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><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>IPv6ProxyNDPAddress=</varname></term>
 616           <listitem><para>An IPv6 address, for which Neighbour Advertisement
 617           messages will be proxied.
 618           Proxy NDP (Neighbor Discovery Protocol) is a technique for IPv6 to
 619           allow routing of addresses to a different destination when peers expect them
 620           to be present on a certain physical link.
 621           In this case a router answers Neighbour Advertisement messages intended for
 622           another machine by offering its own MAC address as destination.
 623           Unlike proxy ARP for IPv4, is not enabled globally, but will only send Neighbour
 624           Advertisement messages for addresses in the IPv6 neighbor proxy table,
 625           which can also be shown by <command>ip -6 neighbour show proxy</command>
 626           This option may be specified more than once. systemd-networkd will control the
 627           per-interface `proxy_ndp` switch for each configured interface, depending on whether
 628           there are <option>IPv6ProxyNDPAddress=</option> entries configured and add these to
 629           the kernels IPv6 neighbor proxy table.
 630           Defaults to unset.
 631         </para></listitem>
 632         </varlistentry>
 633         <varlistentry>
 634           <term><varname>Bridge=</varname></term>
 635           <listitem>
 636             <para>The name of the bridge to add the link to. See
 637             <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 638             </para>
 639           </listitem>
 640         </varlistentry>
 641         <varlistentry>
 642           <term><varname>Bond=</varname></term>
 643           <listitem>
 644             <para>The name of the bond to add the link to. See
 645             <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 646             </para>
 647           </listitem>
 648         </varlistentry>
 649         <varlistentry>
 650           <term><varname>VRF=</varname></term>
 651           <listitem>
 652             <para>The name of the VRF to add the link to. See
 653             <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 654             </para>
 655           </listitem>
 656         </varlistentry>
 657         <varlistentry>
 658           <term><varname>VLAN=</varname></term>
 659           <listitem>
 660             <para>The name of a VLAN to create on the link. See
 661             <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 662             This option may be specified more than once.</para>
 663           </listitem>
 664         </varlistentry>
 665         <varlistentry>
 666           <term><varname>MACVLAN=</varname></term>
 667           <listitem>
 668             <para>The name of a MACVLAN to create on the link. See
 669             <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 670             This option may be specified more than once.</para>
 671           </listitem>
 672         </varlistentry>
 673         <varlistentry>
 674           <term><varname>VXLAN=</varname></term>
 675           <listitem>
 676             <para>The name of a VXLAN to create on the link. See
 677             <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 678             This option may be specified more than once.</para>
 679           </listitem>
 680         </varlistentry>
 681         <varlistentry>
 682           <term><varname>Tunnel=</varname></term>
 683           <listitem>
 684             <para>The name of a Tunnel to create on the link. See
 685             <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 686             This option may be specified more than once.</para>
 687           </listitem>
 688         </varlistentry>
 689       </variablelist>
 690
 691   </refsect1>
 692
 693   <refsect1>
 694     <title>[Address] Section Options</title>
 695
 696       <para>An <literal>[Address]</literal> section accepts the
 697       following keys. Specify several <literal>[Address]</literal>
 698       sections to configure several addresses.</para>
 699
 700       <variablelist class='network-directives'>
 701         <varlistentry>
 702           <term><varname>Address=</varname></term>
 703           <listitem>
 704             <para>As in the <literal>[Network]</literal> section. This
 705             key is mandatory.</para>
 706           </listitem>
 707         </varlistentry>
 708         <varlistentry>
 709           <term><varname>Peer=</varname></term>
 710           <listitem>
 711             <para>The peer address in a point-to-point connection.
 712             Accepts the same format as the <literal>Address</literal>
 713             key.</para>
 714           </listitem>
 715         </varlistentry>
 716         <varlistentry>
 717           <term><varname>Broadcast=</varname></term>
 718           <listitem>
 719             <para>The broadcast address, which must be in the format
 720             described in
 721             <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 722             This key only applies to IPv4 addresses. If it is not
 723             given, it is derived from the <literal>Address</literal>
 724             key.</para>
 725           </listitem>
 726         </varlistentry>
 727         <varlistentry>
 728           <term><varname>Label=</varname></term>
 729           <listitem>
 730             <para>An address label.</para>
 731           </listitem>
 732         </varlistentry>
 733         <varlistentry>
 734           <term><varname>PreferredLifetime=</varname></term>
 735           <listitem>
 736             <para>Allows the default "preferred lifetime" of the address to be overridden.
 737             Only three settings are accepted: <literal>forever</literal> or <literal>infinity</literal>
 738             which is the default and means that the address never expires, and <literal>0</literal> which means
 739             that the address is considered immediately "expired" and will not be used,
 740             unless explicitly requested. A setting of PreferredLifetime=0 is useful for
 741             addresses which are added to be used only by a specific application,
 742             which is then configured to use them explicitly.</para>
 743           </listitem>
 744         </varlistentry>
 745         <varlistentry>
 746           <term><varname>HomeAddress=</varname></term>
 747           <listitem>
 748             <para>Takes a boolean argument. Designates this address the "home address" as defined in
 749             <ulink url="https://tools.ietf.org/html/rfc6275">RFC 6275</ulink>.
