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<refentry id="systemd.netdev" conditional='ENABLE_NETWORKD'>

  <refentryinfo>
    <title>systemd.network</title>
    <productname>systemd</productname>

    <authorgroup>
      <author>
        <contrib>Developer</contrib>
        <firstname>Tom</firstname>
        <surname>Gundersen</surname>
        <email>teg@jklm.no</email>
      </author>
    </authorgroup>
  </refentryinfo>

  <refmeta>
    <refentrytitle>systemd.netdev</refentrytitle>
    <manvolnum>5</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>systemd.netdev</refname>
    <refpurpose>Virtual Network Device configuration</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <para><filename><replaceable>netdev</replaceable>.netdev</filename></para>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para>Network setup is performed by
    <citerefentry><refentrytitle>systemd-networkd</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
    </para>

    <para>The main Virtual Network Device file must have the extension <filename>.netdev</filename>;
    other extensions are ignored. Virtual network devices are created as soon as networkd is
    started. If a netdev with the specified name already exists, networkd will use that as-is rather
    than create its own. Note that the settings of the pre-existing netdev will not be changed by
    networkd.</para>

    <para>The <filename>.netdev</filename> files are read from the files located in the system
    network directory <filename>/usr/lib/systemd/network</filename>, the volatile runtime network
    directory <filename>/run/systemd/network</filename> and the local administration network
    directory <filename>/etc/systemd/network</filename>. All configuration files are collectively
    sorted and processed in lexical order, regardless of the directories in which they live.
    However, files with identical filenames replace each other. Files in <filename>/etc</filename>
    have the highest priority, files in <filename>/run</filename> take precedence over files with
    the same name in <filename>/usr/lib</filename>. This can be used to override a system-supplied
    configuration file with a local file if needed. As a special case, an empty file (file size 0)
    or symlink with the same name pointing to <filename>/dev/null</filename> disables the
    configuration file entirely (it is "masked").</para>

    <para>Along with the netdev file <filename>foo.netdev</filename>, a "drop-in" directory
    <filename>foo.netdev.d/</filename> may exist. All files with the suffix <literal>.conf</literal>
    from this directory will be parsed after the file itself is parsed. This is useful to alter or
    add configuration settings, without having to modify the main configuration file. Each drop-in
    file must have appropriate section headers.</para>

    <para>In addition to <filename>/etc/systemd/network</filename>, drop-in <literal>.d</literal>
    directories can be placed in <filename>/usr/lib/systemd/network</filename> or
    <filename>/run/systemd/network</filename> directories. Drop-in files in
    <filename>/etc</filename> take precedence over those in <filename>/run</filename> which in turn
    take precedence over those in <filename>/usr/lib</filename>. Drop-in files under any of these
    directories take precedence over the main netdev file wherever located. (Of course, since
    <filename>/run</filename> is temporary and <filename>/usr/lib</filename> is for vendors, it is
    unlikely drop-ins should be used in either of those places.)</para>
  </refsect1>

  <refsect1>
    <title>Supported netdev kinds</title>

    <para>The following kinds of virtual network devices may be
    configured in <filename>.netdev</filename> files:</para>

    <table>
      <title>Supported kinds of virtual network devices</title>

      <tgroup cols='2'>
        <colspec colname='kind' />
        <colspec colname='explanation' />
        <thead><row>
          <entry>Kind</entry>
          <entry>Description</entry>
        </row></thead>
        <tbody>
          <row><entry><varname>bond</varname></entry>
          <entry>A bond device is an aggregation of all its slave devices. See <ulink url="https://www.kernel.org/doc/Documentation/networking/bonding.txt">Linux Ethernet Bonding Driver HOWTO</ulink> for details.Local configuration</entry></row>

          <row><entry><varname>bridge</varname></entry>
          <entry>A bridge device is a software switch, and each of its slave devices and the bridge itself are ports of the switch.</entry></row>

          <row><entry><varname>dummy</varname></entry>
          <entry>A dummy device drops all packets sent to it.</entry></row>

          <row><entry><varname>gre</varname></entry>
          <entry>A Level 3 GRE tunnel over IPv4. See <ulink url="https://tools.ietf.org/html/rfc2784">RFC 2784</ulink> for details.</entry></row>

          <row><entry><varname>gretap</varname></entry>
          <entry>A Level 2 GRE tunnel over IPv4.</entry></row>

          <row><entry><varname>ip6gre</varname></entry>
          <entry>A Level 3 GRE tunnel over IPv6.</entry></row>

