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>SendHostname=</varname></term>
1002           <listitem>
1003             <para>When true (the default), the machine's hostname will
1004             be sent to the DHCP server.</para>
1005           </listitem>
1006         </varlistentry>
1007         <varlistentry>
1008           <term><varname>UseHostname=</varname></term>
1009           <listitem>
1010             <para>When true (the default), the hostname received from
1011             the DHCP server will be set as the transient hostname of the system
1012             </para>
1013           </listitem>
1014         </varlistentry>
1015         <varlistentry>
1016         <term><varname>Hostname=</varname></term>
1017         <listitem>
1018           <para>Use this value for the hostname which is sent to the
1019           DHCP server, instead of machine's hostname.</para>
1020         </listitem>
1021       </varlistentry>
1022         <varlistentry>
1023           <term><varname>UseDomains=</varname></term>
1024           <listitem>
1025             <para>Takes a boolean argument, or the special value <literal>route</literal>. When true, the domain name
1026             received from the DHCP server will be used as DNS search domain over this link, similar to the effect of
1027             the <option>Domains=</option> setting. If set to <literal>route</literal>, the domain name received from
1028             the DHCP server will be used for routing DNS queries only, but not for searching, similar to the effect of
1029             the <option>Domains=</option> setting when the argument is prefixed with <literal>~</literal>. Defaults to
1030             false.</para>
1031
1032             <para>It is recommended to enable this option only on trusted networks, as setting this affects resolution
1033             of all host names, in particular of single-label names. It is generally safer to use the supplied domain
1034             only as routing domain, rather than as search domain, in order to not have it affect local resolution of
1035             single-label names.</para>
1036
1037             <para>When set to true, this setting corresponds to the <option>domain</option> option in <citerefentry
1038             project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
1039           </listitem>
1040         </varlistentry>
1041         <varlistentry>
1042           <term><varname>UseRoutes=</varname></term>
1043           <listitem>
1044             <para>When true (the default), the static routes will be requested from the DHCP server and added to the
1045               routing table with a metric of 1024, and a scope of "global", "link" or "host", depending on the route's
1046               destination and gateway. If the destination is on the local host, e.g., 127.x.x.x, or the same as the
1047               link's own address, the scope will be set to "host". Otherwise if the gateway is null (a direct route), a
1048               "link" scope will be used. For anything else, scope defaults to "global".</para>
1049           </listitem>
1050         </varlistentry>
1051
1052         <varlistentry>
1053           <term><varname>UseTimezone=</varname></term>
1054
1055           <listitem><para>When true, the timezone received from the
1056           DHCP server will be set as timezone of the local
1057           system. Defaults to <literal>no</literal>.</para></listitem>
1058         </varlistentry>
1059
1060         <varlistentry>
1061           <term><varname>CriticalConnection=</varname></term>
1062           <listitem>
1063             <para>When true, the connection will never be torn down
1064             even if the DHCP lease expires. This is contrary to the
1065             DHCP specification, but may be the best choice if, say,
1066             the root filesystem relies on this connection. Defaults to
1067             false.</para>
1068           </listitem>
1069         </varlistentry>
1070
1071         <varlistentry>
1072           <term><varname>ClientIdentifier=</varname></term>
1073           <listitem>
1074             <para>The DHCPv4 client identifier to use. Either <literal>mac</literal> to use the MAC address of the link
1075             or <literal>duid</literal> (the default, see below) to use an RFC4361-compliant Client ID.</para>
1076           </listitem>
1077         </varlistentry>
1078
1079         <varlistentry>
1080           <term><varname>VendorClassIdentifier=</varname></term>
1081           <listitem>
1082             <para>The vendor class identifier used to identify vendor
1083             type and configuration.</para>
1084           </listitem>
1085         </varlistentry>
1086
1087         <varlistentry>
1088           <term><varname>DUIDType=</varname></term>
1089           <listitem>
1090             <para>Override the global <varname>DUIDType</varname> setting for this network. See
1091             <citerefentry><refentrytitle>networkd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1092             for a description of possible values.</para>
1093           </listitem>
1094         </varlistentry>
1095
1096         <varlistentry>
1097           <term><varname>DUIDRawData=</varname></term>
1098           <listitem>
1099             <para>Override the global <varname>DUIDRawData</varname> setting for this network. See
1100             <citerefentry><refentrytitle>networkd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1101             for a description of possible values.</para>
1102           </listitem>
1103         </varlistentry>
1104
1105         <varlistentry>
1106           <term><varname>IAID=</varname></term>
1107           <listitem>
1108             <para>The DHCP Identity Association Identifier (IAID) for the interface, a 32-bit unsigned integer.</para>
1109           </listitem>
1110         </varlistentry>
1111
1112         <varlistentry>
1113           <term><varname>RequestBroadcast=</varname></term>
1114           <listitem>
1115             <para>Request the server to use broadcast messages before
1116             the IP address has been configured. This is necessary for
1117             devices that cannot receive RAW packets, or that cannot
1118             receive packets at all before an IP address has been
1119             configured. On the other hand, this must not be enabled on
1120             networks where broadcasts are filtered out.</para>
1121           </listitem>
1122         </varlistentry>
1123
1124         <varlistentry>
1125           <term><varname>RouteMetric=</varname></term>
1126           <listitem>
1127             <para>Set the routing metric for routes specified by the
1128             DHCP server.</para>
1129           </listitem>
1130         </varlistentry>
1131
1132         <varlistentry>
1133           <term><varname>RouteTable=<replaceable>num</replaceable></varname></term>
1134           <listitem>
1135             <para>The table identifier for DHCP routes (a number between 1 and 4294967295, or 0 to unset).
