man/systemd.network.xml

   1 <?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4
   5 <!--
   6   SPDX-License-Identifier: LGPL-2.1+
   7
   8   This file is part of systemd.
   9
  10   Copyright 2013 Tom Gundersen
  11
  12   systemd is free software; you can redistribute it and/or modify it
  13   under the terms of the GNU Lesser General Public License as published by
  14   the Free Software Foundation; either version 2.1 of the License, or
  15   (at your option) any later version.
  16
  17   systemd is distributed in the hope that it will be useful, but
  18   WITHOUT ANY WARRANTY; without even the implied warranty of
  19   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  20   Lesser General Public License for more details.
  21
  22   You should have received a copy of the GNU Lesser General Public License
  23   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  24 -->
  25
  26 <refentry id="systemd.network" conditional='ENABLE_NETWORKD'>
  27
  28   <refentryinfo>
  29     <title>systemd.network</title>
  30     <productname>systemd</productname>
  31
  32     <authorgroup>
  33       <author>
  34         <contrib>Developer</contrib>
  35         <firstname>Tom</firstname>
  36         <surname>Gundersen</surname>
  37         <email>teg@jklm.no</email>
  38       </author>
  39     </authorgroup>
  40   </refentryinfo>
  41
  42   <refmeta>
  43     <refentrytitle>systemd.network</refentrytitle>
  44     <manvolnum>5</manvolnum>
  45   </refmeta>
  46
  47   <refnamediv>
  48     <refname>systemd.network</refname>
  49     <refpurpose>Network configuration</refpurpose>
  50   </refnamediv>
  51
  52   <refsynopsisdiv>
  53     <para><filename><replaceable>network</replaceable>.network</filename></para>
  54   </refsynopsisdiv>
  55
  56   <refsect1>
  57     <title>Description</title>
  58
  59     <para>Network setup is performed by
  60     <citerefentry><refentrytitle>systemd-networkd</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
  61     </para>
  62
  63     <para>The main network file must have the extension <filename>.network</filename>; other
  64     extensions are ignored. Networks are applied to links whenever the links appear.</para>
  65
  66     <para>The <filename>.network</filename> files are read from the files located in the system
  67     network directory <filename>/usr/lib/systemd/network</filename>, the volatile runtime network
  68     directory <filename>/run/systemd/network</filename> and the local administration network
  69     directory <filename>/etc/systemd/network</filename>. All configuration files are collectively
  70     sorted and processed in lexical order, regardless of the directories in which they live.
  71     However, files with identical filenames replace each other. Files in <filename>/etc</filename>
  72     have the highest priority, files in <filename>/run</filename> take precedence over files with
  73     the same name in <filename>/usr/lib</filename>. This can be used to override a system-supplied
  74     configuration file with a local file if needed. As a special case, an empty file (file size 0)
  75     or symlink with the same name pointing to <filename>/dev/null</filename> disables the
  76     configuration file entirely (it is "masked").</para>
  77
  78     <para>Along with the network file <filename>foo.network</filename>, a "drop-in" directory
  79     <filename>foo.network.d/</filename> may exist. All files with the suffix
  80     <literal>.conf</literal> from this directory will be parsed after the file itself is
  81     parsed. This is useful to alter or add configuration settings, without having to modify the main
  82     configuration file. Each drop-in file must have appropriate section headers.</para>
  83
  84     <para>In addition to <filename>/etc/systemd/network</filename>, drop-in <literal>.d</literal>
  85     directories can be placed in <filename>/usr/lib/systemd/network</filename> or
  86     <filename>/run/systemd/network</filename> directories. Drop-in files in
  87     <filename>/etc</filename> take precedence over those in <filename>/run</filename> which in turn
  88     take precedence over those in <filename>/usr/lib</filename>. Drop-in files under any of these
  89     directories take precedence over the main netdev file wherever located. (Of course, since
  90     <filename>/run</filename> is temporary and <filename>/usr/lib</filename> is for vendors, it is
  91     unlikely drop-ins should be used in either of those places.)</para>
  92
  93     <para>Note that an interface without any static IPv6 addresses configured, and neither DHCPv6
  94     nor IPv6LL enabled, shall be considered to have no IPv6 support. IPv6 will be automatically
  95     disabled for that interface by writing "1" to
  96     <filename>/proc/sys/net/ipv6/conf/<replaceable>ifname</replaceable>/disable_ipv6</filename>.
  97     </para>
  98   </refsect1>
  99
 100   <refsect1>
 101     <title>[Match] Section Options</title>
 102
 103       <para>The network file contains a <literal>[Match]</literal>
 104       section, which determines if a given network file may be applied
 105       to a given device; and a <literal>[Network]</literal> section
 106       specifying how the device should be configured. The first (in
 107       lexical order) of the network files that matches a given device
 108       is applied, all later files are ignored, even if they match as
 109       well.</para>
 110
 111       <para>A network file is said to match a device if each of the
 112       entries in the <literal>[Match]</literal> section matches, or if
 113       the section is empty. The following keys are accepted:</para>
 114
 115       <variablelist class='network-directives'>
 116         <varlistentry>
 117           <term><varname>MACAddress=</varname></term>
 118           <listitem>
 119             <para>The hardware address of the interface (use full colon-delimited hexadecimal, e.g.,
 120             01:23:45:67:89:ab).</para>
 121           </listitem>
 122         </varlistentry>
 123         <varlistentry>
 124           <term><varname>Path=</varname></term>
 125           <listitem>
 126             <para>A whitespace-separated list of shell-style globs
 127             matching the persistent path, as exposed by the udev
 128             property <literal>ID_PATH</literal>. If the list is
 129             prefixed with a "!", the test is inverted; i.e. it is
 130             true when <literal>ID_PATH</literal> does not match any
 131             item in the list.</para>
 132           </listitem>
 133         </varlistentry>
 134         <varlistentry>
 135           <term><varname>Driver=</varname></term>
 136           <listitem>
 137             <para>A whitespace-separated list of shell-style globs
 138             matching the driver currently bound to the device, as
 139             exposed by the udev property <literal>DRIVER</literal>
 140             of its parent device, or if that is not set the driver
 141             as exposed by <literal>ethtool -i</literal> of the
 142             device itself. If the list is prefixed with a "!", the
 143             test is inverted.</para>
 144           </listitem>
 145         </varlistentry>
 146         <varlistentry>
 147           <term><varname>Type=</varname></term>
 148           <listitem>
 149             <para>A whitespace-separated list of shell-style globs
 150             matching the device type, as exposed by the udev property
 151             <literal>DEVTYPE</literal>. If the list is prefixed with
 152             a "!", the test is inverted.</para>
 153           </listitem>
 154         </varlistentry>
 155         <varlistentry>
 156           <term><varname>Name=</varname></term>
 157           <listitem>
 158             <para>A whitespace-separated list of shell-style globs
 159             matching the device name, as exposed by the udev property
 160             <literal>INTERFACE</literal>. If the list is prefixed
 161             with a "!", the test is inverted.</para>
 162           </listitem>
 163         </varlistentry>
 164         <varlistentry>
 165           <term><varname>Host=</varname></term>
 166           <listitem>
 167             <para>Matches against the hostname or machine ID of the
 168             host. See <literal>ConditionHost=</literal> in
 169             <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 170             for details.
 171             </para>
 172           </listitem>
 173         </varlistentry>
 174         <varlistentry>
 175           <term><varname>Virtualization=</varname></term>
 176           <listitem>
 177             <para>Checks whether the system is executed in a virtualized
 178             environment and optionally test whether it is a specific
 179             implementation. See <literal>ConditionVirtualization=</literal> in
 180             <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 181             for details.
 182             </para>
 183           </listitem>
 184         </varlistentry>
 185         <varlistentry>
 186           <term><varname>KernelCommandLine=</varname></term>
 187           <listitem>
 188             <para>Checks whether a specific kernel command line option is
 189             set (or if prefixed with the exclamation mark unset). See
 190             <literal>ConditionKernelCommandLine=</literal> in
 191             <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 192             for details.
 193             </para>
 194           </listitem>
 195         </varlistentry>
 196         <varlistentry>
 197           <term><varname>Architecture=</varname></term>
 198           <listitem>
 199             <para>Checks whether the system is running on a specific
 200             architecture. See <literal>ConditionArchitecture=</literal> in
 201             <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 202             for details.
 203             </para>
 204           </listitem>
 205         </varlistentry>
 206       </variablelist>
 207
 208   </refsect1>
 209
 210   <refsect1>
 211     <title>[Link] Section Options</title>
 212
 213     <para> The <literal>[Link]</literal> section accepts the following keys:</para>
 214
 215     <variablelist class='network-directives'>
 216       <varlistentry>
 217         <term><varname>MACAddress=</varname></term>
 218         <listitem>
 219           <para>The hardware address to set for the device.</para>
 220         </listitem>
 221       </varlistentry>
 222       <varlistentry>
 223         <term><varname>MTUBytes=</varname></term>
 224         <listitem>
 225           <para>The maximum transmission unit in bytes to set for the
 226           device. The usual suffixes K, M, G, are supported and are
 227           understood to the base of 1024.</para>
 228           <para>Note that if IPv6 is enabled on the interface, and the MTU is chosen
 229           below 1280 (the minimum MTU for IPv6) it will automatically be increased to this value.</para>
 230         </listitem>
 231       </varlistentry>
 232       <varlistentry>
 233         <term><varname>ARP=</varname></term>
 234         <listitem>
 235           <para> A boolean. Enables or disables the ARP (low-level Address Resolution Protocol)
 236           for this interface. Defaults to unset, which means that the kernel default will be used.</para>
 237           <para> For example, disabling ARP is useful when creating multiple MACVLAN or VLAN virtual
 238           interfaces atop a single lower-level physical interface, which will then only serve as a
 239           link/"bridge" device aggregating traffic to the same physical link and not participate in
 240           the network otherwise.</para>
 241         </listitem>
 242       </varlistentry>
 243       <varlistentry>
 244         <term><varname>Unmanaged=</varname></term>
 245         <listitem>
 246           <para>A boolean. When <literal>yes</literal>, no attempts are
 247           made to bring up or configure matching links, equivalent to
 248           when there are no matching network files. Defaults to
 249           <literal>no</literal>.</para>
 250           <para>This is useful for preventing later matching network
 251           files from interfering with certain interfaces that are fully
 252           controlled by other applications.</para>
 253         </listitem>
 254       </varlistentry>
 255     </variablelist>
 256   </refsect1>
 257
 258   <refsect1>
 259     <title>[Network] Section Options</title>
 260
 261       <para>The <literal>[Network]</literal> section accepts the following keys:</para>
