man/systemd.network.xml

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  10   Copyright 2013 Tom Gundersen
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  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       <varlistentry>
 256         <term><varname>RequiredForOnline=</varname></term>
 257         <listitem>
 258           <para>A boolean. When <literal>yes</literal>, the network is deemed
 259           required when determining whether the system is online when running
 260           <literal>systemd-networkd-wait-online</literal>.
 261           When <literal>no</literal>, the network is ignored when checking for
 262           online state. Defaults to <literal>yes</literal>.</para>
 263           <para>The network will be brought up normally in all cases, but in
 264           the event that there is no address being assigned by DHCP or the
 265           cable is not plugged in, the link will simply remain offline and be
 266           skipped automatically by <literal>systemd-networkd-wait-online</literal>
 267           if <literal>RequiredForOnline=true</literal>.</para>
 268         </listitem>
 269       </varlistentry>
 270     </variablelist>
 271   </refsect1>
 272
 273   <refsect1>
 274     <title>[Network] Section Options</title>
 275
 276       <para>The <literal>[Network]</literal> section accepts the following keys:</para>
 277
 278       <variablelist class='network-directives'>
 279         <varlistentry>
 280           <term><varname>Description=</varname></term>
 281           <listitem>
 282             <para>A description of the device. This is only used for
 283             presentation purposes.</para>
 284           </listitem>
 285         </varlistentry>
 286         <varlistentry>
 287           <term><varname>DHCP=</varname></term>
 288           <listitem>
 289             <para>Enables DHCPv4 and/or DHCPv6 client support. Accepts
 290             <literal>yes</literal>, <literal>no</literal>,
 291             <literal>ipv4</literal>, or <literal>ipv6</literal>. Defaults
 292             to <literal>no</literal>.</para>
 293
 294             <para>Note that DHCPv6 will by default be triggered by Router
 295             Advertisement, if that is enabled, regardless of this parameter.
 296             By enabling DHCPv6 support explicitly, the DHCPv6 client will
 297             be started regardless of the presence of routers on the link,
 298             or what flags the routers pass. See
 299             <literal>IPv6AcceptRA=</literal>.</para>
 300
 301             <para>Furthermore, note that by default the domain name
 302             specified through DHCP is not used for name resolution.
 303             See option <option>UseDomains=</option> below.</para>
 304
 305             <para>See the <literal>[DHCP]</literal> section below for further configuration options for the DHCP client
 306             support.</para>
 307           </listitem>
 308         </varlistentry>
 309         <varlistentry>
 310           <term><varname>DHCPServer=</varname></term>
 311           <listitem>
 312             <para>A boolean. Enables DHCPv4 server support. Defaults
 313             to <literal>no</literal>. Further settings for the DHCP
 314             server may be set in the <literal>[DHCPServer]</literal>
 315             section described below.</para>
 316           </listitem>
 317         </varlistentry>
 318         <varlistentry>
 319           <term><varname>LinkLocalAddressing=</varname></term>
 320           <listitem>
 321             <para>Enables link-local address autoconfiguration. Accepts
 322             <literal>yes</literal>, <literal>no</literal>,
 323             <literal>ipv4</literal>, or <literal>ipv6</literal>. Defaults to
 324             <literal>ipv6</literal>.</para>
 325           </listitem>
 326         </varlistentry>
 327         <varlistentry>
 328           <term><varname>IPv4LLRoute=</varname></term>
 329           <listitem>
 330             <para>A boolean. When true, sets up the route needed for
 331             non-IPv4LL hosts to communicate with IPv4LL-only hosts. Defaults
 332             to false.
 333             </para>
 334           </listitem>
 335         </varlistentry>
 336         <varlistentry>
 337           <term><varname>IPv6Token=</varname></term>
 338           <listitem>
 339             <para>An IPv6 address with the top 64 bits unset. When set, indicates the
 340             64-bit interface part of SLAAC IPv6 addresses for this link. Note that
 341             the token is only ever used for SLAAC, and not for DHCPv6 addresses, even
 342             in the case DHCP is requested by router advertisement. By default, the
 343             token is autogenerated.</para>
 344           </listitem>
 345         </varlistentry>
 346         <varlistentry>
 347           <term><varname>LLMNR=</varname></term>
 348           <listitem>
 349             <para>A boolean or <literal>resolve</literal>. When true,
 350             enables <ulink
 351             url="https://tools.ietf.org/html/rfc4795">Link-Local
 352             Multicast Name Resolution</ulink> on the link. When set to
 353             <literal>resolve</literal>, only resolution is enabled,
 354             but not host registration and announcement. Defaults to
 355             true. This setting is read by
 356             <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 357           </listitem>
 358         </varlistentry>
 359         <varlistentry>
 360           <term><varname>MulticastDNS=</varname></term>
 361           <listitem>
 362             <para>A boolean or <literal>resolve</literal>. When true,
 363             enables <ulink
 364             url="https://tools.ietf.org/html/rfc6762">Multicast
 365             DNS</ulink> support on the link. When set to
 366             <literal>resolve</literal>, only resolution is enabled,
 367             but not host or service registration and
 368             announcement. Defaults to false. This setting is read by
 369             <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 370           </listitem>
 371         </varlistentry>
 372         <varlistentry>
 373           <term><varname>DNSSEC=</varname></term>
 374           <listitem>
 375             <para>A boolean or
 376             <literal>allow-downgrade</literal>. When true, enables
 377             <ulink
 378             url="https://tools.ietf.org/html/rfc4033">DNSSEC</ulink>
 379             DNS validation support on the link. When set to
 380             <literal>allow-downgrade</literal>, compatibility with
 381             non-DNSSEC capable networks is increased, by automatically
 382             turning off DNSSEC in this case. This option defines a
 383             per-interface setting for
 384             <citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>'s
 385             global <varname>DNSSEC=</varname> option. Defaults to
 386             false. This setting is read by
 387             <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 388           </listitem>
 389         </varlistentry>
 390         <varlistentry>
 391           <term><varname>DNSSECNegativeTrustAnchors=</varname></term>
 392           <listitem><para>A space-separated list of DNSSEC negative
 393           trust anchor domains. If specified and DNSSEC is enabled,
 394           look-ups done via the interface's DNS server will be subject
 395           to the list of negative trust anchors, and not require
 396           authentication for the specified domains, or anything below
 397           it. Use this to disable DNSSEC authentication for specific
 398           private domains, that cannot be proven valid using the
 399           Internet DNS hierarchy. Defaults to the empty list. This
 400           setting is read by
 401           <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 402           </listitem>
 403         </varlistentry>
 404         <varlistentry>
 405           <term><varname>LLDP=</varname></term>
 406           <listitem>
 407             <para>Controls support for Ethernet LLDP packet reception. LLDP is a link-layer protocol commonly
 408             implemented on professional routers and bridges which announces which physical port a system is connected
 409             to, as well as other related data. Accepts a boolean or the special value
 410             <literal>routers-only</literal>. When true, incoming LLDP packets are accepted and a database of all LLDP
 411             neighbors maintained. If <literal>routers-only</literal> is set only LLDP data of various types of routers
 412             is collected and LLDP data about other types of devices ignored (such as stations, telephones and
 413             others). If false, LLDP reception is disabled. Defaults to <literal>routers-only</literal>. Use
 414             <citerefentry><refentrytitle>networkctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> to query the
 415             collected neighbor data. LLDP is only available on Ethernet links. See <varname>EmitLLDP=</varname> below
 416             for enabling LLDP packet emission from the local system.
 417             </para>
 418           </listitem>
 419         </varlistentry>
 420         <varlistentry>
 421           <term><varname>EmitLLDP=</varname></term>
 422           <listitem>
 423             <para>Controls support for Ethernet LLDP packet emission. Accepts a boolean parameter or the special values
 424             <literal>nearest-bridge</literal>, <literal>non-tpmr-bridge</literal> and
 425             <literal>customer-bridge</literal>.  Defaults to false, which turns off LLDP packet emission. If not false,
 426             a short LLDP packet with information about the local system is sent out in regular intervals on the
 427             link. The LLDP packet will contain information about the local host name, the local machine ID (as stored
 428             in <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>) and the
 429             local interface name, as well as the pretty hostname of the system (as set in
 430             <citerefentry><refentrytitle>machine-info</refentrytitle><manvolnum>5</manvolnum></citerefentry>). LLDP
 431             emission is only available on Ethernet links. Note that this setting passes data suitable for
 432             identification of host to the network and should thus not be enabled on untrusted networks, where such
 433             identification data should not be made available. Use this option to permit other systems to identify on
 434             which interfaces they are connected to this system. The three special values control propagation of the
 435             LLDP packets. The <literal>nearest-bridge</literal> setting permits propagation only to the nearest
 436             connected bridge, <literal>non-tpmr-bridge</literal> permits propagation across Two-Port MAC Relays, but
 437             not any other bridges, and <literal>customer-bridge</literal> permits propagation until a customer bridge
 438             is reached. For details about these concepts, see <ulink
 439             url="http://standards.ieee.org/getieee802/download/802.1AB-2009.pdf">IEEE 802.1AB-2009</ulink>. Note that
 440             configuring this setting to true is equivalent to <literal>nearest-bridge</literal>, the recommended and
 441             most restricted level of propagation. See <varname>LLDP=</varname> above for an option to enable LLDP
 442             reception.</para>
 443           </listitem>
 444         </varlistentry>
 445         <varlistentry>
 446           <term><varname>BindCarrier=</varname></term>
 447           <listitem>
 448             <para>A link name or a list of link names. When set, controls the behavior of the current
 449             link. When all links in the list are in an operational down state, the current link is brought
 450             down. When at least one link has carrier, the current interface is brought up.