 750             Supported only on IPv6. Defaults to false.</para>
 751           </listitem>
 752         </varlistentry>
 753         <varlistentry>
 754           <term><varname>DuplicateAddressDetection=</varname></term>
 755           <listitem>
 756             <para>Takes a boolean argument. Do not perform Duplicate Address Detection
 757             <ulink url="https://tools.ietf.org/html/rfc4862">RFC 4862</ulink> when adding this address.
 758             Supported only on IPv6. Defaults to false.</para>
 759           </listitem>
 760         </varlistentry>
 761         <varlistentry>
 762           <term><varname>ManageTemporaryAddress=</varname></term>
 763           <listitem>
 764             <para>Takes a boolean argument. If true the kernel manage temporary addresses created
 765             from this one as template on behalf of Privacy Extensions
 766             <ulink url="https://tools.ietf.org/html/rfc3041">RFC 3041</ulink>.  For this to become
 767             active, the use_tempaddr sysctl setting has to be set to a value greater than zero.
 768             The given address needs to have a prefix length of 64. This flag allows to use privacy
 769             extensions in a manually configured network, just like if stateless auto-configuration
 770             was active. Defaults to false. </para>
 771           </listitem>
 772         </varlistentry>
 773         <varlistentry>
 774           <term><varname>PrefixRoute=</varname></term>
 775           <listitem>
 776             <para>Takes a boolean argument. When adding or modifying an IPv6 address, the userspace
 777             application needs a way to suppress adding a prefix route. This is for example relevant
 778             together with IFA_F_MANAGERTEMPADDR, where userspace creates autoconf generated addresses,
 779             but depending on on-link, no route for the prefix should be added. Defaults to false.</para>
 780           </listitem>
 781         </varlistentry>
 782         <varlistentry>
 783           <term><varname>AutoJoin=</varname></term>
 784           <listitem>
 785             <para>Takes a boolean argument. Joining multicast group on ethernet level via
 786             <command>ip maddr</command> command would not work if we have an Ethernet switch that does
 787             IGMP snooping since the switch would not replicate multicast packets on  ports that did not
 788             have IGMP reports for the multicast addresses. Linux vxlan interfaces created via
 789             <command>ip link add vxlan</command> or networkd's netdev kind vxlan have the group option
 790             that enables then to do the required join. By extending ip address command with option
 791             <literal>autojoin</literal> we can get similar functionality for openvswitch (OVS) vxlan
 792             interfaces as well as other tunneling mechanisms that need to receive multicast traffic.
 793             Defaults to <literal>no</literal>.</para>
 794           </listitem>
 795         </varlistentry>
 796       </variablelist>
 797   </refsect1>
 798
 799     <refsect1>
 800     <title>[IPv6AddressLabel] Section Options</title>
 801
 802       <para>An <literal>[IPv6AddressLabel]</literal> section accepts the
 803       following keys. Specify several <literal>[IPv6AddressLabel]</literal>
 804       sections to configure several addresse labels. IPv6 address labels are
 805       used for address selection. See <ulink url="https://tools.ietf.org/html/rfc3484">RFC 3484</ulink>.
 806       Precedence is managed by userspace, and only the label itself is stored in the kernel</para>
 807
 808       <variablelist class='network-directives'>
 809         <varlistentry>
 810           <term><varname>Label=</varname></term>
 811           <listitem>
 812             <para> The label for the prefix (an unsigned integer) ranges 0 to 4294967294.
 813             0xffffffff is reserved. This key is mandatory.</para>
 814           </listitem>
 815         </varlistentry>
 816         <varlistentry>
 817           <term><varname>Prefix=</varname></term>
 818           <listitem>
 819             <para>IPv6 prefix is an address with a prefix length, separated by a slash <literal>/</literal> character.
 820             This key is mandatory. </para>
 821           </listitem>
 822         </varlistentry>
 823       </variablelist>
 824   </refsect1>
 825
 826   <refsect1>
 827     <title>[Route] Section Options</title>
 828       <para>The <literal>[Route]</literal> section accepts the
 829       following keys. Specify several <literal>[Route]</literal>
 830       sections to configure several routes.</para>
 831
 832       <variablelist class='network-directives'>
 833         <varlistentry>
 834           <term><varname>Gateway=</varname></term>
 835           <listitem>
 836             <para>As in the <literal>[Network]</literal> section.</para>
 837           </listitem>
 838         </varlistentry>
 839          <varlistentry>
 840            <term><varname>GatewayOnlink=</varname></term>
 841            <listitem>
 842              <para>The <literal>GatewayOnlink</literal> option tells the kernel that it does not have
 843              to check if the gateway is reachable directly by the current machine (i.e., the kernel does
 844              not need to check if the gateway is attached to the local network), so that we can insert the
 845              route in the kernel table without it being complained about. A boolean, defaults to <literal>no</literal>.
