formatnetwork.html.in

<html>
  <body>
    <h1>Network XML format</h1>

    <ul id="toc">
    </ul>

    <p>
      This page provides an introduction to the network XML format. For background
      information on the concepts referred to here, consult the <a href="archnetwork.html">network driver architecture</a>
      page.
    </p>

    <h2><a name="elements">Element and attribute overview</a></h2>

    <p>
      The root element required for all virtual networks is
      named <code>network</code> and has no configurable attributes
      (although <span class="since">since 0.10.0</span> there is one
      optional read-only attribute - when examining the live
      configuration of a network, the
      attribute <code>connections</code>, if present, specifies the
      number of guest interfaces currently connected via this
      network).  The network XML format is
      available <span class="since">since 0.3.0</span>
    </p>

    <h3><a name="elementsMetadata">General metadata</a></h3>

    <p>
      The first elements provide basic metadata about the virtual
      network.
    </p>

    <pre>
      &lt;network ipv6='yes'&gt;
        &lt;name&gt;default&lt;/name&gt;
        &lt;uuid&gt;3e3fce45-4f53-4fa7-bb32-11f34168b82b&lt;/uuid&gt;
        ...</pre>

    <dl>
      <dt><code>name</code></dt>
      <dd>The content of the <code>name</code> 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. <span class="since">Since 0.3.0</span></dd>
      <dt><code>uuid</code></dt>
      <dd>The content of the <code>uuid</code> element provides
        a globally unique identifier for the virtual network.
        The format must be RFC 4122 compliant, eg <code>3e3fce45-4f53-4fa7-bb32-11f34168b82b</code>.
        If omitted when defining/creating a new network, a random
        UUID is generated. <span class="since">Since 0.3.0</span></dd>
      <dt><code>ipv6='yes'</code></dt>
      <dd>The new, optional parameter <code>ipv6='yes'</code> 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.
        <span class="since">Since 1.0.1</span></dd>
    </dl>

    <h3><a name="elementsConnect">Connectivity</a></h3>

    <p>
      The next set of elements control how a virtual network is
      provided connectivity to the physical LAN (if at all).
    </p>

    <pre>
        ...
        &lt;bridge name="virbr0" stp="on" delay="5"/&gt;
        &lt;domain name="example.com"/&gt;
        &lt;forward mode="nat" dev="eth0"/&gt;
        ...</pre>

    <dl>
      <dt><code>bridge</code></dt>
      <dd>The <code>name</code> attribute on the <code>bridge</code> 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 <code>vir</code>, but the name
        <code>virbr0</code> is reserved for the "default" virtual
        network.  This element should always be provided when defining
        a new network with a <code>&lt;forward&gt;</code> mode of
        "nat" or "route" (or an isolated network with
        no <code>&lt;forward&gt;</code> element).
        Attribute <code>stp</code> specifies if Spanning Tree Protocol
        is 'on' or 'off' (default is
        'on'). Attribute <code>delay</code> sets the bridge's forward
        delay value in seconds (default is 0).
        <span class="since">Since 0.3.0</span>
      </dd>
      <dt><code>domain</code></dt>
      <dd>
        The <code>name</code> attribute on the <code>domain</code>
        element defines the DNS domain of the DHCP server. This
        element is optional, and is only used for those networks with
        a <code>&lt;forward&gt;</code> mode of "nat" or "route" (or an
        isolated network with no <code>&lt;forward&gt;</code>
        element). <span class="since">Since 0.4.5</span>
      </dd>
      <dt><code>forward</code></dt>
      <dd>Inclusion of the <code>forward</code> element indicates that
        the virtual network is to be connected to the physical
        LAN.<span class="since">Since 0.3.0.</span>
        The <code>mode</code> attribute determines the method of
        forwarding. If there is no <code>forward</code> 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 <code>mode</code> (if there is a <code>forward</code>
        element but mode is not specified, <code>mode='nat'</code> is
        assumed):
        <dl>
          <dt><code>nat</code></dt>
          <dd>
            All traffic between guests connected to this network and
            the physical network will be forwarded to the physical
            network via the host's IP routing stack, after the guest's
            IP address is translated to appear as the host machine's
            public IP address (a.k.a. Network Address Translation, or
            "NAT"). This allows multiple guests, all having access to
            the physical network, on a host that is only allowed a
            single public IP address. If a network has any IPv6
            addresses defined, the IPv6 traffic will be forwarded
            using plain routing, since IPv6 has no concept of NAT.
            Firewall rules will allow outbound connections to any
            other network device whether ethernet, wireless, dialup,
            or VPN. If the <code>dev</code> 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.<span class="since">Since
            0.4.2</span>