 451             </para>
 452           </listitem>
 453         </varlistentry>
 454         <varlistentry>
 455           <term><varname>Address=</varname></term>
 456           <listitem>
 457             <para>A static IPv4 or IPv6 address and its prefix length,
 458             separated by a <literal>/</literal> character. Specify
 459             this key more than once to configure several addresses.
 460             The format of the address must be as described in
 461             <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 462             This is a short-hand for an [Address] section only
 463             containing an Address key (see below). This option may be
 464             specified more than once.
 465             </para>
 466
 467             <para>If the specified address is 0.0.0.0 (for IPv4) or
 468             [::] (for IPv6), a new address range of the requested size
 469             is automatically allocated from a system-wide pool of
 470             unused ranges. The allocated range is checked against all
 471             current network interfaces and all known network
 472             configuration files to avoid address range conflicts. The
 473             default system-wide pool consists of 192.168.0.0/16,
 474             172.16.0.0/12 and 10.0.0.0/8 for IPv4, and fc00::/7 for
 475             IPv6. This functionality is useful to manage a large
 476             number of dynamically created network interfaces with the
 477             same network configuration and automatic address range
 478             assignment.</para>
 479
 480           </listitem>
 481         </varlistentry>
 482         <varlistentry>
 483           <term><varname>Gateway=</varname></term>
 484           <listitem>
 485             <para>The gateway address, which must be in the format
 486             described in
 487             <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 488             This is a short-hand for a [Route] section only containing
 489             a Gateway key. This option may be specified more than
 490             once.</para>
 491           </listitem>
 492         </varlistentry>
 493         <varlistentry>
 494           <term><varname>DNS=</varname></term>
 495           <listitem>
 496             <para>A DNS server address, which must be in the format
 497             described in
 498             <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 499             This option may be specified more than once. This setting is read by
 500             <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 501           </listitem>
 502         </varlistentry>
 503         <varlistentry>
 504           <term><varname>Domains=</varname></term>
 505           <listitem>
 506             <para>A list of domains which should be resolved using the DNS servers on this link. Each item in the list
 507             should be a domain name, optionally prefixed with a tilde (<literal>~</literal>). The domains with the
 508             prefix are called "routing-only domains". The domains without the prefix are called "search domains" and
 509             are first used as search suffixes for extending single-label host names (host names containing no dots) to
 510             become fully qualified domain names (FQDNs). If a single-label host name is resolved on this interface,
 511             each of the specified search domains are appended to it in turn, converting it into a fully qualified
 512             domain name, until one of them may be successfully resolved.</para>
 513
 514             <para>Both "search" and "routing-only" domains are used for routing of DNS queries: look-ups for host names
 515             ending in those domains (hence also single label names, if any "search domains" are listed), are routed to
 516             the DNS servers configured for this interface. The domain routing logic is particularly useful on
 517             multi-homed hosts with DNS servers serving particular private DNS zones on each interface.</para>
 518
 519             <para>The "routing-only" domain <literal>~.</literal> (the tilde indicating definition of a routing domain,
 520             the dot referring to the DNS root domain which is the implied suffix of all valid DNS names) has special
 521             effect. It causes all DNS traffic which does not match another configured domain routing entry to be routed
 522             to DNS servers specified for this interface. This setting is useful to prefer a certain set of DNS servers
 523             if a link on which they are connected is available.</para>
 524
 525             <para>This setting is read by
 526             <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
 527             "Search domains" correspond to the <varname>domain</varname> and <varname>search</varname> entries in
 528             <citerefentry project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 529             Domain name routing has no equivalent in the traditional glibc API, which has no concept of domain
 530             name servers limited to a specific link.</para>
 531           </listitem>
 532         </varlistentry>
 533         <varlistentry>
 534           <term><varname>NTP=</varname></term>
 535           <listitem>
 536             <para>An NTP server address. This option may be specified more than once. This setting is read by
 537             <citerefentry><refentrytitle>systemd-timesyncd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 538           </listitem>
 539         </varlistentry>
 540         <varlistentry>
 541           <term><varname>IPForward=</varname></term>
 542           <listitem><para>Configures IP packet forwarding for the
 543           system. If enabled, incoming packets on any network
 544           interface will be forwarded to any other interfaces
 545           according to the routing table. Takes either a boolean
 546           argument, or the values <literal>ipv4</literal> or
 547           <literal>ipv6</literal>, which only enable IP packet
 548           forwarding for the specified address family.  This controls
 549           the <filename>net.ipv4.ip_forward</filename> and
 550           <filename>net.ipv6.conf.all.forwarding</filename> sysctl
 551           options of the network interface (see <ulink
 552           url="https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt">ip-sysctl.txt</ulink>
 553           for details about sysctl options). Defaults to
 554           <literal>no</literal>.</para>
 555
 556           <para>Note: this setting controls a global kernel option,
 557           and does so one way only: if a network that has this setting
 558           enabled is set up the global setting is turned on.  However,
 559           it is never turned off again, even after all networks with
 560           this setting enabled are shut down again.</para>
 561
 562           <para>To allow IP packet forwarding only between specific
 563           network interfaces use a firewall.</para>
 564           </listitem>
 565         </varlistentry>
 566         <varlistentry>
 567           <term><varname>IPMasquerade=</varname></term>
 568           <listitem><para>Configures IP masquerading for the network
 569           interface. If enabled, packets forwarded from the network
 570           interface will be appear as coming from the local host.
 571           Takes a boolean argument. Implies
 572           <varname>IPForward=ipv4</varname>. Defaults to
 573           <literal>no</literal>.</para></listitem>
 574         </varlistentry>
 575         <varlistentry>
 576           <term><varname>IPv6PrivacyExtensions=</varname></term>
 577           <listitem><para>Configures use of stateless temporary
 578           addresses that change over time (see <ulink
 579           url="https://tools.ietf.org/html/rfc4941">RFC 4941</ulink>,
 580           Privacy Extensions for Stateless Address Autoconfiguration
 581           in IPv6). Takes a boolean or the special values
 582           <literal>prefer-public</literal> and
 583           <literal>kernel</literal>. When true, enables the privacy
 584           extensions and prefers temporary addresses over public
 585           addresses. When <literal>prefer-public</literal>, enables the
 586           privacy extensions, but prefers public addresses over
 587           temporary addresses. When false, the privacy extensions
 588           remain disabled. When <literal>kernel</literal>, the kernel's
 589           default setting will be left in place.  Defaults to
 590           <literal>no</literal>.</para></listitem>
 591         </varlistentry>
 592         <varlistentry>
 593           <term><varname>IPv6AcceptRA=</varname></term>
 594           <listitem><para>Enable or disable IPv6 Router Advertisement (RA) reception support for the interface.  Takes
 595           a boolean parameter. If true, RAs are accepted; if false, RAs are ignored, independently of the local
 596           forwarding state. When not set, the kernel default is used, and RAs are accepted only when local forwarding
 597           is disabled for that interface.  When RAs are accepted, they may trigger the start of the DHCPv6 client if
 598           the relevant flags are set in the RA data, or if no routers are found on the link.</para>
 599
 600           <para>Further settings for the IPv6 RA support may be configured in the
 601           <literal>[IPv6AcceptRA]</literal> section, see below.</para>
 602
 603           <para>Also see <ulink
 604           url="https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt">ip-sysctl.txt</ulink> in the kernel
 605           documentation regarding <literal>accept_ra</literal>, but note that systemd's setting of
 606           <constant>1</constant> (i.e. true) corresponds to kernel's setting of <constant>2</constant>.</para>
 607         </listitem>
 608         </varlistentry>
 609         <varlistentry>
 610           <term><varname>IPv6DuplicateAddressDetection=</varname></term>
 611           <listitem><para>Configures the amount of IPv6 Duplicate
 612           Address Detection (DAD) probes to send. Defaults to unset.
 613         </para></listitem>
 614         </varlistentry>
 615         <varlistentry>
 616           <term><varname>IPv6HopLimit=</varname></term>
 617           <listitem><para>Configures IPv6 Hop Limit. For each router that
 618           forwards the packet, the hop limit is decremented by 1. When the
 619           hop limit field reaches zero, the packet is discarded.