 846              </para>
 847            </listitem>
 848          </varlistentry>
 849         <varlistentry>
 850           <term><varname>Destination=</varname></term>
 851           <listitem>
 852             <para>The destination prefix of the route. Possibly
 853             followed by a slash and the prefix length. If omitted, a
 854             full-length host route is assumed.</para>
 855           </listitem>
 856         </varlistentry>
 857         <varlistentry>
 858           <term><varname>Source=</varname></term>
 859           <listitem>
 860             <para>The source prefix of the route. Possibly followed by
 861             a slash and the prefix length. If omitted, a full-length
 862             host route is assumed.</para>
 863           </listitem>
 864         </varlistentry>
 865         <varlistentry>
 866           <term><varname>Metric=</varname></term>
 867           <listitem>
 868             <para>The metric of the route (an unsigned integer).</para>
 869           </listitem>
 870         </varlistentry>
 871         <varlistentry>
 872           <term><varname>IPv6Preference=</varname></term>
 873           <listitem>
 874             <para>Specifies the route preference as defined in <ulink
 875             url="https://tools.ietf.org/html/rfc4191">RFC4191</ulink> for Router Discovery messages.
 876             Which can be one of <literal>low</literal> the route has a lowest priority,
 877             <literal>medium</literal> the route has a default priority or
 878             <literal>high</literal> the route has a highest priority.</para>
 879           </listitem>
 880         </varlistentry>
 881         <varlistentry>
 882           <term><varname>Scope=</varname></term>
 883           <listitem>
 884             <para>The scope of the route, which can be <literal>global</literal>,
 885             <literal>link</literal> or <literal>host</literal>. Defaults to
 886             <literal>global</literal>.</para>
 887           </listitem>
 888         </varlistentry>
 889         <varlistentry>
 890           <term><varname>PreferredSource=</varname></term>
 891           <listitem>
 892             <para>The preferred source address of the route. The address
 893             must be in the format described in
 894             <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
 895           </listitem>
 896         </varlistentry>
 897         <varlistentry>
 898           <term><varname>Table=<replaceable>num</replaceable></varname></term>
 899           <listitem>
 900           <para>The table identifier for the route (a number between 1 and 4294967295, or 0 to unset).
 901           The table can be retrieved using <command>ip route show table <replaceable>num</replaceable></command>.
 902           </para>
 903           </listitem>
 904         </varlistentry>
 905       </variablelist>
 906   </refsect1>
 907
 908   <refsect1>
 909     <title>[DHCP] Section Options</title>
 910       <para>The <literal>[DHCP]</literal> section configures the
 911       DHCPv4 and DHCP6 client, if it is enabled with the
 912       <varname>DHCP=</varname> setting described above:</para>
 913
 914       <variablelist class='network-directives'>
 915         <varlistentry>
 916           <term><varname>UseDNS=</varname></term>
 917           <listitem>
 918             <para>When true (the default), the DNS servers received
 919             from the DHCP server will be used and take precedence over
 920             any statically configured ones.</para>
 921
 922             <para>This corresponds to the <option>nameserver</option>
 923             option in <citerefentry
 924             project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
 925           </listitem>
 926         </varlistentry>
 927         <varlistentry>
 928           <term><varname>UseNTP=</varname></term>
 929           <listitem>
 930             <para>When true (the default), the NTP servers received
 931             from the DHCP server will be used by systemd-timesyncd
 932             and take precedence over any statically configured ones.</para>
 933           </listitem>
 934         </varlistentry>
 935         <varlistentry>
 936           <term><varname>UseMTU=</varname></term>
 937           <listitem>
 938             <para>When true, the interface maximum transmission unit
 939             from the DHCP server will be used on the current link.