            <p><span class="since">Since 1.0.3</span> it is possible to
            specify a public IPv4 address range to be used for the NAT by
            using the <code>&lt;nat&gt;</code> and
            <code>&lt;address&gt;</code> subelements.
            <pre>
...
  &lt;forward mode='nat'&gt;
    &lt;nat&gt;
      &lt;address start='1.2.3.4' end='1.2.3.10'/&gt;
    &lt;/nat&gt;
  &lt;/forward&gt;
...
            </pre>
            An singe IPv4 address can be set by setting
            <code>start</code> and <code>end</code> attributes to
            the same value.
            </p>
          </dd>

          <dt><code>route</code></dt>
          <dd>
            Guest network traffic will be forwarded to the physical
            network via the host's IP routing stack, but without
            having NAT applied. Again, if the <code>dev</code>
            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 <a href="formatnwfilter.html">nwfilter rules</a>
            on the guest's interfaces.)
            <span class="since">Since 0.4.2</span>
          </dd>

          <dt><code>bridge</code></dt>
          <dd>
            This network describes either 1) an existing host bridge
            that was configured outside of libvirt (if
            a <code>&lt;bridge name='xyz'/&gt;</code> element has been
            specified, <span class="since">Since 0.9.4</span>), 2) an
            existing Open vSwitch bridge that was configured outside of
            libvirt (if both a <code>&lt;bridge name='xyz'/&gt;</code>
            element <b>and</b> a <code>&lt;virtualport
            type='openvswitch'/&gt;</code> have been
            specified <span class="since">Since 0.10.0</span>) 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 <code>&lt;interface&gt;</code>
            subelements, <span class="since">Since 0.9.4</span>)
            (see <a href="formatdomain.html#elementsNICSDirect">Direct
            attachment to physical interface</a> for descriptions of
            the various macvtap modes). libvirt doesn't attempt to
            manage the bridge interface at all, thus
            the <code>&lt;bridge&gt;</code> element's <code>stp</code>
            and <code>delay</code> 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.<span class="since">Since 0.9.4</span>
          </dd>
          <dt><code>private</code></dt>
          <dd>
            This network uses a macvtap "direct" connection in
            "private" mode to connect each guest to the network. The
            physical interface to be used will be picked from among
            those listed in <code>&lt;interface&gt;</code> subelements
            of the <code>&lt;forward&gt;</code> element; when using
            802.1Qbh mode (as indicated by
            the <code>&lt;virtualport&gt;</code> 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).<span class="since">Since
            0.9.4</span>
          </dd>
          <dt><code>vepa</code></dt>
          <dd>
            This network uses a macvtap "direct" connection in "vepa"
            mode to connect each guest to the network (this requires
            that the physical interfaces used be connected to a
            vepa-capable hardware switch. The physical interface to be
            used will be picked from among those listed
            in <code>&lt;interface&gt;</code> subelements of
            the <code>&lt;forward&gt;</code> element; multiple guest
            interfaces can share each physical interface (libvirt will
            attempt to balance usage between all available
            interfaces).<span class="since">Since 0.9.4</span>
          </dd>
          <dt><code>passthrough</code></dt>
          <dd>
            This network uses a macvtap "direct" connection in
            "passthrough" mode to connect each guest to the network
            (note that this is <i>not</i> the same thing as "PCI
            passthrough"). The physical interface to be used will be
            picked from among those listed
            in <code>&lt;interface&gt;</code> subelements of
            the <code>&lt;forward&gt;</code> 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).<span class="since">Since 0.9.4</span>
          </dd>
          <dt><code>hostdev</code></dt>
          <dd>
            This network facilitates PCI Passthrough of a network
            device.  A network device is chosen from the interface
            pool and directly assigned to the guest using generic
            device passthrough, after first optionally setting the
            device's MAC address and vlan tag to the configured value,
            and optionally associating the device with an 802.1Qbh
            capable switch using a <code>&lt;virtualport&gt;</code>
            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 <code>&lt; hostdev&gt;</code> device
            definition. <span class="since"> Since 0.10.0</span>