 262
 263       <variablelist class='network-directives'>
 264         <varlistentry>
 265           <term><varname>Description=</varname></term>
 266           <listitem>
 267             <para>A description of the device. This is only used for
 268             presentation purposes.</para>
 269           </listitem>
 270         </varlistentry>
 271         <varlistentry>
 272           <term><varname>DHCP=</varname></term>
 273           <listitem>
 274             <para>Enables DHCPv4 and/or DHCPv6 client support. Accepts
 275             <literal>yes</literal>, <literal>no</literal>,
 276             <literal>ipv4</literal>, or <literal>ipv6</literal>. Defaults
 277             to <literal>no</literal>.</para>
 278
 279             <para>Note that DHCPv6 will by default be triggered by Router
 280             Advertisement, if that is enabled, regardless of this parameter.
 281             By enabling DHCPv6 support explicitly, the DHCPv6 client will
 282             be started regardless of the presence of routers on the link,
 283             or what flags the routers pass. See
 284             <literal>IPv6AcceptRA=</literal>.</para>
 285
 286             <para>Furthermore, note that by default the domain name
 287             specified through DHCP is not used for name resolution.
 288             See option <option>UseDomains=</option> below.</para>
 289
 290             <para>See the <literal>[DHCP]</literal> section below for further configuration options for the DHCP client
 291             support.</para>
 292           </listitem>
 293         </varlistentry>
 294         <varlistentry>
 295           <term><varname>DHCPServer=</varname></term>
 296           <listitem>
 297             <para>A boolean. Enables DHCPv4 server support. Defaults
 298             to <literal>no</literal>. Further settings for the DHCP
 299             server may be set in the <literal>[DHCPServer]</literal>
 300             section described below.</para>
 301           </listitem>
 302         </varlistentry>
 303         <varlistentry>
 304           <term><varname>LinkLocalAddressing=</varname></term>
 305           <listitem>
 306             <para>Enables link-local address autoconfiguration. Accepts
 307             <literal>yes</literal>, <literal>no</literal>,
 308             <literal>ipv4</literal>, or <literal>ipv6</literal>. Defaults to
 309             <literal>ipv6</literal>.</para>
 310           </listitem>
 311         </varlistentry>
 312         <varlistentry>
 313           <term><varname>IPv4LLRoute=</varname></term>
 314           <listitem>
 315             <para>A boolean. When true, sets up the route needed for
 316             non-IPv4LL hosts to communicate with IPv4LL-only hosts. Defaults
 317             to false.
 318             </para>
 319           </listitem>
 320         </varlistentry>
 321         <varlistentry>
 322           <term><varname>IPv6Token=</varname></term>
 323           <listitem>
 324             <para>An IPv6 address with the top 64 bits unset. When set, indicates the
 325             64-bit interface part of SLAAC IPv6 addresses for this link. Note that
 326             the token is only ever used for SLAAC, and not for DHCPv6 addresses, even
 327             in the case DHCP is requested by router advertisement. By default, the
 328             token is autogenerated.</para>
 329           </listitem>
 330         </varlistentry>
 331         <varlistentry>
 332           <term><varname>LLMNR=</varname></term>
 333           <listitem>
 334             <para>A boolean or <literal>resolve</literal>. When true,
 335             enables <ulink
 336             url="https://tools.ietf.org/html/rfc4795">Link-Local
 337             Multicast Name Resolution</ulink> on the link. When set to
 338             <literal>resolve</literal>, only resolution is enabled,
 339             but not host registration and announcement. Defaults to
 340             true. This setting is read by
 341             <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 342           </listitem>
 343         </varlistentry>
 344         <varlistentry>
 345           <term><varname>MulticastDNS=</varname></term>
 346           <listitem>
 347             <para>A boolean or <literal>resolve</literal>. When true,
 348             enables <ulink
 349             url="https://tools.ietf.org/html/rfc6762">Multicast
 350             DNS</ulink> support on the link. When set to
 351             <literal>resolve</literal>, only resolution is enabled,
 352             but not host or service registration and
 353             announcement. Defaults to false. This setting is read by
 354             <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 355           </listitem>
 356         </varlistentry>
 357         <varlistentry>
 358           <term><varname>DNSSEC=</varname></term>
 359           <listitem>
 360             <para>A boolean or
 361             <literal>allow-downgrade</literal>. When true, enables
 362             <ulink
 363             url="https://tools.ietf.org/html/rfc4033">DNSSEC</ulink>
 364             DNS validation support on the link. When set to
 365             <literal>allow-downgrade</literal>, compatibility with
 366             non-DNSSEC capable networks is increased, by automatically
 367             turning off DNSSEC in this case. This option defines a
 368             per-interface setting for
 369             <citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>'s
 370             global <varname>DNSSEC=</varname> option. Defaults to
 371             false. This setting is read by
 372             <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 373           </listitem>
 374         </varlistentry>
 375         <varlistentry>
 376           <term><varname>DNSSECNegativeTrustAnchors=</varname></term>
 377           <listitem><para>A space-separated list of DNSSEC negative
 378           trust anchor domains. If specified and DNSSEC is enabled,
 379           look-ups done via the interface's DNS server will be subject
 380           to the list of negative trust anchors, and not require
 381           authentication for the specified domains, or anything below
 382           it. Use this to disable DNSSEC authentication for specific
 383           private domains, that cannot be proven valid using the
 384           Internet DNS hierarchy. Defaults to the empty list. This
 385           setting is read by
 386           <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 387           </listitem>
 388         </varlistentry>
 389         <varlistentry>
 390           <term><varname>LLDP=</varname></term>
 391           <listitem>
 392             <para>Controls support for Ethernet LLDP packet reception. LLDP is a link-layer protocol commonly
 393             implemented on professional routers and bridges which announces which physical port a system is connected
 394             to, as well as other related data. Accepts a boolean or the special value
 395             <literal>routers-only</literal>. When true, incoming LLDP packets are accepted and a database of all LLDP
 396             neighbors maintained. If <literal>routers-only</literal> is set only LLDP data of various types of routers
 397             is collected and LLDP data about other types of devices ignored (such as stations, telephones and
 398             others). If false, LLDP reception is disabled. Defaults to <literal>routers-only</literal>. Use
 399             <citerefentry><refentrytitle>networkctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> to query the
 400             collected neighbor data. LLDP is only available on Ethernet links. See <varname>EmitLLDP=</varname> below
 401             for enabling LLDP packet emission from the local system.
 402             </para>
 403           </listitem>
 404         </varlistentry>
 405         <varlistentry>
 406           <term><varname>EmitLLDP=</varname></term>
 407           <listitem>
 408             <para>Controls support for Ethernet LLDP packet emission. Accepts a boolean parameter or the special values
 409             <literal>nearest-bridge</literal>, <literal>non-tpmr-bridge</literal> and
 410             <literal>customer-bridge</literal>.  Defaults to false, which turns off LLDP packet emission. If not false,
 411             a short LLDP packet with information about the local system is sent out in regular intervals on the
 412             link. The LLDP packet will contain information about the local host name, the local machine ID (as stored
 413             in <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>) and the
 414             local interface name, as well as the pretty hostname of the system (as set in
 415             <citerefentry><refentrytitle>machine-info</refentrytitle><manvolnum>5</manvolnum></citerefentry>). LLDP
 416             emission is only available on Ethernet links. Note that this setting passes data suitable for
 417             identification of host to the network and should thus not be enabled on untrusted networks, where such
 418             identification data should not be made available. Use this option to permit other systems to identify on
 419             which interfaces they are connected to this system. The three special values control propagation of the
 420             LLDP packets. The <literal>nearest-bridge</literal> setting permits propagation only to the nearest
 421             connected bridge, <literal>non-tpmr-bridge</literal> permits propagation across Two-Port MAC Relays, but
 422             not any other bridges, and <literal>customer-bridge</literal> permits propagation until a customer bridge
 423             is reached. For details about these concepts, see <ulink
 424             url="http://standards.ieee.org/getieee802/download/802.1AB-2009.pdf">IEEE 802.1AB-2009</ulink>. Note that
 425             configuring this setting to true is equivalent to <literal>nearest-bridge</literal>, the recommended and
 426             most restricted level of propagation. See <varname>LLDP=</varname> above for an option to enable LLDP
 427             reception.</para>
 428           </listitem>
 429         </varlistentry>
 430         <varlistentry>
 431           <term><varname>BindCarrier=</varname></term>
 432           <listitem>
 433             <para>A link name or a list of link names. When set, controls the behavior of the current
 434             link. When all links in the list are in an operational down state, the current link is brought
 435             down. When at least one link has carrier, the current interface is brought up.
 436             </para>
 437           </listitem>
 438         </varlistentry>
 439         <varlistentry>
 440           <term><varname>Address=</varname></term>
 441           <listitem>
 442             <para>A static IPv4 or IPv6 address and its prefix length,
 443             separated by a <literal>/</literal> character. Specify
 444             this key more than once to configure several addresses.
 445             The format of the address must be as described in
 446             <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 447             This is a short-hand for an [Address] section only
 448             containing an Address key (see below). This option may be
 449             specified more than once.