1136             The table can be retrieved using <command>ip route show table <replaceable>num</replaceable></command>.
1137             </para>
1138           </listitem>
1139         </varlistentry>
1140
1141         <varlistentry>
1142           <term><varname>ListenPort=</varname></term>
1143           <listitem>
1144             <para>Allow setting custom port for the DHCP client to listen on.</para>
1145           </listitem>
1146         </varlistentry>
1147       </variablelist>
1148     </refsect1>
1149
1150   <refsect1>
1151     <title>[IPv6AcceptRA] Section Options</title>
1152       <para>The <literal>[IPv6AcceptRA]</literal> section configures the IPv6 Router Advertisement
1153       (RA) client, if it is enabled with the <varname>IPv6AcceptRA=</varname> setting described
1154       above:</para>
1155
1156       <variablelist class='network-directives'>
1157         <varlistentry>
1158           <term><varname>UseDNS=</varname></term>
1159           <listitem>
1160             <para>When true (the default), the DNS servers received in the Router Advertisement will be used and take
1161             precedence over any statically configured ones.</para>
1162
1163             <para>This corresponds to the <option>nameserver</option> option in <citerefentry
1164             project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
1165           </listitem>
1166         </varlistentry>
1167
1168         <varlistentry>
1169           <term><varname>UseDomains=</varname></term>
1170           <listitem>
1171             <para>Takes a boolean argument, or the special value <literal>route</literal>. When true, the domain name
1172             received via IPv6 Router Advertisement (RA) will be used as DNS search domain over this link, similar to
1173             the effect of the <option>Domains=</option> setting. If set to <literal>route</literal>, the domain name
1174             received via IPv6 RA will be used for routing DNS queries only, but not for searching, similar to the
1175             effect of the <option>Domains=</option> setting when the argument is prefixed with
1176             <literal>~</literal>. Defaults to false.</para>
1177
1178             <para>It is recommended to enable this option only on trusted networks, as setting this affects resolution
1179             of all host names, in particular of single-label names. It is generally safer to use the supplied domain
1180             only as routing domain, rather than as search domain, in order to not have it affect local resolution of
1181             single-label names.</para>
1182
1183             <para>When set to true, this setting corresponds to the <option>domain</option> option in <citerefentry
1184             project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
1185           </listitem>
1186         </varlistentry>
1187
1188         <varlistentry>
1189           <term><varname>RouteTable=<replaceable>num</replaceable></varname></term>
1190           <listitem>
1191             <para>The table identifier for the routes received in the Router Advertisement
1192             (a number between 1 and 4294967295, or 0 to unset).
1193             The table can be retrieved using <command>ip route show table <replaceable>num</replaceable></command>.
1194             </para>
1195           </listitem>
1196         </varlistentry>
1197       </variablelist>
1198   </refsect1>
1199
1200
1201   <refsect1>
1202     <title>[DHCPServer] Section Options</title>
1203     <para>The <literal>[DHCPServer]</literal> section contains
1204     settings for the DHCP server, if enabled via the
1205     <varname>DHCPServer=</varname> option described above:</para>
1206
1207     <variablelist class='network-directives'>
1208
1209       <varlistentry>
1210         <term><varname>PoolOffset=</varname></term>
1211         <term><varname>PoolSize=</varname></term>
1212
1213         <listitem><para>Configures the pool of addresses to hand out. The pool
1214         is a contiguous sequence of IP addresses in the subnet configured for
1215         the server address, which does not include the subnet nor the broadcast
1216         address. <varname>PoolOffset=</varname> takes the offset of the pool
1217         from the start of subnet, or zero to use the default value.