            <p>Note that this "intelligent passthrough" of network
            devices is very similar to the functionality of a
            standard <code>&lt; hostdev&gt;</code> device, the
            difference being that this method allows specifying a MAC
            address, vlan tag, and <code>&lt;virtualport &gt;</code>
            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
            <code>&lt;hostdev&gt;</code> device definition in the
            domain's configuration to assign the device to the guest
            instead of defining an <code>&lt;interface
            type='network'&gt;</code> pointing to a network
            with <code>&lt;forward mode='hostdev'/&gt;</code>.
            </p>
          </dd>
        </dl>
        As mentioned above, a <code>&lt;forward&gt;</code> element can
        have multiple <code>&lt;interface&gt;</code> subelements, each
        one giving the name of a physical interface that can be used
        for this network <span class="since">Since 0.9.4</span>:
        <pre>
...
  &lt;forward mode='passthrough'&gt;
    &lt;interface dev='eth10'/&gt;
    &lt;interface dev='eth11'/&gt;
    &lt;interface dev='eth12'/&gt;
    &lt;interface dev='eth13'/&gt;
    &lt;interface dev='eth14'/&gt;
  &lt;/forward&gt;
...
        </pre>
        <p>
          <span class="since">since 0.10.0</span>,
          <code>&lt;interface&gt;</code> also has an optional read-only
          attribute - when examining the live configuration of a
          network, the attribute <code>connections</code>, if present,
          specifies the number of guest interfaces currently connected
          via this physical interface.
        </p>
        <p>
          Additionally, <span class="since">since 0.9.10</span>, libvirt
          allows a shorthand for specifying all virtual interfaces
          associated with a single physical function, by using
          the <code>&lt;pf&gt;</code> subelement to call out the
          corresponding physical interface associated with multiple
          virtual interfaces:
        </p>
        <pre>
...
  &lt;forward mode='passthrough'&gt;
    &lt;pf dev='eth0'/&gt;
  &lt;/forward&gt;
...
        </pre>

        <p>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.</p>

        <p>
          <span class="since">since 0.10.0</span> When using forward
          mode 'hostdev', the interface pool is specified with a list
          of <code>&lt;address&gt;</code> elements, each of which has
          <code>&lt; type&gt;</code> (must always be <code>'pci'</code>,
          <code>&lt;domain&gt;</code>, <code>&lt;bus&gt;</code>,
          <code>&lt;slot&gt;</code>, and <code>&lt;function&gt;</code>
          attributes.
        </p>
        <pre>
...
  &lt;forward mode='hostdev' managed='yes'&gt;
    &lt;address type='pci' domain='0' bus='4' slot='0' function='1'/&gt;
    &lt;address type='pci' domain='0' bus='4' slot='0' function='2'/&gt;
    &lt;address type='pci' domain='0' bus='4' slot='0' function='3'/&gt;
  &lt;/forward&gt;
...
        </pre>

        Alternatively the interface pool can also be defined using a
        single physical function  <code>&lt;pf&gt;</code> subelement to
        call out the  corresponding physical interface associated with
        multiple virtual interfaces (similar to passthrough mode):