          <row><entry><varname>ip6tnl</varname></entry>
          <entry>An IPv4 or IPv6 tunnel over IPv6</entry></row>

          <row><entry><varname>ip6gretap</varname></entry>
          <entry>A Level 2 GRE tunnel over IPv6.</entry></row>

          <row><entry><varname>ipip</varname></entry>
          <entry>An IPv4 over IPv4 tunnel.</entry></row>

          <row><entry><varname>ipvlan</varname></entry>
          <entry>An ipvlan device is a stacked device which receives packets from its underlying device based on IP address filtering.</entry></row>

          <row><entry><varname>macvlan</varname></entry>
          <entry>A macvlan device is a stacked device which receives packets from its underlying device based on MAC address filtering.</entry></row>

          <row><entry><varname>macvtap</varname></entry>
          <entry>A macvtap device is a stacked device which receives packets from its underlying device based on MAC address filtering.</entry></row>

          <row><entry><varname>sit</varname></entry>
          <entry>An IPv6 over IPv4 tunnel.</entry></row>

          <row><entry><varname>tap</varname></entry>
          <entry>A persistent Level 2 tunnel between a network device and a device node.</entry></row>

          <row><entry><varname>tun</varname></entry>
          <entry>A persistent Level 3 tunnel between a network device and a device node.</entry></row>

          <row><entry><varname>veth</varname></entry>
          <entry>An Ethernet tunnel between a pair of network devices.</entry></row>

          <row><entry><varname>vlan</varname></entry>
          <entry>A VLAN is a stacked device which receives packets from its underlying device based on VLAN tagging. See <ulink url="http://www.ieee802.org/1/pages/802.1Q.html">IEEE 802.1Q</ulink> for details.</entry></row>

          <row><entry><varname>vti</varname></entry>
          <entry>An IPv4 over IPSec tunnel.</entry></row>

          <row><entry><varname>vti6</varname></entry>
          <entry>An IPv6 over IPSec tunnel.</entry></row>

          <row><entry><varname>vxlan</varname></entry>
          <entry>A virtual extensible LAN (vxlan), for connecting Cloud computing deployments.</entry></row>

          <row><entry><varname>vrf</varname></entry>
          <entry>A Virtual Routing and Forwarding (<ulink url="https://www.kernel.org/doc/Documentation/networking/vrf.txt">VRF</ulink>) interface to create separate routing and forwarding domains.</entry></row>

          <row><entry><varname>vcan</varname></entry>
          <entry>The virtual CAN driver (vcan). Similar to the network loopback devices, vcan offers a virtual local CAN interface.</entry></row>

        </tbody>
      </tgroup>
    </table>

  </refsect1>

  <refsect1>
    <title>[Match] Section Options</title>

    <para>A virtual network device is only created if the
    <literal>[Match]</literal> section matches the current
    environment, or if the section is empty. The following keys are
    accepted:</para>

    <variablelist class='network-directives'>
      <varlistentry>
        <term><varname>Host=</varname></term>
        <listitem>
          <para>Matches against the hostname or machine ID of the
          host. See <literal>ConditionHost=</literal> in
          <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
          for details.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>Virtualization=</varname></term>
        <listitem>
          <para>Checks whether the system is executed in a virtualized
          environment and optionally test whether it is a specific
          implementation. See
          <literal>ConditionVirtualization=</literal> in
          <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
          for details.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>KernelCommandLine=</varname></term>
        <listitem>
          <para>Checks whether a specific kernel command line option
          is set (or if prefixed with the exclamation mark unset). See
          <literal>ConditionKernelCommandLine=</literal> in
          <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
          for details.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>Architecture=</varname></term>
        <listitem>
          <para>Checks whether the system is running on a specific
          architecture. See <literal>ConditionArchitecture=</literal> in
          <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
          for details.
          </para>
        </listitem>
      </varlistentry>
    </variablelist>

  </refsect1>

  <refsect1>
    <title>[NetDev] Section Options</title>

      <para>The <literal>[NetDev]</literal> section accepts the
      following keys:</para>

