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>Network files must have the extension
  62     <filename>.network</filename>; other extensions are ignored.
  63     Networks are applied to links whenever the links appear.</para>
  64
  65     <para>The <filename>.network</filename> files are read from the
  66     files located in the system network directory
  67     <filename>/usr/lib/systemd/network</filename>, the volatile
  68     runtime network directory
  69     <filename>/run/systemd/network</filename> and the local
  70     administration network directory
  71     <filename>/etc/systemd/network</filename>. All configuration files
  72     are collectively sorted and processed in lexical order, regardless
  73     of the directories in which they live. However, files with
  74     identical filenames replace each other. Files in
  75     <filename>/etc</filename> have the highest priority, files in
  76     <filename>/run</filename> take precedence over files with the same
  77     name in <filename>/usr/lib</filename>. This can be used to
  78     override a system-supplied configuration file with a local file if
  79     needed. As a special case, an empty file (file size 0) or symlink
  80     with the same name pointing to <filename>/dev/null</filename>
  81     disables the configuration file entirely (it is "masked").</para>
  82   </refsect1>
  83
  84   <refsect1>
  85     <title>[Match] Section Options</title>
  86
  87       <para>The network file contains a <literal>[Match]</literal>
  88       section, which determines if a given network file may be applied
  89       to a given device; and a <literal>[Network]</literal> section
  90       specifying how the device should be configured. The first (in
  91       lexical order) of the network files that matches a given device
  92       is applied, all later files are ignored, even if they match as
  93       well.</para>
  94
  95       <para>A network file is said to match a device if each of the
  96       entries in the <literal>[Match]</literal> section matches, or if
  97       the section is empty. The following keys are accepted:</para>
  98
  99       <variablelist class='network-directives'>
 100         <varlistentry>
 101           <term><varname>MACAddress=</varname></term>
 102           <listitem>
 103             <para>The hardware address.</para>
 104           </listitem>
 105         </varlistentry>
 106         <varlistentry>
 107           <term><varname>Path=</varname></term>
 108           <listitem>
 109             <para>A whitespace-separated list of shell-style globs
 110             matching the persistent path, as exposed by the udev
 111             property <literal>ID_PATH</literal>.</para>
 112           </listitem>
 113         </varlistentry>
 114         <varlistentry>
 115           <term><varname>Driver=</varname></term>
 116           <listitem>
 117             <para>A whitespace-separated list of shell-style globs
 118             matching the driver currently bound to the device, as
 119             exposed by the udev property <literal>DRIVER</literal>
 120             of its parent device, or if that is not set the driver
 121             as exposed by <literal>ethtool -i</literal> of the
 122             device itself.</para>
 123           </listitem>
 124         </varlistentry>
 125         <varlistentry>
 126           <term><varname>Type=</varname></term>
 127           <listitem>
 128             <para>A whitespace-separated list of shell-style globs
 129             matching the device type, as exposed by the udev property
 130             <literal>DEVTYPE</literal>.</para>
 131           </listitem>
 132         </varlistentry>
 133         <varlistentry>
 134           <term><varname>Name=</varname></term>
 135           <listitem>
 136             <para>A whitespace-separated list of shell-style globs
 137             matching the device name, as exposed by the udev property
 138             <literal>INTERFACE</literal>.</para>
 139           </listitem>
 140         </varlistentry>
 141         <varlistentry>
 142           <term><varname>Host=</varname></term>
 143           <listitem>
 144             <para>Matches against the hostname or machine ID of the
 145             host. See <literal>ConditionHost=</literal> in
 146             <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 147             for details.
 148             </para>
 149           </listitem>
 150         </varlistentry>
 151         <varlistentry>
 152           <term><varname>Virtualization=</varname></term>
 153           <listitem>
 154             <para>Checks whether the system is executed in a virtualized
 155             environment and optionally test whether it is a specific
 156             implementation. See <literal>ConditionVirtualization=</literal> in
 157             <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 158             for details.
 159             </para>
 160           </listitem>
 161         </varlistentry>
 162         <varlistentry>
 163           <term><varname>KernelCommandLine=</varname></term>
 164           <listitem>
 165             <para>Checks whether a specific kernel command line option is
 166             set (or if prefixed with the exclamation mark unset). See
 167             <literal>ConditionKernelCommandLine=</literal> in
 168             <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 169             for details.
 170             </para>
 171           </listitem>
 172         </varlistentry>
 173         <varlistentry>
 174           <term><varname>Architecture=</varname></term>
 175           <listitem>
 176             <para>Checks whether the system is running on a specific
 177             architecture. See <literal>ConditionArchitecture=</literal> in
 178             <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 179             for details.