 450             </para>
 451
 452             <para>If the specified address is 0.0.0.0 (for IPv4) or
 453             [::] (for IPv6), a new address range of the requested size
 454             is automatically allocated from a system-wide pool of
 455             unused ranges. The allocated range is checked against all
 456             current network interfaces and all known network
 457             configuration files to avoid address range conflicts. The
 458             default system-wide pool consists of 192.168.0.0/16,
 459             172.16.0.0/12 and 10.0.0.0/8 for IPv4, and fc00::/7 for
 460             IPv6. This functionality is useful to manage a large
 461             number of dynamically created network interfaces with the
 462             same network configuration and automatic address range
 463             assignment.</para>
 464
 465           </listitem>
 466         </varlistentry>
 467         <varlistentry>
 468           <term><varname>Gateway=</varname></term>
 469           <listitem>
 470             <para>The gateway address, which must be in the format
 471             described in
 472             <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 473             This is a short-hand for a [Route] section only containing
 474             a Gateway key. This option may be specified more than
 475             once.</para>
 476           </listitem>
 477         </varlistentry>
 478         <varlistentry>
 479           <term><varname>DNS=</varname></term>
 480           <listitem>
 481             <para>A DNS server address, which must be in the format
 482             described in
 483             <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 484             This option may be specified more than once. This setting is read by
 485             <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 486           </listitem>
 487         </varlistentry>
 488         <varlistentry>
 489           <term><varname>Domains=</varname></term>
 490           <listitem>
 491             <para>A list of domains which should be resolved using the DNS servers on this link. Each item in the list
 492             should be a domain name, optionally prefixed with a tilde (<literal>~</literal>). The domains with the
 493             prefix are called "routing-only domains". The domains without the prefix are called "search domains" and
 494             are first used as search suffixes for extending single-label host names (host names containing no dots) to
 495             become fully qualified domain names (FQDNs). If a single-label host name is resolved on this interface,
 496             each of the specified search domains are appended to it in turn, converting it into a fully qualified
 497             domain name, until one of them may be successfully resolved.</para>
 498
 499             <para>Both "search" and "routing-only" domains are used for routing of DNS queries: look-ups for host names
 500             ending in those domains (hence also single label names, if any "search domains" are listed), are routed to
 501             the DNS servers configured for this interface. The domain routing logic is particularly useful on
 502             multi-homed hosts with DNS servers serving particular private DNS zones on each interface.</para>
 503
 504             <para>The "routing-only" domain <literal>~.</literal> (the tilde indicating definition of a routing domain,
 505             the dot referring to the DNS root domain which is the implied suffix of all valid DNS names) has special
 506             effect. It causes all DNS traffic which does not match another configured domain routing entry to be routed
 507             to DNS servers specified for this interface. This setting is useful to prefer a certain set of DNS servers
 508             if a link on which they are connected is available.</para>
 509
 510             <para>This setting is read by
 511             <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
 512             "Search domains" correspond to the <varname>domain</varname> and <varname>search</varname> entries in
 513             <citerefentry project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 514             Domain name routing has no equivalent in the traditional glibc API, which has no concept of domain
 515             name servers limited to a specific link.</para>
 516           </listitem>
 517         </varlistentry>
 518         <varlistentry>
 519           <term><varname>NTP=</varname></term>
 520           <listitem>
 521             <para>An NTP server address. This option may be specified more than once. This setting is read by
 522             <citerefentry><refentrytitle>systemd-timesyncd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 523           </listitem>
 524         </varlistentry>
 525         <varlistentry>
 526           <term><varname>IPForward=</varname></term>
 527           <listitem><para>Configures IP packet forwarding for the
 528           system. If enabled, incoming packets on any network
 529           interface will be forwarded to any other interfaces
 530           according to the routing table. Takes either a boolean
 531           argument, or the values <literal>ipv4</literal> or
 532           <literal>ipv6</literal>, which only enable IP packet
 533           forwarding for the specified address family.  This controls
 534           the <filename>net.ipv4.ip_forward</filename> and
 535           <filename>net.ipv6.conf.all.forwarding</filename> sysctl
 536           options of the network interface (see <ulink
 537           url="https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt">ip-sysctl.txt</ulink>
 538           for details about sysctl options). Defaults to
 539           <literal>no</literal>.</para>
 540
 541           <para>Note: this setting controls a global kernel option,
 542           and does so one way only: if a network that has this setting
 543           enabled is set up the global setting is turned on.  However,
 544           it is never turned off again, even after all networks with
 545           this setting enabled are shut down again.</para>
 546
 547           <para>To allow IP packet forwarding only between specific
 548           network interfaces use a firewall.</para>
 549           </listitem>
 550         </varlistentry>
 551         <varlistentry>
 552           <term><varname>IPMasquerade=</varname></term>
 553           <listitem><para>Configures IP masquerading for the network
 554           interface. If enabled, packets forwarded from the network
 555           interface will be appear as coming from the local host.
 556           Takes a boolean argument. Implies
 557           <varname>IPForward=ipv4</varname>. Defaults to
 558           <literal>no</literal>.</para></listitem>
 559         </varlistentry>
 560         <varlistentry>
 561           <term><varname>IPv6PrivacyExtensions=</varname></term>
 562           <listitem><para>Configures use of stateless temporary
 563           addresses that change over time (see <ulink
 564           url="https://tools.ietf.org/html/rfc4941">RFC 4941</ulink>,
 565           Privacy Extensions for Stateless Address Autoconfiguration
 566           in IPv6). Takes a boolean or the special values
 567           <literal>prefer-public</literal> and
 568           <literal>kernel</literal>. When true, enables the privacy
 569           extensions and prefers temporary addresses over public
 570           addresses. When <literal>prefer-public</literal>, enables the
 571           privacy extensions, but prefers public addresses over
 572           temporary addresses. When false, the privacy extensions
 573           remain disabled. When <literal>kernel</literal>, the kernel's
 574           default setting will be left in place.  Defaults to
 575           <literal>no</literal>.</para></listitem>
 576         </varlistentry>
 577         <varlistentry>
 578           <term><varname>IPv6AcceptRA=</varname></term>
 579           <listitem><para>Enable or disable IPv6 Router Advertisement (RA) reception support for the interface.  Takes
 580           a boolean parameter. If true, RAs are accepted; if false, RAs are ignored, independently of the local
 581           forwarding state. When not set, the kernel default is used, and RAs are accepted only when local forwarding
 582           is disabled for that interface.  When RAs are accepted, they may trigger the start of the DHCPv6 client if
 583           the relevant flags are set in the RA data, or if no routers are found on the link.</para>
 584
 585           <para>Further settings for the IPv6 RA support may be configured in the
 586           <literal>[IPv6AcceptRA]</literal> section, see below.</para>
 587
 588           <para>Also see <ulink
 589           url="https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt">ip-sysctl.txt</ulink> in the kernel
 590           documentation regarding <literal>accept_ra</literal>, but note that systemd's setting of
 591           <constant>1</constant> (i.e. true) corresponds to kernel's setting of <constant>2</constant>.</para>
 592         </listitem>
 593         </varlistentry>
 594         <varlistentry>
 595           <term><varname>IPv6DuplicateAddressDetection=</varname></term>
 596           <listitem><para>Configures the amount of IPv6 Duplicate
 597           Address Detection (DAD) probes to send. Defaults to unset.
 598         </para></listitem>
 599         </varlistentry>
 600         <varlistentry>
 601           <term><varname>IPv6HopLimit=</varname></term>
 602           <listitem><para>Configures IPv6 Hop Limit. For each router that
 603           forwards the packet, the hop limit is decremented by 1. When the
 604           hop limit field reaches zero, the packet is discarded.
 605           Defaults to unset.
 606         </para></listitem>
 607         </varlistentry>
 608         <varlistentry>
 609           <term><varname>IPv4ProxyARP=</varname></term>
 610           <listitem><para>A boolean. Configures proxy ARP for IPv4. Proxy ARP is the technique in which one host,
 611           usually a router, answers ARP requests intended for another machine. By "faking" its identity,
 612           the router accepts responsibility for routing packets to the "real" destination. (see <ulink
 613           url="https://tools.ietf.org/html/rfc1027">RFC 1027</ulink>.
 614           Defaults to unset.
 615         </para></listitem>
 616         </varlistentry>
 617         <varlistentry>
 618           <term><varname>IPv6ProxyNDP=</varname></term>
 619           <listitem><para>A boolean. Configures proxy NDP for IPv6. Proxy NDP (Neighbor Discovery
 620           Protocol) is a technique for IPv6 to allow routing of addresses to a different
 621           destination when peers expect them to be present on a certain physical link.
 622           In this case a router answers Neighbour Advertisement messages intended for
 623           another machine by offering its own MAC address as destination.
 624           Unlike proxy ARP for IPv4, it is not enabled globally, but will only send Neighbour
 625           Advertisement messages for addresses in the IPv6 neighbor proxy table,
 626           which can also be shown by <command>ip -6 neighbour show proxy</command>.
 627           systemd-networkd will control the per-interface `proxy_ndp` switch for each configured
 628           interface depending on this option.
 629           Defautls to unset.
 630         </para></listitem>
 631         </varlistentry>
 632         <varlistentry>
 633           <term><varname>IPv6ProxyNDPAddress=</varname></term>
 634           <listitem><para>An IPv6 address, for which Neighbour Advertisement messages will be
 635           proxied. This option may be specified more than once. systemd-networkd will add the
 636           <option>IPv6ProxyNDPAddress=</option> entries to the kernel's IPv6 neighbor proxy table.
 637           This option implies <option>IPv6ProxyNDP=true</option> but has no effect if
 638           <option>IPv6ProxyNDP</option> has been set to false. Defaults to unset.
 639         </para></listitem>
 640         </varlistentry>
 641         <varlistentry>
 642           <term><varname>IPv6PrefixDelegation=</varname></term>
 643           <listitem><para>Whether to enable or disable Router Advertisement sending on a link.
 644           Defaults to <literal>false</literal>. See the <literal>[IPv6PrefixDelegation]</literal>
 645           and the <literal>[IPv6Prefix]</literal> sections for configuration options.