      <variablelist class='network-directives'>
        <varlistentry>
          <term><varname>Description=</varname></term>
          <listitem>
            <para>A free-form description of the netdev.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Name=</varname></term>
          <listitem>
            <para>The interface name used when creating the netdev.
            This option is compulsory.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Kind=</varname></term>
          <listitem>
            <para>The netdev kind. This option is compulsory. See the
            <literal>Supported netdev kinds</literal> section for the
            valid keys.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>MTUBytes=</varname></term>
          <listitem>
            <para>The maximum transmission unit in bytes to set for
            the device. The usual suffixes K, M, G, are supported and
            are understood to the base of 1024. This key is not
            currently supported for <literal>tun</literal> or
            <literal>tap</literal> devices.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>MACAddress=</varname></term>
          <listitem>
            <para>The MAC address to use for the device. If none is
            given, one is generated based on the interface name and
            the
            <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
            This key is not currently supported for
            <literal>tun</literal> or <literal>tap</literal> devices.
            </para>
          </listitem>
        </varlistentry>
      </variablelist>
  </refsect1>

    <refsect1>
    <title>[Bridge] Section Options</title>

      <para>The <literal>[Bridge]</literal> section only applies for
      netdevs of kind <literal>bridge</literal>, and accepts the
      following keys:</para>

      <variablelist class='network-directives'>
        <varlistentry>
          <term><varname>HelloTimeSec=</varname></term>
          <listitem>
            <para>HelloTimeSec specifies the number of seconds between two hello packets
            sent out by the root bridge and the designated bridges. Hello packets are
            used to communicate information about the topology throughout the entire
            bridged local area network.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>MaxAgeSec=</varname></term>
          <listitem>
            <para>MaxAgeSec specifies the number of seconds of maximum message age.
            If the last seen (received) hello packet is more than this number of
            seconds old, the bridge in question will start the takeover procedure
            in attempt to become the Root Bridge itself.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>ForwardDelaySec=</varname></term>
          <listitem>
            <para>ForwardDelaySec specifies the number of seconds spent in each
            of the Listening and Learning states before the Forwarding state is entered.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>AgeingTimeSec=</varname></term>
          <listitem>
            <para>This specifies the number of seconds a MAC Address will be kept in
            the forwarding database after having a packet received from this MAC Address.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Priority=</varname></term>
          <listitem>
            <para>The priority of the bridge. An integer between 0 and 65535. A lower value
            means higher priority. The bridge having the lowest priority will be elected as root bridge.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>DefaultPVID=</varname></term>
          <listitem>
            <para>This specifies the default port VLAN ID of a newly attached bridge port.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>MulticastQuerier=</varname></term>
          <listitem>
            <para>A boolean. This setting controls the IFLA_BR_MCAST_QUERIER option in the kernel.
            If enabled, the kernel will send general ICMP queries from a zero source address.
            This feature should allow faster convergence on startup, but it causes some
            multicast-aware switches to misbehave and disrupt forwarding of multicast packets.
            When unset, the kernel's default setting applies.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>MulticastSnooping=</varname></term>
          <listitem>
            <para>A boolean. This setting controls the IFLA_BR_MCAST_SNOOPING option in the kernel.
            If enabled, IGMP snooping monitors the Internet Group Management Protocol (IGMP) traffic
            between hosts and multicast routers. When unset, the kernel's default setting applies.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>VLANFiltering=</varname></term>
          <listitem>
            <para>A boolean. This setting controls the IFLA_BR_VLAN_FILTERING option in the kernel.
            If enabled, the bridge will be started in VLAN-filtering mode. When unset, the kernel's
            default setting applies.
            </para>
          </listitem>
        </varlistentry>
          <varlistentry>
          <term><varname>STP=</varname></term>
          <listitem>
            <para>A boolean. This enables the bridge's Spanning Tree Protocol (STP). When unset,
            the kernel's default setting applies.
            </para>
          </listitem>
        </varlistentry>
      </variablelist>
  </refsect1>

  <refsect1>
    <title>[VLAN] Section Options</title>

      <para>The <literal>[VLAN]</literal> section only applies for
      netdevs of kind <literal>vlan</literal>, and accepts the
      following key:</para>

      <variablelist class='network-directives'>
        <varlistentry>
          <term><varname>Id=</varname></term>
          <listitem>
            <para>The VLAN ID to use. An integer in the range 0–4094.
            This option is compulsory.</para>
          </listitem>
        </varlistentry>
      </variablelist>

  </refsect1>

  <refsect1>
    <title>[MACVLAN] Section Options</title>

    <para>The <literal>[MACVLAN]</literal> section only applies for
    netdevs of kind <literal>macvlan</literal>, and accepts the
    following key:</para>