 940             Defaults to false.</para>
 941           </listitem>
 942         </varlistentry>
 943         <varlistentry>
 944           <term><varname>SendHostname=</varname></term>
 945           <listitem>
 946             <para>When true (the default), the machine's hostname will
 947             be sent to the DHCP server.</para>
 948           </listitem>
 949         </varlistentry>
 950         <varlistentry>
 951           <term><varname>UseHostname=</varname></term>
 952           <listitem>
 953             <para>When true (the default), the hostname received from
 954             the DHCP server will be set as the transient hostname of the system
 955             </para>
 956           </listitem>
 957         </varlistentry>
 958         <varlistentry>
 959         <term><varname>Hostname=</varname></term>
 960         <listitem>
 961           <para>Use this value for the hostname which is sent to the
 962           DHCP server, instead of machine's hostname.</para>
 963         </listitem>
 964       </varlistentry>
 965         <varlistentry>
 966           <term><varname>UseDomains=</varname></term>
 967           <listitem>
 968             <para>Takes a boolean argument, or the special value <literal>route</literal>. When true, the domain name
 969             received from the DHCP server will be used as DNS search domain over this link, similar to the effect of
 970             the <option>Domains=</option> setting. If set to <literal>route</literal>, the domain name received from
 971             the DHCP server will be used for routing DNS queries only, but not for searching, similar to the effect of
 972             the <option>Domains=</option> setting when the argument is prefixed with <literal>~</literal>. Defaults to
 973             false.</para>
 974
 975             <para>It is recommended to enable this option only on trusted networks, as setting this affects resolution
 976             of all host names, in particular of single-label names. It is generally safer to use the supplied domain
 977             only as routing domain, rather than as search domain, in order to not have it affect local resolution of
 978             single-label names.</para>
 979
 980             <para>When set to true, this setting corresponds to the <option>domain</option> 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>UseRoutes=</varname></term>
 986           <listitem>
 987             <para>When true (the default), the static routes will be
 988             requested from the DHCP server and added to the routing
 989             table with a metric of 1024.</para>
 990           </listitem>
 991         </varlistentry>
 992
 993         <varlistentry>
 994           <term><varname>UseTimezone=</varname></term>
 995
 996           <listitem><para>When true, the timezone received from the
 997           DHCP server will be set as timezone of the local
 998           system. Defaults to <literal>no</literal>.</para></listitem>
 999         </varlistentry>
1000
1001         <varlistentry>
1002           <term><varname>CriticalConnection=</varname></term>
1003           <listitem>
1004             <para>When true, the connection will never be torn down
1005             even if the DHCP lease expires. This is contrary to the
1006             DHCP specification, but may be the best choice if, say,
1007             the root filesystem relies on this connection. Defaults to
1008             false.</para>
1009           </listitem>
1010         </varlistentry>
1011
1012         <varlistentry>
1013           <term><varname>ClientIdentifier=</varname></term>
1014           <listitem>
1015             <para>The DHCPv4 client identifier to use. Either <literal>mac</literal> to use the MAC address of the link
1016             or <literal>duid</literal> (the default, see below) to use an RFC4361-compliant Client ID.</para>
1017           </listitem>
1018         </varlistentry>
1019
1020         <varlistentry>
1021           <term><varname>VendorClassIdentifier=</varname></term>
1022           <listitem>
1023             <para>The vendor class identifier used to identify vendor
1024             type and configuration.</para>
1025           </listitem>
1026         </varlistentry>
1027
1028         <varlistentry>
1029           <term><varname>DUIDType=</varname></term>
1030           <listitem>
1031             <para>Override the global <varname>DUIDType</varname> setting for this network. See
1032             <citerefentry><refentrytitle>networkd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1033             for a description of possible values.</para>
1034           </listitem>
1035         </varlistentry>
1036
1037         <varlistentry>
1038           <term><varname>DUIDRawData=</varname></term>
1039           <listitem>
1040             <para>Override the global <varname>DUIDRawData</varname> setting for this network. See
1041             <citerefentry><refentrytitle>networkd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1042             for a description of possible values.</para>
1043           </listitem>
1044         </varlistentry>
1045
1046         <varlistentry>
1047           <term><varname>IAID=</varname></term>
1048           <listitem>
1049             <para>The DHCP Identity Association Identifier (IAID) for the interface, a 32-bit unsigned integer.</para>
1050           </listitem>
1051         </varlistentry>
1052
1053         <varlistentry>
1054           <term><varname>RequestBroadcast=</varname></term>
1055           <listitem>
1056             <para>Request the server to use broadcast messages before
1057             the IP address has been configured. This is necessary for
1058             devices that cannot receive RAW packets, or that cannot
1059             receive packets at all before an IP address has been
1060             configured. On the other hand, this must not be enabled on
1061             networks where broadcasts are filtered out.</para>
1062           </listitem>
1063         </varlistentry>
1064
1065         <varlistentry>
1066           <term><varname>RouteMetric=</varname></term>
1067           <listitem>
1068             <para>Set the routing metric for routes specified by the
1069             DHCP server.</para>
1070           </listitem>
1071         </varlistentry>
1072
1073         <varlistentry>
1074           <term><varname>RouteTable=<replaceable>num</replaceable></varname></term>
1075           <listitem>
1076             <para>The table identifier for DHCP routes (a number between 1 and 4294967295, or 0 to unset).