 646           </para></listitem>
 647         </varlistentry>
 648         <varlistentry>
 649           <term><varname>Bridge=</varname></term>
 650           <listitem>
 651             <para>The name of the bridge to add the link to. See
 652             <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 653             </para>
 654           </listitem>
 655         </varlistentry>
 656         <varlistentry>
 657           <term><varname>Bond=</varname></term>
 658           <listitem>
 659             <para>The name of the bond to add the link to. See
 660             <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 661             </para>
 662           </listitem>
 663         </varlistentry>
 664         <varlistentry>
 665           <term><varname>VRF=</varname></term>
 666           <listitem>
 667             <para>The name of the VRF to add the link to. See
 668             <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 669             </para>
 670           </listitem>
 671         </varlistentry>
 672         <varlistentry>
 673           <term><varname>VLAN=</varname></term>
 674           <listitem>
 675             <para>The name of a VLAN to create on the link. See
 676             <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 677             This option may be specified more than once.</para>
 678           </listitem>
 679         </varlistentry>
 680         <varlistentry>
 681           <term><varname>MACVLAN=</varname></term>
 682           <listitem>
 683             <para>The name of a MACVLAN to create on the link. See
 684             <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 685             This option may be specified more than once.</para>
 686           </listitem>
 687         </varlistentry>
 688         <varlistentry>
 689           <term><varname>VXLAN=</varname></term>
 690           <listitem>
 691             <para>The name of a VXLAN to create on the link. See
 692             <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 693             This option may be specified more than once.</para>
 694           </listitem>
 695         </varlistentry>
 696         <varlistentry>
 697           <term><varname>Tunnel=</varname></term>
 698           <listitem>
 699             <para>The name of a Tunnel to create on the link. See
 700             <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 701             This option may be specified more than once.</para>
 702           </listitem>
 703         </varlistentry>
 704       <varlistentry>
 705         <term><varname>ActiveSlave=</varname></term>
 706         <listitem>
 707           <para>A boolean. Specifies the new active slave. The <literal>ActiveSlave=</literal>
 708           option is only valid for following modes:
 709           <literal>active-backup</literal>,
 710           <literal>balance-alb</literal> and
 711           <literal>balance-tlb</literal>. Defaults to false.
 712           </para>
 713         </listitem>
 714       </varlistentry>
 715       <varlistentry>
 716         <term><varname>PrimarySlave=</varname></term>
 717         <listitem>
 718           <para>A boolean. Specifies which slave is the primary device. The specified
 719           device will always be the active slave while it is available. Only when the
 720           primary is off-line will alternate devices be used.  This is useful when
 721           one slave is preferred over another, e.g. when one slave has higher throughput
 722           than another. The <literal>PrimarySlave=</literal> option is only valid for
 723           following modes:
 724           <literal>active-backup</literal>,
 725           <literal>balance-alb</literal> and
 726           <literal>balance-tlb</literal>. Defaults to false.
 727           </para>
 728         </listitem>
 729       </varlistentry>
 730       <varlistentry>
 731         <term><varname>ConfigureWithoutCarrier=</varname></term>
 732         <listitem>
 733           <para>A boolean. Allows networkd to configure a specific link even if it has no carrier.
 734           Defaults to false.
 735           </para>
 736         </listitem>
 737       </varlistentry>
 738       </variablelist>
 739
 740   </refsect1>
 741
 742   <refsect1>
 743     <title>[Address] Section Options</title>
 744
 745       <para>An <literal>[Address]</literal> section accepts the
 746       following keys. Specify several <literal>[Address]</literal>
 747       sections to configure several addresses.</para>
 748
 749       <variablelist class='network-directives'>
 750         <varlistentry>
 751           <term><varname>Address=</varname></term>
 752           <listitem>
 753             <para>As in the <literal>[Network]</literal> section. This
 754             key is mandatory.</para>
 755           </listitem>
 756         </varlistentry>
 757         <varlistentry>
 758           <term><varname>Peer=</varname></term>
 759           <listitem>
 760             <para>The peer address in a point-to-point connection.
 761             Accepts the same format as the <literal>Address</literal>
 762             key.</para>
 763           </listitem>
 764         </varlistentry>
 765         <varlistentry>
 766           <term><varname>Broadcast=</varname></term>
 767           <listitem>
 768             <para>The broadcast address, which must be in the format
 769             described in
 770             <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 771             This key only applies to IPv4 addresses. If it is not
 772             given, it is derived from the <literal>Address</literal>
 773             key.</para>
 774           </listitem>
 775         </varlistentry>
 776         <varlistentry>
 777           <term><varname>Label=</varname></term>
 778           <listitem>
 779             <para>An address label.</para>
 780           </listitem>
 781         </varlistentry>
 782         <varlistentry>
 783           <term><varname>PreferredLifetime=</varname></term>
 784           <listitem>
 785             <para>Allows the default "preferred lifetime" of the address to be overridden.
 786             Only three settings are accepted: <literal>forever</literal> or <literal>infinity</literal>
 787             which is the default and means that the address never expires, and <literal>0</literal> which means
 788             that the address is considered immediately "expired" and will not be used,
 789             unless explicitly requested. A setting of PreferredLifetime=0 is useful for
 790             addresses which are added to be used only by a specific application,
 791             which is then configured to use them explicitly.</para>
 792           </listitem>
 793         </varlistentry>
 794         <varlistentry>
 795           <term><varname>Scope=</varname></term>
 796           <listitem>
 797             <para>The scope of the address, which can be <literal>global</literal>,
 798             <literal>link</literal> or <literal>host</literal> or an unsigned integer ranges 0 to 255.
 799             Defaults to <literal>global</literal>.</para>
 800           </listitem>
 801         </varlistentry>
 802         <varlistentry>
 803           <term><varname>HomeAddress=</varname></term>
 804           <listitem>
 805             <para>Takes a boolean argument. Designates this address the "home address" as defined in
 806             <ulink url="https://tools.ietf.org/html/rfc6275">RFC 6275</ulink>.
 807             Supported only on IPv6. Defaults to false.</para>
 808           </listitem>
 809         </varlistentry>
 810         <varlistentry>
 811           <term><varname>DuplicateAddressDetection=</varname></term>
 812           <listitem>
 813             <para>Takes a boolean argument. Do not perform Duplicate Address Detection
 814             <ulink url="https://tools.ietf.org/html/rfc4862">RFC 4862</ulink> when adding this address.
 815             Supported only on IPv6. Defaults to false.</para>
 816           </listitem>
 817         </varlistentry>
 818         <varlistentry>
 819           <term><varname>ManageTemporaryAddress=</varname></term>
 820           <listitem>
 821             <para>Takes a boolean argument. If true the kernel manage temporary addresses created
 822             from this one as template on behalf of Privacy Extensions
 823             <ulink url="https://tools.ietf.org/html/rfc3041">RFC 3041</ulink>.  For this to become
 824             active, the use_tempaddr sysctl setting has to be set to a value greater than zero.
 825             The given address needs to have a prefix length of 64. This flag allows to use privacy
 826             extensions in a manually configured network, just like if stateless auto-configuration
 827             was active. Defaults to false. </para>
 828           </listitem>
 829         </varlistentry>
 830         <varlistentry>
 831           <term><varname>PrefixRoute=</varname></term>
 832           <listitem>
 833             <para>Takes a boolean argument. When adding or modifying an IPv6 address, the userspace
 834             application needs a way to suppress adding a prefix route. This is for example relevant
 835             together with IFA_F_MANAGERTEMPADDR, where userspace creates autoconf generated addresses,
 836             but depending on on-link, no route for the prefix should be added. Defaults to false.</para>
 837           </listitem>
 838         </varlistentry>
 839         <varlistentry>
 840           <term><varname>AutoJoin=</varname></term>
 841           <listitem>
 842             <para>Takes a boolean argument. Joining multicast group on ethernet level via
 843             <command>ip maddr</command> command would not work if we have an Ethernet switch that does
 844             IGMP snooping since the switch would not replicate multicast packets on  ports that did not
 845             have IGMP reports for the multicast addresses. Linux vxlan interfaces created via
 846             <command>ip link add vxlan</command> or networkd's netdev kind vxlan have the group option
 847             that enables then to do the required join. By extending ip address command with option
 848             <literal>autojoin</literal> we can get similar functionality for openvswitch (OVS) vxlan
 849             interfaces as well as other tunneling mechanisms that need to receive multicast traffic.
 850             Defaults to <literal>no</literal>.</para>
 851           </listitem>
 852         </varlistentry>
 853       </variablelist>
 854   </refsect1>
 855
 856     <refsect1>
 857     <title>[IPv6AddressLabel] Section Options</title>
 858
 859       <para>An <literal>[IPv6AddressLabel]</literal> section accepts the
 860       following keys. Specify several <literal>[IPv6AddressLabel]</literal>
 861       sections to configure several address labels. IPv6 address labels are
 862       used for address selection. See <ulink url="https://tools.ietf.org/html/rfc3484">RFC 3484</ulink>.
 863       Precedence is managed by userspace, and only the label itself is stored in the kernel</para>
 864
 865       <variablelist class='network-directives'>
 866         <varlistentry>
 867           <term><varname>Label=</varname></term>
 868           <listitem>
 869             <para> The label for the prefix (an unsigned integer) ranges 0 to 4294967294.
 870             0xffffffff is reserved. This key is mandatory.</para>
 871           </listitem>
 872         </varlistentry>
 873         <varlistentry>
 874           <term><varname>Prefix=</varname></term>
 875           <listitem>
 876             <para>IPv6 prefix is an address with a prefix length, separated by a slash <literal>/</literal> character.