1218         <varname>PoolSize=</varname> takes the number of IP addresses in the
1219         pool or zero to use the default value. By default, the pool starts at
1220         the first address after the subnet address and takes up the rest of
1221         the subnet, excluding the broadcast address. If the pool includes
1222         the server address (the default), this is reserved and not handed
1223         out to clients.</para></listitem>
1224       </varlistentry>
1225
1226       <varlistentry>
1227         <term><varname>DefaultLeaseTimeSec=</varname></term>
1228         <term><varname>MaxLeaseTimeSec=</varname></term>
1229
1230         <listitem><para>Control the default and maximum DHCP lease
1231         time to pass to clients. These settings take time values in seconds or
1232         another common time unit, depending on the suffix. The default
1233         lease time is used for clients that did not ask for a specific
1234         lease time. If a client asks for a lease time longer than the
1235         maximum lease time, it is automatically shortened to the
1236         specified time. The default lease time defaults to 1h, the
1237         maximum lease time to 12h. Shorter lease times are beneficial
1238         if the configuration data in DHCP leases changes frequently
1239         and clients shall learn the new settings with shorter
1240         latencies. Longer lease times reduce the generated DHCP
1241         network traffic.</para></listitem>
1242       </varlistentry>
1243
1244       <varlistentry>
1245         <term><varname>EmitDNS=</varname></term>
1246         <term><varname>DNS=</varname></term>
1247
1248         <listitem><para>Configures whether the DHCP leases handed out
1249         to clients shall contain DNS server information. The
1250         <varname>EmitDNS=</varname> setting takes a boolean argument
1251         and defaults to <literal>yes</literal>. The DNS servers to
1252         pass to clients may be configured with the
1253         <varname>DNS=</varname> option, which takes a list of IPv4
1254         addresses. If the <varname>EmitDNS=</varname> option is
1255         enabled but no servers configured, the servers are
1256         automatically propagated from an "uplink" interface that has
1257         appropriate servers set. The "uplink" interface is determined
1258         by the default route of the system with the highest
1259         priority. Note that this information is acquired at the time
1260         the lease is handed out, and does not take uplink interfaces
1261         into account that acquire DNS or NTP server information at a
1262         later point. DNS server propagation does not take
1263         <filename>/etc/resolv.conf</filename> into account. Also, note
1264         that the leases are not refreshed if the uplink network
1265         configuration changes. To ensure clients regularly acquire the
1266         most current uplink DNS server information, it is thus
1267         advisable to shorten the DHCP lease time via
1268         <varname>MaxLeaseTimeSec=</varname> described
1269         above.</para></listitem>
1270       </varlistentry>
1271
1272       <varlistentry>
1273         <term><varname>EmitNTP=</varname></term>
1274         <term><varname>NTP=</varname></term>
1275
1276         <listitem><para>Similar to the <varname>EmitDNS=</varname> and
1277         <varname>DNS=</varname> settings described above, these
1278         settings configure whether and what NTP server information
1279         shall be emitted as part of the DHCP lease. The same syntax,
1280         propagation semantics and defaults apply as for
1281         <varname>EmitDNS=</varname> and
1282         <varname>DNS=</varname>.</para></listitem>
1283       </varlistentry>
1284
1285       <varlistentry>
1286         <term><varname>EmitRouter=</varname></term>
1287
1288         <listitem><para>Similar to the <varname>EmitDNS=</varname>
1289         setting described above, this setting configures whether the
1290         DHCP lease should contain the router option. The same syntax,
1291         propagation semantics and defaults apply as for
1292         <varname>EmitDNS=</varname>.</para></listitem>
1293       </varlistentry>
1294
1295       <varlistentry>
1296         <term><varname>EmitTimezone=</varname></term>
1297         <term><varname>Timezone=</varname></term>
1298
1299         <listitem><para>Configures whether the DHCP leases handed out
1300         to clients shall contain timezone information. The
1301         <varname>EmitTimezone=</varname> setting takes a boolean
1302         argument and defaults to <literal>yes</literal>. The
1303         <varname>Timezone=</varname> setting takes a timezone string
1304         (such as <literal>Europe/Berlin</literal> or
1305         <literal>UTC</literal>) to pass to clients. If no explicit
1306         timezone is set, the system timezone of the local host is
1307         propagated, as determined by the
1308         <filename>/etc/localtime</filename> symlink.</para></listitem>
1309       </varlistentry>
1310
1311     </variablelist>
1312   </refsect1>
1313
1314   <refsect1>
1315     <title>[Bridge] Section Options</title>
1316       <para>The <literal>[Bridge]</literal> section accepts the
1317       following keys.</para>
1318       <variablelist class='network-directives'>
1319         <varlistentry>
1320           <term><varname>UnicastFlood=</varname></term>
1321           <listitem>
1322             <para>A boolean. Controls whether the bridge should flood
1323             traffic for which an FDB entry is missing and the destination
1324             is unknown through this port. Defaults to on.