 620           Defaults to unset.
 621         </para></listitem>
 622         </varlistentry>
 623         <varlistentry>
 624           <term><varname>IPv4ProxyARP=</varname></term>
 625           <listitem><para>A boolean. Configures proxy ARP for IPv4. Proxy ARP is the technique in which one host,
 626           usually a router, answers ARP requests intended for another machine. By "faking" its identity,
 627           the router accepts responsibility for routing packets to the "real" destination. (see <ulink
 628           url="https://tools.ietf.org/html/rfc1027">RFC 1027</ulink>.
 629           Defaults to unset.
 630         </para></listitem>
 631         </varlistentry>
 632         <varlistentry>
 633           <term><varname>IPv6ProxyNDP=</varname></term>
 634           <listitem><para>A boolean. Configures proxy NDP for IPv6. Proxy NDP (Neighbor Discovery
 635           Protocol) is a technique for IPv6 to allow routing of addresses to a different
 636           destination when peers expect them to be present on a certain physical link.
 637           In this case a router answers Neighbour Advertisement messages intended for
 638           another machine by offering its own MAC address as destination.
 639           Unlike proxy ARP for IPv4, it is not enabled globally, but will only send Neighbour
 640           Advertisement messages for addresses in the IPv6 neighbor proxy table,
 641           which can also be shown by <command>ip -6 neighbour show proxy</command>.
 642           systemd-networkd will control the per-interface `proxy_ndp` switch for each configured
 643           interface depending on this option.
 644           Defautls to unset.
 645         </para></listitem>
 646         </varlistentry>
 647         <varlistentry>
 648           <term><varname>IPv6ProxyNDPAddress=</varname></term>
 649           <listitem><para>An IPv6 address, for which Neighbour Advertisement messages will be
 650           proxied. This option may be specified more than once. systemd-networkd will add the
 651           <option>IPv6ProxyNDPAddress=</option> entries to the kernel's IPv6 neighbor proxy table.
 652           This option implies <option>IPv6ProxyNDP=true</option> but has no effect if
 653           <option>IPv6ProxyNDP</option> has been set to false. Defaults to unset.
 654         </para></listitem>
 655         </varlistentry>
 656         <varlistentry>
 657           <term><varname>IPv6PrefixDelegation=</varname></term>
 658           <listitem><para>Whether to enable or disable Router Advertisement sending on a link.
 659           Defaults to <literal>false</literal>. See the <literal>[IPv6PrefixDelegation]</literal>
 660           and the <literal>[IPv6Prefix]</literal> sections for configuration options.
 661           </para></listitem>
 662         </varlistentry>
 663         <varlistentry>
 664           <term><varname>Bridge=</varname></term>
 665           <listitem>
 666             <para>The name of the bridge to add the link to. See
 667             <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 668             </para>
 669           </listitem>
 670         </varlistentry>
 671         <varlistentry>
 672           <term><varname>Bond=</varname></term>
 673           <listitem>
 674             <para>The name of the bond to add the link to. See
 675             <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 676             </para>
 677           </listitem>
 678         </varlistentry>
 679         <varlistentry>
 680           <term><varname>VRF=</varname></term>
 681           <listitem>
 682             <para>The name of the VRF to add the link to. See
 683             <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 684             </para>
 685           </listitem>
 686         </varlistentry>
 687         <varlistentry>
 688           <term><varname>VLAN=</varname></term>
 689           <listitem>
 690             <para>The name of a VLAN to create on the link. See
 691             <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 692             This option may be specified more than once.</para>
 693           </listitem>
 694         </varlistentry>
 695         <varlistentry>
 696           <term><varname>MACVLAN=</varname></term>
 697           <listitem>
 698             <para>The name of a MACVLAN to create on the link. See
 699             <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 700             This option may be specified more than once.</para>
 701           </listitem>
 702         </varlistentry>
 703         <varlistentry>
 704           <term><varname>VXLAN=</varname></term>
 705           <listitem>
 706             <para>The name of a VXLAN to create on the link. See
 707             <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 708             This option may be specified more than once.</para>
 709           </listitem>
 710         </varlistentry>
 711         <varlistentry>
 712           <term><varname>Tunnel=</varname></term>
 713           <listitem>
 714             <para>The name of a Tunnel to create on the link. See
 715             <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 716             This option may be specified more than once.</para>
 717           </listitem>
 718         </varlistentry>
 719       <varlistentry>
 720         <term><varname>ActiveSlave=</varname></term>
 721         <listitem>
 722           <para>A boolean. Specifies the new active slave. The <literal>ActiveSlave=</literal>
 723           option is only valid for 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>PrimarySlave=</varname></term>
 732         <listitem>
 733           <para>A boolean. Specifies which slave is the primary device. The specified
 734           device will always be the active slave while it is available. Only when the
 735           primary is off-line will alternate devices be used.  This is useful when
 736           one slave is preferred over another, e.g. when one slave has higher throughput
 737           than another. The <literal>PrimarySlave=</literal> option is only valid for
 738           following modes:
 739           <literal>active-backup</literal>,
 740           <literal>balance-alb</literal> and
 741           <literal>balance-tlb</literal>. Defaults to false.
 742           </para>
 743         </listitem>
 744       </varlistentry>
 745       <varlistentry>
 746         <term><varname>ConfigureWithoutCarrier=</varname></term>
 747         <listitem>
 748           <para>A boolean. Allows networkd to configure a specific link even if it has no carrier.
 749           Defaults to false.
 750           </para>
 751         </listitem>
 752       </varlistentry>
 753       </variablelist>
 754
 755   </refsect1>
 756
 757   <refsect1>
 758     <title>[Address] Section Options</title>
 759
 760       <para>An <literal>[Address]</literal> section accepts the
 761       following keys. Specify several <literal>[Address]</literal>
 762       sections to configure several addresses.</para>
 763
 764       <variablelist class='network-directives'>
 765         <varlistentry>
 766           <term><varname>Address=</varname></term>
 767           <listitem>
 768             <para>As in the <literal>[Network]</literal> section. This
 769             key is mandatory.</para>
 770           </listitem>
 771         </varlistentry>
 772         <varlistentry>
 773           <term><varname>Peer=</varname></term>
 774           <listitem>
 775             <para>The peer address in a point-to-point connection.
 776             Accepts the same format as the <literal>Address</literal>
 777             key.</para>
 778           </listitem>
 779         </varlistentry>
 780         <varlistentry>
 781           <term><varname>Broadcast=</varname></term>
 782           <listitem>
 783             <para>The broadcast address, which must be in the format
 784             described in
 785             <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 786             This key only applies to IPv4 addresses. If it is not
 787             given, it is derived from the <literal>Address</literal>
 788             key.</para>
 789           </listitem>
 790         </varlistentry>
 791         <varlistentry>
 792           <term><varname>Label=</varname></term>
 793           <listitem>
 794             <para>An address label.</para>
 795           </listitem>
 796         </varlistentry>
 797         <varlistentry>
 798           <term><varname>PreferredLifetime=</varname></term>
 799           <listitem>
 800             <para>Allows the default "preferred lifetime" of the address to be overridden.
 801             Only three settings are accepted: <literal>forever</literal> or <literal>infinity</literal>
 802             which is the default and means that the address never expires, and <literal>0</literal> which means
 803             that the address is considered immediately "expired" and will not be used,
 804             unless explicitly requested. A setting of PreferredLifetime=0 is useful for
 805             addresses which are added to be used only by a specific application,
 806             which is then configured to use them explicitly.</para>
 807           </listitem>
 808         </varlistentry>
 809         <varlistentry>
 810           <term><varname>Scope=</varname></term>
 811           <listitem>
 812             <para>The scope of the address, which can be <literal>global</literal>,
 813             <literal>link</literal> or <literal>host</literal> or an unsigned integer ranges 0 to 255.
 814             Defaults to <literal>global</literal>.</para>
 815           </listitem>
 816         </varlistentry>
 817         <varlistentry>
 818           <term><varname>HomeAddress=</varname></term>
 819           <listitem>
 820             <para>Takes a boolean argument. Designates this address the "home address" as defined in
 821             <ulink url="https://tools.ietf.org/html/rfc6275">RFC 6275</ulink>.
 822             Supported only on IPv6. Defaults to false.</para>
 823           </listitem>
 824         </varlistentry>
 825         <varlistentry>
 826           <term><varname>DuplicateAddressDetection=</varname></term>
 827           <listitem>
 828             <para>Takes a boolean argument. Do not perform Duplicate Address Detection
 829             <ulink url="https://tools.ietf.org/html/rfc4862">RFC 4862</ulink> when adding this address.
 830             Supported only on IPv6. Defaults to false.</para>
 831           </listitem>
 832         </varlistentry>
 833         <varlistentry>
 834           <term><varname>ManageTemporaryAddress=</varname></term>
 835           <listitem>
 836             <para>Takes a boolean argument. If true the kernel manage temporary addresses created
 837             from this one as template on behalf of Privacy Extensions
 838             <ulink url="https://tools.ietf.org/html/rfc3041">RFC 3041</ulink>.  For this to become
 839             active, the use_tempaddr sysctl setting has to be set to a value greater than zero.