 877             This key is mandatory. </para>
 878           </listitem>
 879         </varlistentry>
 880       </variablelist>
 881   </refsect1>
 882
 883  <refsect1>
 884     <title>[RoutingPolicyRule] Section Options</title>
 885
 886       <para>An <literal>[RoutingPolicyRule]</literal> section accepts the
 887       following keys. Specify several <literal>[RoutingPolicyRule]</literal>
 888       sections to configure several rules.</para>
 889
 890       <variablelist class='network-directives'>
 891         <varlistentry>
 892           <term><varname>TypeOfService=</varname></term>
 893           <listitem>
 894             <para>Specifies the type of service to match a number between 0 to 255.</para>
 895           </listitem>
 896         </varlistentry>
 897         <varlistentry>
 898           <term><varname>From=</varname></term>
 899           <listitem>
 900             <para>Specifies the source address prefix to match. Possibly followed by a slash and the prefix length.</para>
 901           </listitem>
 902         </varlistentry>
 903         <varlistentry>
 904           <term><varname>To=</varname></term>
 905           <listitem>
 906             <para>Specifies the destination address prefix to match. Possibly followed by a slash and the prefix length.</para>
 907           </listitem>
 908         </varlistentry>
 909         <varlistentry>
 910           <term><varname>FirewallMark=</varname></term>
 911           <listitem>
 912             <para>Specifies the iptables firewall mark value to match (a number between 1 and 4294967295).</para>
 913           </listitem>
 914         </varlistentry>
 915         <varlistentry>
 916           <term><varname>Table=</varname></term>
 917           <listitem>
 918             <para>Specifies the routing table identifier to lookup if the rule
 919             selector matches. The table identifier for a route (a number between 1 and 4294967295).</para>
 920           </listitem>
 921         </varlistentry>
 922         <varlistentry>
 923           <term><varname>Priority=</varname></term>
 924           <listitem>
 925             <para>Specifies the priority of this rule. <varname>Priority=</varname> is an unsigned
 926             integer. Higher number means lower priority, and rules get processed in order of increasing number.</para>
 927           </listitem>
 928         </varlistentry>
 929         <varlistentry>
 930           <term><varname>IncomingInterface=</varname></term>
 931           <listitem>
 932             <para>Specifies incoming device to match. If the interface is loopback, the rule only matches packets originating from this host.</para>
 933           </listitem>
 934         </varlistentry>
 935         <varlistentry>
 936           <term><varname>OutgoingInterface=</varname></term>
 937           <listitem>
 938             <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>
 939           </listitem>
 940         </varlistentry>
 941       </variablelist>
 942   </refsect1>
 943
 944   <refsect1>
 945     <title>[Route] Section Options</title>
 946       <para>The <literal>[Route]</literal> section accepts the
 947       following keys. Specify several <literal>[Route]</literal>
 948       sections to configure several routes.</para>
 949
 950       <variablelist class='network-directives'>
 951         <varlistentry>
 952           <term><varname>Gateway=</varname></term>
 953           <listitem>
 954             <para>As in the <literal>[Network]</literal> section.</para>
 955           </listitem>
 956         </varlistentry>
 957          <varlistentry>
 958            <term><varname>GatewayOnlink=</varname></term>
 959            <listitem>
 960              <para>The <literal>GatewayOnlink</literal> option tells the kernel that it does not have
 961              to check if the gateway is reachable directly by the current machine (i.e., the kernel does
 962              not need to check if the gateway is attached to the local network), so that we can insert the
 963              route in the kernel table without it being complained about. A boolean, defaults to <literal>no</literal>.
 964              </para>
 965            </listitem>
 966          </varlistentry>
 967         <varlistentry>
 968           <term><varname>Destination=</varname></term>
 969           <listitem>
 970             <para>The destination prefix of the route. Possibly
 971             followed by a slash and the prefix length. If omitted, a
 972             full-length host route is assumed.</para>
 973           </listitem>
 974         </varlistentry>
 975         <varlistentry>
 976           <term><varname>Source=</varname></term>
 977           <listitem>
 978             <para>The source prefix of the route. Possibly followed by
 979             a slash and the prefix length. If omitted, a full-length
 980             host route is assumed.</para>
 981           </listitem>
 982         </varlistentry>
 983         <varlistentry>
 984           <term><varname>Metric=</varname></term>
 985           <listitem>
 986             <para>The metric of the route (an unsigned integer).</para>
 987           </listitem>
 988         </varlistentry>
 989         <varlistentry>
 990           <term><varname>IPv6Preference=</varname></term>
 991           <listitem>
 992             <para>Specifies the route preference as defined in <ulink
 993             url="https://tools.ietf.org/html/rfc4191">RFC4191</ulink> for Router Discovery messages.
 994             Which can be one of <literal>low</literal> the route has a lowest priority,
 995             <literal>medium</literal> the route has a default priority or
 996             <literal>high</literal> the route has a highest priority.</para>
 997           </listitem>
 998         </varlistentry>
 999         <varlistentry>
1000           <term><varname>Scope=</varname></term>
1001           <listitem>
1002             <para>The scope of the route, which can be <literal>global</literal>,
1003             <literal>link</literal> or <literal>host</literal>. Defaults to
1004             <literal>global</literal>.</para>
1005           </listitem>
1006         </varlistentry>
1007         <varlistentry>
1008           <term><varname>PreferredSource=</varname></term>
1009           <listitem>
1010             <para>The preferred source address of the route. The address
1011             must be in the format described in
1012             <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
1013           </listitem>
1014         </varlistentry>
1015         <varlistentry>
1016           <term><varname>Table=<replaceable>num</replaceable></varname></term>
1017           <listitem>
1018           <para>The table identifier for the route (a number between 1 and 4294967295, or 0 to unset).
1019           The table can be retrieved using <command>ip route show table <replaceable>num</replaceable></command>.
1020           </para>
1021           </listitem>
1022         </varlistentry>
1023         <varlistentry>
1024           <term><varname>Protocol=</varname></term>
1025           <listitem>
1026             <para>The Protocol identifier for the route. Takes a number between 0 and 255 or the special values
1027             <literal>kernel</literal>, <literal>boot</literal> and <literal>static</literal>. Defaults to
1028             <literal>static</literal>.
1029             </para>
1030           </listitem>
1031         </varlistentry>
1032         <varlistentry>
1033           <term><varname>Type=</varname></term>
1034           <listitem>
1035             <para>The Type identifier for special route types, which can be
1036             <literal>unicast</literal> route to a destination network address which describes the path to the destination,
1037             <literal>blackhole</literal> packets are discarded silently,
1038             <literal>unreachable</literal> packets are discarded and the ICMP message host unreachable is generated,
1039             <literal>prohibit</literal> packets are discarded and the ICMP message communication administratively
1040             prohibited is generated. Defaults to <literal>unicast</literal>.
1041             </para>
1042           </listitem>
1043         </varlistentry>
1044
1045       </variablelist>
1046   </refsect1>
1047
1048   <refsect1>
1049     <title>[DHCP] Section Options</title>
1050       <para>The <literal>[DHCP]</literal> section configures the
1051       DHCPv4 and DHCP6 client, if it is enabled with the
1052       <varname>DHCP=</varname> setting described above:</para>
1053
1054       <variablelist class='network-directives'>
1055         <varlistentry>
1056           <term><varname>UseDNS=</varname></term>
1057           <listitem>
1058             <para>When true (the default), the DNS servers received
1059             from the DHCP server will be used and take precedence over
1060             any statically configured ones.</para>
1061
1062             <para>This corresponds to the <option>nameserver</option>
1063             option in <citerefentry
1064             project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
1065           </listitem>
1066         </varlistentry>
1067         <varlistentry>
1068           <term><varname>UseNTP=</varname></term>
1069           <listitem>
1070             <para>When true (the default), the NTP servers received
1071             from the DHCP server will be used by systemd-timesyncd
1072             and take precedence over any statically configured ones.</para>
1073           </listitem>
1074         </varlistentry>
1075         <varlistentry>
1076           <term><varname>UseMTU=</varname></term>
1077           <listitem>
1078             <para>When true, the interface maximum transmission unit
1079             from the DHCP server will be used on the current link.
1080             Defaults to false.</para>
1081           </listitem>
1082         </varlistentry>
1083         <varlistentry>
1084           <term><varname>Anonymize=</varname></term>
1085           <listitem>
1086             <para>Takes a boolean argument. When true, the options sent to the DHCP server will
1087             follow the <ulink url="https://tools.ietf.org/html/rfc7844">RFC 7844</ulink>
1088             (Anonymity Profiles for DHCP Clients) to minimize disclosure of identifying information.
1089             Defaults to false.</para>
1090
1091             <para>This option should only be set to true when
1092             <varname>MACAddressPolicy=</varname> is set to <literal>random</literal>
1093             (see <citerefentry
1094             project='man-pages'><refentrytitle>systemd.link</refentrytitle><manvolnum>5</manvolnum></citerefentry>).</para>
1095
1096             <para>Note that this configuration will overwrite others.