1077             The table can be retrieved using <command>ip route show table <replaceable>num</replaceable></command>.
1078             </para>
1079           </listitem>
1080         </varlistentry>
1081
1082         <varlistentry>
1083           <term><varname>ListenPort=</varname></term>
1084           <listitem>
1085             <para>Allow setting custom port for the DHCP client to listen on.</para>
1086           </listitem>
1087         </varlistentry>
1088       </variablelist>
1089     </refsect1>
1090
1091   <refsect1>
1092     <title>[IPv6AcceptRA] Section Options</title>
1093       <para>The <literal>[IPv6AcceptRA]</literal> section configures the IPv6 Router Advertisement
1094       (RA) client, if it is enabled with the <varname>IPv6AcceptRA=</varname> setting described
1095       above:</para>
1096
1097       <variablelist class='network-directives'>
1098         <varlistentry>
1099           <term><varname>UseDNS=</varname></term>
1100           <listitem>
1101             <para>When true (the default), the DNS servers received in the Router Advertisement will be used and take
1102             precedence over any statically configured ones.</para>
1103
1104             <para>This corresponds to the <option>nameserver</option> option in <citerefentry
1105             project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
1106           </listitem>
1107         </varlistentry>
1108
1109         <varlistentry>
1110           <term><varname>UseDomains=</varname></term>
1111           <listitem>
1112             <para>Takes a boolean argument, or the special value <literal>route</literal>. When true, the domain name
1113             received via IPv6 Router Advertisement (RA) will be used as DNS search domain over this link, similar to
1114             the effect of the <option>Domains=</option> setting. If set to <literal>route</literal>, the domain name
1115             received via IPv6 RA will be used for routing DNS queries only, but not for searching, similar to the
1116             effect of the <option>Domains=</option> setting when the argument is prefixed with
1117             <literal>~</literal>. Defaults to false.</para>
1118
1119             <para>It is recommended to enable this option only on trusted networks, as setting this affects resolution
1120             of all host names, in particular of single-label names. It is generally safer to use the supplied domain
1121             only as routing domain, rather than as search domain, in order to not have it affect local resolution of
1122             single-label names.</para>
1123
1124             <para>When set to true, this setting corresponds to the <option>domain</option> option in <citerefentry
1125             project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
1126           </listitem>
1127         </varlistentry>
1128
1129         <varlistentry>
1130           <term><varname>RouteTable=<replaceable>num</replaceable></varname></term>
1131           <listitem>
1132             <para>The table identifier for the routes received in the Router Advertisement
1133             (a number between 1 and 4294967295, or 0 to unset).
1134             The table can be retrieved using <command>ip route show table <replaceable>num</replaceable></command>.
1135             </para>
1136           </listitem>
1137         </varlistentry>
1138       </variablelist>
1139   </refsect1>
1140
1141
1142   <refsect1>
1143     <title>[DHCPServer] Section Options</title>
1144     <para>The <literal>[DHCPServer]</literal> section contains
1145     settings for the DHCP server, if enabled via the
1146     <varname>DHCPServer=</varname> option described above:</para>
1147
1148     <variablelist class='network-directives'>
1149
1150       <varlistentry>
1151         <term><varname>PoolOffset=</varname></term>
1152         <term><varname>PoolSize=</varname></term>
1153
1154         <listitem><para>Configures the pool of addresses to hand out. The pool
1155         is a contiguous sequence of IP addresses in the subnet configured for
1156         the server address, which does not include the subnet nor the broadcast
1157         address. <varname>PoolOffset=</varname> takes the offset of the pool
1158         from the start of subnet, or zero to use the default value.
1159         <varname>PoolSize=</varname> takes the number of IP addresses in the
1160         pool or zero to use the default value. By default, the pool starts at
1161         the first address after the subnet address and takes up the rest of
1162         the subnet, excluding the broadcast address. If the pool includes
1163         the server address (the default), this is reserved and not handed
1164         out to clients.</para></listitem>
1165       </varlistentry>
1166
1167       <varlistentry>
1168         <term><varname>DefaultLeaseTimeSec=</varname></term>
1169         <term><varname>MaxLeaseTimeSec=</varname></term>
1170
1171         <listitem><para>Control the default and maximum DHCP lease
1172         time to pass to clients. These settings take time values in seconds or
1173         another common time unit, depending on the suffix. The default
1174         lease time is used for clients that did not ask for a specific
1175         lease time. If a client asks for a lease time longer than the
1176         maximum lease time, it is automatically shortened to the
1177         specified time. The default lease time defaults to 1h, the
1178         maximum lease time to 12h. Shorter lease times are beneficial
1179         if the configuration data in DHCP leases changes frequently
1180         and clients shall learn the new settings with shorter
1181         latencies. Longer lease times reduce the generated DHCP
1182         network traffic.</para></listitem>
1183       </varlistentry>
1184
1185       <varlistentry>
1186         <term><varname>EmitDNS=</varname></term>
1187         <term><varname>DNS=</varname></term>
1188
1189         <listitem><para>Configures whether the DHCP leases handed out
1190         to clients shall contain DNS server information. The
1191         <varname>EmitDNS=</varname> setting takes a boolean argument
1192         and defaults to <literal>yes</literal>. The DNS servers to
