man: improve the explanation of "Defaults to unset"

[thirdparty/systemd.git] / man / systemd.network.xml

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

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

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

  <refnamediv>
    <refname>systemd.network</refname>
    <refpurpose>Network configuration</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <para><filename><replaceable>network</replaceable>.network</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 network file must have the extension <filename>.network</filename>; other
    extensions are ignored. Networks are applied to links whenever the links appear.</para>

    <para>The <filename>.network</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 network file <filename>foo.network</filename>, a "drop-in" directory
    <filename>foo.network.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>

    <para>Note that an interface without any static IPv6 addresses configured, and neither DHCPv6
    nor IPv6LL enabled, shall be considered to have no IPv6 support. IPv6 will be automatically
    disabled for that interface by writing "1" to
    <filename>/proc/sys/net/ipv6/conf/<replaceable>ifname</replaceable>/disable_ipv6</filename>.
    </para>
  </refsect1>

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

      <para>The network file contains a <literal>[Match]</literal>
      section, which determines if a given network file may be applied
      to a given device; and a <literal>[Network]</literal> section
      specifying how the device should be configured. The first (in
      lexical order) of the network files that matches a given device
      is applied, all later files are ignored, even if they match as
      well.</para>

      <para>A network file is said to match a device if each of the
      entries in the <literal>[Match]</literal> section matches, or if
      the section is empty. The following keys are accepted:</para>

      <variablelist class='network-directives'>
        <varlistentry>
          <term><varname>MACAddress=</varname></term>
          <listitem>
            <para>A whitespace-separated list of hardware addresses. Use full colon-, hyphen- or dot-delimited hexadecimal. See the example below.
            This option may appear more than one, in which case the lists are merged. If the empty string is assigned to this option, the list
            of hardware addresses defined prior to this is reset.</para>

            <para>Example:
            <programlisting>MACAddress=01:23:45:67:89:ab 00-11-22-33-44-55 AABB.CCDD.EEFF</programlisting></para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Path=</varname></term>
          <listitem>
            <para>A whitespace-separated list of shell-style globs
            matching the persistent path, as exposed by the udev
            property <literal>ID_PATH</literal>. If the list is
            prefixed with a "!", the test is inverted; i.e. it is
            true when <literal>ID_PATH</literal> does not match any
            item in the list.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Driver=</varname></term>
          <listitem>
            <para>A whitespace-separated list of shell-style globs
            matching the driver currently bound to the device, as
            exposed by the udev property <literal>DRIVER</literal>
            of its parent device, or if that is not set the driver
            as exposed by <literal>ethtool -i</literal> of the
            device itself. If the list is prefixed with a "!", the
            test is inverted.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Type=</varname></term>
          <listitem>
            <para>A whitespace-separated list of shell-style globs
            matching the device type, as exposed by the udev property
            <literal>DEVTYPE</literal>. If the list is prefixed with
            a "!", the test is inverted.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Name=</varname></term>
          <listitem>
            <para>A whitespace-separated list of shell-style globs
            matching the device name, as exposed by the udev property
            <literal>INTERFACE</literal>. If the list is prefixed
            with a "!", the test is inverted.</para>
          </listitem>
        </varlistentry>
        <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>KernelVersion=</varname></term>
          <listitem>
            <para>Checks whether the kernel version (as reported by <command>uname -r</command>) matches a certain
            expression (or if prefixed with the exclamation mark does not match it). See
            <literal>ConditionKernelVersion=</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>[Link] Section Options</title>

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

    <variablelist class='network-directives'>
      <varlistentry>
        <term><varname>MACAddress=</varname></term>
        <listitem>
          <para>The hardware address to set for the device.</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.</para>
          <para>Note that if IPv6 is enabled on the interface, and the MTU is chosen
          below 1280 (the minimum MTU for IPv6) it will automatically be increased to this value.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>ARP=</varname></term>
        <listitem>
          <para>A boolean. Enables or disables the ARP (low-level Address Resolution Protocol)
          for this interface. When unset, the kernel's default will be used.</para>
          <para> For example, disabling ARP is useful when creating multiple MACVLAN or VLAN virtual
          interfaces atop a single lower-level physical interface, which will then only serve as a
          link/"bridge" device aggregating traffic to the same physical link and not participate in
          the network otherwise.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>Multicast=</varname></term>
        <listitem>
          <para>A boolean. Enables or disables the multicast flag on the device.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>AllMulticast=</varname></term>
        <listitem>
          <para>A boolean. When this flag is set the driver retrieves all multicast packets from the network.
          This happens when multicast routing is enabled.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>Unmanaged=</varname></term>
        <listitem>
          <para>A boolean. When <literal>yes</literal>, no attempts are
          made to bring up or configure matching links, equivalent to
          when there are no matching network files. Defaults to
          <literal>no</literal>.</para>
          <para>This is useful for preventing later matching network
          files from interfering with certain interfaces that are fully
          controlled by other applications.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>RequiredForOnline=</varname></term>
        <listitem>
          <para>A boolean. When <literal>yes</literal>, the network is deemed
          required when determining whether the system is online when running
          <literal>systemd-networkd-wait-online</literal>.
          When <literal>no</literal>, the network is ignored when checking for
          online state. Defaults to <literal>yes</literal>.</para>
          <para>The network will be brought up normally in all cases, but in
          the event that there is no address being assigned by DHCP or the
          cable is not plugged in, the link will simply remain offline and be
          skipped automatically by <literal>systemd-networkd-wait-online</literal>
          if <literal>RequiredForOnline=no</literal>.</para>
        </listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

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

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

      <variablelist class='network-directives'>
        <varlistentry>
          <term><varname>Description=</varname></term>
          <listitem>
            <para>A description of the device. This is only used for
            presentation purposes.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>DHCP=</varname></term>
          <listitem>
            <para>Enables DHCPv4 and/or DHCPv6 client support. Accepts
            <literal>yes</literal>, <literal>no</literal>,
            <literal>ipv4</literal>, or <literal>ipv6</literal>. Defaults
            to <literal>no</literal>.</para>

            <para>Note that DHCPv6 will by default be triggered by Router
            Advertisement, if that is enabled, regardless of this parameter.
            By enabling DHCPv6 support explicitly, the DHCPv6 client will
            be started regardless of the presence of routers on the link,
            or what flags the routers pass. See
            <literal>IPv6AcceptRA=</literal>.</para>

            <para>Furthermore, note that by default the domain name
            specified through DHCP is not used for name resolution.
            See option <option>UseDomains=</option> below.</para>

