore floor can be applied only
on inbound and not outbound.
Attributes average, peak, and
burst are available
since 0.9.4, while the
floor attribute is available
since 1.0.1.
<network>
<name>ovs-net</name>
<forward mode='bridge'/>
<bridge name='ovsbr0'/>
<virtualport type='openvswitch'>
<parameters interfaceid='09b11c53-8b5c-4eeb-8f00-d84eaa0aaa4f'/>
</virtualport>
<vlan trunk='yes'>
<tag id='42' nativeMode='untagged'/>
<tag id='47'/>
</vlan>
<portgroup name='dontpanic'>
<vlan>
<tag id='42'/>
</vlan>
</portgroup>
</network>
If (and only if) the network connection used by the guest
supports VLAN tagging transparent to the guest, an
optional <vlan> element can specify one or
more VLAN tags to apply to the guest's network
traffic Since 0.10.0. Network
connections that support guest-transparent VLAN tagging include
1) type='bridge' interfaces connected to an Open vSwitch bridge
Since 0.10.0, 2) SRIOV Virtual
Functions (VF) used via type='hostdev' (direct device
assignment) Since 0.10.0, and 3)
SRIOV VFs used via type='direct' with mode='passthrough'
(macvtap "passthru" mode) Since
1.3.5. All other connection types, including standard
linux bridges and libvirt's own virtual networks, do not
support it. 802.1Qbh (vn-link) and 802.1Qbg (VEPA) switches
provide their own way (outside of libvirt) to tag guest traffic
onto a specific VLAN. Each tag is given in a
separate <tag> subelement
of <vlan> (for example: <tag
id='42'/>). For VLAN trunking of multiple tags (which
is supported only on Open vSwitch connections),
multiple <tag> subelements can be specified,
which implies that the user wants to do VLAN trunking on the
interface for all the specified tags. In the case that VLAN
trunking of a single tag is desired, the optional
attribute trunk='yes' can be added to the toplevel
<vlan> element to differentiate trunking of a
single tag from normal tagging.
For network connections using Open vSwitch it is also possible
to configure 'native-tagged' and 'native-untagged' VLAN modes
Since 1.1.0. This is done with the
optional nativeMode attribute on
the <tag> subelement: nativeMode
may be set to 'tagged' or 'untagged'. The id
attribute of the <tag> subelement
containing nativeMode sets which VLAN is considered
to be the "native" VLAN for this interface, and
the nativeMode attribute determines whether or not
traffic for that VLAN will be tagged.
<vlan> elements can also be specified in
a <portgroup> element, as well as directly in
a domain's <interface> element. In the case
that a vlan tag is specified in multiple locations, the setting
in <interface> takes precedence, followed by
the setting in the <portgroup> selected by
the interface config. The <vlan>
in <network> will be selected only if none is
given in <portgroup>
or <interface>.
<network> <name>isolated-ports</name> <forward mode='bridge'/> <bridge name='br0'/> <port isolated='yes'/> </network>
Since 6.1.0. The port
element property isolated, when set
to yes (default setting is no) is used
to isolate the network traffic of each guest on the network from
all other guests connected to the network; it does not have an
effect on communication between the guests and the host, or
between the guests and destinations beyond this network. This
setting is only supported for networks that use a Linux host
bridge to connect guest interfaces via a standard tap device
(i.e. those with a forward mode of nat, route, open, bridge, or
no forward mode).
...
<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' trustGuestRxFilters='no'>
<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>
...
Since 0.9.4
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.
Since 0.9.4 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
attributes and subelements associated with it. The currently supported
subelements are <bandwidth>
(described 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>
specified directly in the domain XML will take precedence over
any setting in the chosen portgroup. if
a <virtualport> is specified in the portgroup
(and/or directly in the network definition), the multiple
virtualports will be merged, and any parameter that is specified
in more than one virtualport, and is not identical, will be
considered an error, and will prevent the interface from
starting.
portgroups also support the optional
parameter trustGuestRxFilters which can be used to
set that attribute of the same name for each domain interface
using this portgroup (since
1.2.10). See
the Network
interfaces section of the domain XML documentation for more
details. Note that an explicit setting of this attribute in the
portgroup overrides the network-wide setting, and an explicit
setting in the individual domain interface will override the
setting in the portgroup.