 840             The given address needs to have a prefix length of 64. This flag allows to use privacy
 841             extensions in a manually configured network, just like if stateless auto-configuration
 842             was active. Defaults to false. </para>
 843           </listitem>
 844         </varlistentry>
 845         <varlistentry>
 846           <term><varname>PrefixRoute=</varname></term>
 847           <listitem>
 848             <para>Takes a boolean argument. When adding or modifying an IPv6 address, the userspace
 849             application needs a way to suppress adding a prefix route. This is for example relevant
 850             together with IFA_F_MANAGERTEMPADDR, where userspace creates autoconf generated addresses,
 851             but depending on on-link, no route for the prefix should be added. Defaults to false.</para>
 852           </listitem>
 853         </varlistentry>
 854         <varlistentry>
 855           <term><varname>AutoJoin=</varname></term>
 856           <listitem>
 857             <para>Takes a boolean argument. Joining multicast group on ethernet level via
 858             <command>ip maddr</command> command would not work if we have an Ethernet switch that does
 859             IGMP snooping since the switch would not replicate multicast packets on  ports that did not
 860             have IGMP reports for the multicast addresses. Linux vxlan interfaces created via
 861             <command>ip link add vxlan</command> or networkd's netdev kind vxlan have the group option
 862             that enables then to do the required join. By extending ip address command with option
 863             <literal>autojoin</literal> we can get similar functionality for openvswitch (OVS) vxlan
 864             interfaces as well as other tunneling mechanisms that need to receive multicast traffic.
 865             Defaults to <literal>no</literal>.</para>
 866           </listitem>
 867         </varlistentry>
 868       </variablelist>
 869   </refsect1>
 870
 871     <refsect1>
 872     <title>[IPv6AddressLabel] Section Options</title>
 873
 874       <para>An <literal>[IPv6AddressLabel]</literal> section accepts the
 875       following keys. Specify several <literal>[IPv6AddressLabel]</literal>
 876       sections to configure several address labels. IPv6 address labels are
 877       used for address selection. See <ulink url="https://tools.ietf.org/html/rfc3484">RFC 3484</ulink>.
 878       Precedence is managed by userspace, and only the label itself is stored in the kernel</para>
 879
 880       <variablelist class='network-directives'>
 881         <varlistentry>
 882           <term><varname>Label=</varname></term>
 883           <listitem>
 884             <para> The label for the prefix (an unsigned integer) ranges 0 to 4294967294.
 885             0xffffffff is reserved. This key is mandatory.</para>
 886           </listitem>
 887         </varlistentry>
 888         <varlistentry>
 889           <term><varname>Prefix=</varname></term>
 890           <listitem>
 891             <para>IPv6 prefix is an address with a prefix length, separated by a slash <literal>/</literal> character.
 892             This key is mandatory. </para>
 893           </listitem>
 894         </varlistentry>
 895       </variablelist>
 896   </refsect1>
 897
 898  <refsect1>
 899     <title>[RoutingPolicyRule] Section Options</title>
 900
 901       <para>An <literal>[RoutingPolicyRule]</literal> section accepts the
 902       following keys. Specify several <literal>[RoutingPolicyRule]</literal>
 903       sections to configure several rules.</para>
 904
 905       <variablelist class='network-directives'>
 906         <varlistentry>
 907           <term><varname>TypeOfService=</varname></term>
 908           <listitem>
 909             <para>Specifies the type of service to match a number between 0 to 255.</para>
 910           </listitem>
 911         </varlistentry>
 912         <varlistentry>
 913           <term><varname>From=</varname></term>
 914           <listitem>
 915             <para>Specifies the source address prefix to match. Possibly followed by a slash and the prefix length.</para>
 916           </listitem>
 917         </varlistentry>
 918         <varlistentry>
 919           <term><varname>To=</varname></term>
 920           <listitem>
 921             <para>Specifies the destination address prefix to match. Possibly followed by a slash and the prefix length.</para>
 922           </listitem>
 923         </varlistentry>
 924         <varlistentry>
 925           <term><varname>FirewallMark=</varname></term>
 926           <listitem>
 927             <para>Specifies the iptables firewall mark value to match (a number between 1 and 4294967295).</para>
 928           </listitem>
 929         </varlistentry>
 930         <varlistentry>
 931           <term><varname>Table=</varname></term>
 932           <listitem>
 933             <para>Specifies the routing table identifier to lookup if the rule
 934             selector matches. The table identifier for a route (a number between 1 and 4294967295).</para>
 935           </listitem>
 936         </varlistentry>
 937         <varlistentry>
 938           <term><varname>Priority=</varname></term>
 939           <listitem>
 940             <para>Specifies the priority of this rule. <varname>Priority=</varname> is an unsigned
 941             integer. Higher number means lower priority, and rules get processed in order of increasing number.</para>
 942           </listitem>
 943         </varlistentry>
 944         <varlistentry>
 945           <term><varname>IncomingInterface=</varname></term>
 946           <listitem>
 947             <para>Specifies incoming device to match. If the interface is loopback, the rule only matches packets originating from this host.</para>
 948           </listitem>
 949         </varlistentry>
 950         <varlistentry>
 951           <term><varname>OutgoingInterface=</varname></term>
 952           <listitem>
 953             <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>
 954           </listitem>
 955         </varlistentry>
 956       </variablelist>
 957   </refsect1>
 958
 959   <refsect1>
 960     <title>[Route] Section Options</title>
 961       <para>The <literal>[Route]</literal> section accepts the
 962       following keys. Specify several <literal>[Route]</literal>
 963       sections to configure several routes.</para>
 964
 965       <variablelist class='network-directives'>
 966         <varlistentry>
 967           <term><varname>Gateway=</varname></term>
 968           <listitem>
 969             <para>As in the <literal>[Network]</literal> section.</para>
 970           </listitem>
 971         </varlistentry>
 972          <varlistentry>
 973            <term><varname>GatewayOnlink=</varname></term>
 974            <listitem>
 975              <para>The <literal>GatewayOnlink</literal> option tells the kernel that it does not have
 976              to check if the gateway is reachable directly by the current machine (i.e., the kernel does
 977              not need to check if the gateway is attached to the local network), so that we can insert the
 978              route in the kernel table without it being complained about. A boolean, defaults to <literal>no</literal>.
 979              </para>
 980            </listitem>
 981          </varlistentry>
 982         <varlistentry>
 983           <term><varname>Destination=</varname></term>
 984           <listitem>
 985             <para>The destination prefix of the route. Possibly
 986             followed by a slash and the prefix length. If omitted, a
 987             full-length host route is assumed.</para>
 988           </listitem>
 989         </varlistentry>
 990         <varlistentry>
 991           <term><varname>Source=</varname></term>
 992           <listitem>
 993             <para>The source prefix of the route. Possibly followed by
 994             a slash and the prefix length. If omitted, a full-length
 995             host route is assumed.</para>
 996           </listitem>
 997         </varlistentry>
 998         <varlistentry>
 999           <term><varname>Metric=</varname></term>
1000           <listitem>
1001             <para>The metric of the route (an unsigned integer).</para>
1002           </listitem>
1003         </varlistentry>
1004         <varlistentry>
1005           <term><varname>IPv6Preference=</varname></term>
1006           <listitem>
1007             <para>Specifies the route preference as defined in <ulink
1008             url="https://tools.ietf.org/html/rfc4191">RFC4191</ulink> for Router Discovery messages.
1009             Which can be one of <literal>low</literal> the route has a lowest priority,
1010             <literal>medium</literal> the route has a default priority or
1011             <literal>high</literal> the route has a highest priority.</para>
1012           </listitem>
1013         </varlistentry>
1014         <varlistentry>
1015           <term><varname>Scope=</varname></term>
1016           <listitem>
1017             <para>The scope of the route, which can be <literal>global</literal>,
1018             <literal>link</literal> or <literal>host</literal>. Defaults to
1019             <literal>global</literal>.</para>
1020           </listitem>
1021         </varlistentry>
1022         <varlistentry>
1023           <term><varname>PreferredSource=</varname></term>
1024           <listitem>
1025             <para>The preferred source address of the route. The address
1026             must be in the format described in
1027             <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
1028           </listitem>
1029         </varlistentry>
1030         <varlistentry>
1031           <term><varname>Table=<replaceable>num</replaceable></varname></term>
1032           <listitem>
1033           <para>The table identifier for the route (a number between 1 and 4294967295, or 0 to unset).
1034           The table can be retrieved using <command>ip route show table <replaceable>num</replaceable></command>.
1035           </para>
1036           </listitem>
1037         </varlistentry>
1038         <varlistentry>
1039           <term><varname>Protocol=</varname></term>
1040           <listitem>
1041             <para>The Protocol identifier for the route. Takes a number between 0 and 255 or the special values
1042             <literal>kernel</literal>, <literal>boot</literal> and <literal>static</literal>. Defaults to
1043             <literal>static</literal>.