 180             </para>
 181           </listitem>
 182         </varlistentry>
 183       </variablelist>
 184
 185   </refsect1>
 186
 187   <refsect1>
 188     <title>[Link] Section Options</title>
 189
 190     <para> The <literal>[Link]</literal> section accepts the following keys:</para>
 191
 192     <variablelist class='network-directives'>
 193       <varlistentry>
 194         <term><varname>MACAddress=</varname></term>
 195         <listitem>
 196           <para>The hardware address.</para>
 197         </listitem>
 198       </varlistentry>
 199       <varlistentry>
 200         <term><varname>MTUBytes=</varname></term>
 201         <listitem>
 202           <para>The maximum transmission unit in bytes to set for the
 203           device. The usual suffixes K, M, G, are supported and are
 204           understood to the base of 1024.</para>
 205         </listitem>
 206       </varlistentry>
 207     </variablelist>
 208   </refsect1>
 209
 210   <refsect1>
 211     <title>[Network] Section Options</title>
 212
 213       <para>The <literal>[Network]</literal> section accepts the following keys:</para>
 214
 215       <variablelist class='network-directives'>
 216         <varlistentry>
 217           <term><varname>Description=</varname></term>
 218           <listitem>
 219             <para>A description of the device. This is only used for
 220             presentation purposes.</para>
 221           </listitem>
 222         </varlistentry>
 223         <varlistentry>
 224           <term><varname>DHCP=</varname></term>
 225           <listitem>
 226             <para>Enables DHCPv4 and/or DHCPv6 client support. Accepts
 227             <literal>yes</literal>, <literal>no</literal>,
 228             <literal>ipv4</literal>, or <literal>ipv6</literal>.</para>
 229
 230             <para>Note that DHCPv6 will by default be triggered by Router
 231             Advertisment, if that is enabled, regardless of this parameter.
 232             By enabling DHCPv6 support explicitly, the DHCPv6 client will
 233             be started regardless of the presence of routers on the link,
 234             or what flags the routers pass. See
 235             <literal>IPv6AcceptRouterAdvertisements=</literal>.</para>
 236
 237             <para>Furthermore, note that by default the domain name
 238             specified through DHCP is not used for name resolution.
 239             See option <option>UseDomains=</option> below.</para>
 240           </listitem>
 241         </varlistentry>
 242         <varlistentry>
 243           <term><varname>DHCPServer=</varname></term>
 244           <listitem>
 245             <para>A boolean. Enables DHCPv4 server support. Defaults
 246             to <literal>no</literal>. Further settings for the DHCP
 247             server may be set in the <literal>[DHCPServer]</literal>
 248             section described below.</para>
 249           </listitem>
 250         </varlistentry>
 251         <varlistentry>
 252           <term><varname>LinkLocalAddressing=</varname></term>
 253           <listitem>
 254             <para>Enables link-local address autoconfiguration. Accepts
 255             <literal>yes</literal>, <literal>no</literal>,
 256             <literal>ipv4</literal>, or <literal>ipv6</literal>. Defaults to
 257             <literal>ipv6</literal>.</para>
 258           </listitem>
 259         </varlistentry>
 260         <varlistentry>
 261           <term><varname>IPv4LLRoute=</varname></term>
 262           <listitem>
 263             <para>A boolean. When true, sets up the route needed for
 264             non-IPv4LL hosts to communicate with IPv4LL-only hosts. Defaults
 265             to false.
 266             </para>
 267           </listitem>
 268         </varlistentry>
 269         <varlistentry>
 270           <term><varname>IPv6Token=</varname></term>
 271           <listitem>
 272             <para>An IPv6 address with the top 64 bits unset. When set, indicates the
 273             64-bit interface part of SLAAC IPv6 addresses for this link. By default,
 274             it is autogenerated.</para>
 275           </listitem>
 276         </varlistentry>
 277         <varlistentry>
 278           <term><varname>LLMNR=</varname></term>
 279           <listitem>
 280             <para>A boolean or <literal>resolve</literal>. When true, enables
 281             Link-Local Multicast Name Resolution on the link. When set to
 282             <literal>resolve</literal>, only resolution is enabled, but not
 283             announcement. Defaults to true.</para>
 284           </listitem>
 285         </varlistentry>
 286         <varlistentry>
 287           <term><varname>LLDP=</varname></term>
 288           <listitem>
 289             <para>A boolean. When true, enables LLDP link receive support.
 290             </para>
 291           </listitem>
 292         </varlistentry>
 293         <varlistentry>
 294           <term><varname>BindCarrier=</varname></term>
 295           <listitem>
 296             <para>A port or a list of ports. When set, controls the
 297             behavior of the current interface. When all ports in the list
 298             are in an operational down state, the current interface is brought
 299             down. When at least one port has carrier, the current interface
 300             is brought up.
 301             </para>
 302           </listitem>
 303         </varlistentry>
 304         <varlistentry>
 305           <term><varname>Address=</varname></term>
 306           <listitem>
 307             <para>A static IPv4 or IPv6 address and its prefix length,
 308             separated by a <literal>/</literal> character. Specify
 309             this key more than once to configure several addresses.