1097             In concrete, the following variables will be ignored:
1098             <varname>SendHostname=</varname>, <varname>ClientIdentifier=</varname>,
1099             <varname>UseRoutes=</varname>, <varname>SendHostname=</varname>,
1100             <varname>UseMTU=</varname>, <varname>VendorClassIdentifier=</varname>,
1101             <varname>UseTimezone=</varname>.</para>
1102           </listitem>
1103         </varlistentry>
1104         <varlistentry>
1105           <term><varname>SendHostname=</varname></term>
1106           <listitem>
1107             <para>When true (the default), the machine's hostname will
1108             be sent to the DHCP server.</para>
1109           </listitem>
1110         </varlistentry>
1111         <varlistentry>
1112           <term><varname>UseHostname=</varname></term>
1113           <listitem>
1114             <para>When true (the default), the hostname received from
1115             the DHCP server will be set as the transient hostname of the system
1116             </para>
1117           </listitem>
1118         </varlistentry>
1119         <varlistentry>
1120         <term><varname>Hostname=</varname></term>
1121         <listitem>
1122           <para>Use this value for the hostname which is sent to the
1123           DHCP server, instead of machine's hostname.</para>
1124         </listitem>
1125       </varlistentry>
1126         <varlistentry>
1127           <term><varname>UseDomains=</varname></term>
1128           <listitem>
1129             <para>Takes a boolean argument, or the special value <literal>route</literal>. When true, the domain name
1130             received from the DHCP server will be used as DNS search domain over this link, similar to the effect of
1131             the <option>Domains=</option> setting. If set to <literal>route</literal>, the domain name received from
1132             the DHCP server will be used for routing DNS queries only, but not for searching, similar to the effect of
1133             the <option>Domains=</option> setting when the argument is prefixed with <literal>~</literal>. Defaults to
1134             false.</para>
1135
1136             <para>It is recommended to enable this option only on trusted networks, as setting this affects resolution
1137             of all host names, in particular of single-label names. It is generally safer to use the supplied domain
1138             only as routing domain, rather than as search domain, in order to not have it affect local resolution of
1139             single-label names.</para>
1140
1141             <para>When set to true, this setting corresponds to the <option>domain</option> option in <citerefentry
1142             project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
1143           </listitem>
1144         </varlistentry>
1145         <varlistentry>
1146           <term><varname>UseRoutes=</varname></term>
1147           <listitem>
1148             <para>When true (the default), the static routes will be requested from the DHCP server and added to the
1149               routing table with a metric of 1024, and a scope of "global", "link" or "host", depending on the route's
1150               destination and gateway. If the destination is on the local host, e.g., 127.x.x.x, or the same as the
1151               link's own address, the scope will be set to "host". Otherwise if the gateway is null (a direct route), a
1152               "link" scope will be used. For anything else, scope defaults to "global".</para>
1153           </listitem>
1154         </varlistentry>
1155
1156         <varlistentry>
1157           <term><varname>UseTimezone=</varname></term>
1158
1159           <listitem><para>When true, the timezone received from the
1160           DHCP server will be set as timezone of the local
1161           system. Defaults to <literal>no</literal>.</para></listitem>
1162         </varlistentry>
1163
1164         <varlistentry>
1165           <term><varname>CriticalConnection=</varname></term>
1166           <listitem>
1167             <para>When true, the connection will never be torn down
1168             even if the DHCP lease expires. This is contrary to the
1169             DHCP specification, but may be the best choice if, say,
1170             the root filesystem relies on this connection. Defaults to
1171             false.</para>
1172           </listitem>
1173         </varlistentry>
1174
1175         <varlistentry>
1176           <term><varname>ClientIdentifier=</varname></term>
1177           <listitem>
1178             <para>The DHCPv4 client identifier to use. Either <literal>mac</literal> to use the MAC address of the link
1179             or <literal>duid</literal> (the default, see below) to use an RFC4361-compliant Client ID.</para>
1180           </listitem>
1181         </varlistentry>
1182
1183         <varlistentry>
1184           <term><varname>VendorClassIdentifier=</varname></term>
1185           <listitem>
1186             <para>The vendor class identifier used to identify vendor
1187             type and configuration.</para>
1188           </listitem>
1189         </varlistentry>
1190
1191         <varlistentry>
1192           <term><varname>DUIDType=</varname></term>
1193           <listitem>
1194             <para>Override the global <varname>DUIDType</varname> setting for this network. See
1195             <citerefentry><refentrytitle>networkd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1196             for a description of possible values.</para>
1197           </listitem>
1198         </varlistentry>
1199
1200         <varlistentry>
1201           <term><varname>DUIDRawData=</varname></term>
1202           <listitem>
1203             <para>Override the global <varname>DUIDRawData</varname> setting for this network. See
1204             <citerefentry><refentrytitle>networkd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1205             for a description of possible values.</para>
1206           </listitem>
1207         </varlistentry>
1208
1209         <varlistentry>
1210           <term><varname>IAID=</varname></term>
1211           <listitem>
1212             <para>The DHCP Identity Association Identifier (IAID) for the interface, a 32-bit unsigned integer.</para>
1213           </listitem>
1214         </varlistentry>
1215
1216         <varlistentry>
1217           <term><varname>RequestBroadcast=</varname></term>
1218           <listitem>
1219             <para>Request the server to use broadcast messages before
1220             the IP address has been configured. This is necessary for
1221             devices that cannot receive RAW packets, or that cannot
1222             receive packets at all before an IP address has been
1223             configured. On the other hand, this must not be enabled on
1224             networks where broadcasts are filtered out.</para>
1225           </listitem>
1226         </varlistentry>
1227
1228         <varlistentry>
1229           <term><varname>RouteMetric=</varname></term>
1230           <listitem>
1231             <para>Set the routing metric for routes specified by the
1232             DHCP server.</para>
1233           </listitem>
1234         </varlistentry>
1235
1236         <varlistentry>
1237           <term><varname>RouteTable=<replaceable>num</replaceable></varname></term>
1238           <listitem>
1239             <para>The table identifier for DHCP routes (a number between 1 and 4294967295, or 0 to unset).
1240             The table can be retrieved using <command>ip route show table <replaceable>num</replaceable></command>.
1241             </para>
1242             <para>When used in combination with <varname>VRF=</varname> the
1243             VRF's routing table is used unless this parameter is specified.
1244             </para>
1245           </listitem>
1246         </varlistentry>
1247
1248         <varlistentry>
1249           <term><varname>ListenPort=</varname></term>
1250           <listitem>
1251             <para>Allow setting custom port for the DHCP client to listen on.</para>
1252           </listitem>
1253         </varlistentry>
1254       </variablelist>
1255     </refsect1>
1256
1257   <refsect1>
1258     <title>[IPv6AcceptRA] Section Options</title>
1259       <para>The <literal>[IPv6AcceptRA]</literal> section configures the IPv6 Router Advertisement
1260       (RA) client, if it is enabled with the <varname>IPv6AcceptRA=</varname> setting described
1261       above:</para>
1262
1263       <variablelist class='network-directives'>
1264         <varlistentry>
1265           <term><varname>UseDNS=</varname></term>
1266           <listitem>
1267             <para>When true (the default), the DNS servers received in the Router Advertisement will be used and take
1268             precedence over any statically configured ones.</para>
1269
1270             <para>This corresponds to the <option>nameserver</option> option in <citerefentry
1271             project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
1272           </listitem>
1273         </varlistentry>
1274
1275         <varlistentry>
1276           <term><varname>UseDomains=</varname></term>
1277           <listitem>
1278             <para>Takes a boolean argument, or the special value <literal>route</literal>. When true, the domain name
1279             received via IPv6 Router Advertisement (RA) will be used as DNS search domain over this link, similar to
1280             the effect of the <option>Domains=</option> setting. If set to <literal>route</literal>, the domain name
1281             received via IPv6 RA will be used for routing DNS queries only, but not for searching, similar to the
1282             effect of the <option>Domains=</option> setting when the argument is prefixed with
1283             <literal>~</literal>. Defaults to false.</para>
1284
1285             <para>It is recommended to enable this option only on trusted networks, as setting this affects resolution
1286             of all host names, in particular of single-label names. It is generally safer to use the supplied domain
1287             only as routing domain, rather than as search domain, in order to not have it affect local resolution of
1288             single-label names.</para>
1289
1290             <para>When set to true, this setting corresponds to the <option>domain</option> option in <citerefentry
1291             project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
1292           </listitem>
1293         </varlistentry>
1294
1295         <varlistentry>
1296           <term><varname>RouteTable=<replaceable>num</replaceable></varname></term>
1297           <listitem>
1298             <para>The table identifier for the routes received in the Router Advertisement
1299             (a number between 1 and 4294967295, or 0 to unset).
1300             The table can be retrieved using <command>ip route show table <replaceable>num</replaceable></command>.
1301             </para>
1302           </listitem>
1303         </varlistentry>
1304       </variablelist>
1305   </refsect1>
1306
1307
1308   <refsect1>
1309     <title>[DHCPServer] Section Options</title>
1310     <para>The <literal>[DHCPServer]</literal> section contains
1311     settings for the DHCP server, if enabled via the
1312     <varname>DHCPServer=</varname> option described above:</para>
1313
1314     <variablelist class='network-directives'>
1315
1316       <varlistentry>
1317         <term><varname>PoolOffset=</varname></term>
1318         <term><varname>PoolSize=</varname></term>
1319
1320         <listitem><para>Configures the pool of addresses to hand out. The pool
1321         is a contiguous sequence of IP addresses in the subnet configured for
1322         the server address, which does not include the subnet nor the broadcast
1323         address. <varname>PoolOffset=</varname> takes the offset of the pool
1324         from the start of subnet, or zero to use the default value.