            <para>See the <literal>[DHCP]</literal> section below for further configuration options for the DHCP client
            support.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>DHCPServer=</varname></term>
          <listitem>
            <para>A boolean. Enables DHCPv4 server support. Defaults
            to <literal>no</literal>. Further settings for the DHCP
            server may be set in the <literal>[DHCPServer]</literal>
            section described below.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>LinkLocalAddressing=</varname></term>
          <listitem>
            <para>Enables link-local address autoconfiguration. Accepts
            <literal>yes</literal>, <literal>no</literal>,
            <literal>ipv4</literal>, or <literal>ipv6</literal>. Defaults to
            <literal>ipv6</literal>.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>IPv4LLRoute=</varname></term>
          <listitem>
            <para>A boolean. When true, sets up the route needed for
            non-IPv4LL hosts to communicate with IPv4LL-only hosts. Defaults
            to false.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>IPv6Token=</varname></term>
          <listitem>
            <para>An IPv6 address with the top 64 bits unset. When set, indicates the
            64-bit interface part of SLAAC IPv6 addresses for this link. Note that
            the token is only ever used for SLAAC, and not for DHCPv6 addresses, even
            in the case DHCP is requested by router advertisement. By default, the
            token is autogenerated.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>LLMNR=</varname></term>
          <listitem>
            <para>A boolean or <literal>resolve</literal>. When true,
            enables <ulink
            url="https://tools.ietf.org/html/rfc4795">Link-Local
            Multicast Name Resolution</ulink> on the link. When set to
            <literal>resolve</literal>, only resolution is enabled,
            but not host registration and announcement. Defaults to
            true. This setting is read by
            <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>MulticastDNS=</varname></term>
          <listitem>
            <para>A boolean or <literal>resolve</literal>. When true,
            enables <ulink
            url="https://tools.ietf.org/html/rfc6762">Multicast
            DNS</ulink> support on the link. When set to
            <literal>resolve</literal>, only resolution is enabled,
            but not host or service registration and
            announcement. Defaults to false. This setting is read by
            <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>DNSOverTLS=</varname></term>
          <listitem>
            <para>Takes false or
            <literal>opportunistic</literal>. When set to <literal>opportunistic</literal>, enables
            <ulink
            url="https://tools.ietf.org/html/rfc7858">DNS-over-TLS</ulink>
            support on the link. This option defines a
            per-interface setting for
            <citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>'s
            global <varname>DNSOverTLS=</varname> option. Defaults to
            false. This setting is read by
            <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>DNSSEC=</varname></term>
          <listitem>
            <para>A boolean or
            <literal>allow-downgrade</literal>. When true, enables
            <ulink
            url="https://tools.ietf.org/html/rfc4033">DNSSEC</ulink>
            DNS validation support on the link. When set to
            <literal>allow-downgrade</literal>, compatibility with
            non-DNSSEC capable networks is increased, by automatically
            turning off DNSSEC in this case. This option defines a
            per-interface setting for
            <citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>'s
            global <varname>DNSSEC=</varname> option. Defaults to
            false. This setting is read by
            <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>DNSSECNegativeTrustAnchors=</varname></term>
          <listitem><para>A space-separated list of DNSSEC negative
          trust anchor domains. If specified and DNSSEC is enabled,
          look-ups done via the interface's DNS server will be subject
          to the list of negative trust anchors, and not require
          authentication for the specified domains, or anything below
          it. Use this to disable DNSSEC authentication for specific
          private domains, that cannot be proven valid using the
          Internet DNS hierarchy. Defaults to the empty list. This
          setting is read by
          <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>LLDP=</varname></term>
          <listitem>
            <para>Controls support for Ethernet LLDP packet reception. LLDP is a link-layer protocol commonly
            implemented on professional routers and bridges which announces which physical port a system is connected
            to, as well as other related data. Accepts a boolean or the special value
            <literal>routers-only</literal>. When true, incoming LLDP packets are accepted and a database of all LLDP
            neighbors maintained. If <literal>routers-only</literal> is set only LLDP data of various types of routers
            is collected and LLDP data about other types of devices ignored (such as stations, telephones and
            others). If false, LLDP reception is disabled. Defaults to <literal>routers-only</literal>. Use
            <citerefentry><refentrytitle>networkctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> to query the
            collected neighbor data. LLDP is only available on Ethernet links. See <varname>EmitLLDP=</varname> below
            for enabling LLDP packet emission from the local system.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>EmitLLDP=</varname></term>
          <listitem>
            <para>Controls support for Ethernet LLDP packet emission. Accepts a boolean parameter or the special values
            <literal>nearest-bridge</literal>, <literal>non-tpmr-bridge</literal> and
            <literal>customer-bridge</literal>.  Defaults to false, which turns off LLDP packet emission. If not false,
            a short LLDP packet with information about the local system is sent out in regular intervals on the
            link. The LLDP packet will contain information about the local host name, the local machine ID (as stored
            in <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>) and the
            local interface name, as well as the pretty hostname of the system (as set in
            <citerefentry><refentrytitle>machine-info</refentrytitle><manvolnum>5</manvolnum></citerefentry>). LLDP
            emission is only available on Ethernet links. Note that this setting passes data suitable for
            identification of host to the network and should thus not be enabled on untrusted networks, where such
            identification data should not be made available. Use this option to permit other systems to identify on
            which interfaces they are connected to this system. The three special values control propagation of the
            LLDP packets. The <literal>nearest-bridge</literal> setting permits propagation only to the nearest
            connected bridge, <literal>non-tpmr-bridge</literal> permits propagation across Two-Port MAC Relays, but
            not any other bridges, and <literal>customer-bridge</literal> permits propagation until a customer bridge
            is reached. For details about these concepts, see <ulink
            url="https://standards.ieee.org/findstds/standard/802.1AB-2016.html">IEEE 802.1AB-2016</ulink>. Note that
            configuring this setting to true is equivalent to <literal>nearest-bridge</literal>, the recommended and
            most restricted level of propagation. See <varname>LLDP=</varname> above for an option to enable LLDP
            reception.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>BindCarrier=</varname></term>
          <listitem>
            <para>A link name or a list of link names. When set, controls the behavior of the current
            link. When all links in the list are in an operational down state, the current link is brought
            down. When at least one link has carrier, the current interface is brought up.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Address=</varname></term>
          <listitem>
            <para>A static IPv4 or IPv6 address and its prefix length,
            separated by a <literal>/</literal> character. Specify
            this key more than once to configure several addresses.
            The format of the address must be as described in
            <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
            This is a short-hand for an [Address] section only
            containing an Address key (see below). This option may be
            specified more than once.
            </para>

            <para>If the specified address is 0.0.0.0 (for IPv4) or
            [::] (for IPv6), a new address range of the requested size
            is automatically allocated from a system-wide pool of
            unused ranges. The allocated range is checked against all
            current network interfaces and all known network
            configuration files to avoid address range conflicts. The
            default system-wide pool consists of 192.168.0.0/16,
            172.16.0.0/12 and 10.0.0.0/8 for IPv4, and fc00::/7 for
            IPv6. This functionality is useful to manage a large
            number of dynamically created network interfaces with the
            same network configuration and automatic address range
            assignment.</para>

          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Gateway=</varname></term>
          <listitem>
            <para>The gateway address, which must be in the format
            described in
            <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
            This is a short-hand for a [Route] section only containing
            a Gateway key. This option may be specified more than
            once.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>DNS=</varname></term>
          <listitem>
            <para>A DNS server address, which must be in the format
            described in
            <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
            This option may be specified more than once. This setting is read by
            <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Domains=</varname></term>
          <listitem>
            <para>A list of domains which should be resolved using the DNS servers on this link. Each item in the list
            should be a domain name, optionally prefixed with a tilde (<literal>~</literal>). The domains with the
            prefix are called "routing-only domains". The domains without the prefix are called "search domains" and
            are first used as search suffixes for extending single-label host names (host names containing no dots) to
            become fully qualified domain names (FQDNs). If a single-label host name is resolved on this interface,
            each of the specified search domains are appended to it in turn, converting it into a fully qualified
            domain name, until one of them may be successfully resolved.</para>

            <para>Both "search" and "routing-only" domains are used for routing of DNS queries: look-ups for host names
            ending in those domains (hence also single label names, if any "search domains" are listed), are routed to
            the DNS servers configured for this interface. The domain routing logic is particularly useful on
            multi-homed hosts with DNS servers serving particular private DNS zones on each interface.</para>

            <para>The "routing-only" domain <literal>~.</literal> (the tilde indicating definition of a routing domain,
            the dot referring to the DNS root domain which is the implied suffix of all valid DNS names) has special
            effect. It causes all DNS traffic which does not match another configured domain routing entry to be routed
            to DNS servers specified for this interface. This setting is useful to prefer a certain set of DNS servers
            if a link on which they are connected is available.</para>

            <para>This setting is read by
            <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
            "Search domains" correspond to the <varname>domain</varname> and <varname>search</varname> entries in
            <citerefentry project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
            Domain name routing has no equivalent in the traditional glibc API, which has no concept of domain
            name servers limited to a specific link.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>NTP=</varname></term>
          <listitem>
            <para>An NTP server address. This option may be specified more than once. This setting is read by
            <citerefentry><refentrytitle>systemd-timesyncd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>IPForward=</varname></term>
          <listitem><para>Configures IP packet forwarding for the
          system. If enabled, incoming packets on any network
          interface will be forwarded to any other interfaces
          according to the routing table. Takes either a boolean
          argument, or the values <literal>ipv4</literal> or
          <literal>ipv6</literal>, which only enable IP packet
          forwarding for the specified address family.  This controls
          the <filename>net.ipv4.ip_forward</filename> and
          <filename>net.ipv6.conf.all.forwarding</filename> sysctl
          options of the network interface (see <ulink
          url="https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt">ip-sysctl.txt</ulink>
          for details about sysctl options). Defaults to
          <literal>no</literal>.</para>

          <para>Note: this setting controls a global kernel option,
          and does so one way only: if a network that has this setting
          enabled is set up the global setting is turned on.  However,
          it is never turned off again, even after all networks with
          this setting enabled are shut down again.</para>