1325             </para>
1326           </listitem>
1327         </varlistentry>
1328         <varlistentry>
1329           <term><varname>HairPin=</varname></term>
1330           <listitem>
1331             <para>A boolean. Configures whether traffic may be sent back
1332             out of the port on which it was received. By default, this
1333             flag is false, and the bridge will not forward traffic back
1334             out of the receiving port.</para>
1335           </listitem>
1336         </varlistentry>
1337         <varlistentry>
1338           <term><varname>UseBPDU=</varname></term>
1339           <listitem>
1340             <para>A boolean. Configures whether STP Bridge Protocol Data Units will be
1341             processed by the bridge port. Defaults to yes.</para>
1342           </listitem>
1343         </varlistentry>
1344         <varlistentry>
1345           <term><varname>FastLeave=</varname></term>
1346           <listitem>
1347             <para>A boolean. This flag allows the bridge to immediately stop multicast
1348             traffic on a port that receives an IGMP Leave message. It is only used with
1349             IGMP snooping if enabled on the bridge. Defaults to off.</para>
1350           </listitem>
1351         </varlistentry>
1352         <varlistentry>
1353           <term><varname>AllowPortToBeRoot=</varname></term>
1354           <listitem>
1355             <para>A boolean. Configures whether a given port is allowed to
1356             become a root port. Only used when STP is enabled on the bridge.
1357             Defaults to on.</para>
1358           </listitem>
1359         </varlistentry>
1360         <varlistentry>
1361           <term><varname>Cost=</varname></term>
1362           <listitem>
1363             <para>Sets the "cost" of sending packets of this interface.
1364             Each port in a bridge may have a different speed and the cost
1365             is used to decide which link to use. Faster interfaces
1366             should have lower costs. It is an integer value between 1 and
1367             65535.</para>
1368           </listitem>
1369         </varlistentry>
1370         <varlistentry>
1371           <term><varname>Priority=</varname></term>
1372           <listitem>
1373             <para>Sets the "priority" of sending packets on this interface.
1374             Each port in a bridge may have a different priority which is used
1375             to decide which link to use. Lower value means higher priority.
1376             It is an integer value between 0 to 63. Networkd does not set any
1377             default, meaning the kernel default value of 32 is used.</para>
1378           </listitem>
1379         </varlistentry>
1380       </variablelist>
1381   </refsect1>
1382   <refsect1>
1383     <title>[BridgeFDB] Section Options</title>
1384       <para>The <literal>[BridgeFDB]</literal> section manages the
1385       forwarding database table of a port and accepts the following
1386       keys. Specify several <literal>[BridgeFDB]</literal> sections to
1387       configure several static MAC table entries.</para>
1388
1389       <variablelist class='network-directives'>
1390         <varlistentry>
1391           <term><varname>MACAddress=</varname></term>
1392           <listitem>
1393             <para>As in the <literal>[Network]</literal> section. This
1394             key is mandatory.</para>
1395           </listitem>
1396         </varlistentry>
1397         <varlistentry>
1398           <term><varname>VLANId=</varname></term>
1399           <listitem>
1400             <para>The VLAN ID for the new static MAC table entry. If
1401             omitted, no VLAN ID info is appended to the new static MAC
1402             table entry.</para>
1403           </listitem>
1404         </varlistentry>
1405       </variablelist>
1406   </refsect1>
1407   <refsect1>
1408     <title>[BridgeVLAN] Section Options</title>
1409       <para>The <literal>[BridgeVLAN]</literal> section manages the VLAN ID configuration of a bridge port and accepts
1410       the following keys. Specify several <literal>[BridgeVLAN]</literal> sections to configure several VLAN entries.