1044             </para>
1045           </listitem>
1046         </varlistentry>
1047         <varlistentry>
1048           <term><varname>Type=</varname></term>
1049           <listitem>
1050             <para>The Type identifier for special route types, which can be
1051             <literal>unicast</literal> route to a destination network address which describes the path to the destination,
1052             <literal>blackhole</literal> packets are discarded silently,
1053             <literal>unreachable</literal> packets are discarded and the ICMP message host unreachable is generated,
1054             <literal>prohibit</literal> packets are discarded and the ICMP message communication administratively
1055             prohibited is generated. Defaults to <literal>unicast</literal>.
1056             </para>
1057           </listitem>
1058         </varlistentry>
1059
1060       </variablelist>
1061   </refsect1>
1062
1063   <refsect1>
1064     <title>[DHCP] Section Options</title>
1065       <para>The <literal>[DHCP]</literal> section configures the
1066       DHCPv4 and DHCP6 client, if it is enabled with the
1067       <varname>DHCP=</varname> setting described above:</para>
1068
1069       <variablelist class='network-directives'>
1070         <varlistentry>
1071           <term><varname>UseDNS=</varname></term>
1072           <listitem>
1073             <para>When true (the default), the DNS servers received
1074             from the DHCP server will be used and take precedence over
1075             any statically configured ones.</para>
1076
1077             <para>This corresponds to the <option>nameserver</option>
1078             option in <citerefentry
1079             project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
1080           </listitem>
1081         </varlistentry>
1082         <varlistentry>
1083           <term><varname>UseNTP=</varname></term>
1084           <listitem>
1085             <para>When true (the default), the NTP servers received
1086             from the DHCP server will be used by systemd-timesyncd
1087             and take precedence over any statically configured ones.</para>
1088           </listitem>
1089         </varlistentry>
1090         <varlistentry>
1091           <term><varname>UseMTU=</varname></term>
1092           <listitem>
1093             <para>When true, the interface maximum transmission unit
1094             from the DHCP server will be used on the current link.
1095             Defaults to false.</para>
1096           </listitem>
1097         </varlistentry>
1098         <varlistentry>
1099           <term><varname>Anonymize=</varname></term>
1100           <listitem>
1101             <para>Takes a boolean argument. When true, the options sent to the DHCP server will
1102             follow the <ulink url="https://tools.ietf.org/html/rfc7844">RFC 7844</ulink>
1103             (Anonymity Profiles for DHCP Clients) to minimize disclosure of identifying information.
1104             Defaults to false.</para>
1105
1106             <para>This option should only be set to true when
1107             <varname>MACAddressPolicy=</varname> is set to <literal>random</literal>
1108             (see <citerefentry
1109             project='man-pages'><refentrytitle>systemd.link</refentrytitle><manvolnum>5</manvolnum></citerefentry>).</para>
1110
1111             <para>Note that this configuration will overwrite others.
1112             In concrete, the following variables will be ignored:
1113             <varname>SendHostname=</varname>, <varname>ClientIdentifier=</varname>,
1114             <varname>UseRoutes=</varname>, <varname>SendHostname=</varname>,
1115             <varname>UseMTU=</varname>, <varname>VendorClassIdentifier=</varname>,
1116             <varname>UseTimezone=</varname>.</para>
1117           </listitem>
1118         </varlistentry>
1119         <varlistentry>
1120           <term><varname>SendHostname=</varname></term>
1121           <listitem>
1122             <para>When true (the default), the machine's hostname will
1123             be sent to the DHCP server.</para>
1124           </listitem>
1125         </varlistentry>
1126         <varlistentry>
1127           <term><varname>UseHostname=</varname></term>
1128           <listitem>
1129             <para>When true (the default), the hostname received from
1130             the DHCP server will be set as the transient hostname of the system
1131             </para>
1132           </listitem>
1133         </varlistentry>
1134         <varlistentry>
1135         <term><varname>Hostname=</varname></term>
1136         <listitem>
1137           <para>Use this value for the hostname which is sent to the
1138           DHCP server, instead of machine's hostname.</para>
1139         </listitem>
1140       </varlistentry>
1141         <varlistentry>
1142           <term><varname>UseDomains=</varname></term>
1143           <listitem>
1144             <para>Takes a boolean argument, or the special value <literal>route</literal>. When true, the domain name
1145             received from the DHCP server will be used as DNS search domain over this link, similar to the effect of
1146             the <option>Domains=</option> setting. If set to <literal>route</literal>, the domain name received from
1147             the DHCP server will be used for routing DNS queries only, but not for searching, similar to the effect of
1148             the <option>Domains=</option> setting when the argument is prefixed with <literal>~</literal>. Defaults to
1149             false.</para>
1150
1151             <para>It is recommended to enable this option only on trusted networks, as setting this affects resolution
1152             of all host names, in particular of single-label names. It is generally safer to use the supplied domain
1153             only as routing domain, rather than as search domain, in order to not have it affect local resolution of
1154             single-label names.</para>
1155
1156             <para>When set to true, this setting corresponds to the <option>domain</option> option in <citerefentry
1157             project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
1158           </listitem>
1159         </varlistentry>
1160         <varlistentry>
1161           <term><varname>UseRoutes=</varname></term>
1162           <listitem>
1163             <para>When true (the default), the static routes will be requested from the DHCP server and added to the
1164               routing table with a metric of 1024, and a scope of "global", "link" or "host", depending on the route's
1165               destination and gateway. If the destination is on the local host, e.g., 127.x.x.x, or the same as the
1166               link's own address, the scope will be set to "host". Otherwise if the gateway is null (a direct route), a
1167               "link" scope will be used. For anything else, scope defaults to "global".</para>
1168           </listitem>
1169         </varlistentry>
1170
1171         <varlistentry>
1172           <term><varname>UseTimezone=</varname></term>
1173
1174           <listitem><para>When true, the timezone received from the
1175           DHCP server will be set as timezone of the local
1176           system. Defaults to <literal>no</literal>.</para></listitem>
1177         </varlistentry>
1178
1179         <varlistentry>
1180           <term><varname>CriticalConnection=</varname></term>
1181           <listitem>
1182             <para>When true, the connection will never be torn down
1183             even if the DHCP lease expires. This is contrary to the
1184             DHCP specification, but may be the best choice if, say,
1185             the root filesystem relies on this connection. Defaults to
1186             false.</para>
1187           </listitem>
1188         </varlistentry>
1189
1190         <varlistentry>
1191           <term><varname>ClientIdentifier=</varname></term>
1192           <listitem>
1193             <para>The DHCPv4 client identifier to use. Either <literal>mac</literal> to use the MAC address of the link
1194             or <literal>duid</literal> (the default, see below) to use an RFC4361-compliant Client ID.</para>
1195           </listitem>
1196         </varlistentry>
1197
1198         <varlistentry>
1199           <term><varname>VendorClassIdentifier=</varname></term>
1200           <listitem>
1201             <para>The vendor class identifier used to identify vendor
1202             type and configuration.</para>
1203           </listitem>
1204         </varlistentry>
1205
1206         <varlistentry>
1207           <term><varname>DUIDType=</varname></term>
1208           <listitem>
1209             <para>Override the global <varname>DUIDType</varname> setting for this network. See
1210             <citerefentry><refentrytitle>networkd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1211             for a description of possible values.</para>
1212           </listitem>
1213         </varlistentry>
1214
1215         <varlistentry>
1216           <term><varname>DUIDRawData=</varname></term>
1217           <listitem>
1218             <para>Override the global <varname>DUIDRawData</varname> setting for this network. See
1219             <citerefentry><refentrytitle>networkd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1220             for a description of possible values.</para>
1221           </listitem>
1222         </varlistentry>
1223
1224         <varlistentry>
1225           <term><varname>IAID=</varname></term>
1226           <listitem>
1227             <para>The DHCP Identity Association Identifier (IAID) for the interface, a 32-bit unsigned integer.</para>
1228           </listitem>
1229         </varlistentry>
1230
1231         <varlistentry>
1232           <term><varname>RequestBroadcast=</varname></term>
1233           <listitem>
1234             <para>Request the server to use broadcast messages before
1235             the IP address has been configured. This is necessary for
1236             devices that cannot receive RAW packets, or that cannot
1237             receive packets at all before an IP address has been
1238             configured. On the other hand, this must not be enabled on
1239             networks where broadcasts are filtered out.</para>
1240           </listitem>
1241         </varlistentry>
1242
1243         <varlistentry>
1244           <term><varname>RouteMetric=</varname></term>
1245           <listitem>
1246             <para>Set the routing metric for routes specified by the
1247             DHCP server.</para>
1248           </listitem>
1249         </varlistentry>
1250
1251         <varlistentry>
1252           <term><varname>RouteTable=<replaceable>num</replaceable></varname></term>
1253           <listitem>
1254             <para>The table identifier for DHCP routes (a number between 1 and 4294967295, or 0 to unset).