          <para>To allow IP packet forwarding only between specific
          network interfaces use a firewall.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>IPMasquerade=</varname></term>
          <listitem><para>Configures IP masquerading for the network
          interface. If enabled, packets forwarded from the network
          interface will be appear as coming from the local host.
          Takes a boolean argument. Implies
          <varname>IPForward=ipv4</varname>. Defaults to
          <literal>no</literal>.</para></listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>IPv6PrivacyExtensions=</varname></term>
          <listitem><para>Configures use of stateless temporary
          addresses that change over time (see <ulink
          url="https://tools.ietf.org/html/rfc4941">RFC 4941</ulink>,
          Privacy Extensions for Stateless Address Autoconfiguration
          in IPv6). Takes a boolean or the special values
          <literal>prefer-public</literal> and
          <literal>kernel</literal>. When true, enables the privacy
          extensions and prefers temporary addresses over public
          addresses. When <literal>prefer-public</literal>, enables the
          privacy extensions, but prefers public addresses over
          temporary addresses. When false, the privacy extensions
          remain disabled. When <literal>kernel</literal>, the kernel's
          default setting will be left in place.  Defaults to
          <literal>no</literal>.</para></listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>IPv6AcceptRA=</varname></term>
          <listitem><para>Enable or disable IPv6 Router Advertisement (RA) reception support for the interface.  Takes
          a boolean parameter. If true, RAs are accepted; if false, RAs are ignored, independently of the local
          forwarding state. When not set, the kernel default is used, and RAs are accepted only when local forwarding
          is disabled for that interface.  When RAs are accepted, they may trigger the start of the DHCPv6 client if
          the relevant flags are set in the RA data, or if no routers are found on the link.</para>

          <para>Further settings for the IPv6 RA support may be configured in the
          <literal>[IPv6AcceptRA]</literal> section, see below.</para>

          <para>Also see <ulink
          url="https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt">ip-sysctl.txt</ulink> in the kernel
          documentation regarding <literal>accept_ra</literal>, but note that systemd's setting of
          <constant>1</constant> (i.e. true) corresponds to kernel's setting of <constant>2</constant>.</para>
        </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>IPv6DuplicateAddressDetection=</varname></term>
          <listitem><para>Configures the amount of IPv6 Duplicate
          Address Detection (DAD) probes to send. When unset, the kernel's default will be used.
        </para></listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>IPv6HopLimit=</varname></term>
          <listitem><para>Configures IPv6 Hop Limit. For each router that
          forwards the packet, the hop limit is decremented by 1. When the
          hop limit field reaches zero, the packet is discarded.
          When unset, the kernel's default will be used.
        </para></listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>IPv4ProxyARP=</varname></term>
          <listitem><para>A boolean. Configures proxy ARP for IPv4. Proxy ARP is the technique in which one host,
          usually a router, answers ARP requests intended for another machine. By "faking" its identity,
          the router accepts responsibility for routing packets to the "real" destination. (see <ulink
          url="https://tools.ietf.org/html/rfc1027">RFC 1027</ulink>.
          When unset, the kernel's default will be used.
        </para></listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>IPv6ProxyNDP=</varname></term>
          <listitem><para>A boolean. Configures proxy NDP for IPv6. Proxy NDP (Neighbor Discovery
          Protocol) is a technique for IPv6 to allow routing of addresses to a different
          destination when peers expect them to be present on a certain physical link.
          In this case a router answers Neighbour Advertisement messages intended for
          another machine by offering its own MAC address as destination.
          Unlike proxy ARP for IPv4, it is not enabled globally, but will only send Neighbour
          Advertisement messages for addresses in the IPv6 neighbor proxy table,
          which can also be shown by <command>ip -6 neighbour show proxy</command>.
          systemd-networkd will control the per-interface `proxy_ndp` switch for each configured
          interface depending on this option.
          When unset, the kernel's default will be used.
        </para></listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>IPv6ProxyNDPAddress=</varname></term>
          <listitem><para>An IPv6 address, for which Neighbour Advertisement messages will be
          proxied. This option may be specified more than once. systemd-networkd will add the
          <option>IPv6ProxyNDPAddress=</option> entries to the kernel's IPv6 neighbor proxy table.
          This option implies <option>IPv6ProxyNDP=yes</option> but has no effect if
          <option>IPv6ProxyNDP</option> has been set to false. When unset, the kernel's default will be used.
        </para></listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>IPv6PrefixDelegation=</varname></term>
          <listitem><para>Whether to enable or disable Router Advertisement sending on a link.
          Allowed values are <literal>static</literal> which distributes prefixes as defined in
          the <literal>[IPv6PrefixDelegation]</literal> and any <literal>[IPv6Prefix]</literal>
          sections, <literal>dhcpv6</literal> which requests prefixes using a DHCPv6 client
          configured for another link and any values configured in the
          <literal>[IPv6PrefixDelegation]</literal> section while ignoring all static prefix
          configuration sections, <literal>yes</literal> which uses both static configuration
          and DHCPv6, and <literal>false</literal> which turns off IPv6 prefix delegation
          altogether. Defaults to <literal>false</literal>. See the
          <literal>[IPv6PrefixDelegation]</literal> and the <literal>[IPv6Prefix]</literal>
          sections for more configuration options.
          </para></listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>IPv6MTUBytes=</varname></term>
          <listitem><para>Configures IPv6 maximum transmission unit (MTU).
          An integer greater than or equal to 1280 bytes. When unset, the kernel's default will be used.
          </para></listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Bridge=</varname></term>
          <listitem>
            <para>The name of the bridge to add the link to. See
            <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Bond=</varname></term>
          <listitem>
            <para>The name of the bond to add the link to. See
            <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>VRF=</varname></term>
          <listitem>
            <para>The name of the VRF to add the link to. See
            <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>VLAN=</varname></term>
          <listitem>
            <para>The name of a VLAN to create on the link. See
            <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
            This option may be specified more than once.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>IPVLAN=</varname></term>
          <listitem>
            <para>The name of a IPVLAN to create on the link. See
            <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
            This option may be specified more than once.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>MACVLAN=</varname></term>
          <listitem>
            <para>The name of a MACVLAN to create on the link. See
            <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
            This option may be specified more than once.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>VXLAN=</varname></term>
          <listitem>
            <para>The name of a VXLAN to create on the link. See
            <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
            This option may be specified more than once.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Tunnel=</varname></term>
          <listitem>
            <para>The name of a Tunnel to create on the link. See
            <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
            This option may be specified more than once.</para>
          </listitem>
        </varlistentry>
      <varlistentry>
        <term><varname>ActiveSlave=</varname></term>
        <listitem>
          <para>A boolean. Specifies the new active slave. The <literal>ActiveSlave=</literal>
          option is only valid for following modes:
          <literal>active-backup</literal>,
          <literal>balance-alb</literal> and
          <literal>balance-tlb</literal>. Defaults to false.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>PrimarySlave=</varname></term>
        <listitem>
          <para>A boolean. Specifies which slave is the primary device. The specified
          device will always be the active slave while it is available. Only when the
          primary is off-line will alternate devices be used.  This is useful when
          one slave is preferred over another, e.g. when one slave has higher throughput
          than another. The <literal>PrimarySlave=</literal> option is only valid for
          following modes:
          <literal>active-backup</literal>,
          <literal>balance-alb</literal> and
          <literal>balance-tlb</literal>. Defaults to false.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>ConfigureWithoutCarrier=</varname></term>
        <listitem>
          <para>A boolean. Allows networkd to configure a specific link even if it has no carrier.
          Defaults to false.
          </para>
        </listitem>
      </varlistentry>
      </variablelist>

  </refsect1>

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

      <para>An <literal>[Address]</literal> section accepts the
      following keys. Specify several <literal>[Address]</literal>
      sections to configure several addresses.</para>