    <variablelist class='network-directives'>
      <varlistentry>
        <term><varname>Mode=</varname></term>
        <listitem>
          <para>The MACVLAN mode to use. The supported options are
          <literal>private</literal>,
          <literal>vepa</literal>,
          <literal>bridge</literal>, and
          <literal>passthru</literal>.
          </para>
        </listitem>
      </varlistentry>
    </variablelist>

  </refsect1>

    <refsect1>
    <title>[MACVTAP] Section Options</title>

    <para>The <literal>[MACVTAP]</literal> section applies for
    netdevs of kind <literal>macvtap</literal> and accepts the
    same key as <literal>[MACVLAN]</literal>.</para>

    </refsect1>

  <refsect1>
    <title>[IPVLAN] Section Options</title>

    <para>The <literal>[IPVLAN]</literal> section only applies for
    netdevs of kind <literal>ipvlan</literal>, and accepts the
    following key:</para>

    <variablelist class='network-directives'>
      <varlistentry>
        <term><varname>Mode=</varname></term>
          <listitem>
            <para>The IPVLAN mode to use. The supported options are
            <literal>L2</literal> and <literal>L3</literal>.
            </para>
          </listitem>
      </varlistentry>
    </variablelist>

  </refsect1>

  <refsect1>
    <title>[VXLAN] Section Options</title>
    <para>The <literal>[VXLAN]</literal> section only applies for
    netdevs of kind <literal>vxlan</literal>, and accepts the
    following keys:</para>

    <variablelist class='network-directives'>
      <varlistentry>
        <term><varname>Id=</varname></term>
        <listitem>
          <para>The VXLAN ID to use.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>Group=</varname></term>
        <listitem>
          <para>An assigned multicast group IP address.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>TOS=</varname></term>
        <listitem>
          <para>The Type Of Service byte value for a vxlan interface.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>TTL=</varname></term>
        <listitem>
          <para>A fixed Time To Live N on Virtual eXtensible Local
          Area Network packets. N is a number in the range 1–255. 0
          is a special value meaning that packets inherit the TTL
          value.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>MacLearning=</varname></term>
        <listitem>
          <para>A boolean. When true, enables dynamic MAC learning
          to discover remote MAC addresses.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>FDBAgeingSec=</varname></term>
        <listitem>
          <para>The lifetime of Forwarding Database entry learnt by
          the kernel, in seconds.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>MaximumFDBEntries=</varname></term>
        <listitem>
          <para>Configures maximum number of FDB entries.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>ARPProxy=</varname></term>
        <listitem>
          <para>A boolean. When true, enables ARP proxying.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>L2MissNotification=</varname></term>
        <listitem>
          <para>A boolean. When true, enables netlink LLADDR miss
          notifications.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>L3MissNotification=</varname></term>
        <listitem>
          <para>A boolean. When true, enables netlink IP address miss
          notifications.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>RouteShortCircuit=</varname></term>
        <listitem>
          <para>A boolean. When true, route short circuiting is turned
          on.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>UDPChecksum=</varname></term>
        <listitem>
          <para>A boolean. When true, transmitting UDP checksums when doing VXLAN/IPv4 is turned on.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>UDP6ZeroChecksumTx=</varname></term>
        <listitem>
          <para>A boolean. When true, sending zero checksums in VXLAN/IPv6 is turned on.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>UDP6ZeroChecksumRx=</varname></term>
        <listitem>
          <para>A boolean. When true, receiving zero checksums in VXLAN/IPv6 is turned on.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>RemoteChecksumTx=</varname></term>
        <listitem>
          <para>A boolean. When true, remote transmit checksum offload of VXLAN is turned on.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>RemoteChecksumRx=</varname></term>
        <listitem>
          <para>A boolean. When true, remote receive checksum offload in VXLAN is turned on.</para>
        </listitem>
      </varlistentry>
    <varlistentry>
      <term><varname>GroupPolicyExtension=</varname></term>
      <listitem>
        <para>A boolean. When true, it enables Group Policy VXLAN extension security label mechanism
        across network peers based on VXLAN. For details about the Group Policy VXLAN, see the
        <ulink url="https://tools.ietf.org/html/draft-smith-vxlan-group-policy">
        VXLAN Group Policy </ulink> document. Defaults to false.</para>
      </listitem>
    </varlistentry>
    <varlistentry>
      <term><varname>DestinationPort=</varname></term>
      <listitem>
        <para>Configures the default destination UDP port on a per-device basis.
        If destination port is not specified then Linux kernel default will be used.
        Set destination port 4789 to get the IANA assigned value,
        and destination port 0 to get default values.</para>
      </listitem>
    </varlistentry>
    <varlistentry>
      <term><varname>PortRange=</varname></term>
        <listitem>
          <para>Configures VXLAN port range. VXLAN bases source
          UDP port based on flow to help the receiver to be able
          to load balance based on outer header flow. It
          restricts the port range to the normal UDP local
          ports, and allows overriding via configuration.</para>
        </listitem>
      </varlistentry>
    </variablelist>
  </refsect1>
  <refsect1>
    <title>[Tunnel] Section Options</title>