1325         <varname>PoolSize=</varname> takes the number of IP addresses in the
1326         pool or zero to use the default value. By default, the pool starts at
1327         the first address after the subnet address and takes up the rest of
1328         the subnet, excluding the broadcast address. If the pool includes
1329         the server address (the default), this is reserved and not handed
1330         out to clients.</para></listitem>
1331       </varlistentry>
1332
1333       <varlistentry>
1334         <term><varname>DefaultLeaseTimeSec=</varname></term>
1335         <term><varname>MaxLeaseTimeSec=</varname></term>
1336
1337         <listitem><para>Control the default and maximum DHCP lease
1338         time to pass to clients. These settings take time values in seconds or
1339         another common time unit, depending on the suffix. The default
1340         lease time is used for clients that did not ask for a specific
1341         lease time. If a client asks for a lease time longer than the
1342         maximum lease time, it is automatically shortened to the
1343         specified time. The default lease time defaults to 1h, the
1344         maximum lease time to 12h. Shorter lease times are beneficial
1345         if the configuration data in DHCP leases changes frequently
1346         and clients shall learn the new settings with shorter
1347         latencies. Longer lease times reduce the generated DHCP
1348         network traffic.</para></listitem>
1349       </varlistentry>
1350
1351       <varlistentry>
1352         <term><varname>EmitDNS=</varname></term>
1353         <term><varname>DNS=</varname></term>
1354
1355         <listitem><para>Configures whether the DHCP leases handed out
1356         to clients shall contain DNS server information. The
1357         <varname>EmitDNS=</varname> setting takes a boolean argument
1358         and defaults to <literal>yes</literal>. The DNS servers to
1359         pass to clients may be configured with the
1360         <varname>DNS=</varname> option, which takes a list of IPv4
1361         addresses. If the <varname>EmitDNS=</varname> option is
1362         enabled but no servers configured, the servers are
1363         automatically propagated from an "uplink" interface that has
1364         appropriate servers set. The "uplink" interface is determined
1365         by the default route of the system with the highest
1366         priority. Note that this information is acquired at the time
1367         the lease is handed out, and does not take uplink interfaces
1368         into account that acquire DNS or NTP server information at a
1369         later point. DNS server propagation does not take
1370         <filename>/etc/resolv.conf</filename> into account. Also, note
1371         that the leases are not refreshed if the uplink network
1372         configuration changes. To ensure clients regularly acquire the
1373         most current uplink DNS server information, it is thus
1374         advisable to shorten the DHCP lease time via
1375         <varname>MaxLeaseTimeSec=</varname> described
1376         above.</para></listitem>
1377       </varlistentry>
1378
1379       <varlistentry>
1380         <term><varname>EmitNTP=</varname></term>
1381         <term><varname>NTP=</varname></term>
1382
1383         <listitem><para>Similar to the <varname>EmitDNS=</varname> and
1384         <varname>DNS=</varname> settings described above, these
1385         settings configure whether and what NTP server information
1386         shall be emitted as part of the DHCP lease. The same syntax,
1387         propagation semantics and defaults apply as for
1388         <varname>EmitDNS=</varname> and
1389         <varname>DNS=</varname>.</para></listitem>
1390       </varlistentry>
1391
1392       <varlistentry>
1393         <term><varname>EmitRouter=</varname></term>
1394
1395         <listitem><para>Similar to the <varname>EmitDNS=</varname>
1396         setting described above, this setting configures whether the
1397         DHCP lease should contain the router option. The same syntax,
1398         propagation semantics and defaults apply as for
1399         <varname>EmitDNS=</varname>.</para></listitem>
1400       </varlistentry>
1401
1402       <varlistentry>
1403         <term><varname>EmitTimezone=</varname></term>
1404         <term><varname>Timezone=</varname></term>
1405
1406         <listitem><para>Configures whether the DHCP leases handed out
1407         to clients shall contain timezone information. The
1408         <varname>EmitTimezone=</varname> setting takes a boolean
1409         argument and defaults to <literal>yes</literal>. The
1410         <varname>Timezone=</varname> setting takes a timezone string
1411         (such as <literal>Europe/Berlin</literal> or
1412         <literal>UTC</literal>) to pass to clients. If no explicit
1413         timezone is set, the system timezone of the local host is
1414         propagated, as determined by the
1415         <filename>/etc/localtime</filename> symlink.</para></listitem>
1416       </varlistentry>
1417
1418     </variablelist>
1419   </refsect1>
1420
1421   <refsect1>
1422     <title>[IPv6PrefixDelegation] Section Options</title>
1423     <para>The <literal>[IPv6PrefixDelegation]</literal> section contains
1424     settings for sending IPv6 Router Advertisements and whether to act as
1425     a router, if enabled via the <varname>IPv6PrefixDelegation=</varname>
1426     option described above. IPv6 network prefixes are defined with one or
1427     more <literal>[IPv6Prefix]</literal> sections.</para>
1428
1429     <variablelist class='network-directives'>
1430
1431       <varlistentry>
1432         <term><varname>Managed=</varname></term>
1433         <term><varname>OtherInformation=</varname></term>
1434
1435         <listitem><para>Controls whether a DHCPv6 server is used to acquire IPv6
1436         addresses on the network link when <varname>Managed=</varname> boolean
1437         is set to <literal>true</literal> or if only additional network
1438         information can be obtained via DHCPv6 for the network link when
1439         <varname>OtherInformation=</varname> boolean is set to
1440         <literal>true</literal>. Both settings default to
1441         <literal>false</literal>, which means that a DHCPv6 server is not being
1442         used.</para></listitem>
1443       </varlistentry>
1444
1445       <varlistentry>
1446         <term><varname>RouterLifetimeSec=</varname></term>
1447
1448         <listitem><para>Configures the IPv6 router lifetime in seconds. If set,
1449         this host also announces itself in Router Advertisements as an IPv6
1450         router for the network link. Defaults to unset, which means the host is
1451         not acting as a router.</para>
1452         </listitem>
1453       </varlistentry>
1454
1455       <varlistentry>
1456         <term><varname>RouterPreference=</varname></term>
1457
1458         <listitem><para>Configures IPv6 router preference if
1459         <varname>RouterLifetimeSec=</varname> is non-zero. Valid values are
1460         <literal>high</literal>, <literal>medium</literal> and
1461         <literal>low</literal>, with <literal>normal</literal> and
1462         <literal>default</literal> added as synonyms for
1463         <literal>medium</literal> just to make configuration easier. See
1464         <ulink url="https://tools.ietf.org/html/rfc4191">RFC 4191</ulink>
1465         for details. Defaults to <literal>medium</literal>.</para></listitem>
1466       </varlistentry>
1467
1468       <varlistentry>
1469         <term><varname>EmitDNS=</varname></term>
1470         <term><varname>DNS=</varname></term>
1471
1472         <listitem><para><varname>DNS=</varname> specifies a list of recursive
1473         DNS server IPv6 addresses that distributed via Router Advertisement
1474         messages when <varname>EmitDNS=</varname> is true. If <varname>DNS=
1475         </varname> is empty, DNS servers are read from the
1476         <literal>[Network]</literal> section. If the
1477         <literal>[Network]</literal> section does not contain any DNS servers
1478         either, DNS servers from the uplink with the highest priority default
1479         route are used. When <varname>EmitDNS=</varname> is false, no DNS server
1480         information is sent in Router Advertisement messages.
1481         <varname>EmitDNS=</varname> defaults to true.
1482         </para></listitem>
1483       </varlistentry>
1484
1485       <varlistentry>
1486         <term><varname>EmitDomains=</varname></term>
1487         <term><varname>Domains=</varname></term>
1488
1489         <listitem><para>A list of DNS search domains distributed via Router
1490         Advertisement messages when <varname>EmitDomains=</varname> is true. If
1491         <varname>Domains=</varname> is empty, DNS search domains are read from the
1492         <literal>[Network]</literal> section. If the <literal>[Network]</literal>
1493         section does not contain any DNS search domains either, DNS search
1494         domains from the uplink with the highest priority default route are
1495         used. When <varname>EmitDomains=</varname> is false, no DNS search domain
1496         information is sent in Router Advertisement messages.
1497         <varname>EmitDomains=</varname> defaults to true.
1498         </para></listitem>
1499       </varlistentry>
1500
1501       <varlistentry>
1502         <term><varname>DNSLifetimeSec=</varname></term>
1503
1504         <listitem><para>Lifetime in seconds for the DNS server addresses listed
1505         in <varname>DNS=</varname> and search domains listed in
1506         <varname>Domains=</varname>.</para></listitem>
1507       </varlistentry>
1508
1509     </variablelist>
1510     </refsect1>
1511
1512       <refsect1>
1513     <title>[IPv6Prefix] Section Options</title>
1514     <para>One or more <literal>[IPv6Prefix]</literal> sections contain the IPv6
1515     prefixes that are announced via Router Advertisements. See
1516     <ulink url="https://tools.ietf.org/html/rfc4861">RFC 4861</ulink>
1517     for further details.</para>
1518
1519     <variablelist class='network-directives'>
1520
1521       <varlistentry>
1522         <term><varname>AddressAutoconfiguration=</varname></term>
1523         <term><varname>OnLink=</varname></term>
1524
1525         <listitem><para>Boolean values to specify whether IPv6 addresses can be
1526         autoconfigured with this prefix and whether the prefix can be used for
1527         onlink determination. Both settings default to <literal>true</literal>
1528         in order to ease configuration.
1529         </para></listitem>
1530       </varlistentry>
1531
1532       <varlistentry>
1533         <term><varname>Prefix=</varname></term>
1534
1535         <listitem><para>The IPv6 prefix that is to be distributed to hosts.
1536         Similarly to configuring static IPv6 addresses, the setting is
1537         configured as an IPv6 prefix and its prefix length, separated by a
1538         <literal>/</literal> character. Use multiple
1539         <literal>[IPv6Prefix]</literal> sections to configure multiple IPv6
1540         prefixes since prefix lifetimes, address autoconfiguration and onlink
1541         status may differ from one prefix to another.</para></listitem>
1542       </varlistentry>
1543
1544       <varlistentry>
1545         <term><varname>PreferredLifetimeSec=</varname></term>
1546         <term><varname>ValidLifetimeSec=</varname></term>
1547
1548         <listitem><para>Preferred and valid lifetimes for the prefix measured in
1549         seconds. <varname>PreferredLifetimeSec=</varname> defaults to 604800
1550         seconds (one week) and <varname>ValidLifetimeSec=</varname> defaults
1551         to 2592000 seconds (30 days).</para></listitem>
1552       </varlistentry>
1553
1554     </variablelist>
1555     </refsect1>
1556
1557     <refsect1>
1558     <title>[Bridge] Section Options</title>
1559       <para>The <literal>[Bridge]</literal> section accepts the
1560       following keys.</para>
1561       <variablelist class='network-directives'>
1562         <varlistentry>
1563           <term><varname>UnicastFlood=</varname></term>
1564           <listitem>
1565             <para>A boolean. Controls whether the bridge should flood
1566             traffic for which an FDB entry is missing and the destination
1567             is unknown through this port. Defaults to on.
1568             </para>
1569           </listitem>
1570         </varlistentry>
1571         <varlistentry>
1572           <term><varname>HairPin=</varname></term>
1573           <listitem>
1574             <para>A boolean. Configures whether traffic may be sent back
1575             out of the port on which it was received. By default, this
1576             flag is false, and the bridge will not forward traffic back
1577             out of the receiving port.</para>
1578           </listitem>
1579         </varlistentry>
1580         <varlistentry>
1581           <term><varname>UseBPDU=</varname></term>
1582           <listitem>
1583             <para>A boolean. Configures whether STP Bridge Protocol Data Units will be
1584             processed by the bridge port. Defaults to yes.</para>
1585           </listitem>
1586         </varlistentry>
1587         <varlistentry>
1588           <term><varname>FastLeave=</varname></term>
1589           <listitem>
1590             <para>A boolean. This flag allows the bridge to immediately stop multicast
1591             traffic on a port that receives an IGMP Leave message. It is only used with
1592             IGMP snooping if enabled on the bridge. Defaults to off.</para>
1593           </listitem>
1594         </varlistentry>
1595         <varlistentry>
1596           <term><varname>AllowPortToBeRoot=</varname></term>
1597           <listitem>
1598             <para>A boolean. Configures whether a given port is allowed to
1599             become a root port. Only used when STP is enabled on the bridge.
1600             Defaults to on.</para>
1601           </listitem>
1602         </varlistentry>
1603         <varlistentry>
1604           <term><varname>Cost=</varname></term>
1605           <listitem>
1606             <para>Sets the "cost" of sending packets of this interface.
1607             Each port in a bridge may have a different speed and the cost
1608             is used to decide which link to use. Faster interfaces
1609             should have lower costs. It is an integer value between 1 and
1610             65535.</para>
1611           </listitem>
1612         </varlistentry>
1613         <varlistentry>
1614           <term><varname>Priority=</varname></term>
1615           <listitem>
1616             <para>Sets the "priority" of sending packets on this interface.