        <pre>
...
  &lt;forward mode='hostdev' managed='yes'&gt;
    &lt;pf dev='eth0'/&gt;
  &lt;/forward&gt;
...
        </pre>

      </dd>
    </dl>
    <h5><a name="elementQoS">Quality of service</a></h5>

<pre>
...
  &lt;forward mode='nat' dev='eth0'/&gt;
  <b>&lt;bandwidth&gt;
    &lt;inbound average='1000' peak='5000' burst='5120'/&gt;
    &lt;outbound average='128' peak='256' burst='256'/&gt;
  &lt;/bandwidth&gt;</b>
...</pre>

      <p>
        This part of network XML provides setting quality of service. Incoming
        and outgoing traffic can be shaped independently. The
        <code>bandwidth</code> element can have at most one <code>inbound</code>
        and at most one <code>outbound</code> 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
        <code>inbound</code> only, and vice versa. Each of these elements have one
        mandatory attribute <code>average</code>. It specifies average bit rate on
        interface being shaped. Then there are two optional attributes:
        <code>peak</code>, which specifies maximum rate at which bridge can send
        data, and <code>burst</code>, amount of bytes that can be burst at
        <code>peak</code> speed. Accepted values for attributes are integer
        numbers, The units for <code>average</code> and <code>peak</code> attributes
        are kilobytes per second, and for the <code>burst</code> just kilobytes.
        The rate is shared equally within domains connected to the network.
        Moreover, <code>bandwidth</code> element can be included in
        <code>portgroup</code> element.
        <span class="since">Since 0.9.4</span>
      </p>

    <h5><a name="elementVlanTag">Setting VLAN tag (on supported network types only)</a></h5>

<pre>
  ...
  &lt;devices&gt;
    &lt;interface type='bridge'&gt;
      <b>&lt;vlan trunk='yes'&gt;</b>
        <b>&lt;tag id='42'/&gt;</b>
        <b>&lt;tag id='47'/&gt;</b>
      <b>&lt;/vlan&gt;</b>
      &lt;source bridge='ovsbr0'/&gt;
      &lt;virtualport type='openvswitch'&gt;
        &lt;parameters interfaceid='09b11c53-8b5c-4eeb-8f00-d84eaa0aaa4f'/&gt;
      &lt;/virtualport&gt;
    &lt;/interface&gt;
  &lt;devices&gt;
  ...</pre>

    <p>
      If (and only if) the network type supports vlan tagging
      transparent to the guest, an optional <code>&lt;vlan&gt;</code>
      element can specify one or more vlan tags to apply to the
      traffic of all guests using this
      network <span class="since">Since 0.10.0</span>. (openvswitch
      and type='hostdev' SR-IOV networks do support transparent vlan
      tagging of guest traffic; everything else, including standard
      linux bridges and libvirt's own virtual networks, <b>do not</b>
      support it. 802.1Qbh (vn-link) and 802.1Qbg (VEPA) switches
      provide their own way (outside of libvirt) to tag guest traffic
      onto specific vlans.) As expected, the <code>tag</code>
      attribute specifies which vlan tag to use. If a network has more
      than one <code>&lt;vlan&gt;</code> element defined, it is
      assumed that the user wants to do VLAN trunking using all the
      specified tags. In the case that vlan trunking with a single tag
      is desired, the optional attribute <code>trunk='yes'</code> can
      be added to the vlan element.
    </p>
    <p>
      <code>&lt;vlan&gt;</code> elements can also be specified in
      a <code>&lt;portgroup&gt;</code> element, as well as directly in
      a domain's <code>&lt;interface&gt;</code> element. In the case
      that a vlan tag is specified in multiple locations, the setting
      in <code>&lt;interface&gt;</code> takes precedence, followed by
      the setting in the <code>&lt;portgroup&gt;</code> selected by
      the interface config. The <code>&lt;vlan&gt;</code>
      in <code>&lt;network&gt;</code> will be selected only if none is
      given in <code>&lt;portgroup&gt;</code>
      or <code>&lt;interface&gt;</code>.
    </p>