      <variablelist class='network-directives'>
        <varlistentry>
          <term><varname>Address=</varname></term>
          <listitem>
            <para>As in the <literal>[Network]</literal> section. This
            key is mandatory.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Peer=</varname></term>
          <listitem>
            <para>The peer address in a point-to-point connection.
            Accepts the same format as the <literal>Address</literal>
            key.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Broadcast=</varname></term>
          <listitem>
            <para>The broadcast address, which must be in the format
            described in
            <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
            This key only applies to IPv4 addresses. If it is not
            given, it is derived from the <literal>Address</literal>
            key.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Label=</varname></term>
          <listitem>
            <para>An address label.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>PreferredLifetime=</varname></term>
          <listitem>
            <para>Allows the default "preferred lifetime" of the address to be overridden.
            Only three settings are accepted: <literal>forever</literal> or <literal>infinity</literal>
            which is the default and means that the address never expires, and <literal>0</literal> which means
            that the address is considered immediately "expired" and will not be used,
            unless explicitly requested. A setting of PreferredLifetime=0 is useful for
            addresses which are added to be used only by a specific application,
            which is then configured to use them explicitly.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Scope=</varname></term>
          <listitem>
            <para>The scope of the address, which can be <literal>global</literal>,
            <literal>link</literal> or <literal>host</literal> or an unsigned integer ranges 0 to 255.
            Defaults to <literal>global</literal>.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>HomeAddress=</varname></term>
          <listitem>
            <para>Takes a boolean argument. Designates this address the "home address" as defined in
            <ulink url="https://tools.ietf.org/html/rfc6275">RFC 6275</ulink>.
            Supported only on IPv6. Defaults to false.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>DuplicateAddressDetection=</varname></term>
          <listitem>
            <para>Takes a boolean argument. Do not perform Duplicate Address Detection
            <ulink url="https://tools.ietf.org/html/rfc4862">RFC 4862</ulink> when adding this address.
            Supported only on IPv6. Defaults to false.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>ManageTemporaryAddress=</varname></term>
          <listitem>
            <para>Takes a boolean argument. If true the kernel manage temporary addresses created
            from this one as template on behalf of Privacy Extensions
            <ulink url="https://tools.ietf.org/html/rfc3041">RFC 3041</ulink>.  For this to become
            active, the use_tempaddr sysctl setting has to be set to a value greater than zero.
            The given address needs to have a prefix length of 64. This flag allows to use privacy
            extensions in a manually configured network, just like if stateless auto-configuration
            was active. Defaults to false. </para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>PrefixRoute=</varname></term>
          <listitem>
            <para>Takes a boolean argument. When adding or modifying an IPv6 address, the userspace
            application needs a way to suppress adding a prefix route. This is for example relevant
            together with IFA_F_MANAGERTEMPADDR, where userspace creates autoconf generated addresses,
            but depending on on-link, no route for the prefix should be added. Defaults to false.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>AutoJoin=</varname></term>
          <listitem>
            <para>Takes a boolean argument. Joining multicast group on ethernet level via
            <command>ip maddr</command> command would not work if we have an Ethernet switch that does
            IGMP snooping since the switch would not replicate multicast packets on  ports that did not
            have IGMP reports for the multicast addresses. Linux vxlan interfaces created via
            <command>ip link add vxlan</command> or networkd's netdev kind vxlan have the group option
            that enables then to do the required join. By extending ip address command with option
            <literal>autojoin</literal> we can get similar functionality for openvswitch (OVS) vxlan
            interfaces as well as other tunneling mechanisms that need to receive multicast traffic.
            Defaults to <literal>no</literal>.</para>
          </listitem>
        </varlistentry>
      </variablelist>
  </refsect1>

    <refsect1>
    <title>[IPv6AddressLabel] Section Options</title>

      <para>An <literal>[IPv6AddressLabel]</literal> section accepts the
      following keys. Specify several <literal>[IPv6AddressLabel]</literal>
      sections to configure several address labels. IPv6 address labels are
      used for address selection. See <ulink url="https://tools.ietf.org/html/rfc3484">RFC 3484</ulink>.
      Precedence is managed by userspace, and only the label itself is stored in the kernel</para>

      <variablelist class='network-directives'>
        <varlistentry>
          <term><varname>Label=</varname></term>
          <listitem>
            <para> The label for the prefix (an unsigned integer) ranges 0 to 4294967294.
            0xffffffff is reserved. This key is mandatory.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Prefix=</varname></term>
          <listitem>
            <para>IPv6 prefix is an address with a prefix length, separated by a slash <literal>/</literal> character.
            This key is mandatory. </para>
          </listitem>
        </varlistentry>
      </variablelist>
  </refsect1>

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

      <para>An <literal>[RoutingPolicyRule]</literal> section accepts the
      following keys. Specify several <literal>[RoutingPolicyRule]</literal>
      sections to configure several rules.</para>

      <variablelist class='network-directives'>
        <varlistentry>
          <term><varname>TypeOfService=</varname></term>
          <listitem>
            <para>Specifies the type of service to match a number between 0 to 255.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>From=</varname></term>
          <listitem>
            <para>Specifies the source address prefix to match. Possibly followed by a slash and the prefix length.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>To=</varname></term>
          <listitem>
            <para>Specifies the destination address prefix to match. Possibly followed by a slash and the prefix length.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>FirewallMark=</varname></term>
          <listitem>
            <para>Specifies the iptables firewall mark value to match (a number between 1 and 4294967295).</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Table=</varname></term>
          <listitem>
            <para>Specifies the routing table identifier to lookup if the rule
            selector matches. The table identifier for a route (a number between 1 and 4294967295).</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Priority=</varname></term>
          <listitem>
            <para>Specifies the priority of this rule. <varname>Priority=</varname> is an unsigned
            integer. Higher number means lower priority, and rules get processed in order of increasing number.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>IncomingInterface=</varname></term>
          <listitem>
            <para>Specifies incoming device to match. If the interface is loopback, the rule only matches packets originating from this host.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>OutgoingInterface=</varname></term>
          <listitem>
            <para>Specifies the outgoing device to match. The outgoing interface is only available for packets originating from local sockets that are bound to a device.</para>
          </listitem>
        </varlistentry>
      </variablelist>
  </refsect1>

  <refsect1>
    <title>[Route] Section Options</title>
      <para>The <literal>[Route]</literal> section accepts the
      following keys. Specify several <literal>[Route]</literal>
      sections to configure several routes.</para>