1193         pass to clients may be configured with the
1194         <varname>DNS=</varname> option, which takes a list of IPv4
1195         addresses. If the <varname>EmitDNS=</varname> option is
1196         enabled but no servers configured, the servers are
1197         automatically propagated from an "uplink" interface that has
1198         appropriate servers set. The "uplink" interface is determined
1199         by the default route of the system with the highest
1200         priority. Note that this information is acquired at the time
1201         the lease is handed out, and does not take uplink interfaces
1202         into account that acquire DNS or NTP server information at a
1203         later point. DNS server propagation does not take
1204         <filename>/etc/resolv.conf</filename> into account. Also, note
1205         that the leases are not refreshed if the uplink network
1206         configuration changes. To ensure clients regularly acquire the
1207         most current uplink DNS server information, it is thus
1208         advisable to shorten the DHCP lease time via
1209         <varname>MaxLeaseTimeSec=</varname> described
1210         above.</para></listitem>
1211       </varlistentry>
1212
1213       <varlistentry>
1214         <term><varname>EmitNTP=</varname></term>
1215         <term><varname>NTP=</varname></term>
1216
1217         <listitem><para>Similar to the <varname>EmitDNS=</varname> and
1218         <varname>DNS=</varname> settings described above, these
1219         settings configure whether and what NTP server information
1220         shall be emitted as part of the DHCP lease. The same syntax,
1221         propagation semantics and defaults apply as for
1222         <varname>EmitDNS=</varname> and
1223         <varname>DNS=</varname>.</para></listitem>
1224       </varlistentry>
1225
1226       <varlistentry>
1227         <term><varname>EmitRouter=</varname></term>
1228
1229         <listitem><para>Similar to the <varname>EmitDNS=</varname>
1230         setting described above, this setting configures whether the
1231         DHCP lease should contain the router option. The same syntax,
1232         propagation semantics and defaults apply as for
1233         <varname>EmitDNS=</varname>.</para></listitem>
1234       </varlistentry>
1235
1236       <varlistentry>
1237         <term><varname>EmitTimezone=</varname></term>
1238         <term><varname>Timezone=</varname></term>
1239
1240         <listitem><para>Configures whether the DHCP leases handed out
1241         to clients shall contain timezone information. The
1242         <varname>EmitTimezone=</varname> setting takes a boolean
1243         argument and defaults to <literal>yes</literal>. The
1244         <varname>Timezone=</varname> setting takes a timezone string
1245         (such as <literal>Europe/Berlin</literal> or
1246         <literal>UTC</literal>) to pass to clients. If no explicit
1247         timezone is set, the system timezone of the local host is
1248         propagated, as determined by the
1249         <filename>/etc/localtime</filename> symlink.</para></listitem>
1250       </varlistentry>
1251
1252     </variablelist>
1253   </refsect1>
1254
1255   <refsect1>
1256     <title>[Bridge] Section Options</title>
1257       <para>The <literal>[Bridge]</literal> section accepts the
1258       following keys.</para>
1259       <variablelist class='network-directives'>
1260         <varlistentry>
1261           <term><varname>UnicastFlood=</varname></term>
1262           <listitem>
1263             <para>A boolean. Controls whether the bridge should flood
1264             traffic for which an FDB entry is missing and the destination
1265             is unknown through this port. Defaults to on.
1266             </para>
1267           </listitem>
1268         </varlistentry>
1269         <varlistentry>
1270           <term><varname>HairPin=</varname></term>
1271           <listitem>
1272             <para>A boolean. Configures whether traffic may be sent back
1273             out of the port on which it was received. By default, this
1274             flag is false, and the bridge will not forward traffic back
1275             out of the receiving port.</para>
1276           </listitem>
1277         </varlistentry>
1278         <varlistentry>
1279           <term><varname>UseBPDU=</varname></term>
1280           <listitem>
1281             <para>A boolean. Configures whether STP Bridge Protocol Data Units will be
1282             processed by the bridge port. Defaults to yes.</para>
1283           </listitem>
1284         </varlistentry>
1285         <varlistentry>
1286           <term><varname>FastLeave=</varname></term>
1287           <listitem>
1288             <para>A boolean. This flag allows the bridge to immediately stop multicast
1289             traffic on a port that receives an IGMP Leave message. It is only used with
1290             IGMP snooping if enabled on the bridge. Defaults to off.</para>
1291           </listitem>
1292         </varlistentry>
1293         <varlistentry>
1294           <term><varname>AllowPortToBeRoot=</varname></term>
1295           <listitem>
1296             <para>A boolean. Configures whether a given port is allowed to
1297             become a root port. Only used when STP is enabled on the bridge.
1298             Defaults to on.</para>
1299           </listitem>
1300         </varlistentry>
1301         <varlistentry>
1302           <term><varname>Cost=</varname></term>
1303           <listitem>
1304             <para>Sets the "cost" of sending packets of this interface.
1305             Each port in a bridge may have a different speed and the cost
1306             is used to decide which link to use. Faster interfaces
1307             should have lower costs. It is an interger value between 1 and
1308             65535.</para>
1309           </listitem>
1310         </varlistentry>
1311         <varlistentry>
1312           <term><varname>Priority=</varname></term>
1313           <listitem>
1314             <para>Sets the "priority" of sending packets on this interface.
1315             Each port in a bridge may have a different priority which is used
1316             to decide which link to use. Lower value means higher priority.