    <h5><a name="elementsPortgroup">Portgroups</a></h5>

<pre>
...
  &lt;forward mode='private'/&gt;
    &lt;interface dev="eth20"/&gt;
    &lt;interface dev="eth21"/&gt;
    &lt;interface dev="eth22"/&gt;
    &lt;interface dev="eth23"/&gt;
    &lt;interface dev="eth24"/&gt;
  &lt;/forward&gt;
  <b>&lt;portgroup name='engineering' default='yes'&gt;
    &lt;virtualport type='802.1Qbh'&gt;
      &lt;parameters profileid='test'/&gt;
    &lt;/virtualport&gt;
    &lt;bandwidth&gt;
      &lt;inbound average='1000' peak='5000' burst='5120'/&gt;
      &lt;outbound average='1000' peak='5000' burst='5120'/&gt;
    &lt;/bandwidth&gt;
  &lt;/portgroup&gt;</b>
  <b>&lt;portgroup name='sales'&gt;
    &lt;virtualport type='802.1Qbh'&gt;
      &lt;parameters profileid='salestest'/&gt;
    &lt;/virtualport&gt;
    &lt;bandwidth&gt;
      &lt;inbound average='500' peak='2000' burst='2560'/&gt;
      &lt;outbound average='128' peak='256' burst='256'/&gt;
    &lt;/bandwidth&gt;
  &lt;/portgroup&gt;</b>
...</pre>

    <p>
      <span class="since">Since 0.9.4</span>
      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.
      <span class="since">Since 0.9.4</span> 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 <code>&lt;bandwidth&gt;</code>
      (documented <a href="formatdomain.html#elementQoS">here</a>)
      and <code>&lt;virtualport&gt;</code>
      (documented <a href="formatdomain.html#elementsNICSDirect">here</a>).
      If a domain interface definition specifies a portgroup (by
      adding a <code>portgroup</code> attribute to
      the <code>&lt;source&gt;</code> 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 <code>default='yes'</code>, 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 <code>&lt;bandwidth&gt;</code>

      specified directly in the domain XML will take precedence over
      any setting in the chosen portgroup. if
      a <code>&lt;virtualport&gt;</code> 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.
    </p>

    <h3><a name="elementsAddress">Addressing</a></h3>

    <p>
      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 <code>forward</code> element specified), and for those with
      a forward mode of 'route' or 'nat'.
    </p>

    <pre>
        ...
        &lt;mac address='00:16:3E:5D:C7:9E'/&gt;
        &lt;domain name="example.com"/&gt;
        &lt;dns&gt;
          &lt;txt name="example" value="example value" /&gt;
          &lt;srv service='name' protocol='tcp' domain='test-domain-name' target='.' port='1024' priority='10' weight='10'/&gt;
          &lt;host ip='192.168.122.2'&gt;
            &lt;hostname&gt;myhost&lt;/hostname&gt;
            &lt;hostname&gt;myhostalias&lt;/hostname&gt;
          &lt;/host&gt;
        &lt;/dns&gt;
        &lt;ip address="192.168.122.1" netmask="255.255.255.0"&gt;
          &lt;dhcp&gt;
            &lt;range start="192.168.122.100" end="192.168.122.254" /&gt;
            &lt;host mac="00:16:3e:77:e2:ed" name="foo.example.com" ip="192.168.122.10" /&gt;
            &lt;host mac="00:16:3e:3e:a9:1a" name="bar.example.com" ip="192.168.122.11" /&gt;
          &lt;/dhcp&gt;
        &lt;/ip&gt;
        &lt;ip family="ipv6" address="2001:db8:ca2:2::1" prefix="64" /&gt;
      &lt;/network&gt;</pre>