1255             The table can be retrieved using <command>ip route show table <replaceable>num</replaceable></command>.
1256             </para>
1257             <para>When used in combination with <varname>VRF=</varname> the
1258             VRF's routing table is used unless this parameter is specified.
1259             </para>
1260           </listitem>
1261         </varlistentry>
1262
1263         <varlistentry>
1264           <term><varname>ListenPort=</varname></term>
1265           <listitem>
1266             <para>Allow setting custom port for the DHCP client to listen on.</para>
1267           </listitem>
1268         </varlistentry>
1269       </variablelist>
1270     </refsect1>
1271
1272   <refsect1>
1273     <title>[IPv6AcceptRA] Section Options</title>
1274       <para>The <literal>[IPv6AcceptRA]</literal> section configures the IPv6 Router Advertisement
1275       (RA) client, if it is enabled with the <varname>IPv6AcceptRA=</varname> setting described
1276       above:</para>
1277
1278       <variablelist class='network-directives'>
1279         <varlistentry>
1280           <term><varname>UseDNS=</varname></term>
1281           <listitem>
1282             <para>When true (the default), the DNS servers received in the Router Advertisement will be used and take
1283             precedence over any statically configured ones.</para>
1284
1285             <para>This corresponds to the <option>nameserver</option> option in <citerefentry
1286             project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
1287           </listitem>
1288         </varlistentry>
1289
1290         <varlistentry>
1291           <term><varname>UseDomains=</varname></term>
1292           <listitem>
1293             <para>Takes a boolean argument, or the special value <literal>route</literal>. When true, the domain name
1294             received via IPv6 Router Advertisement (RA) will be used as DNS search domain over this link, similar to
1295             the effect of the <option>Domains=</option> setting. If set to <literal>route</literal>, the domain name
1296             received via IPv6 RA will be used for routing DNS queries only, but not for searching, similar to the
1297             effect of the <option>Domains=</option> setting when the argument is prefixed with
1298             <literal>~</literal>. Defaults to false.</para>
1299
1300             <para>It is recommended to enable this option only on trusted networks, as setting this affects resolution
1301             of all host names, in particular of single-label names. It is generally safer to use the supplied domain
1302             only as routing domain, rather than as search domain, in order to not have it affect local resolution of
1303             single-label names.</para>
1304
1305             <para>When set to true, this setting corresponds to the <option>domain</option> option in <citerefentry
1306             project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
1307           </listitem>
1308         </varlistentry>
1309
1310         <varlistentry>
1311           <term><varname>RouteTable=<replaceable>num</replaceable></varname></term>
1312           <listitem>
1313             <para>The table identifier for the routes received in the Router Advertisement
1314             (a number between 1 and 4294967295, or 0 to unset).
1315             The table can be retrieved using <command>ip route show table <replaceable>num</replaceable></command>.
1316             </para>
1317           </listitem>
1318         </varlistentry>
1319       </variablelist>
1320   </refsect1>
1321
1322
1323   <refsect1>
1324     <title>[DHCPServer] Section Options</title>
1325     <para>The <literal>[DHCPServer]</literal> section contains
1326     settings for the DHCP server, if enabled via the
1327     <varname>DHCPServer=</varname> option described above:</para>
1328
1329     <variablelist class='network-directives'>
1330
1331       <varlistentry>
1332         <term><varname>PoolOffset=</varname></term>
1333         <term><varname>PoolSize=</varname></term>
1334
1335         <listitem><para>Configures the pool of addresses to hand out. The pool
1336         is a contiguous sequence of IP addresses in the subnet configured for
1337         the server address, which does not include the subnet nor the broadcast
1338         address. <varname>PoolOffset=</varname> takes the offset of the pool
1339         from the start of subnet, or zero to use the default value.
1340         <varname>PoolSize=</varname> takes the number of IP addresses in the
1341         pool or zero to use the default value. By default, the pool starts at
1342         the first address after the subnet address and takes up the rest of
1343         the subnet, excluding the broadcast address. If the pool includes
1344         the server address (the default), this is reserved and not handed
1345         out to clients.</para></listitem>
1346       </varlistentry>
1347
1348       <varlistentry>
1349         <term><varname>DefaultLeaseTimeSec=</varname></term>
1350         <term><varname>MaxLeaseTimeSec=</varname></term>
1351
1352         <listitem><para>Control the default and maximum DHCP lease
1353         time to pass to clients. These settings take time values in seconds or
1354         another common time unit, depending on the suffix. The default
1355         lease time is used for clients that did not ask for a specific
1356         lease time. If a client asks for a lease time longer than the
1357         maximum lease time, it is automatically shortened to the
1358         specified time. The default lease time defaults to 1h, the
1359         maximum lease time to 12h. Shorter lease times are beneficial
1360         if the configuration data in DHCP leases changes frequently
1361         and clients shall learn the new settings with shorter
1362         latencies. Longer lease times reduce the generated DHCP
1363         network traffic.</para></listitem>
1364       </varlistentry>
1365
1366       <varlistentry>
1367         <term><varname>EmitDNS=</varname></term>
1368         <term><varname>DNS=</varname></term>
1369
1370         <listitem><para>Configures whether the DHCP leases handed out
1371         to clients shall contain DNS server information. The
1372         <varname>EmitDNS=</varname> setting takes a boolean argument
1373         and defaults to <literal>yes</literal>. The DNS servers to
1374         pass to clients may be configured with the
1375         <varname>DNS=</varname> option, which takes a list of IPv4
1376         addresses. If the <varname>EmitDNS=</varname> option is
1377         enabled but no servers configured, the servers are
1378         automatically propagated from an "uplink" interface that has
1379         appropriate servers set. The "uplink" interface is determined
1380         by the default route of the system with the highest
1381         priority. Note that this information is acquired at the time
1382         the lease is handed out, and does not take uplink interfaces
1383         into account that acquire DNS or NTP server information at a
1384         later point. DNS server propagation does not take
1385         <filename>/etc/resolv.conf</filename> into account. Also, note
1386         that the leases are not refreshed if the uplink network
1387         configuration changes. To ensure clients regularly acquire the
1388         most current uplink DNS server information, it is thus
1389         advisable to shorten the DHCP lease time via
1390         <varname>MaxLeaseTimeSec=</varname> described
1391         above.</para></listitem>
1392       </varlistentry>
1393
1394       <varlistentry>
1395         <term><varname>EmitNTP=</varname></term>
1396         <term><varname>NTP=</varname></term>
1397
1398         <listitem><para>Similar to the <varname>EmitDNS=</varname> and
1399         <varname>DNS=</varname> settings described above, these
1400         settings configure whether and what NTP server information
1401         shall be emitted as part of the DHCP lease. The same syntax,
1402         propagation semantics and defaults apply as for
1403         <varname>EmitDNS=</varname> and
1404         <varname>DNS=</varname>.</para></listitem>
1405       </varlistentry>
1406
1407       <varlistentry>
1408         <term><varname>EmitRouter=</varname></term>
1409
1410         <listitem><para>Similar to the <varname>EmitDNS=</varname>
1411         setting described above, this setting configures whether the
1412         DHCP lease should contain the router option. The same syntax,
1413         propagation semantics and defaults apply as for
1414         <varname>EmitDNS=</varname>.</para></listitem>
1415       </varlistentry>
1416
1417       <varlistentry>
1418         <term><varname>EmitTimezone=</varname></term>
1419         <term><varname>Timezone=</varname></term>
1420
1421         <listitem><para>Configures whether the DHCP leases handed out
1422         to clients shall contain timezone information. The
1423         <varname>EmitTimezone=</varname> setting takes a boolean
1424         argument and defaults to <literal>yes</literal>. The
1425         <varname>Timezone=</varname> setting takes a timezone string
1426         (such as <literal>Europe/Berlin</literal> or
1427         <literal>UTC</literal>) to pass to clients. If no explicit
1428         timezone is set, the system timezone of the local host is
1429         propagated, as determined by the
1430         <filename>/etc/localtime</filename> symlink.</para></listitem>
1431       </varlistentry>
1432
1433     </variablelist>
1434   </refsect1>
1435
1436   <refsect1>
1437     <title>[IPv6PrefixDelegation] Section Options</title>
1438     <para>The <literal>[IPv6PrefixDelegation]</literal> section contains
1439     settings for sending IPv6 Router Advertisements and whether to act as
1440     a router, if enabled via the <varname>IPv6PrefixDelegation=</varname>
1441     option described above. IPv6 network prefixes are defined with one or
1442     more <literal>[IPv6Prefix]</literal> sections.</para>
1443
1444     <variablelist class='network-directives'>
1445
1446       <varlistentry>
1447         <term><varname>Managed=</varname></term>
1448         <term><varname>OtherInformation=</varname></term>
1449
1450         <listitem><para>Controls whether a DHCPv6 server is used to acquire IPv6
1451         addresses on the network link when <varname>Managed=</varname> boolean
1452         is set to <literal>true</literal> or if only additional network
1453         information can be obtained via DHCPv6 for the network link when
1454         <varname>OtherInformation=</varname> boolean is set to
1455         <literal>true</literal>. Both settings default to
1456         <literal>false</literal>, which means that a DHCPv6 server is not being
1457         used.</para></listitem>
1458       </varlistentry>
1459
1460       <varlistentry>
1461         <term><varname>RouterLifetimeSec=</varname></term>
1462
1463         <listitem><para>Configures the IPv6 router lifetime in seconds. If set,
1464         this host also announces itself in Router Advertisements as an IPv6
1465         router for the network link. Defaults to unset, which means the host is
1466         not acting as a router.</para>
1467         </listitem>
1468       </varlistentry>
1469
1470       <varlistentry>
1471         <term><varname>RouterPreference=</varname></term>
1472
1473         <listitem><para>Configures IPv6 router preference if
1474         <varname>RouterLifetimeSec=</varname> is non-zero. Valid values are
1475         <literal>high</literal>, <literal>medium</literal> and
1476         <literal>low</literal>, with <literal>normal</literal> and
1477         <literal>default</literal> added as synonyms for
1478         <literal>medium</literal> just to make configuration easier. See
1479         <ulink url="https://tools.ietf.org/html/rfc4191">RFC 4191</ulink>
1480         for details. Defaults to <literal>medium</literal>.</para></listitem>
1481       </varlistentry>
1482
1483       <varlistentry>
1484         <term><varname>EmitDNS=</varname></term>
1485         <term><varname>DNS=</varname></term>
1486
1487         <listitem><para><varname>DNS=</varname> specifies a list of recursive
1488         DNS server IPv6 addresses that distributed via Router Advertisement
1489         messages when <varname>EmitDNS=</varname> is true. If <varname>DNS=
1490         </varname> is empty, DNS servers are read from the
1491         <literal>[Network]</literal> section. If the
1492         <literal>[Network]</literal> section does not contain any DNS servers
1493         either, DNS servers from the uplink with the highest priority default
1494         route are used. When <varname>EmitDNS=</varname> is false, no DNS server
1495         information is sent in Router Advertisement messages.