      <variablelist class='network-directives'>
        <varlistentry>
          <term><varname>Gateway=</varname></term>
          <listitem>
            <para>As in the <literal>[Network]</literal> section.</para>
          </listitem>
        </varlistentry>
         <varlistentry>
           <term><varname>GatewayOnlink=</varname></term>
           <listitem>
             <para>The <literal>GatewayOnlink</literal> option tells the kernel that it does not have
             to check if the gateway is reachable directly by the current machine (i.e., the kernel does
             not need to check if the gateway is attached to the local network), so that we can insert the
             route in the kernel table without it being complained about. A boolean, defaults to <literal>no</literal>.
             </para>
           </listitem>
         </varlistentry>
        <varlistentry>
          <term><varname>Destination=</varname></term>
          <listitem>
            <para>The destination prefix of the route. Possibly
            followed by a slash and the prefix length. If omitted, a
            full-length host route is assumed.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Source=</varname></term>
          <listitem>
            <para>The source prefix of the route. Possibly followed by
            a slash and the prefix length. If omitted, a full-length
            host route is assumed.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Metric=</varname></term>
          <listitem>
            <para>The metric of the route (an unsigned integer).</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>IPv6Preference=</varname></term>
          <listitem>
            <para>Specifies the route preference as defined in <ulink
            url="https://tools.ietf.org/html/rfc4191">RFC4191</ulink> for Router Discovery messages.
            Which can be one of <literal>low</literal> the route has a lowest priority,
            <literal>medium</literal> the route has a default priority or
            <literal>high</literal> the route has a highest priority.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Scope=</varname></term>
          <listitem>
            <para>The scope of the route, which can be <literal>global</literal>,
            <literal>link</literal> or <literal>host</literal>. Defaults to
            <literal>global</literal>.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>PreferredSource=</varname></term>
          <listitem>
            <para>The preferred source address of the route. The address
            must be in the format described in
            <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Table=<replaceable>num</replaceable></varname></term>
          <listitem>
          <para>The table identifier for the route (a number between 1 and 4294967295, or 0 to unset).
          The table can be retrieved using <command>ip route show table <replaceable>num</replaceable></command>.
          </para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Protocol=</varname></term>
          <listitem>
            <para>The protocol identifier for the route. Takes a number between 0 and 255 or the special values
            <literal>kernel</literal>, <literal>boot</literal> and <literal>static</literal>. Defaults to
            <literal>static</literal>.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Type=</varname></term>
          <listitem>
            <para>Specifies the type for the route. If <literal>unicast</literal>, a regular route is defined, i.e. a
            route indicating the path to take to a destination network address. If <literal>blackhole</literal>, packets
            to the defined route are discarded silently. If <literal>unreachable</literal>, packets to the defined route
            are discarded and the ICMP message "Host Unreachable" is generated. If <literal>prohibit</literal>, packets
            to the defined route are discarded and the ICMP message "Communication Administratively Prohibited" is
            generated. If <literal>throw</literal>, route lookup in the current routing table will fail and the route
            selection process will return to Routing Policy Database (RPDB). Defaults to <literal>unicast</literal>.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>InitialCongestionWindow=</varname></term>
          <listitem>
            <para>The TCP initial congestion window is used during the start of a TCP connection. During the start of a TCP
            session, when a client requests a resource, the server's initial congestion window determines how many data bytes
            will be sent during the initial burst of data. Takes a size in bytes between 1 and 4294967295 (2^32 - 1). The usual
            suffixes K, M, G are supported and are understood to the base of 1024. When unset, the kernel's default will be used.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>InitialAdvertisedReceiveWindow=</varname></term>
          <listitem>
            <para>The TCP initial advertised receive window is the amount of receive data (in bytes) that can initally be buffered at one time
            on a connection. The sending host can send only that amount of data before waiting for an acknowledgment and window update
            from the receiving host. Takes a size in bytes between 1 and 4294967295 (2^32 - 1). The usual suffixes K, M, G are supported
            and are understood to the base of 1024. When unset, the kernel's default will be used.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>QuickAck=</varname></term>
          <listitem>
            <para>Takes a boolean argument. When true enables TCP quick ack mode for the route. When unset, the kernel's default will be used.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry>
        <term><varname>MTUBytes=</varname></term>
        <listitem>
          <para>The maximum transmission unit in bytes to set for the
          route. The usual suffixes K, M, G, are supported and are
          understood to the base of 1024.</para>
          <para>Note that if IPv6 is enabled on the interface, and the MTU is chosen
          below 1280 (the minimum MTU for IPv6) it will automatically be increased to this value.</para>
        </listitem>
      </varlistentry>
      </variablelist>
  </refsect1>

  <refsect1>
    <title>[DHCP] Section Options</title>
      <para>The <literal>[DHCP]</literal> section configures the
      DHCPv4 and DHCP6 client, if it is enabled with the
      <varname>DHCP=</varname> setting described above:</para>

      <variablelist class='network-directives'>
        <varlistentry>
          <term><varname>UseDNS=</varname></term>
          <listitem>
            <para>When true (the default), the DNS servers received
            from the DHCP server will be used and take precedence over
            any statically configured ones.</para>

            <para>This corresponds to the <option>nameserver</option>
            option in <citerefentry
            project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>UseNTP=</varname></term>
          <listitem>
            <para>When true (the default), the NTP servers received
            from the DHCP server will be used by systemd-timesyncd
            and take precedence over any statically configured ones.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>UseMTU=</varname></term>
          <listitem>
            <para>When true, the interface maximum transmission unit
            from the DHCP server will be used on the current link.
            If <varname>MTUBytes=</varname> is set, then this setting is ignored.
            Defaults to false.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Anonymize=</varname></term>
          <listitem>
            <para>Takes a boolean argument. When true, the options sent to the DHCP server will
            follow the <ulink url="https://tools.ietf.org/html/rfc7844">RFC 7844</ulink>
            (Anonymity Profiles for DHCP Clients) to minimize disclosure of identifying information.
            Defaults to false.</para>

            <para>This option should only be set to true when
            <varname>MACAddressPolicy=</varname> is set to <literal>random</literal>
            (see <citerefentry
            project='man-pages'><refentrytitle>systemd.link</refentrytitle><manvolnum>5</manvolnum></citerefentry>).</para>

            <para>Note that this configuration will overwrite others.
            In concrete, the following variables will be ignored:
            <varname>SendHostname=</varname>, <varname>ClientIdentifier=</varname>,
            <varname>UseRoutes=</varname>, <varname>SendHostname=</varname>,
            <varname>UseMTU=</varname>, <varname>VendorClassIdentifier=</varname>,
            <varname>UseTimezone=</varname>.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>SendHostname=</varname></term>
          <listitem>
            <para>When true (the default), the machine's hostname will be sent to the DHCP server.
            Note that the machine's hostname must consist only of 7-bit ASCII lower-case characters and
            no spaces or dots, and be formatted as a valid DNS domain name. Otherwise, the hostname is not
            sent even if this is set to true.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>UseHostname=</varname></term>
          <listitem>
            <para>When true (the default), the hostname received from
            the DHCP server will be set as the transient hostname of the system.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Hostname=</varname></term>
          <listitem>
            <para>Use this value for the hostname which is sent to the DHCP server, instead of machine's hostname.
            Note that the specified hostname must consist only of 7-bit ASCII lower-case characters and
            no spaces or dots, and be formatted as a valid DNS domain name.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>UseDomains=</varname></term>
          <listitem>
            <para>Takes a boolean argument, or the special value <literal>route</literal>. When true, the domain name
            received from the DHCP server will be used as DNS search domain over this link, similar to the effect of
            the <option>Domains=</option> setting. If set to <literal>route</literal>, the domain name received from
            the DHCP server will be used for routing DNS queries only, but not for searching, similar to the effect of
            the <option>Domains=</option> setting when the argument is prefixed with <literal>~</literal>. Defaults to
            false.</para>

            <para>It is recommended to enable this option only on trusted networks, as setting this affects resolution
            of all host names, in particular of single-label names. It is generally safer to use the supplied domain
            only as routing domain, rather than as search domain, in order to not have it affect local resolution of
            single-label names.</para>

            <para>When set to true, this setting corresponds to the <option>domain</option> option in <citerefentry
            project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>UseRoutes=</varname></term>
          <listitem>
            <para>When true (the default), the static routes will be requested from the DHCP server and added to the
              routing table with a metric of 1024, and a scope of "global", "link" or "host", depending on the route's
              destination and gateway. If the destination is on the local host, e.g., 127.x.x.x, or the same as the
              link's own address, the scope will be set to "host". Otherwise if the gateway is null (a direct route), a
              "link" scope will be used. For anything else, scope defaults to "global".</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term><varname>UseTimezone=</varname></term>