Static route definitions are used to provide routing information to the virtualization host for networks which are not directly reachable from the virtualization host, but *are* reachable from a guest domain that is itself reachable from the host since 1.0.6.
As shown in this example, it is possible to define a virtual network interface with no IPv4 or IPv6 addresses. Such networks are useful to provide host connectivity to networks which are only reachable via a guest. A guest with connectivity both to the guest-only network and to another network that is directly reachable from the host can act as a gateway between the networks. A static route added to the "host-visible" network definition provides the routing information so that IP packets can be sent from the virtualization host to guests on the hidden network.
Here is a fragment of a definition which shows the static
route specification as well as the IPv4 and IPv6 definitions
for network addresses which are referred to in the
gateway gateway address specifications. Note
that the third static route specification includes the
metric attribute specification with a value of 2.
This particular route would *not* be preferred if there was
another existing rout on the system with the same address and
prefix but with a lower value for the metric. If there is a
route in the host system configuration that should be overridden
by a route in a virtual network whenever the virtual network is
running, the configuration for the system-defined route should
be modified to have a higher metric, and the route on the
virtual network given a lower metric (for example, the default
metric of "1").
...
<ip address="192.168.122.1" netmask="255.255.255.0">
<dhcp>
<range start="192.168.122.128" end="192.168.122.254"/>
</dhcp>
</ip>
<route address="192.168.222.0" prefix="24" gateway="192.168.122.2"/>
<ip family="ipv6" address="2001:db8:ca2:2::1" prefix="64"/>
<route family="ipv6" address="2001:db8:ca2:3::" prefix="64" gateway="2001:db8:ca2:2::2"/>
<route family="ipv6" address="2001:db9:4:1::" prefix="64" gateway="2001:db8:ca2:2::3" metric='2'/>
...
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'/>
<domain name="example.com"/>
<dns>
<txt name="example" value="example value"/>
<forwarder addr="8.8.8.8"/>
<forwarder domain='example.com' addr="8.8.4.4"/>
<forwarder domain='www.example.com'/>
<srv service='name' protocol='tcp' domain='test-domain-name' target='.'
port='1024' priority='10' weight='10'/>
<host ip='192.168.122.2'>
<hostname>myhost</hostname>
<hostname>myhostalias</hostname>
</host>
</dns>
<ip address="192.168.122.1" netmask="255.255.255.0" localPtr="yes">
<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" localPtr="yes"/>
<route family="ipv6" address="2001:db9:ca1:1::" prefix="64" gateway="2001:db8:ca2:2::2"/>
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
dns
The dns element can have an optional enable
attribute Since 2.2.0.
If enable is "no", then no DNS server will be
setup by libvirt for this network (and any other
configuration in <dns> will be ignored).
If enable is "yes" or unspecified (including
the complete absence of any <dns>
element) then a DNS server will be setup by libvirt to
listen on all IP addresses specified in the network's
configuration.
The dns element
can have an optional forwardPlainNames
attribute Since 1.1.2.
If forwardPlainNames is "no", then DNS resolution
requests for names that are not qualified with a domain
(i.e. names with no "." character) will not be forwarded to
the host's upstream DNS server - they will only be resolved if
they are known locally within the virtual network's own DNS
server. If forwardPlainNames is "yes",
unqualified names will be forwarded to the upstream DNS
server if they can't be resolved by the virtual network's own
DNS server.
<dns> are:
forwarder<forwarder> elements. Each
forwarder element defines an alternate DNS server to use
for some, or all, DNS requests sent to this network's DNS
server. There are two attributes - domain,
and addr; at least one of these must be
specified in any <forwarder>
element. If both domain and addr
are specified, then all requests that match the given
domain will be forwarded to the DNS server at addr. If
only domain is specified, then all matching
domains will be resolved locally (or via the host's
standard DNS forwarding if they can't be resolved
locally). If an addr is specified by itself,
then all DNS requests to the network's DNS server will be
forwarded to the DNS server at that address with no
exceptions. addr Since
1.1.3, domain Since
2.2.0.
txtdns 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
srvdns element can have also 0 or more srv
record elements. Each srv record element defines a DNS SRV record
and has 2 mandatory and 5 optional attributes. The mandatory attributes
are service name and protocol (tcp, udp)
and the optional attributes are target,
port, priority, weight and
domain as defined in DNS server SRV RFC (RFC 2782).