1496         <varname>EmitDNS=</varname> defaults to true.
1497         </para></listitem>
1498       </varlistentry>
1499
1500       <varlistentry>
1501         <term><varname>EmitDomains=</varname></term>
1502         <term><varname>Domains=</varname></term>
1503
1504         <listitem><para>A list of DNS search domains distributed via Router
1505         Advertisement messages when <varname>EmitDomains=</varname> is true. If
1506         <varname>Domains=</varname> is empty, DNS search domains are read from the
1507         <literal>[Network]</literal> section. If the <literal>[Network]</literal>
1508         section does not contain any DNS search domains either, DNS search
1509         domains from the uplink with the highest priority default route are
1510         used. When <varname>EmitDomains=</varname> is false, no DNS search domain
1511         information is sent in Router Advertisement messages.
1512         <varname>EmitDomains=</varname> defaults to true.
1513         </para></listitem>
1514       </varlistentry>
1515
1516       <varlistentry>
1517         <term><varname>DNSLifetimeSec=</varname></term>
1518
1519         <listitem><para>Lifetime in seconds for the DNS server addresses listed
1520         in <varname>DNS=</varname> and search domains listed in
1521         <varname>Domains=</varname>.</para></listitem>
1522       </varlistentry>
1523
1524     </variablelist>
1525     </refsect1>
1526
1527       <refsect1>
1528     <title>[IPv6Prefix] Section Options</title>
1529     <para>One or more <literal>[IPv6Prefix]</literal> sections contain the IPv6
1530     prefixes that are announced via Router Advertisements. See
1531     <ulink url="https://tools.ietf.org/html/rfc4861">RFC 4861</ulink>
1532     for further details.</para>
1533
1534     <variablelist class='network-directives'>
1535
1536       <varlistentry>
1537         <term><varname>AddressAutoconfiguration=</varname></term>
1538         <term><varname>OnLink=</varname></term>
1539
1540         <listitem><para>Boolean values to specify whether IPv6 addresses can be
1541         autoconfigured with this prefix and whether the prefix can be used for
1542         onlink determination. Both settings default to <literal>true</literal>
1543         in order to ease configuration.
1544         </para></listitem>
1545       </varlistentry>
1546
1547       <varlistentry>
1548         <term><varname>Prefix=</varname></term>
1549
1550         <listitem><para>The IPv6 prefix that is to be distributed to hosts.
1551         Similarly to configuring static IPv6 addresses, the setting is
1552         configured as an IPv6 prefix and its prefix length, separated by a
1553         <literal>/</literal> character. Use multiple
1554         <literal>[IPv6Prefix]</literal> sections to configure multiple IPv6
1555         prefixes since prefix lifetimes, address autoconfiguration and onlink
1556         status may differ from one prefix to another.</para></listitem>
1557       </varlistentry>
1558
1559       <varlistentry>
1560         <term><varname>PreferredLifetimeSec=</varname></term>
1561         <term><varname>ValidLifetimeSec=</varname></term>
1562
1563         <listitem><para>Preferred and valid lifetimes for the prefix measured in
1564         seconds. <varname>PreferredLifetimeSec=</varname> defaults to 604800
1565         seconds (one week) and <varname>ValidLifetimeSec=</varname> defaults
1566         to 2592000 seconds (30 days).</para></listitem>
1567       </varlistentry>
1568
1569     </variablelist>
1570     </refsect1>
1571
1572     <refsect1>
1573     <title>[Bridge] Section Options</title>
1574       <para>The <literal>[Bridge]</literal> section accepts the
1575       following keys.</para>
1576       <variablelist class='network-directives'>
1577         <varlistentry>
1578           <term><varname>UnicastFlood=</varname></term>
1579           <listitem>
1580             <para>A boolean. Controls whether the bridge should flood
1581             traffic for which an FDB entry is missing and the destination
1582             is unknown through this port. Defaults to on.
1583             </para>
1584           </listitem>
1585         </varlistentry>
1586         <varlistentry>
1587           <term><varname>HairPin=</varname></term>
1588           <listitem>
1589             <para>A boolean. Configures whether traffic may be sent back
1590             out of the port on which it was received. By default, this
1591             flag is false, and the bridge will not forward traffic back
1592             out of the receiving port.</para>
1593           </listitem>
1594         </varlistentry>
1595         <varlistentry>
1596           <term><varname>UseBPDU=</varname></term>
1597           <listitem>
1598             <para>A boolean. Configures whether STP Bridge Protocol Data Units will be
1599             processed by the bridge port. Defaults to yes.</para>
1600           </listitem>
1601         </varlistentry>
1602         <varlistentry>
1603           <term><varname>FastLeave=</varname></term>
1604           <listitem>
1605             <para>A boolean. This flag allows the bridge to immediately stop multicast
1606             traffic on a port that receives an IGMP Leave message. It is only used with
1607             IGMP snooping if enabled on the bridge. Defaults to off.</para>
1608           </listitem>
1609         </varlistentry>
1610         <varlistentry>
1611           <term><varname>AllowPortToBeRoot=</varname></term>
1612           <listitem>
1613             <para>A boolean. Configures whether a given port is allowed to
1614             become a root port. Only used when STP is enabled on the bridge.
1615             Defaults to on.</para>
1616           </listitem>
1617         </varlistentry>
1618         <varlistentry>
1619           <term><varname>Cost=</varname></term>
1620           <listitem>
1621             <para>Sets the "cost" of sending packets of this interface.
1622             Each port in a bridge may have a different speed and the cost
1623             is used to decide which link to use. Faster interfaces
1624             should have lower costs. It is an integer value between 1 and
1625             65535.</para>
1626           </listitem>
1627         </varlistentry>
1628         <varlistentry>
1629           <term><varname>Priority=</varname></term>
1630           <listitem>
1631             <para>Sets the "priority" of sending packets on this interface.
1632             Each port in a bridge may have a different priority which is used
1633             to decide which link to use. Lower value means higher priority.
1634             It is an integer value between 0 to 63. Networkd does not set any
1635             default, meaning the kernel default value of 32 is used.</para>
1636           </listitem>
1637         </varlistentry>
1638       </variablelist>
1639   </refsect1>
1640   <refsect1>
1641     <title>[BridgeFDB] Section Options</title>
1642       <para>The <literal>[BridgeFDB]</literal> section manages the
1643       forwarding database table of a port and accepts the following
1644       keys. Specify several <literal>[BridgeFDB]</literal> sections to
1645       configure several static MAC table entries.</para>
1646
1647       <variablelist class='network-directives'>
1648         <varlistentry>
1649           <term><varname>MACAddress=</varname></term>
1650           <listitem>
1651             <para>As in the <literal>[Network]</literal> section. This
1652             key is mandatory.</para>
1653           </listitem>
1654         </varlistentry>
1655         <varlistentry>
1656           <term><varname>VLANId=</varname></term>
1657           <listitem>
1658             <para>The VLAN ID for the new static MAC table entry. If
1659             omitted, no VLAN ID info is appended to the new static MAC
1660             table entry.</para>
1661           </listitem>
1662         </varlistentry>
1663       </variablelist>
1664   </refsect1>
1665   <refsect1>
1666     <title>[BridgeVLAN] Section Options</title>
1667       <para>The <literal>[BridgeVLAN]</literal> section manages the VLAN ID configuration of a bridge port and accepts
1668       the following keys. Specify several <literal>[BridgeVLAN]</literal> sections to configure several VLAN entries.