    <para>The <literal>[Tunnel]</literal> section only applies for
    netdevs of kind
    <literal>ipip</literal>,
    <literal>sit</literal>,
    <literal>gre</literal>,
    <literal>gretap</literal>,
    <literal>ip6gre</literal>,
    <literal>ip6gretap</literal>,
    <literal>vti</literal>,
    <literal>vti6</literal>, and
    <literal>ip6tnl</literal> and accepts
    the following keys:</para>

    <variablelist class='network-directives'>
      <varlistentry>
        <term><varname>Local=</varname></term>
        <listitem>
          <para>A static local address for tunneled packets. It must
          be an address on another interface of this host.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>Remote=</varname></term>
        <listitem>
          <para>The remote endpoint of the tunnel.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>TOS=</varname></term>
        <listitem>
          <para>The Type Of Service byte value for a tunnel interface.
          For details about the TOS, see the
          <ulink url="http://tools.ietf.org/html/rfc1349"> Type of
          Service in the Internet Protocol Suite </ulink> document.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>TTL=</varname></term>
        <listitem>
          <para>A fixed Time To Live N on tunneled packets. N is a
          number in the range 1–255. 0 is a special value meaning that
          packets inherit the TTL value. The default value for IPv4
          tunnels is: inherit. The default value for IPv6 tunnels is
          64.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>DiscoverPathMTU=</varname></term>
        <listitem>
          <para>A boolean. When true, enables Path MTU Discovery on
          the tunnel.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>IPv6FlowLabel=</varname></term>
        <listitem>
          <para>Configures the 20-bit flow label (see <ulink url="https://tools.ietf.org/html/rfc6437">
          RFC 6437</ulink>) field in the IPv6 header (see <ulink url="https://tools.ietf.org/html/rfc2460">
          RFC 2460</ulink>), which is used by a node to label packets of a flow.
          It is only used for IPv6 tunnels.
          A flow label of zero is used to indicate packets that have
          not been labeled.
          It can be configured to a value in the range 0–0xFFFFF, or be
          set to <literal>inherit</literal>, in which case the original flowlabel is used.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>CopyDSCP=</varname></term>
        <listitem>
          <para>A boolean. When true, the Differentiated Service Code
          Point (DSCP) field will be copied to the inner header from
          outer header during the decapsulation of an IPv6 tunnel
          packet. DSCP is a field in an IP packet that enables different
          levels of service to be assigned to network traffic.
          Defaults to <literal>no</literal>.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>EncapsulationLimit=</varname></term>
        <listitem>
          <para>The Tunnel Encapsulation Limit option specifies how many additional
          levels of encapsulation are permitted to be prepended to the packet.
          For example, a Tunnel Encapsulation Limit option containing a limit
          value of zero means that a packet carrying that option may not enter
          another tunnel before exiting the current tunnel.
          (see <ulink url="https://tools.ietf.org/html/rfc2473#section-4.1.1"> RFC 2473</ulink>).
          The valid range is 0–255 and <literal>none</literal>. Defaults to 4.
        </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>Key=</varname></term>
        <listitem>
          <para>The <varname>Key=</varname> parameter specifies the same key to use in
          both directions (<varname>InputKey=</varname> and <varname>OutputKey=</varname>).
          The <varname>Key=</varname> is either a number or an IPv4 address-like dotted quad.
          It is used as mark-configured SAD/SPD entry as part of the lookup key (both in data
          and control path) in ip xfrm (framework used to implement IPsec protocol).
          See <ulink url="http://man7.org/linux/man-pages/man8/ip-xfrm.8.html">
          ip-xfrm — transform configuration</ulink> for details. It is only used for VTI/VTI6
          tunnels.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>InputKey=</varname></term>
        <listitem>
          <para>The <varname>InputKey=</varname> parameter specifies the key to use for input.
          The format is same as <varname>Key=</varname>. It is only used for VTI/VTI6 tunnels.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>OutputKey=</varname></term>
        <listitem>
          <para>The <varname>OutputKey=</varname> parameter specifies the key to use for output.
          The format is same as <varname>Key=</varname>. It is only used for VTI/VTI6 tunnels.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>Mode=</varname></term>
        <listitem>
          <para>An <literal>ip6tnl</literal> tunnel can be in one of three
          modes
          <literal>ip6ip6</literal> for IPv6 over IPv6,
          <literal>ipip6</literal> for IPv4 over IPv6 or
          <literal>any</literal> for either.
          </para>
        </listitem>
      </varlistentry>
    </variablelist>
  </refsect1>
  <refsect1>
    <title>[Peer] Section Options</title>

