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