1669       The <varname>VLANFiltering=</varname> option has to be enabled, see <literal>[Bridge]</literal> section in
1670       <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
1671
1672       <variablelist class='network-directives'>
1673         <varlistentry>
1674           <term><varname>VLAN=</varname></term>
1675           <listitem>
1676             <para>The VLAN ID allowed on the port. This can be either a single ID or a range M-N. VLAN IDs are valid
1677             from 1 to 4094.</para>
1678           </listitem>
1679         </varlistentry>
1680         <varlistentry>
1681           <term><varname>EgressUntagged=</varname></term>
1682           <listitem>
1683             <para>The VLAN ID specified here will be used to untag frames on egress. Configuring
1684             <varname>EgressUntagged=</varname> implicates the use of <varname>VLAN=</varname> above and will enable the
1685             VLAN ID for ingress as well. This can be either a single ID or a range M-N.</para>
1686           </listitem>
1687         </varlistentry>
1688         <varlistentry>
1689           <term><varname>PVID=</varname></term>
1690           <listitem>
1691             <para>The Port VLAN ID specified here is assigned to all untagged frames at ingress.
1692             <varname>PVID=</varname> can be used only once. Configuring <varname>PVID=</varname> implicates the use of
1693             <varname>VLAN=</varname> above and will enable the VLAN ID for ingress as well.</para>
1694           </listitem>
1695         </varlistentry>
1696       </variablelist>
1697   </refsect1>
1698
1699   <refsect1>
1700     <title>Examples</title>
1701     <example>
1702       <title>Static network configuration</title>
1703
1704       <programlisting># /etc/systemd/network/50-static.network
1705 [Match]
1706 Name=enp2s0
1707
1708 [Network]
1709 Address=192.168.0.15/24
1710 Gateway=192.168.0.1</programlisting>
1711
1712       <para>This brings interface <literal>enp2s0</literal> up with a static address. The
1713       specified gateway will be used for a default route.</para>
1714     </example>
1715
1716     <example>
1717       <title>DHCP on ethernet links</title>
1718
1719       <programlisting># /etc/systemd/network/80-dhcp.network
1720 [Match]
1721 Name=en*
1722
1723 [Network]
1724 DHCP=yes</programlisting>
1725
1726       <para>This will enable DHCPv4 and DHCPv6 on all interfaces with names starting with
1727       <literal>en</literal> (i.e. ethernet interfaces).</para>
1728     </example>
1729
1730     <example>
1731       <title>A bridge with two enslaved links</title>
1732
1733       <programlisting># /etc/systemd/network/25-bridge-static.network
1734 [Match]
1735 Name=bridge0
1736
1737 [Network]
1738 Address=192.168.0.15/24
1739 Gateway=192.168.0.1
1740 DNS=192.168.0.1</programlisting>
1741
1742       <programlisting># /etc/systemd/network/25-bridge-slave-interface-1.network
1743 [Match]
1744 Name=enp2s0
1745
1746 [Network]
1747 Bridge=bridge0</programlisting>
1748
1749       <programlisting># /etc/systemd/network/25-bridge-slave-interface-2.network
1750 [Match]
1751 Name=wlp3s0
1752
1753 [Network]
1754 Bridge=bridge0</programlisting>
1755
1756       <para>This creates a bridge and attaches devices <literal>enp2s0</literal> and
1757       <literal>wlp3s0</literal> to it. The bridge will have the specified static address
1758       and network assigned, and a default route via the specified gateway will be
1759       added. The specified DNS server will be added to the global list of DNS resolvers.
1760       </para>
1761     </example>
1762
1763     <example>
1764       <title></title>
1765
1766       <programlisting>
1767 # /etc/systemd/network/20-bridge-slave-interface-vlan.network
1768 [Match]
1769 Name=enp2s0
1770
1771 [Network]
1772 Bridge=bridge0
1773
1774 [BridgeVLAN]
1775 VLAN=1-32
1776 PVID=42
1777 EgressUntagged=42
1778
1779 [BridgeVLAN]
1780 VLAN=100-200
1781
1782 [BridgeVLAN]
1783 EgressUntagged=300-400</programlisting>
1784
1785     <para>This overrides the configuration specified in the previous example for the
1786     interface <literal>enp2s0</literal>, and enables VLAN on that bridge port. VLAN IDs
1787     1-32, 42, 100-400 will be allowed. Packets tagged with VLAN IDs 42, 300-400 will be
1788     untagged when they leave on this interface. Untagged packets which arrive on this
1789     interface will be assigned VLAN ID 42.</para>
1790     </example>
1791
1792     <example>
1793       <title>Various tunnels</title>
1794
1795       <programlisting>/etc/systemd/network/25-tunnels.network
1796 [Match]
1797 Name=ens1
1798
1799 [Network]
1800 Tunnel=ipip-tun
1801 Tunnel=sit-tun
1802 Tunnel=gre-tun
1803 Tunnel=vti-tun
1804       </programlisting>
1805
1806       <programlisting>/etc/systemd/network/25-tunnel-ipip.netdev
1807 [NetDev]
1808 Name=ipip-tun
1809 Kind=ipip
1810       </programlisting>
1811
1812       <programlisting>/etc/systemd/network/25-tunnel-sit.netdev
1813 [NetDev]
1814 Name=sit-tun
1815 Kind=sit
1816       </programlisting>
1817
1818       <programlisting>/etc/systemd/network/25-tunnel-gre.netdev
1819 [NetDev]
1820 Name=gre-tun
1821 Kind=gre
1822       </programlisting>
1823
1824       <programlisting>/etc/systemd/network/25-tunnel-vti.netdev
1825 [NetDev]
1826 Name=vti-tun
1827 Kind=vti
1828       </programlisting>
1829
1830       <para>This will bring interface <literal>ens1</literal> up and create an IPIP tunnel,
1831       a SIT tunnel, a GRE tunnel, and a VTI tunnel using it.</para>
1832     </example>
1833
1834     <example>
1835       <title>A bond device</title>
1836
1837       <programlisting># /etc/systemd/network/30-bond1.network
1838 [Match]
1839 Name=bond1
1840
1841 [Network]
1842 DHCP=ipv6
1843 </programlisting>
1844
1845       <programlisting># /etc/systemd/network/30-bond1.netdev
1846 [NetDev]
1847 Name=bond1
1848 Kind=bond
1849 </programlisting>
1850
1851       <programlisting># /etc/systemd/network/30-bond1-dev1.network
1852 [Match]
1853 MACAddress=52:54:00:e9:64:41
1854
1855 [Network]
1856 Bond=bond1
1857 </programlisting>
1858
1859       <programlisting># /etc/systemd/network/30-bond1-dev2.network
1860 [Match]
1861 MACAddress=52:54:00:e9:64:42
1862
1863 [Network]
1864 Bond=bond1
1865 </programlisting>
1866
1867     <para>This will create a bond device <literal>bond1</literal> and enslave the two
1868     devices with MAC addresses 52:54:00:e9:64:41 and 52:54:00:e9:64:42 to it. IPv6 DHCP
1869     will be used to acquire an address.</para>
1870     </example>
1871
1872     <example>
1873       <title>Virtual Routing and Forwarding (VRF)</title>
1874       <para>Add the <literal>bond1</literal> interface to the VRF master interface
1875       <literal>vrf1</literal>. This will redirect routes generated on this interface to be
1876       within the routing table defined during VRF creation. For kernels before 4.8 traffic
1877       won't be redirected towards the VRFs routing table unless specific ip-rules are added.
1878       </para>
1879       <programlisting># /etc/systemd/network/25-vrf.network
1880 [Match]
1881 Name=bond1
1882
1883 [Network]
1884 VRF=vrf1
1885 </programlisting>
1886     </example>
1887
1888     <example>
1889       <title>MacVTap</title>
1890       <para>This brings up a network interface <literal>macvtap-test</literal>
1891       and attaches it to <literal>enp0s25</literal>.</para>
1892       <programlisting># /usr/lib/systemd/network/25-macvtap.network
1893 [Match]
1894 Name=enp0s25
1895
1896 [Network]
1897 MACVTAP=macvtap-test
1898 </programlisting>
1899     </example>
1900   </refsect1>
1901
1902   <refsect1>
1903     <title>See Also</title>
1904     <para>
1905       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1906       <citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
1907       <citerefentry><refentrytitle>systemd.link</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1908       <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1909       <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
1910     </para>
1911   </refsect1>
1912
1913 </refentry>