      <para>The <literal>[Peer]</literal> section only applies for
      netdevs of kind <literal>veth</literal> and accepts the
      following keys:</para>

      <variablelist class='network-directives'>
        <varlistentry>
          <term><varname>Name=</varname></term>
          <listitem>
            <para>The interface name used when creating the netdev.
            This option is compulsory.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>MACAddress=</varname></term>
          <listitem>
            <para>The peer MACAddress, if not set, it is generated in
            the same way as the MAC address of the main
            interface.</para>
          </listitem>
        </varlistentry>
      </variablelist>
  </refsect1>
  <refsect1>
    <title>[Tun] Section Options</title>

    <para>The <literal>[Tun]</literal> section only applies for
    netdevs of kind <literal>tun</literal>, and accepts the following
    keys:</para>

    <variablelist class='network-directives'>
      <varlistentry>
        <term><varname>OneQueue=</varname></term>
        <listitem><para>Takes a boolean argument. Configures whether
        all packets are queued at the device (enabled), or a fixed
        number of packets are queued at the device and the rest at the
        <literal>qdisc</literal>. Defaults to
        <literal>no</literal>.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>MultiQueue=</varname></term>
        <listitem><para>Takes a boolean argument. Configures whether
        to use multiple file descriptors (queues) to parallelize
        packets sending and receiving. Defaults to
        <literal>no</literal>.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>PacketInfo=</varname></term>
        <listitem><para>Takes a boolean argument. Configures whether
        packets should be prepended with four extra bytes (two flag
        bytes and two protocol bytes). If disabled, it indicates that
        the packets will be pure IP packets. Defaults to
        <literal>no</literal>.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>VNetHeader=</varname></term>
        <listitem><para>Takes a boolean argument. Configures
        IFF_VNET_HDR flag for a tap device. It allows sending
        and receiving larger Generic Segmentation Offload (GSO)
        packets. This may increase throughput significantly.
        Defaults to
        <literal>no</literal>.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>User=</varname></term>
        <listitem><para>User to grant access to the
        <filename>/dev/net/tun</filename> device.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>Group=</varname></term>
        <listitem><para>Group to grant access to the
        <filename>/dev/net/tun</filename> device.</para>
        </listitem>
      </varlistentry>

    </variablelist>

  </refsect1>

  <refsect1>
    <title>[Tap] Section Options</title>

    <para>The <literal>[Tap]</literal> section only applies for
    netdevs of kind <literal>tap</literal>, and accepts the same keys
    as the <literal>[Tun]</literal> section.</para>
  </refsect1>

  <refsect1>
    <title>[Bond] Section Options</title>

    <para>The <literal>[Bond]</literal> section accepts the following
    key:</para>