1411       The <varname>VLANFiltering=</varname> option has to be enabled, see <literal>[Bridge]</literal> section in
1412       <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
1413
1414       <variablelist class='network-directives'>
1415         <varlistentry>
1416           <term><varname>VLAN=</varname></term>
1417           <listitem>
1418             <para>The VLAN ID allowed on the port. This can be either a single ID or a range M-N. VLAN IDs are valid
1419             from 1 to 4094.</para>
1420           </listitem>
1421         </varlistentry>
1422         <varlistentry>
1423           <term><varname>EgressUntagged=</varname></term>
1424           <listitem>
1425             <para>The VLAN ID specified here will be used to untag frames on egress. Configuring
1426             <varname>EgressUntagged=</varname> implicates the use of <varname>VLAN=</varname> above and will enable the
1427             VLAN ID for ingress as well. This can be either a single ID or a range M-N.</para>
1428           </listitem>
1429         </varlistentry>
1430         <varlistentry>
1431           <term><varname>PVID=</varname></term>
1432           <listitem>
1433             <para>The Port VLAN ID specified here is assigned to all untagged frames at ingress.
1434             <varname>PVID=</varname> can be used only once. Configuring <varname>PVID=</varname> implicates the use of
1435             <varname>VLAN=</varname> above and will enable the VLAN ID for ingress as well.</para>
1436           </listitem>
1437         </varlistentry>
1438       </variablelist>
1439   </refsect1>
1440
1441   <refsect1>
1442     <title>Examples</title>
1443     <example>
1444       <title>Static network configuration</title>
1445
1446       <programlisting># /etc/systemd/network/50-static.network
1447 [Match]
1448 Name=enp2s0
1449
1450 [Network]
1451 Address=192.168.0.15/24
1452 Gateway=192.168.0.1</programlisting>
1453
1454       <para>This brings interface <literal>enp2s0</literal> up with a static address. The
1455       specified gateway will be used for a default route.</para>
1456     </example>
1457
1458     <example>
1459       <title>DHCP on ethernet links</title>
1460
1461       <programlisting># /etc/systemd/network/80-dhcp.network
1462 [Match]
1463 Name=en*
1464
1465 [Network]
1466 DHCP=yes</programlisting>
1467
1468       <para>This will enable DHCPv4 and DHCPv6 on all interfaces with names starting with
1469       <literal>en</literal> (i.e. ethernet interfaces).</para>
1470     </example>
1471
1472     <example>
1473       <title>A bridge with two enslaved links</title>
1474
1475       <programlisting># /etc/systemd/network/25-bridge-static.network
1476 [Match]
1477 Name=bridge0
1478
1479 [Network]
1480 Address=192.168.0.15/24
1481 Gateway=192.168.0.1
1482 DNS=192.168.0.1</programlisting>
1483
1484       <programlisting># /etc/systemd/network/25-bridge-slave-interface-1.network
1485 [Match]
1486 Name=enp2s0
1487
1488 [Network]
1489 Bridge=bridge0</programlisting>
1490
1491       <programlisting># /etc/systemd/network/25-bridge-slave-interface-2.network
1492 [Match]
1493 Name=wlp3s0
1494
1495 [Network]
1496 Bridge=bridge0</programlisting>
1497
1498       <para>This creates a bridge and attaches devices <literal>enp2s0</literal> and
1499       <literal>wlp3s0</literal> to it. The bridge will have the specified static address
1500       and network assigned, and a default route via the specified gateway will be
1501       added. The specified DNS server will be added to the global list of DNS resolvers.
