man/systemd.network.xml

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