    <variablelist class='network-directives'>
      <varlistentry>
        <term><varname>Mode=</varname></term>
        <listitem>
          <para>Specifies one of the bonding policies. The default is
          <literal>balance-rr</literal> (round robin). Possible values are
          <literal>balance-rr</literal>,
          <literal>active-backup</literal>,
          <literal>balance-xor</literal>,
          <literal>broadcast</literal>,
          <literal>802.3ad</literal>,
          <literal>balance-tlb</literal>, and
          <literal>balance-alb</literal>.
          </para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>TransmitHashPolicy=</varname></term>
        <listitem>
          <para>Selects the transmit hash policy to use for slave
          selection in balance-xor, 802.3ad, and tlb modes. Possible
          values are
          <literal>layer2</literal>,
          <literal>layer3+4</literal>,
          <literal>layer2+3</literal>,
          <literal>encap2+3</literal>, and
          <literal>encap3+4</literal>.
          </para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>LACPTransmitRate=</varname></term>
        <listitem>
          <para>Specifies the rate with which link partner transmits
          Link Aggregation Control Protocol Data Unit packets in
          802.3ad mode. Possible values are <literal>slow</literal>,
          which requests partner to transmit LACPDUs every 30 seconds,
          and <literal>fast</literal>, which requests partner to
          transmit LACPDUs every second. The default value is
          <literal>slow</literal>.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>MIIMonitorSec=</varname></term>
        <listitem>
          <para>Specifies the frequency that Media Independent
          Interface link monitoring will occur. A value of zero
          disables MII link monitoring. This value is rounded down to
          the nearest millisecond. The default value is 0.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>UpDelaySec=</varname></term>
        <listitem>
          <para>Specifies the delay before a link is enabled after a
          link up status has been detected. This value is rounded down
          to a multiple of MIIMonitorSec. The default value is
          0.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>DownDelaySec=</varname></term>
        <listitem>
          <para>Specifies the delay before a link is disabled after a
          link down status has been detected. This value is rounded
          down to a multiple of MIIMonitorSec. The default value is
          0.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>LearnPacketIntervalSec=</varname></term>
        <listitem>
          <para>Specifies the number of seconds between instances where the bonding
          driver sends learning packets to each slave peer switch.
          The valid range is 1–0x7fffffff; the default value is 1. This option
          has an effect only for the balance-tlb and balance-alb modes.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>AdSelect=</varname></term>
        <listitem>
          <para>Specifies the 802.3ad aggregation selection logic to use. Possible values are
          <literal>stable</literal>,
          <literal>bandwidth</literal> and
          <literal>count</literal>.
          </para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>FailOverMACPolicy=</varname></term>
        <listitem>
          <para>Specifies whether the active-backup mode should set all slaves to
          the same MAC address at the time of enslavement or, when enabled, to perform special handling of the
          bond's MAC address in accordance with the selected policy. The default policy is none.
          Possible values are
          <literal>none</literal>,
          <literal>active</literal> and
          <literal>follow</literal>.
          </para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>ARPValidate=</varname></term>
        <listitem>
          <para>Specifies whether or not ARP probes and replies should be
          validated in any mode that supports ARP monitoring, or whether
          non-ARP traffic should be filtered (disregarded) for link
          monitoring purposes. Possible values are
          <literal>none</literal>,
          <literal>active</literal>,
          <literal>backup</literal> and
          <literal>all</literal>.
          </para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>ARPIntervalSec=</varname></term>
        <listitem>
          <para>Specifies the ARP link monitoring frequency in milliseconds.
          A value of 0 disables ARP monitoring. The default value is 0.
          </para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>ARPIPTargets=</varname></term>
        <listitem>
          <para>Specifies the IP addresses to use as ARP monitoring peers when
          ARPIntervalSec is greater than 0. These are the targets of the ARP request
          sent to determine the health of the link to the targets.
          Specify these values in IPv4 dotted decimal format. At least one IP
          address must be given for ARP monitoring to function. The
          maximum number of targets that can be specified is 16. The
          default value is no IP addresses.
          </para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>ARPAllTargets=</varname></term>
        <listitem>
          <para>Specifies the quantity of ARPIPTargets that must be reachable
          in order for the ARP monitor to consider a slave as being up.
          This option affects only active-backup mode for slaves with
          ARPValidate enabled. Possible values are
          <literal>any</literal> and
          <literal>all</literal>.
          </para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>PrimaryReselectPolicy=</varname></term>
        <listitem>
          <para>Specifies the reselection policy for the primary slave.  This
          affects how the primary slave is chosen to become the active slave
          when failure of the active slave or recovery of the primary slave
          occurs. This option is designed to prevent flip-flopping between
          the primary slave and other slaves.  Possible values are
          <literal>always</literal>,
          <literal>better</literal> and
          <literal>failure</literal>.
          </para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>ResendIGMP=</varname></term>
        <listitem>
          <para>Specifies the number of IGMP membership reports to be issued after
          a failover event. One membership report is issued immediately after
          the failover, subsequent packets are sent in each 200ms interval.
          The valid range is 0–255. Defaults to 1. A value of 0
          prevents the IGMP membership report from being issued in response
          to the failover event.
          </para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>PacketsPerSlave=</varname></term>
        <listitem>
          <para>Specify the number of packets to transmit through a slave before
            moving to the next one. When set to 0, then a slave is chosen at
            random. The valid range is 0–65535. Defaults to 1. This option
            only has effect when in balance-rr mode.
          </para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>GratuitousARP=</varname></term>
        <listitem>
          <para>Specify the number of peer notifications (gratuitous ARPs and
            unsolicited IPv6 Neighbor Advertisements) to be issued after a
            failover event.  As soon as the link is up on the new slave,
            a peer notification is sent on the  bonding device and each
            VLAN sub-device.  This is repeated at each link monitor interval
            (ARPIntervalSec or MIIMonitorSec, whichever is active) if the number is
            greater than 1. The valid range is 0–255. The default value is 1.
            These options affect only the active-backup mode.
          </para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>AllSlavesActive=</varname></term>
        <listitem>
          <para>A boolean. Specifies that duplicate frames (received on inactive ports)
          should be dropped when false, or delivered when true. Normally, bonding will drop
          duplicate frames (received on inactive ports), which is desirable for
          most users. But there are some times it is nice to allow duplicate
          frames to be delivered. The default value is false (drop duplicate frames
          received on inactive ports).
          </para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>MinLinks=</varname></term>
        <listitem>
          <para>Specifies the minimum number of links that must be active before
          asserting carrier. The default value is 0.
          </para>
        </listitem>
      </varlistentry>