    <dl>
      <dt><code>mac</code></dt>
      <dd>The <code>address</code> attribute defines a MAC
        (hardware) address formatted as 6 groups of 2-digit
        hexadecimal numbers, the groups separated by colons
        (eg, <code>"52:54:00:1C:DA:2F"</code>).  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. <span class="since">Since 0.8.8</span>
      </dd>
      <dt><code>dns</code></dt><dd>
        The dns element of a network contains configuration information for the
        virtual network's DNS server. <span class="since">Since 0.9.3</span>
        Currently supported elements are:
        <dl>
          <dt><code>txt</code></dt>
          <dd>A <code>dns</code> element can have 0 or more <code>txt</code> 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. <span class="since">Since 0.9.3</span>
          </dd>
          <dt><code>host</code></dt>
          <dd>The <code>host</code> element within <code>dns</code> is the
            definition of DNS hosts to be passed to the DNS service. The IP
            address is identified by the <code>ip</code> attribute and the names
            for that IP address are identified in the <code>hostname</code>
            sub-elements of the <code>host</code> element.
            <span class="since">Since 0.9.3</span>
          </dd>
        </dl>
        <dl>
          <dt><code>srv</code></dt>
          <dd>The <code>dns</code> element can have also 0 or more <code>srv</code>
            record elements. Each <code>srv</code> 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).
            <span class="since">Since 0.9.9</span>
          </dd>
        </dl>
      </dd>
      <dt><code>ip</code></dt>
      <dd>The <code>address</code> 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 <code>netmask</code>
        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 <code>prefix</code>
        attribute, which is an integer (for example, <code>netmask='255.255.255.0'</code>
        could also be given as <code>prefix='24'</code>. The <code>family</code>
        attribute is used to specify the type of address - 'ipv4' or 'ipv6'; if no
        <code>family</code> is given, 'ipv4' is assumed. A network can have more than
        one of each family of address defined, but only a single IPv4 address can have a
        <code>dhcp</code> or <code>tftp</code> element. <span class="since">Since 0.3.0 </span>
        IPv6, multiple addresses on a single network, <code>family</code>, and
        <code>prefix</code> are support <span class="since">Since 0.8.7</span>.
        Similar to IPv4, one IPv6 address per network can also have
        a <code>dhcp</code> definition.  <span class="since">Since 1.0.1</span>

        <dl>
          <dt><code>tftp</code></dt>
          <dd>Immediately within
            the <code>ip</code> element there is an optional <code>tftp</code>
            element. The presence of this element and of its attribute
            <code>root</code> enables TFTP services.  The attribute specifies
            the path to the root directory served via TFTP. <code>tftp</code> is not
            supported for IPv6 addresses, and can only be specified on a single IPv4 address
            per network.
            <span class="since">Since 0.7.1</span>
          </dd>

          <dt><code>dhcp</code></dt>
          <dd>Also within the <code>ip</code> element there is an
            optional <code>dhcp</code> element. The presence of this element
            enables DHCP services on the virtual network. It will further
            contain one or more <code>range</code> elements. The
            <code>dhcp</code> element supported for both
            IPv4 <span class="since">Since 0.3.0</span>
            and IPv6 <span class="since">Since 1.0.1</span>, but
            only for one IP address of each type per network.
            <dl>
              <dt><code>range</code></dt>
              <dd>The <code>start</code> and <code>end</code> attributes on the
                <code>range</code> 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
                <code>ip</code> element.  There may be zero or more
                <code>range</code> elements specified.
                <span class="since">Since 0.3.0</span>
                <code>range</code> can be specified for one IPv4 address,
                one IPv6 address, or both. <span class="since">Since 1.0.1</span>
              </dd>
              <dt><code>host</code></dt>
              <dd>Within the <code>dhcp</code> element there may be zero or more
                <code>host</code> elements.  These specify hosts which will be given
                names and predefined IP addresses by the built-in DHCP server. Any
                IPv4 <code>host</code> element must specify the MAC address of the host to be assigned
                a given name (via the <code>mac</code> attribute), the IP to be
                assigned to that host (via the <code>ip</code> attribute), and the
                name to be given that host by the DHCP server (via the
                <code>name</code> attribute).  <span class="since">Since 0.4.5</span>
                An IPv6 <code>host</code> element differs slightly from that for IPv4:
                there is no <code>mac</code> attribute since a MAC address has no
                defined meaning in IPv6.  Instead, the <code>name</code> 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 instead of the <code>mac</code>
                attribute for IPv4.  <span class="since">Since 1.0.1</span>
              </dd>
              <dt><code>bootp</code></dt>
              <dd>The optional <code>bootp</code>
                element specifies BOOTP options to be provided by the DHCP
                server for IPv4 only.
                Two attributes are supported: <code>file</code> is mandatory and
                gives the file to be used for the boot image; <code>server</code> is
                optional and gives the address of the TFTP server from which the boot
                image will be fetched.  <code>server</code> defaults to the same host
                that runs the DHCP server, as is the case when the <code>tftp</code>
                element is used.  The BOOTP options currently have to be the same
                for all address ranges and statically assigned addresses.<span
                class="since">Since 0.7.1 (<code>server</code> since 0.7.3).</span>
              </dd>
            </dl>
          </dd>
        </dl>
      </dd>
    </dl>