1617             Each port in a bridge may have a different priority which is used
1618             to decide which link to use. Lower value means higher priority.
1619             It is an integer value between 0 to 63. Networkd does not set any
1620             default, meaning the kernel default value of 32 is used.</para>
1621           </listitem>
1622         </varlistentry>
1623       </variablelist>
1624   </refsect1>
1625   <refsect1>
1626     <title>[BridgeFDB] Section Options</title>
1627       <para>The <literal>[BridgeFDB]</literal> section manages the
1628       forwarding database table of a port and accepts the following
1629       keys. Specify several <literal>[BridgeFDB]</literal> sections to
1630       configure several static MAC table entries.</para>
1631
1632       <variablelist class='network-directives'>
1633         <varlistentry>
1634           <term><varname>MACAddress=</varname></term>
1635           <listitem>
1636             <para>As in the <literal>[Network]</literal> section. This
1637             key is mandatory.</para>
1638           </listitem>
1639         </varlistentry>
1640         <varlistentry>
1641           <term><varname>VLANId=</varname></term>
1642           <listitem>
1643             <para>The VLAN ID for the new static MAC table entry. If
1644             omitted, no VLAN ID info is appended to the new static MAC
1645             table entry.</para>
1646           </listitem>
1647         </varlistentry>
1648       </variablelist>
1649   </refsect1>
1650   <refsect1>
1651     <title>[BridgeVLAN] Section Options</title>
1652       <para>The <literal>[BridgeVLAN]</literal> section manages the VLAN ID configuration of a bridge port and accepts
1653       the following keys. Specify several <literal>[BridgeVLAN]</literal> sections to configure several VLAN entries.
1654       The <varname>VLANFiltering=</varname> option has to be enabled, see <literal>[Bridge]</literal> section in
1655       <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
1656
1657       <variablelist class='network-directives'>
1658         <varlistentry>
1659           <term><varname>VLAN=</varname></term>
1660           <listitem>
1661             <para>The VLAN ID allowed on the port. This can be either a single ID or a range M-N. VLAN IDs are valid
1662             from 1 to 4094.</para>
1663           </listitem>
1664         </varlistentry>
1665         <varlistentry>
1666           <term><varname>EgressUntagged=</varname></term>
1667           <listitem>
1668             <para>The VLAN ID specified here will be used to untag frames on egress. Configuring
1669             <varname>EgressUntagged=</varname> implicates the use of <varname>VLAN=</varname> above and will enable the
1670             VLAN ID for ingress as well. This can be either a single ID or a range M-N.</para>
1671           </listitem>
1672         </varlistentry>
1673         <varlistentry>
1674           <term><varname>PVID=</varname></term>
1675           <listitem>
1676             <para>The Port VLAN ID specified here is assigned to all untagged frames at ingress.
1677             <varname>PVID=</varname> can be used only once. Configuring <varname>PVID=</varname> implicates the use of
1678             <varname>VLAN=</varname> above and will enable the VLAN ID for ingress as well.</para>
1679           </listitem>
1680         </varlistentry>
1681       </variablelist>
1682   </refsect1>
1683
1684   <refsect1>
1685     <title>Examples</title>
1686     <example>
1687       <title>Static network configuration</title>
1688
1689       <programlisting># /etc/systemd/network/50-static.network
1690 [Match]
1691 Name=enp2s0
1692
1693 [Network]
1694 Address=192.168.0.15/24
1695 Gateway=192.168.0.1</programlisting>
1696
1697       <para>This brings interface <literal>enp2s0</literal> up with a static address. The
1698       specified gateway will be used for a default route.</para>
1699     </example>
1700
1701     <example>
1702       <title>DHCP on ethernet links</title>
1703
1704       <programlisting># /etc/systemd/network/80-dhcp.network
1705 [Match]
1706 Name=en*
1707
1708 [Network]
1709 DHCP=yes</programlisting>
1710
1711       <para>This will enable DHCPv4 and DHCPv6 on all interfaces with names starting with
1712       <literal>en</literal> (i.e. ethernet interfaces).</para>
1713     </example>
1714
1715     <example>
1716       <title>A bridge with two enslaved links</title>
1717
1718       <programlisting># /etc/systemd/network/25-bridge-static.network
1719 [Match]
1720 Name=bridge0
1721
1722 [Network]
1723 Address=192.168.0.15/24
1724 Gateway=192.168.0.1
1725 DNS=192.168.0.1</programlisting>
1726
1727       <programlisting># /etc/systemd/network/25-bridge-slave-interface-1.network
1728 [Match]
1729 Name=enp2s0
1730
1731 [Network]
1732 Bridge=bridge0</programlisting>
1733
1734       <programlisting># /etc/systemd/network/25-bridge-slave-interface-2.network
1735 [Match]
1736 Name=wlp3s0
1737
1738 [Network]
1739 Bridge=bridge0</programlisting>
1740
1741       <para>This creates a bridge and attaches devices <literal>enp2s0</literal> and
1742       <literal>wlp3s0</literal> to it. The bridge will have the specified static address
1743       and network assigned, and a default route via the specified gateway will be
1744       added. The specified DNS server will be added to the global list of DNS resolvers.
1745       </para>
1746     </example>
1747
1748     <example>
1749       <title></title>
1750
1751       <programlisting>
1752 # /etc/systemd/network/20-bridge-slave-interface-vlan.network
1753 [Match]
1754 Name=enp2s0
1755
1756 [Network]
1757 Bridge=bridge0
1758
1759 [BridgeVLAN]
1760 VLAN=1-32
1761 PVID=42
1762 EgressUntagged=42
1763
1764 [BridgeVLAN]
1765 VLAN=100-200
1766
1767 [BridgeVLAN]
1768 EgressUntagged=300-400</programlisting>
1769
1770     <para>This overrides the configuration specified in the previous example for the
1771     interface <literal>enp2s0</literal>, and enables VLAN on that bridge port. VLAN IDs
1772     1-32, 42, 100-400 will be allowed. Packets tagged with VLAN IDs 42, 300-400 will be
1773     untagged when they leave on this interface. Untagged packets which arrive on this
1774     interface will be assigned VLAN ID 42.</para>
1775     </example>
1776
1777     <example>
1778       <title>Various tunnels</title>
1779
1780       <programlisting>/etc/systemd/network/25-tunnels.network
1781 [Match]
1782 Name=ens1
1783
1784 [Network]
1785 Tunnel=ipip-tun
1786 Tunnel=sit-tun
1787 Tunnel=gre-tun
1788 Tunnel=vti-tun
1789       </programlisting>
1790
1791       <programlisting>/etc/systemd/network/25-tunnel-ipip.netdev
1792 [NetDev]
1793 Name=ipip-tun
1794 Kind=ipip
1795       </programlisting>
1796
1797       <programlisting>/etc/systemd/network/25-tunnel-sit.netdev
1798 [NetDev]
1799 Name=sit-tun
1800 Kind=sit
1801       </programlisting>
1802
1803       <programlisting>/etc/systemd/network/25-tunnel-gre.netdev
1804 [NetDev]
1805 Name=gre-tun
1806 Kind=gre
1807       </programlisting>
1808
1809       <programlisting>/etc/systemd/network/25-tunnel-vti.netdev
1810 [NetDev]
1811 Name=vti-tun
1812 Kind=vti
1813       </programlisting>
1814
1815       <para>This will bring interface <literal>ens1</literal> up and create an IPIP tunnel,
1816       a SIT tunnel, a GRE tunnel, and a VTI tunnel using it.</para>
1817     </example>
1818
1819     <example>
1820       <title>A bond device</title>
1821
1822       <programlisting># /etc/systemd/network/30-bond1.network
1823 [Match]
1824 Name=bond1
1825
1826 [Network]
1827 DHCP=ipv6
1828 </programlisting>
1829
1830       <programlisting># /etc/systemd/network/30-bond1.netdev
1831 [NetDev]
1832 Name=bond1
1833 Kind=bond
1834 </programlisting>
1835
1836       <programlisting># /etc/systemd/network/30-bond1-dev1.network
1837 [Match]
1838 MACAddress=52:54:00:e9:64:41
1839
1840 [Network]
1841 Bond=bond1
1842 </programlisting>
1843
1844       <programlisting># /etc/systemd/network/30-bond1-dev2.network
1845 [Match]
1846 MACAddress=52:54:00:e9:64:42
1847
1848 [Network]
1849 Bond=bond1
1850 </programlisting>
1851
1852     <para>This will create a bond device <literal>bond1</literal> and enslave the two
1853     devices with MAC addresses 52:54:00:e9:64:41 and 52:54:00:e9:64:42 to it. IPv6 DHCP
1854     will be used to acquire an address.</para>
1855     </example>
1856
1857     <example>
1858       <title>Virtual Routing and Forwarding (VRF)</title>
1859       <para>Add the <literal>bond1</literal> interface to the VRF master interface
1860       <literal>vrf1</literal>. This will redirect routes generated on this interface to be
1861       within the routing table defined during VRF creation. For kernels before 4.8 traffic
1862       won't be redirected towards the VRFs routing table unless specific ip-rules are added.
1863       </para>
1864       <programlisting># /etc/systemd/network/25-vrf.network
1865 [Match]
1866 Name=bond1
1867
1868 [Network]
1869 VRF=vrf1
1870 </programlisting>
1871     </example>
1872
1873     <example>
1874       <title>MacVTap</title>
1875       <para>This brings up a network interface <literal>macvtap-test</literal>
1876       and attaches it to <literal>enp0s25</literal>.</para>
1877       <programlisting># /usr/lib/systemd/network/25-macvtap.network
1878 [Match]
1879 Name=enp0s25
1880
1881 [Network]
1882 MACVTAP=macvtap-test
1883 </programlisting>
1884     </example>
1885   </refsect1>
1886
1887   <refsect1>
1888     <title>See Also</title>
1889     <para>
1890       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1891       <citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
1892       <citerefentry><refentrytitle>systemd.link</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1893       <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1894       <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
1895     </para>
1896   </refsect1>
1897
1898 </refentry>