1317             It is an interger value between 0 to 63. Networkd does not set any
1318             default, meaning the kernel default value of 32 is used.</para>
1319           </listitem>
1320         </varlistentry>
1321       </variablelist>
1322   </refsect1>
1323   <refsect1>
1324     <title>[BridgeFDB] Section Options</title>
1325       <para>The <literal>[BridgeFDB]</literal> section manages the
1326       forwarding database table of a port and accepts the following
1327       keys. Specify several <literal>[BridgeFDB]</literal> sections to
1328       configure several static MAC table entries.</para>
1329
1330       <variablelist class='network-directives'>
1331         <varlistentry>
1332           <term><varname>MACAddress=</varname></term>
1333           <listitem>
1334             <para>As in the <literal>[Network]</literal> section. This
1335             key is mandatory.</para>
1336           </listitem>
1337         </varlistentry>
1338         <varlistentry>
1339           <term><varname>VLANId=</varname></term>
1340           <listitem>
1341             <para>The VLAN ID for the new static MAC table entry. If
1342             omitted, no VLAN ID info is appended to the new static MAC
1343             table entry.</para>
1344           </listitem>
1345         </varlistentry>
1346       </variablelist>
1347   </refsect1>
1348   <refsect1>
1349     <title>[BridgeVLAN] Section Options</title>
1350       <para>The <literal>[BridgeVLAN]</literal> section manages the VLAN ID configuration of a bridge port and accepts
1351       the following keys. Specify several <literal>[BridgeVLAN]</literal> sections to configure several VLAN entries.
1352       The <varname>VLANFiltering=</varname> option has to be enabled, see <literal>[Bridge]</literal> section in
1353       <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
1354
1355       <variablelist class='network-directives'>
1356         <varlistentry>
1357           <term><varname>VLAN=</varname></term>
1358           <listitem>
1359             <para>The VLAN ID allowed on the port. This can be either a single ID or a range M-N. VLAN IDs are valid
1360             from 1 to 4094.</para>
1361           </listitem>
1362         </varlistentry>
1363         <varlistentry>
1364           <term><varname>EgressUntagged=</varname></term>
1365           <listitem>
1366             <para>The VLAN ID specified here will be used to untag frames on egress. Configuring
1367             <varname>EgressUntagged=</varname> implicates the use of <varname>VLAN=</varname> above and will enable the
1368             VLAN ID for ingress as well. This can be either a single ID or a range M-N.</para>
1369           </listitem>
1370         </varlistentry>
1371         <varlistentry>
1372           <term><varname>PVID=</varname></term>
1373           <listitem>
1374             <para>The Port VLAN ID specified here is assigned to all untagged frames at ingress.
1375             <varname>PVID=</varname> can be used only once. Configuring <varname>PVID=</varname> implicates the use of
1376             <varname>VLAN=</varname> above and will enable the VLAN ID for ingress as well.</para>
1377           </listitem>
1378         </varlistentry>
1379       </variablelist>
1380   </refsect1>
1381
1382   <refsect1>
1383     <title>Examples</title>
1384     <example>
1385       <title>Static network configuration</title>
1386
1387       <programlisting># /etc/systemd/network/50-static.network
1388 [Match]
1389 Name=enp2s0
1390
1391 [Network]
1392 Address=192.168.0.15/24
1393 Gateway=192.168.0.1</programlisting>
1394
1395       <para>This brings interface <literal>enp2s0</literal> up with a static address. The
1396       specified gateway will be used for a default route.</para>
1397     </example>
1398
1399     <example>
1400       <title>DHCP on ethernet links</title>
1401
1402       <programlisting># /etc/systemd/network/80-dhcp.network
1403 [Match]
1404 Name=en*
1405
1406 [Network]
1407 DHCP=yes</programlisting>
1408
1409       <para>This will enable DHCPv4 and DHCPv6 on all interfaces with names starting with
1410       <literal>en</literal> (i.e. ethernet interfaces).</para>
1411     </example>
1412
1413     <example>
1414       <title>A bridge with two enslaved links</title>
1415
1416       <programlisting># /etc/systemd/network/25-bridge-static.network
1417 [Match]
1418 Name=bridge0
1419
1420 [Network]
1421 Address=192.168.0.15/24
1422 Gateway=192.168.0.1
1423 DNS=192.168.0.1</programlisting>
1424
1425       <programlisting># /etc/systemd/network/25-bridge-slave-interface-1.network
1426 [Match]
1427 Name=enp2s0
1428
1429 [Network]
1430 Bridge=bridge0</programlisting>
1431
1432       <programlisting># /etc/systemd/network/25-bridge-slave-interface-2.network
1433 [Match]
1434 Name=wlp3s0
1435
1436 [Network]
1437 Bridge=bridge0</programlisting>
1438
1439       <para>This creates a bridge and attaches devices <literal>enp2s0</literal> and
1440       <literal>wlp3s0</literal> to it. The bridge will have the specified static address
1441       and network assigned, and a default route via the specified gateway will be
1442       added. The specified DNS server will be added to the global list of DNS resolvers.