    <h2><a name="examples">Example configuration</a></h2>

    <h3><a name="examplesNAT">NAT based network</a></h3>

    <p>
      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.
    </p>

    <pre>
      &lt;network&gt;
        &lt;name&gt;default&lt;/name&gt;
        &lt;bridge name="virbr0" /&gt;
        &lt;forward mode="nat"/&gt;
        &lt;ip address="192.168.122.1" netmask="255.255.255.0"&gt;
          &lt;dhcp&gt;
            &lt;range start="192.168.122.2" end="192.168.122.254" /&gt;
          &lt;/dhcp&gt;
        &lt;/ip&gt;
        &lt;ip family="ipv6" address="2001:db8:ca2:2::1" prefix="64" /&gt;
      &lt;/network&gt;</pre>


    <p>
      Below is a variation of the above example which adds an IPv6
      dhcp range definition.
    </p>

    <pre>
      &lt;network&gt;
        &lt;name&gt;default6&lt;/name&gt;
        &lt;bridge name="virbr0" /&gt;
        &lt;forward mode="nat"/&gt;
        &lt;ip address="192.168.122.1" netmask="255.255.255.0"&gt;
          &lt;dhcp&gt;
            &lt;range start="192.168.122.2" end="192.168.122.254" /&gt;
          &lt;/dhcp&gt;
        &lt;/ip&gt;
        &lt;ip family="ipv6" address="2001:db8:ca2:2::1" prefix="64" &gt;
          &lt;dhcp&gt;
            &lt;range start="2001:db8:ca2:2:1::10" end="2001:db8:ca2:2:1::ff" /&gt;
          &lt;/dhcp&gt;
        &lt;/ip&gt;
      &lt;/network&gt;</pre>

    <h3><a name="examplesRoute">Routed network config</a></h3>

    <p>
      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
      <code>eth1</code> host network device.
    </p>

    <pre>
      &lt;network&gt;
        &lt;name&gt;local&lt;/name&gt;
        &lt;bridge name="virbr1" /&gt;
        &lt;forward mode="route" dev="eth1"/&gt;
        &lt;ip address="192.168.122.1" netmask="255.255.255.0"&gt;
          &lt;dhcp&gt;
            &lt;range start="192.168.122.2" end="192.168.122.254" /&gt;
          &lt;/dhcp&gt;
        &lt;/ip&gt;
        &lt;ip family="ipv6" address="2001:db8:ca2:2::1" prefix="64" /&gt;
      &lt;/network&gt;</pre>

    <p>
      Below is another IPv6 varition.  Instead of a dhcp range being
      specified, this example has a couple of IPv6 host definitions.
    </p>