          <listitem><para>When true, the timezone received from the
          DHCP server will be set as timezone of the local
          system. Defaults to <literal>no</literal>.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term><varname>CriticalConnection=</varname></term>
          <listitem>
            <para>When true, the connection will never be torn down
            even if the DHCP lease expires. This is contrary to the
            DHCP specification, but may be the best choice if, say,
            the root filesystem relies on this connection. Defaults to
            false.</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term><varname>ClientIdentifier=</varname></term>
          <listitem>
            <para>The DHCPv4 client identifier to use. Takes one of <literal>mac</literal>, <literal>duid</literal> or <literal>duid-only</literal>.
            If set to <literal>mac</literal>, the MAC address of the link is used.
            If set to <literal>duid</literal>, an RFC4361-compliant Client ID, which is the combination of IAID and DUID (see below), is used.
            If set to <literal>duid-only</literal>, only DUID is used, this may not be RFC compliant, but some setups may require to use this.
            Defaults to <literal>duid</literal>.</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term><varname>VendorClassIdentifier=</varname></term>
          <listitem>
            <para>The vendor class identifier used to identify vendor
            type and configuration.</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term><varname>UserClass=</varname></term>
          <listitem>
            <para>A DHCPv4 client can use UserClass option to identify the type or category of user or applications
            it represents. The information contained in this option is a string that represents the user class of which
            the client is a member. Each class sets an identifying string of information to be used by the DHCP
            service to classify clients. Takes a whitespace-separated list of strings.</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term><varname>DUIDType=</varname></term>
          <listitem>
            <para>Override the global <varname>DUIDType</varname> setting for this network. See
            <citerefentry><refentrytitle>networkd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
            for a description of possible values.</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term><varname>DUIDRawData=</varname></term>
          <listitem>
            <para>Override the global <varname>DUIDRawData</varname> setting for this network. See
            <citerefentry><refentrytitle>networkd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
            for a description of possible values.</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term><varname>IAID=</varname></term>
          <listitem>
            <para>The DHCP Identity Association Identifier (IAID) for the interface, a 32-bit unsigned integer.</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term><varname>RequestBroadcast=</varname></term>
          <listitem>
            <para>Request the server to use broadcast messages before
            the IP address has been configured. This is necessary for
            devices that cannot receive RAW packets, or that cannot
            receive packets at all before an IP address has been
            configured. On the other hand, this must not be enabled on
            networks where broadcasts are filtered out.</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term><varname>RouteMetric=</varname></term>
          <listitem>
            <para>Set the routing metric for routes specified by the
            DHCP server.</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term><varname>RouteTable=<replaceable>num</replaceable></varname></term>
          <listitem>
            <para>The table identifier for DHCP routes (a number between 1 and 4294967295, or 0 to unset).
            The table can be retrieved using <command>ip route show table <replaceable>num</replaceable></command>.
            </para>
            <para>When used in combination with <varname>VRF=</varname> the
            VRF's routing table is used unless this parameter is specified.
            </para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term><varname>ListenPort=</varname></term>
          <listitem>
            <para>Allow setting custom port for the DHCP client to listen on.</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term><varname>RapidCommit=</varname></term>
          <listitem>
            <para>A boolean. The DHCPv6 client can obtain configuration parameters from a DHCPv6 server through
            a rapid two-message exchange (solicit and reply). When the rapid commit option is enabled by both
            the DHCPv6 client and the DHCPv6 server, the two-message exchange is used, rather than the default
            four-method exchange (solicit, advertise, request, and reply). The two-message exchange provides
            faster client configuration and is beneficial in environments in which networks are under a heavy load.
            See <ulink url="https://tools.ietf.org/html/rfc3315#section-17.2.1">RFC 3315</ulink> for details.
            Defaults to true.</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term><varname>ForceDHCPv6PDOtherInformation=</varname></term>
          <listitem>
            <para>A boolean that enforces DHCPv6 stateful mode when the 'Other information' bit is set in
            Router Advertisement messages. By default setting only the 'O' bit in Router Advertisements
            makes DHCPv6 request network information in a stateless manner using a two-message Information
            Request and Information Reply message exchange.
            <ulink url="https://tools.ietf.org/html/rfc7084">RFC 7084</ulink>, requirement WPD-4, updates
            this behavior for a Customer Edge router so that stateful DHCPv6 Prefix Delegation is also
            requested when only the 'O' bit is set in Router Advertisements. This option enables such a CE
            behavior as it is impossible to automatically distinguish the intention of the 'O' bit otherwise.
            By default this option is set to 'false', enable it if no prefixes are delegated when the device
            should be acting as a CE router.</para>
          </listitem>
        </varlistentry>

      </variablelist>
    </refsect1>

  <refsect1>
    <title>[IPv6AcceptRA] Section Options</title>
      <para>The <literal>[IPv6AcceptRA]</literal> section configures the IPv6 Router Advertisement
      (RA) client, if it is enabled with the <varname>IPv6AcceptRA=</varname> setting described
      above:</para>

      <variablelist class='network-directives'>
        <varlistentry>
          <term><varname>UseDNS=</varname></term>
          <listitem>
            <para>When true (the default), the DNS servers received in the Router Advertisement will be used and take
            precedence over any statically configured ones.</para>

            <para>This corresponds to the <option>nameserver</option> option in <citerefentry
            project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term><varname>UseDomains=</varname></term>
          <listitem>
            <para>Takes a boolean argument, or the special value <literal>route</literal>. When true, the domain name
            received via IPv6 Router Advertisement (RA) will be used as DNS search domain over this link, similar to
            the effect of the <option>Domains=</option> setting. If set to <literal>route</literal>, the domain name
            received via IPv6 RA will be used for routing DNS queries only, but not for searching, similar to the
            effect of the <option>Domains=</option> setting when the argument is prefixed with
            <literal>~</literal>. Defaults to false.</para>

            <para>It is recommended to enable this option only on trusted networks, as setting this affects resolution
            of all host names, in particular of single-label names. It is generally safer to use the supplied domain
            only as routing domain, rather than as search domain, in order to not have it affect local resolution of
            single-label names.</para>

            <para>When set to true, this setting corresponds to the <option>domain</option> option in <citerefentry
            project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term><varname>RouteTable=<replaceable>num</replaceable></varname></term>
          <listitem>
            <para>The table identifier for the routes received in the Router Advertisement
            (a number between 1 and 4294967295, or 0 to unset).
            The table can be retrieved using <command>ip route show table <replaceable>num</replaceable></command>.
            </para>
          </listitem>
        </varlistentry>
      </variablelist>
  </refsect1>

  <refsect1>
    <title>[DHCPServer] Section Options</title>
    <para>The <literal>[DHCPServer]</literal> section contains
    settings for the DHCP server, if enabled via the
    <varname>DHCPServer=</varname> option described above:</para>

    <variablelist class='network-directives'>

      <varlistentry>
        <term><varname>PoolOffset=</varname></term>
        <term><varname>PoolSize=</varname></term>

        <listitem><para>Configures the pool of addresses to hand out. The pool
        is a contiguous sequence of IP addresses in the subnet configured for
        the server address, which does not include the subnet nor the broadcast
        address. <varname>PoolOffset=</varname> takes the offset of the pool
        from the start of subnet, or zero to use the default value.
        <varname>PoolSize=</varname> takes the number of IP addresses in the
        pool or zero to use the default value. By default, the pool starts at
        the first address after the subnet address and takes up the rest of
        the subnet, excluding the broadcast address. If the pool includes
        the server address (the default), this is reserved and not handed
        out to clients.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>DefaultLeaseTimeSec=</varname></term>
        <term><varname>MaxLeaseTimeSec=</varname></term>

        <listitem><para>Control the default and maximum DHCP lease
        time to pass to clients. These settings take time values in seconds or
        another common time unit, depending on the suffix. The default
        lease time is used for clients that did not ask for a specific
        lease time. If a client asks for a lease time longer than the
        maximum lease time, it is automatically shortened to the
        specified time. The default lease time defaults to 1h, the
        maximum lease time to 12h. Shorter lease times are beneficial
        if the configuration data in DHCP leases changes frequently
        and clients shall learn the new settings with shorter
        latencies. Longer lease times reduce the generated DHCP
        network traffic.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>EmitDNS=</varname></term>
        <term><varname>DNS=</varname></term>

        <listitem><para>Configures whether the DHCP leases handed out
        to clients shall contain DNS server information. The
        <varname>EmitDNS=</varname> setting takes a boolean argument
        and defaults to <literal>yes</literal>. The DNS servers to
        pass to clients may be configured with the
        <varname>DNS=</varname> option, which takes a list of IPv4
        addresses. If the <varname>EmitDNS=</varname> option is
        enabled but no servers configured, the servers are
        automatically propagated from an "uplink" interface that has
        appropriate servers set. The "uplink" interface is determined
        by the default route of the system with the highest
        priority. Note that this information is acquired at the time
        the lease is handed out, and does not take uplink interfaces
        into account that acquire DNS or NTP server information at a
        later point. DNS server propagation does not take
        <filename>/etc/resolv.conf</filename> into account. Also, note
        that the leases are not refreshed if the uplink network
        configuration changes. To ensure clients regularly acquire the
        most current uplink DNS server information, it is thus
        advisable to shorten the DHCP lease time via
        <varname>MaxLeaseTimeSec=</varname> described
        above.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>EmitNTP=</varname></term>
        <term><varname>NTP=</varname></term>

        <listitem><para>Similar to the <varname>EmitDNS=</varname> and
        <varname>DNS=</varname> settings described above, these
        settings configure whether and what NTP server information
        shall be emitted as part of the DHCP lease. The same syntax,
        propagation semantics and defaults apply as for
        <varname>EmitDNS=</varname> and
        <varname>DNS=</varname>.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>EmitRouter=</varname></term>

        <listitem><para>Similar to the <varname>EmitDNS=</varname>
        setting described above, this setting configures whether the
        DHCP lease should contain the router option. The same syntax,
        propagation semantics and defaults apply as for
        <varname>EmitDNS=</varname>.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>EmitTimezone=</varname></term>
        <term><varname>Timezone=</varname></term>