Since 0.9.9
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 IPv4 address
will be their IPv4 default route. For IPv6, the default route is
established via Router Advertisement. 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, the
significant bits of the network address can be specified 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. More than one address of each family can
be defined for a network. The optional localPtr attribute
(since 3.0.0) configures the DNS server to
not forward any reverse DNS requests for IP addresses from the network
configured by the address and
netmask/prefix attributes. For some unusual
network prefixes (not divisible by 8 for IPv4 or not divisible by 4 for
IPv6) libvirt may be unable to compute the PTR domain automatically.
The ip element is supported since
0.3.0. IPv6, multiple addresses on a single network,
family, and prefix are supported
since 0.8.7. The ip element may
contain the following elements:
tftptftp element and its mandatory
root attribute enable TFTP services. The attribute
specifies the path to the root directory served via TFTP. The
tftp element is not supported for IPv6 addresses,
and can only be specified on a single IPv4 address per network.
Since 0.7.1
dhcpdhcp element is supported for
both IPv4 (since 0.3.0) and IPv6
(since 1.0.1), but only for one IP
address of each type per network. The following sub-elements are
supported:
rangestart and end attributes on the
range element specify the boundaries of a pool of
addresses to be provided to DHCP clients. These two addresses
must lie within the scope of the network defined on the parent
ip element. There may be zero or more
range elements specified.
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 IPv4 host 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 itself (the
name attribute). The IPv6 host
element differs slightly from that for IPv4: there is no
mac attribute since a MAC address has no defined
meaning in IPv6. Instead, the name attribute is
used to identify the host to be assigned the IPv6 address. For
DHCPv6, the name is the plain name of the client host sent by the
client to the server. Note that this method of assigning a
specific IP address can also be used for IPv4 instead of the
mac attribute.
Since 0.4.5
bootpbootp element specifies BOOTP
options to be provided by the DHCP server for IPv4 only. 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)
A special XML namespace is available for passing options directly to the underlying dnsmasq configuration file since 5.6.0. Usage of XML namespaces comes with no support guarantees, so use at your own risk.
This example XML will pass the option strings foo=bar and
cname=*.foo.example.com,master.example.com directly to the
underlying dnsmasq instance.
<network xmlns:dnsmasq='http://libvirt.org/schemas/network/dnsmasq/1.0'>
...
<dnsmasq:options>
<dnsmasq:option value="foo=bar"/>
<dnsmasq:option value="cname=*.foo.example.com,master.example.com"/>
</dnsmasq:options>
</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>
<ip family="ipv6" address="2001:db8:ca2:2::1" prefix="64"/>
</network>
Below is a variation of the above example which adds an IPv6 dhcp range definition.
<network>
<name>default6</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">
<dhcp>
<range start="2001:db8:ca2:2:1::10" end="2001:db8:ca2:2:1::ff"/>
</dhcp>
</ip>
</network>
Below is a variation for also providing IPv6 NAT. This can be especially useful when using multiple interfaces where some, such as WiFi cards, can not be bridged (usually on a laptop), making it difficult to provide end-to-end IPv6 routing.
<network>
<name>default6</name>
<bridge name="virbr0"/>
<forward mode="nat">
<nat ipv6='yes'>
<port start='1024' end='65535'/>
</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="fdXX:XXXX:XXXX:NNNN:: prefix="64"/>
</ip>
</network>
IPv6 NAT addressing has some caveats over the more straight forward IPv4 case. RFC 4193 defines the address range fd00::/8 for /48 IPv6 private networks. It should be concatenated with a random 40-bit string (i.e. 10 random hexadecimal digits replacing the X values above, RFC 4193 provides an algorithm if you do not have a source of sufficient randomness). This leaves 0 through ffff for subnets (N above) which you can use at will.
