path: root/man/systemd.network.xml

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

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

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

  <refmeta>
    <refentrytitle>systemd.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>Network files 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>,
    disable the configuration file entirely (it is "masked").</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>The hardware address.</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>.</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.</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>.</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>.</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>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.</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>
        </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>.</para>

            <para>Please note that by default the domain name
            specified through DHCP is not used for name resolution.
            See option <option>UseDomains=</option> below.</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 bits interface part of SLAAC IPv6 addresses for this link. By default
            it is autogenerated.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>LLMNR=</varname></term>
          <listitem>
            <para>A boolean or <literal>resolve</literal>. When true, enables
            Link-Local Multicast Name Resolution on the link, when set to
            <literal>resolve</literal> only resolution is enabled, but not
            announcement. Defaults to true.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>LLDP=</varname></term>
          <listitem>
            <para>A boolean. When true, enables LLDP link receive support.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>BindCarrier=</varname></term>
          <listitem>
            <para>A port or a list of ports. When set, controls the
            behavior of the current interface. When all ports in the list
            are in an operational down state, the current interface is brought
            down. When at least one port 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.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Domains=</varname></term>
          <listitem>
            <para>The domains used for DNS resolution over this link.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>NTP=</varname></term>
          <listitem>
            <para>An NTP server address. This option may be specified more than once.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>IPForward=</varname></term>
          <listitem><para>Configures IP forwarding for the network
          interface. If enabled incoming packets on the network
          interface will be forwarded to other interfaces according to
          the routing table. Takes either a boolean argument, or the
          values <literal>ipv4</literal> or <literal>ipv6</literal>,
          which only enables IP forwarding for the specified address
          family, or <literal>kernel</literal>, which preserves existing sysctl settings.
          This controls the
          <filename>net.ipv4.conf.&lt;interface&gt;.forwarding</filename>
          and
          <filename>net.ipv6.conf.&lt;interface&gt;.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: unless this option is turned on, or set to <literal>kernel</literal>,
          no IP forwarding is done on this interface, even if this is
          globally turned on in the kernel, with the
          <filename>net.ipv4.ip_forward</filename>,
          <filename>net.ipv4.conf.all.forwarding</filename>, and
          <filename>net.ipv6.conf.all.forwarding</filename> sysctl
          options.</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>IPv6AcceptRouterAdvertisements=</varname></term>
          <listitem><para>Configures Accept Router Advertisements.
          This is enabled if local forwarding is disabled.
          Disabled if local forwarding is enabled.
          Takes a boolean. Defaults to unset.
        </para></listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Bridge=</varname></term>
          <listitem>
            <para>The name of the bridge to add the link to.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>Bond=</varname></term>
          <listitem>
            <para>The name of the bond to add the link to.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term><varname>VLAN=</varname></term>
          <listitem>
            <para>The name of a VLAN to create on the link. 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. 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. 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. This
            option may be specified more than once.</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>
      </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>Destination=</varname></term>
          <listitem>
            <para>The destination prefix of the route. Possibly
            followed by a slash and the prefixlength. 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 prefixlength. 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>Scope=</varname></term>
          <listitem>
            <para>The scope of the route. One of the values <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>
      </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.
            Defaults to false.</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.</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.</para>
        </listitem>
      </varlistentry>
        <varlistentry>
          <term><varname>UseDomains=</varname></term>
          <listitem>
            <para>When true (not the default), the domain name
            received from the DHCP server will be used for DNS
            resolution over this link. When a name cannot be resolved
            as specified, the domain name will be used a suffix and
            name resolution of that will be attempted.</para>

            <para>This corresponds to the <option>domain</option>
            option in <citerefentry project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
            and should not be enabled on untrusted networks.</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 metric of 1024.</para>
          </listitem>
        </varlistentry>

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

          <listitem><para>When true, the timezone received from the
          DHCP server will be set as 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>DHCP client identifier to use. Either <literal>mac</literal>
            to use the MAC address of the link or <literal>duid</literal>
            (the default) to use a RFC4361-compliant Client ID.</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>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>
      </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 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>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>[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. Defaults to on.
            </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. By default, this
            flag is false, and the bridge will not forward traffic back
            out of the receiving port.</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. Defaults to yes.</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 IGMP Leave message. It is only used with
            IGMP snooping if enabled on the bridge. Defaults to off.</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.
            Defaults to on.</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 different speed and the cost
            is used to decide which link to use. Faster interfaces
            should have lower costs.</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 info is appended to the new static MAC
            table entry.</para>
          </listitem>
        </varlistentry>
      </variablelist>
  </refsect1>

  <refsect1>
    <title>Example</title>
    <example>
      <title>/etc/systemd/network/50-static.network</title>

      <programlisting>[Match]
Name=enp2s0

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

    <example>
      <title>/etc/systemd/network/80-dhcp.network</title>

      <programlisting>[Match]
Name=en*

[Network]
DHCP=yes</programlisting>
    </example>

    <example>
      <title>/etc/systemd/network/25-bridge-static.network</title>

      <programlisting>[Match]
Name=bridge0

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

    <example>
      <title>/etc/systemd/network/25-bridge-slave-interface.network</title>

      <programlisting>[Match]
Name=enp2s0

[Network]
Bridge=bridge0</programlisting>
    </example>
    <example>
      <title>/etc/systemd/network/25-ipip.network</title>

      <programlisting>[Match]
Name=em1

[Network]
Tunnel=ipip-tun</programlisting>
    </example>

    <example>
      <title>/etc/systemd/network/25-sit.network</title>

      <programlisting>[Match]
Name=em1

[Network]
Tunnel=sit-tun</programlisting>
    </example>

    <example>
      <title>/etc/systemd/network/25-gre.network</title>

      <programlisting>[Match]
Name=em1

[Network]
Tunnel=gre-tun</programlisting>
    </example>

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

      <programlisting>[Match]
Name=em1

[Network]
Tunnel=vti-tun</programlisting>
    </example>

    <example>
      <title>/etc/systemd/network/25-bond.network</title>

      <programlisting>[Match]
Name=bond1

[Network]
DHCP=yes
</programlisting>
    </example>

  </refsect1>

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

</refentry>