        <listitem><para>Configures whether the DHCP leases handed out
        to clients shall contain timezone information. The
        <varname>EmitTimezone=</varname> setting takes a boolean
        argument and defaults to <literal>yes</literal>. The
        <varname>Timezone=</varname> setting takes a timezone string
        (such as <literal>Europe/Berlin</literal> or
        <literal>UTC</literal>) to pass to clients. If no explicit
        timezone is set, the system timezone of the local host is
        propagated, as determined by the
        <filename>/etc/localtime</filename> symlink.</para></listitem>
      </varlistentry>

    </variablelist>
  </refsect1>

  <refsect1>
    <title>[IPv6PrefixDelegation] Section Options</title>
    <para>The <literal>[IPv6PrefixDelegation]</literal> section contains
    settings for sending IPv6 Router Advertisements and whether to act as
    a router, if enabled via the <varname>IPv6PrefixDelegation=</varname>
    option described above. IPv6 network prefixes are defined with one or
    more <literal>[IPv6Prefix]</literal> sections.</para>

    <variablelist class='network-directives'>

      <varlistentry>
        <term><varname>Managed=</varname></term>
        <term><varname>OtherInformation=</varname></term>

        <listitem><para>Controls whether a DHCPv6 server is used to acquire IPv6
        addresses on the network link when <varname>Managed=</varname> boolean
        is set to <literal>true</literal> or if only additional network
        information can be obtained via DHCPv6 for the network link when
        <varname>OtherInformation=</varname> boolean is set to
        <literal>true</literal>. Both settings default to
        <literal>false</literal>, which means that a DHCPv6 server is not being
        used.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>RouterLifetimeSec=</varname></term>

        <listitem><para>Configures the IPv6 router lifetime in seconds. If set,
        this host also announces itself in Router Advertisements as an IPv6
        router for the network link. When unset, the host is not acting as a router.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>RouterPreference=</varname></term>

        <listitem><para>Configures IPv6 router preference if
        <varname>RouterLifetimeSec=</varname> is non-zero. Valid values are
        <literal>high</literal>, <literal>medium</literal> and
        <literal>low</literal>, with <literal>normal</literal> and
        <literal>default</literal> added as synonyms for
        <literal>medium</literal> just to make configuration easier. See
        <ulink url="https://tools.ietf.org/html/rfc4191">RFC 4191</ulink>
        for details. Defaults to <literal>medium</literal>.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>EmitDNS=</varname></term>
        <term><varname>DNS=</varname></term>

        <listitem><para><varname>DNS=</varname> specifies a list of recursive
        DNS server IPv6 addresses that distributed via Router Advertisement
        messages when <varname>EmitDNS=</varname> is true. If <varname>DNS=
        </varname> is empty, DNS servers are read from the
        <literal>[Network]</literal> section. If the
        <literal>[Network]</literal> section does not contain any DNS servers
        either, DNS servers from the uplink with the highest priority default
        route are used. When <varname>EmitDNS=</varname> is false, no DNS server
        information is sent in Router Advertisement messages.
        <varname>EmitDNS=</varname> defaults to true.
        </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>EmitDomains=</varname></term>
        <term><varname>Domains=</varname></term>

        <listitem><para>A list of DNS search domains distributed via Router
        Advertisement messages when <varname>EmitDomains=</varname> is true. If
        <varname>Domains=</varname> is empty, DNS search domains are read from the
        <literal>[Network]</literal> section. If the <literal>[Network]</literal>
        section does not contain any DNS search domains either, DNS search
        domains from the uplink with the highest priority default route are
        used. When <varname>EmitDomains=</varname> is false, no DNS search domain
        information is sent in Router Advertisement messages.
        <varname>EmitDomains=</varname> defaults to true.
        </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>DNSLifetimeSec=</varname></term>

        <listitem><para>Lifetime in seconds for the DNS server addresses listed
        in <varname>DNS=</varname> and search domains listed in
        <varname>Domains=</varname>.</para></listitem>
      </varlistentry>

    </variablelist>
    </refsect1>

      <refsect1>
    <title>[IPv6Prefix] Section Options</title>
    <para>One or more <literal>[IPv6Prefix]</literal> sections contain the IPv6
    prefixes that are announced via Router Advertisements. See
    <ulink url="https://tools.ietf.org/html/rfc4861">RFC 4861</ulink>
    for further details.</para>

    <variablelist class='network-directives'>

      <varlistentry>
        <term><varname>AddressAutoconfiguration=</varname></term>
        <term><varname>OnLink=</varname></term>

        <listitem><para>Boolean values to specify whether IPv6 addresses can be
        autoconfigured with this prefix and whether the prefix can be used for
        onlink determination. Both settings default to <literal>true</literal>
        in order to ease configuration.
        </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>Prefix=</varname></term>

        <listitem><para>The IPv6 prefix that is to be distributed to hosts.
        Similarly to configuring static IPv6 addresses, the setting is
        configured as an IPv6 prefix and its prefix length, separated by a
        <literal>/</literal> character. Use multiple
        <literal>[IPv6Prefix]</literal> sections to configure multiple IPv6
        prefixes since prefix lifetimes, address autoconfiguration and onlink
        status may differ from one prefix to another.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>PreferredLifetimeSec=</varname></term>
        <term><varname>ValidLifetimeSec=</varname></term>

        <listitem><para>Preferred and valid lifetimes for the prefix measured in
        seconds. <varname>PreferredLifetimeSec=</varname> defaults to 604800
        seconds (one week) and <varname>ValidLifetimeSec=</varname> defaults
        to 2592000 seconds (30 days).</para></listitem>
      </varlistentry>

    </variablelist>
    </refsect1>

    <refsect1>
    <title>[Bridge] Section Options</title>
      <para>The <literal>[Bridge]</literal> section accepts the
      following keys.</para>
      <variablelist class='network-directives'>
        <varlistentry>
          <term><varname>UnicastFlood=</varname></term>
          <listitem>
            <para>A boolean. Controls whether the bridge should flood
            traffic for which an FDB entry is missing and the destination
            is unknown through this port. When unset, the kernel's default will be used.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>HairPin=</varname></term>
          <listitem>
            <para>A boolean. Configures whether traffic may be sent back
            out of the port on which it was received. When this flag is false, and the bridge
            will not forward traffic back out of the receiving port.
            When unset, the kernel's default will be used.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>UseBPDU=</varname></term>
          <listitem>
            <para>A boolean. Configures whether STP Bridge Protocol Data Units will be
            processed by the bridge port. When unset, the kernel's default will be used.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>FastLeave=</varname></term>
          <listitem>
            <para>A boolean. This flag allows the bridge to immediately stop multicast
            traffic on a port that receives an IGMP Leave message. It is only used with
            IGMP snooping if enabled on the bridge. When unset, the kernel's default will be used.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>AllowPortToBeRoot=</varname></term>
          <listitem>
            <para>A boolean. Configures whether a given port is allowed to
            become a root port. Only used when STP is enabled on the bridge.
            When unset, the kernel's default will be used.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Cost=</varname></term>
          <listitem>
            <para>Sets the "cost" of sending packets of this interface.
            Each port in a bridge may have a different speed and the cost
            is used to decide which link to use. Faster interfaces
            should have lower costs. It is an integer value between 1 and
            65535.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Priority=</varname></term>
          <listitem>
            <para>Sets the "priority" of sending packets on this interface.
            Each port in a bridge may have a different priority which is used
            to decide which link to use. Lower value means higher priority.
            It is an integer value between 0 to 63. Networkd does not set any
            default, meaning the kernel default value of 32 is used.</para>
          </listitem>
        </varlistentry>
      </variablelist>
  </refsect1>
  <refsect1>
    <title>[BridgeFDB] Section Options</title>
      <para>The <literal>[BridgeFDB]</literal> section manages the
      forwarding database table of a port and accepts the following
      keys. Specify several <literal>[BridgeFDB]</literal> sections to
      configure several static MAC table entries.</para>

      <variablelist class='network-directives'>
        <varlistentry>
          <term><varname>MACAddress=</varname></term>
          <listitem>
            <para>As in the <literal>[Network]</literal> section. This
            key is mandatory.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>VLANId=</varname></term>
          <listitem>
            <para>The VLAN ID for the new static MAC table entry. If
            omitted, no VLAN ID information is appended to the new static MAC
            table entry.</para>
          </listitem>
        </varlistentry>
      </variablelist>
  </refsect1>