1443       </para>
1444     </example>
1445
1446     <example>
1447       <title></title>
1448
1449       <programlisting>
1450 # /etc/systemd/network/20-bridge-slave-interface-vlan.network
1451 [Match]
1452 Name=enp2s0
1453
1454 [Network]
1455 Bridge=bridge0
1456
1457 [BridgeVLAN]
1458 VLAN=1-32
1459 PVID=42
1460 EgressUntagged=42
1461
1462 [BridgeVLAN]
1463 VLAN=100-200
1464
1465 [BridgeVLAN]
1466 EgressUntagged=300-400</programlisting>
1467
1468     <para>This overrides the configuration specified in the previous example for the
1469     interface <literal>enp2s0</literal>, and enables VLAN on that bridge port. VLAN IDs
1470     1-32, 42, 100-400 will be allowed. Packets tagged with VLAN IDs 42, 300-400 will be
1471     untagged when they leave on this interface. Untagged packets which arrive on this
1472     interface will be assigned VLAN ID 42.</para>
1473     </example>
1474
1475     <example>
1476       <title>Various tunnels</title>
1477
1478       <programlisting>/etc/systemd/network/25-tunnels.network
1479 [Match]
1480 Name=ens1
1481
1482 [Network]
1483 Tunnel=ipip-tun
1484 Tunnel=sit-tun
1485 Tunnel=gre-tun
1486 Tunnel=vti-tun
1487       </programlisting>
1488
1489       <programlisting>/etc/systemd/network/25-tunnel-ipip.netdev
1490 [NetDev]
1491 Name=ipip-tun
1492 Kind=ipip
1493       </programlisting>
1494
1495       <programlisting>/etc/systemd/network/25-tunnel-sit.netdev
1496 [NetDev]
1497 Name=sit-tun
1498 Kind=sit
1499       </programlisting>
1500
1501       <programlisting>/etc/systemd/network/25-tunnel-gre.netdev
1502 [NetDev]
1503 Name=gre-tun
1504 Kind=gre
1505       </programlisting>
1506
1507       <programlisting>/etc/systemd/network/25-tunnel-vti.netdev
1508 [NetDev]
1509 Name=vti-tun
1510 Kind=vti
1511       </programlisting>
1512
1513       <para>This will bring interface <literal>ens1</literal> up and create an IPIP tunnel,
1514       a SIT tunnel, a GRE tunnel, and a VTI tunnel using it.</para>
1515     </example>
1516
1517     <example>
1518       <title>A bond device</title>
1519
1520       <programlisting># /etc/systemd/network/30-bond1.network
1521 [Match]
1522 Name=bond1
1523
1524 [Network]
1525 DHCP=ipv6
1526 </programlisting>
1527
1528       <programlisting># /etc/systemd/network/30-bond1.netdev
1529 [NetDev]
1530 Name=bond1
1531 Kind=bond
1532 </programlisting>
1533
1534       <programlisting># /etc/systemd/network/30-bond1-dev1.network
1535 [Match]
1536 MACAddress=52:54:00:e9:64:41
1537
1538 [Network]
1539 Bond=bond1
1540 </programlisting>
1541
1542       <programlisting># /etc/systemd/network/30-bond1-dev2.network
1543 [Match]
1544 MACAddress=52:54:00:e9:64:42
1545
1546 [Network]
1547 Bond=bond1
1548 </programlisting>
1549
1550     <para>This will create a bond device <literal>bond1</literal> and enslave the two
1551     devices with MAC addresses 52:54:00:e9:64:41 and 52:54:00:e9:64:42 to it. IPv6 DHCP
1552     will be used to acquire an address.</para>
1553     </example>
1554
1555     <example>
1556       <title>Virtual Routing and Forwarding (VRF)</title>
1557       <para>Add the <literal>bond1</literal> interface to the VRF master interface
1558       <literal>vrf1</literal>. This will redirect routes generated on this interface to be
1559       within the routing table defined during VRF creation. Traffic won't be redirected
1560       towards the VRFs routing table unless specific ip-rules are added.</para>
1561       <programlisting># /etc/systemd/network/25-vrf.network
1562 [Match]
1563 Name=bond1
1564
1565 [Network]
1566 VRF=vrf1
1567 </programlisting>
1568     </example>
1569
1570     <example>
1571       <title>MacVTap</title>
1572       <para>This brings up a network interface <literal>macvtap-test</literal>
1573       and attaches it to <literal>enp0s25</literal>.</para>
1574       <programlisting># /usr/lib/systemd/network/25-macvtap.network
1575 [Match]
1576 Name=enp0s25
1577
1578 [Network]
1579 MACVTAP=macvtap-test
1580 </programlisting>
1581     </example>
1582   </refsect1>
1583
1584   <refsect1>
1585     <title>See Also</title>
1586     <para>
1587       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1588       <citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
1589       <citerefentry><refentrytitle>systemd.link</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1590       <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1591       <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
1592     </para>
1593   </refsect1>
1594
1595 </refentry>