Many operating systems will not consider these addresses as preferential to IPv4, due to some practical history of these addresses being present but unroutable and causing networking issues. On many Linux distributions, you may need to override /etc/gai.conf with values from RFC 3484 to have your IPv6 NAT network correctly preferenced over IPv4.
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>
Below is another IPv6 variation. Instead of a dhcp range being specified, this example has a couple of IPv6 host definitions. Note that most of the dhcp host definitions use an "id" (client id or DUID) since this has proven to be a more reliable way of specifying the interface and its association with an IPv6 address. The first is a DUID-LLT, the second a DUID-LL, and the third a DUID-UUID. Since 1.0.3
<network>
<name>local6</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">
<dhcp>
<host name="paul" ip="2001:db8:ca2:2:3::1"/>
<host id="0:1:0:1:18:aa:62:fe:0:16:3e:44:55:66" ip="2001:db8:ca2:2:3::2"/>
<host id="0:3:0:1:0:16:3e:11:22:33" name="ralph" ip="2001:db8:ca2:2:3::3"/>
<host id="0:4:7e:7d:f0:7d:a8:bc:c5:d2:13:32:11:ed:16:ea:84:63"
name="badbob" ip="2001:db8:ca2:2:3::4"/>
</dhcp>
</ip>
</network>
Below is yet another IPv6 variation. This variation has only IPv6 defined with DHCPv6 on the primary IPv6 network. A static link if defined for a second IPv6 network which will not be directly visible on the bridge interface but there will be a static route defined for this network via the specified gateway. Note that the gateway address must be directly reachable via (on the same subnet as) one of the <ip> addresses defined for this <network>. Since 1.0.6
<network>
<name>net7</name>
<bridge name="virbr7"/>
<forward mode="route"/>
<ip family="ipv6" address="2001:db8:ca2:7::1" prefix="64">
<dhcp>
<range start="2001:db8:ca2:7::100" end="2001:db8:ca2::1ff"/>
<host id="0:4:7e:7d:f0:7d:a8:bc:c5:d2:13:32:11:ed:16:ea:84:63"
name="lucas" ip="2001:db8:ca2:2:3::4"/>
</dhcp>
</ip>
<route family="ipv6" address="2001:db8:ca2:8::" prefix="64" gateway="2001:db8:ca2:7::4"/>
</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 variation of an isolated network defines only IPv6. Note that most of the dhcp host definitions use an "id" (client id or DUID) since this has proven to be a more reliable way of specifying the interface and its association with an IPv6 address. The first is a DUID-LLT, the second a DUID-LL, and the third a DUID-UUID. Since 1.0.3
<network>
<name>sixnet</name>
<bridge name="virbr6"/>
<ip family="ipv6" address="2001:db8:ca2:6::1" prefix="64">
<dhcp>
<host name="peter" ip="2001:db8:ca2:6:6::1"/>
<host id="0:1:0:1:18:aa:62:fe:0:16:3e:44:55:66" ip="2001:db8:ca2:6:6::2"/>
<host id="0:3:0:1:0:16:3e:11:22:33" name="dariusz" ip="2001:db8:ca2:6:6::3"/>
<host id="0:4:7e:7d:f0:7d:a8:bc:c5:d2:13:32:11:ed:16:ea:84:63"
name="anita" ip="2001:db8:ca2:6:6::4"/>
</dhcp>
</ip>
</network>
Since 0.9.4 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>
Since 0.9.4, QEMU and KVM only, requires Linux kernel 2.6.34 or newer 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>
A valid network definition can contain no IPv4 or IPv6 addresses. Such a definition can be used for a "very private" or "very isolated" network since it will not be possible to communicate with the virtualization host via this network. However, this virtual network interface can be used for communication between virtual guest systems. This works for IPv4 and (Since 1.0.1) IPv6. However, the new ipv6='yes' must be added for guest-to-guest IPv6 communication.
<network ipv6='yes'> <name>nogw</name> <uuid>7a3b7497-1ec7-8aef-6d5c-38dff9109e93</uuid> <bridge name="virbr2" stp="on" delay="0"/> <mac address='00:16:3E:5D:C7:9E'/> </network>