    </variablelist>

    <para>For more detail information see
    <ulink url="https://www.kernel.org/doc/Documentation/networking/bonding.txt">
    Linux Ethernet Bonding Driver HOWTO</ulink></para>

  </refsect1>

  <refsect1>
    <title>Example</title>
    <example>
      <title>/etc/systemd/network/25-bridge.netdev</title>

      <programlisting>[NetDev]
Name=bridge0
Kind=bridge</programlisting>
    </example>

    <example>
      <title>/etc/systemd/network/25-vlan1.netdev</title>

      <programlisting>[Match]
Virtualization=no

[NetDev]
Name=vlan1
Kind=vlan

[VLAN]
Id=1</programlisting>
    </example>
    <example>
      <title>/etc/systemd/network/25-ipip.netdev</title>
      <programlisting>[NetDev]
Name=ipip-tun
Kind=ipip
MTUBytes=1480

[Tunnel]
Local=192.168.223.238
Remote=192.169.224.239
TTL=64</programlisting>
    </example>
    <example>
      <title>/etc/systemd/network/25-tap.netdev</title>
      <programlisting>[NetDev]
Name=tap-test
Kind=tap

[Tap]
MultiQueue=true
PacketInfo=true</programlisting> </example>

    <example>
      <title>/etc/systemd/network/25-sit.netdev</title>
      <programlisting>[NetDev]
Name=sit-tun
Kind=sit
MTUBytes=1480

[Tunnel]
Local=10.65.223.238
Remote=10.65.223.239</programlisting>
    </example>

    <example>
      <title>/etc/systemd/network/25-gre.netdev</title>
      <programlisting>[NetDev]
Name=gre-tun
Kind=gre
MTUBytes=1480

[Tunnel]
Local=10.65.223.238
Remote=10.65.223.239</programlisting>
    </example>

    <example>
      <title>/etc/systemd/network/25-vti.netdev</title>

      <programlisting>[NetDev]
Name=vti-tun
Kind=vti
MTUBytes=1480

[Tunnel]
Local=10.65.223.238
Remote=10.65.223.239</programlisting>
    </example>

    <example>
      <title>/etc/systemd/network/25-veth.netdev</title>
      <programlisting>[NetDev]
Name=veth-test
Kind=veth

[Peer]
Name=veth-peer</programlisting>
    </example>

    <example>
      <title>/etc/systemd/network/25-bond.netdev</title>
      <programlisting>[NetDev]
Name=bond1
Kind=bond

[Bond]
Mode=802.3ad
TransmitHashPolicy=layer3+4
MIIMonitorSec=1s
LACPTransmitRate=fast
</programlisting>
    </example>

    <example>
      <title>/etc/systemd/network/25-dummy.netdev</title>
      <programlisting>[NetDev]
Name=dummy-test
Kind=dummy
MACAddress=12:34:56:78:9a:bc</programlisting>
    </example>
    <example>
      <title>/etc/systemd/network/25-vrf.netdev</title>
      <para>Create a VRF interface with table 42.</para>
      <programlisting>[NetDev]
Name=vrf-test
Kind=vrf

[VRF]
TableId=42</programlisting>
    </example>
  </refsect1>
  <refsect1>
    <title>See Also</title>
    <para>
      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd-networkd</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd.link</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>