1502       </para>
1503     </example>
1504
1505     <example>
1506       <title></title>
1507
1508       <programlisting>
1509 # /etc/systemd/network/20-bridge-slave-interface-vlan.network
1510 [Match]
1511 Name=enp2s0
1512
1513 [Network]
1514 Bridge=bridge0
1515
1516 [BridgeVLAN]
1517 VLAN=1-32
1518 PVID=42
1519 EgressUntagged=42
1520
1521 [BridgeVLAN]
1522 VLAN=100-200
1523
1524 [BridgeVLAN]
1525 EgressUntagged=300-400</programlisting>
1526
1527     <para>This overrides the configuration specified in the previous example for the
1528     interface <literal>enp2s0</literal>, and enables VLAN on that bridge port. VLAN IDs
1529     1-32, 42, 100-400 will be allowed. Packets tagged with VLAN IDs 42, 300-400 will be
1530     untagged when they leave on this interface. Untagged packets which arrive on this
1531     interface will be assigned VLAN ID 42.</para>
1532     </example>
1533
1534     <example>
1535       <title>Various tunnels</title>
1536
1537       <programlisting>/etc/systemd/network/25-tunnels.network
1538 [Match]
1539 Name=ens1
1540
1541 [Network]
1542 Tunnel=ipip-tun
1543 Tunnel=sit-tun
1544 Tunnel=gre-tun
1545 Tunnel=vti-tun
1546       </programlisting>
1547
1548       <programlisting>/etc/systemd/network/25-tunnel-ipip.netdev
1549 [NetDev]
1550 Name=ipip-tun
1551 Kind=ipip
1552       </programlisting>
1553
1554       <programlisting>/etc/systemd/network/25-tunnel-sit.netdev
1555 [NetDev]
1556 Name=sit-tun
1557 Kind=sit
1558       </programlisting>
1559
1560       <programlisting>/etc/systemd/network/25-tunnel-gre.netdev
1561 [NetDev]
1562 Name=gre-tun
1563 Kind=gre
1564       </programlisting>
1565
1566       <programlisting>/etc/systemd/network/25-tunnel-vti.netdev
1567 [NetDev]
1568 Name=vti-tun
1569 Kind=vti
1570       </programlisting>
1571
1572       <para>This will bring interface <literal>ens1</literal> up and create an IPIP tunnel,
1573       a SIT tunnel, a GRE tunnel, and a VTI tunnel using it.</para>
1574     </example>
1575
1576     <example>
1577       <title>A bond device</title>
1578
1579       <programlisting># /etc/systemd/network/30-bond1.network
1580 [Match]
1581 Name=bond1
1582
1583 [Network]
1584 DHCP=ipv6
1585 </programlisting>
1586
1587       <programlisting># /etc/systemd/network/30-bond1.netdev
1588 [NetDev]
1589 Name=bond1
1590 Kind=bond
1591 </programlisting>
1592
1593       <programlisting># /etc/systemd/network/30-bond1-dev1.network
1594 [Match]
1595 MACAddress=52:54:00:e9:64:41
1596
1597 [Network]
1598 Bond=bond1
1599 </programlisting>
1600
1601       <programlisting># /etc/systemd/network/30-bond1-dev2.network
1602 [Match]
1603 MACAddress=52:54:00:e9:64:42
1604
1605 [Network]
1606 Bond=bond1
1607 </programlisting>
1608
1609     <para>This will create a bond device <literal>bond1</literal> and enslave the two
1610     devices with MAC addresses 52:54:00:e9:64:41 and 52:54:00:e9:64:42 to it. IPv6 DHCP
1611     will be used to acquire an address.</para>
1612     </example>
1613
1614     <example>
1615       <title>Virtual Routing and Forwarding (VRF)</title>
1616       <para>Add the <literal>bond1</literal> interface to the VRF master interface
1617       <literal>vrf1</literal>. This will redirect routes generated on this interface to be
1618       within the routing table defined during VRF creation. Traffic won't be redirected
1619       towards the VRFs routing table unless specific ip-rules are added.</para>
1620       <programlisting># /etc/systemd/network/25-vrf.network
1621 [Match]
1622 Name=bond1
1623
1624 [Network]
1625 VRF=vrf1
1626 </programlisting>
1627     </example>
1628
1629     <example>
1630       <title>MacVTap</title>
1631       <para>This brings up a network interface <literal>macvtap-test</literal>
1632       and attaches it to <literal>enp0s25</literal>.</para>
1633       <programlisting># /usr/lib/systemd/network/25-macvtap.network
1634 [Match]
1635 Name=enp0s25
1636
1637 [Network]
1638 MACVTAP=macvtap-test
1639 </programlisting>
1640     </example>
1641   </refsect1>
1642
1643   <refsect1>
1644     <title>See Also</title>
1645     <para>
1646       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1647       <citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
1648       <citerefentry><refentrytitle>systemd.link</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1649       <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1650       <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
1651     </para>
1652   </refsect1>
1653
1654 </refentry>