  <refsect1>
    <title>[CAN] Section Options</title>
      <para>The <literal>[CAN]</literal> section manages the Controller Area Network (CAN bus) and accepts the
      following keys.</para>
      <variablelist class='network-directives'>
        <varlistentry>
          <term><varname>BitRate=</varname></term>
          <listitem>
            <para>The bitrate of CAN device in bits per second. The usual SI prefixes (K, M) with the base of 1000 can
            be used here.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>SamplePoint=</varname></term>
          <listitem>
            <para>Optional sample point in percent with one decimal (e.g. <literal>75%</literal>,
            <literal>87.5%</literal>) or permille (e.g. <literal>875‰</literal>).</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>RestartSec=</varname></term>
          <listitem>
            <para>Automatic restart delay time. If set to a non-zero value, a restart of the CAN controller will be
            triggered automatically in case of a bus-off condition after the specified delay time. Subsecond delays can
            be specified using decimals (e.g. <literal>0.1s</literal>) or a <literal>ms</literal> or
            <literal>us</literal> postfix. Using <literal>infinity</literal> or <literal>0</literal> will turn the
            automatic restart off. By default automatic restart is disabled.</para>
          </listitem>
        </varlistentry>
      </variablelist>
  </refsect1>

  <refsect1>
    <title>[BridgeVLAN] Section Options</title>
      <para>The <literal>[BridgeVLAN]</literal> section manages the VLAN ID configuration of a bridge port and accepts
      the following keys. Specify several <literal>[BridgeVLAN]</literal> sections to configure several VLAN entries.
      The <varname>VLANFiltering=</varname> option has to be enabled, see <literal>[Bridge]</literal> section in
      <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>

      <variablelist class='network-directives'>
        <varlistentry>
          <term><varname>VLAN=</varname></term>
          <listitem>
            <para>The VLAN ID allowed on the port. This can be either a single ID or a range M-N. VLAN IDs are valid
            from 1 to 4094.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>EgressUntagged=</varname></term>
          <listitem>
            <para>The VLAN ID specified here will be used to untag frames on egress. Configuring
            <varname>EgressUntagged=</varname> implicates the use of <varname>VLAN=</varname> above and will enable the
            VLAN ID for ingress as well. This can be either a single ID or a range M-N.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>PVID=</varname></term>
          <listitem>
            <para>The Port VLAN ID specified here is assigned to all untagged frames at ingress.
            <varname>PVID=</varname> can be used only once. Configuring <varname>PVID=</varname> implicates the use of
            <varname>VLAN=</varname> above and will enable the VLAN ID for ingress as well.</para>
          </listitem>
        </varlistentry>
      </variablelist>
  </refsect1>

  <refsect1>
    <title>Examples</title>
    <example>
      <title>Static network configuration</title>

      <programlisting># /etc/systemd/network/50-static.network
[Match]
Name=enp2s0

[Network]
Address=192.168.0.15/24
Gateway=192.168.0.1</programlisting>

      <para>This brings interface <literal>enp2s0</literal> up with a static address. The
      specified gateway will be used for a default route.</para>
    </example>

    <example>
      <title>DHCP on ethernet links</title>

      <programlisting># /etc/systemd/network/80-dhcp.network
[Match]
Name=en*

[Network]
DHCP=yes</programlisting>

      <para>This will enable DHCPv4 and DHCPv6 on all interfaces with names starting with
      <literal>en</literal> (i.e. ethernet interfaces).</para>
    </example>

    <example>
      <title>A bridge with two enslaved links</title>

      <programlisting># /etc/systemd/network/25-bridge-static.network
[Match]
Name=bridge0

[Network]
Address=192.168.0.15/24
Gateway=192.168.0.1
DNS=192.168.0.1</programlisting>

      <programlisting># /etc/systemd/network/25-bridge-slave-interface-1.network
[Match]
Name=enp2s0

[Network]
Bridge=bridge0</programlisting>

      <programlisting># /etc/systemd/network/25-bridge-slave-interface-2.network
[Match]
Name=wlp3s0

[Network]
Bridge=bridge0</programlisting>

      <para>This creates a bridge and attaches devices <literal>enp2s0</literal> and
      <literal>wlp3s0</literal> to it. The bridge will have the specified static address
      and network assigned, and a default route via the specified gateway will be
      added. The specified DNS server will be added to the global list of DNS resolvers.
      </para>
    </example>

    <example>
      <title></title>

      <programlisting>
# /etc/systemd/network/20-bridge-slave-interface-vlan.network
[Match]
Name=enp2s0

[Network]
Bridge=bridge0

[BridgeVLAN]
VLAN=1-32
PVID=42
EgressUntagged=42

[BridgeVLAN]
VLAN=100-200

[BridgeVLAN]
EgressUntagged=300-400</programlisting>

    <para>This overrides the configuration specified in the previous example for the
    interface <literal>enp2s0</literal>, and enables VLAN on that bridge port. VLAN IDs
    1-32, 42, 100-400 will be allowed. Packets tagged with VLAN IDs 42, 300-400 will be
    untagged when they leave on this interface. Untagged packets which arrive on this
    interface will be assigned VLAN ID 42.</para>
    </example>

    <example>
      <title>Various tunnels</title>

      <programlisting>/etc/systemd/network/25-tunnels.network
[Match]
Name=ens1

[Network]
Tunnel=ipip-tun
Tunnel=sit-tun
Tunnel=gre-tun
Tunnel=vti-tun
      </programlisting>

      <programlisting>/etc/systemd/network/25-tunnel-ipip.netdev
[NetDev]
Name=ipip-tun
Kind=ipip
      </programlisting>

      <programlisting>/etc/systemd/network/25-tunnel-sit.netdev
[NetDev]
Name=sit-tun
Kind=sit
      </programlisting>

      <programlisting>/etc/systemd/network/25-tunnel-gre.netdev
[NetDev]
Name=gre-tun
Kind=gre
      </programlisting>

      <programlisting>/etc/systemd/network/25-tunnel-vti.netdev
[NetDev]
Name=vti-tun
Kind=vti
      </programlisting>

      <para>This will bring interface <literal>ens1</literal> up and create an IPIP tunnel,
      a SIT tunnel, a GRE tunnel, and a VTI tunnel using it.</para>
    </example>

    <example>
      <title>A bond device</title>

      <programlisting># /etc/systemd/network/30-bond1.network
[Match]
Name=bond1

[Network]
DHCP=ipv6
</programlisting>

      <programlisting># /etc/systemd/network/30-bond1.netdev
[NetDev]
Name=bond1
Kind=bond
</programlisting>

      <programlisting># /etc/systemd/network/30-bond1-dev1.network
[Match]
MACAddress=52:54:00:e9:64:41

[Network]
Bond=bond1
</programlisting>

      <programlisting># /etc/systemd/network/30-bond1-dev2.network
[Match]
MACAddress=52:54:00:e9:64:42

[Network]
Bond=bond1
</programlisting>

    <para>This will create a bond device <literal>bond1</literal> and enslave the two
    devices with MAC addresses 52:54:00:e9:64:41 and 52:54:00:e9:64:42 to it. IPv6 DHCP
    will be used to acquire an address.</para>
    </example>

    <example>
      <title>Virtual Routing and Forwarding (VRF)</title>
      <para>Add the <literal>bond1</literal> interface to the VRF master interface
      <literal>vrf1</literal>. This will redirect routes generated on this interface to be
      within the routing table defined during VRF creation. For kernels before 4.8 traffic
      won't be redirected towards the VRFs routing table unless specific ip-rules are added.
      </para>
      <programlisting># /etc/systemd/network/25-vrf.network
[Match]
Name=bond1

[Network]
VRF=vrf1
</programlisting>
    </example>

    <example>
      <title>MacVTap</title>
      <para>This brings up a network interface <literal>macvtap-test</literal>
      and attaches it to <literal>enp0s25</literal>.</para>
      <programlisting># /usr/lib/systemd/network/25-macvtap.network
[Match]
Name=enp0s25

[Network]
MACVTAP=macvtap-test
</programlisting>
    </example>
  </refsect1>

  <refsect1>
    <title>See Also</title>
    <para>
      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd.link</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>