    <pre>
      &lt;network&gt;
        &lt;name&gt;local6&lt;/name&gt;
        &lt;bridge name="virbr1" /&gt;
        &lt;forward mode="route" dev="eth1"/&gt;
        &lt;ip address="192.168.122.1" netmask="255.255.255.0"&gt;
          &lt;dhcp&gt;
            &lt;range start="192.168.122.2" end="192.168.122.254" /&gt;
          &lt;/dhcp&gt;
        &lt;/ip&gt;
        &lt;ip family="ipv6" address="2001:db8:ca2:2::1" prefix="64" &gt;
          &lt;dhcp&gt;
            &lt;host name="paul"   ip="2001:db8:ca2:2:3::1" /&gt;
            &lt;host name="bob"    ip="2001:db8:ca2:2:3::2" /&gt;
          &lt;/dhcp&gt;
        &lt;/ip&gt;
      &lt;/network&gt;</pre>

    <h3><a name="examplesPrivate">Isolated network config</a></h3>

    <p>
      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 <code>forward</code> element in the XML
      description.
    </p>

    <pre>
      &lt;network&gt;
        &lt;name&gt;private&lt;/name&gt;
        &lt;bridge name="virbr2" /&gt;
        &lt;ip address="192.168.152.1" netmask="255.255.255.0"&gt;
          &lt;dhcp&gt;
            &lt;range start="192.168.152.2" end="192.168.152.254" /&gt;
          &lt;/dhcp&gt;
        &lt;/ip&gt;
        &lt;ip family="ipv6" address="2001:db8:ca2:3::1" prefix="64" /&gt;
      &lt;/network&gt;</pre>

    <h3><a name="examplesPrivate6">Isolated IPv6 network config</a></h3>

    <p>
      This variation of an isolated network defines only IPv6.
    </p>

    <pre>
      &lt;network&gt;
        &lt;name&gt;sixnet&lt;/name&gt;
        &lt;bridge name="virbr6" /&gt;
        &lt;ip family="ipv6" address="2001:db8:ca2:6::1" prefix="64" &gt;
          &lt;dhcp&gt;
            &lt;host name="peter"   ip="2001:db8:ca2:6:6::1" /&gt;
            &lt;host name="dariusz" ip="2001:db8:ca2:6:6::2" /&gt;
          &lt;/dhcp&gt;
        &lt;/ip&gt;
      &lt;/network&gt;</pre>

    <h3><a name="examplesBridge">Using an existing host bridge</a></h3>

    <p>
      <span class="since">Since 0.9.4</span>
      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).
    </p>

    <pre>
      &lt;network&gt;
        &lt;name&gt;host-bridge&lt;/name&gt;
        &lt;forward mode="bridge"/&gt;
        &lt;bridge name="br0"/&gt;
      &lt;/network&gt;</pre>

    <h3><a name="examplesDirect">Using a macvtap "direct" connection</a></h3>

    <p>
      <span class="since">Since 0.9.4, QEMU and KVM only, requires
      Linux kernel 2.6.34 or newer</span>
      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.
    </p>

    <pre>
      &lt;network&gt;
        &lt;name&gt;direct-macvtap&lt;/name&gt;
        &lt;forward mode="bridge"&gt;
          &lt;interface dev="eth20"/&gt;
          &lt;interface dev="eth21"/&gt;
          &lt;interface dev="eth22"/&gt;
          &lt;interface dev="eth23"/&gt;
          &lt;interface dev="eth24"/&gt;
        &lt;/forward&gt;
      &lt;/network&gt;</pre>

    <h3><a name="examplesNoGateway">Network config with no gateway addresses</a></h3>

    <p>
    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 <span class="since">(Since 1.0.1)</span> IPv6.
    However, the new ipv6='yes' must be added for guest-to-guest IPv6
    communication.
    </p>

    <pre>
      &lt;network ipv6='yes'&gt;
        &lt;name&gt;nogw&lt;/name&gt;
        &lt;uuid&gt;7a3b7497-1ec7-8aef-6d5c-38dff9109e93&lt;/uuid&gt;
        &lt;bridge name="virbr2" stp="on" delay="0" /&gt;
        &lt;mac address='00:16:3E:5D:C7:9E'/&gt;
      &lt;/network&gt;</pre>

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