 310             The format of the address must be as described in
 311             <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 312             This is a short-hand for an [Address] section only
 313             containing an Address key (see below). This option may be
 314             specified more than once.
 315             </para>
 316
 317             <para>If the specified address is 0.0.0.0 (for IPv4) or
 318             [::] (for IPv6), a new address range of the requested size
 319             is automatically allocated from a system-wide pool of
 320             unused ranges. The allocated range is checked against all
 321             current network interfaces and all known network
 322             configuration files to avoid address range conflicts. The
 323             default system-wide pool consists of 192.168.0.0/16,
 324             172.16.0.0/12 and 10.0.0.0/8 for IPv4, and fc00::/7 for
 325             IPv6. This functionality is useful to manage a large
 326             number of dynamically created network interfaces with the
 327             same network configuration and automatic address range
 328             assignment.</para>
 329
 330           </listitem>
 331         </varlistentry>
 332         <varlistentry>
 333           <term><varname>Gateway=</varname></term>
 334           <listitem>
 335             <para>The gateway address, which must be in the format
 336             described in
 337             <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 338             This is a short-hand for a [Route] section only containing
 339             a Gateway key. This option may be specified more than
 340             once.</para>
 341           </listitem>
 342         </varlistentry>
 343         <varlistentry>
 344           <term><varname>DNS=</varname></term>
 345           <listitem>
 346             <para>A DNS server address, which must be in the format
 347             described in
 348             <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 349             This option may be specified more than once.</para>
 350           </listitem>
 351         </varlistentry>
 352         <varlistentry>
 353           <term><varname>Domains=</varname></term>
 354           <listitem>
 355             <para>The domains used for DNS resolution over this link.</para>
 356           </listitem>
 357         </varlistentry>
 358         <varlistentry>
 359           <term><varname>NTP=</varname></term>
 360           <listitem>
 361             <para>An NTP server address. This option may be specified more than once.</para>
 362           </listitem>
 363         </varlistentry>
 364         <varlistentry>
 365           <term><varname>IPForward=</varname></term>
 366           <listitem><para>Configures IP packet forwarding for the
 367           system. If enabled, incoming packets on any network
 368           interface will be forwarded to any other interfaces
 369           according to the routing table. Takes either a boolean
 370           argument, or the values <literal>ipv4</literal> or
 371           <literal>ipv6</literal>, which only enable IP packet
 372           forwarding for the specified address family.  This controls
 373           the <filename>net.ipv4.ip_forward</filename> and
 374           <filename>net.ipv6.conf.all.forwarding</filename> sysctl
 375           options of the network interface (see <ulink
 376           url="https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt">ip-sysctl.txt</ulink>
 377           for details about sysctl options). Defaults to
 378           <literal>no</literal>.</para>
 379
 380           <para>Note: this setting controls a global kernel option,
 381           and does so one way only: if a network that has this setting
 382           enabled is set up the global setting is turned on.  However,
 383           it is never turned off again, even after all networks with
 384           this setting enabled are shut down again.</para>
 385
 386           <para>To allow IP packet forwarding only between specific
 387           network interfaces use a firewall.</para>
 388           </listitem>
 389         </varlistentry>
 390         <varlistentry>
 391           <term><varname>IPMasquerade=</varname></term>
 392           <listitem><para>Configures IP masquerading for the network
 393           interface. If enabled, packets forwarded from the network
 394           interface will be appear as coming from the local host.
 395           Takes a boolean argument. Implies
 396           <varname>IPForward=ipv4</varname>. Defaults to
 397           <literal>no</literal>.</para></listitem>
 398         </varlistentry>
 399         <varlistentry>
 400           <term><varname>IPv6PrivacyExtensions=</varname></term>
 401           <listitem><para>Configures use of stateless temporary
 402           addresses that change over time (see <ulink
 403           url="https://tools.ietf.org/html/rfc4941">RFC 4941</ulink>,
 404           Privacy Extensions for Stateless Address Autoconfiguration
 405           in IPv6). Takes a boolean or the special values
 406           <literal>prefer-public</literal> and
 407           <literal>kernel</literal>. When true, enables the privacy
 408           extensions and prefers temporary addresses over public
 409           addresses. When <literal>prefer-public</literal>, enables the
 410           privacy extensions, but prefers public addresses over
 411           temporary addresses. When false, the privacy extensions
 412           remain disabled. When <literal>kernel</literal>, the kernel's
 413           default setting will be left in place.  Defaults to
 414           <literal>no</literal>.</para></listitem>
 415         </varlistentry>
 416         <varlistentry>
 417           <term><varname>IPv6AcceptRouterAdvertisements=</varname></term>
 418           <listitem><para>Force the setting of the <filename>accept_ra</filename>
 419           (router advertisements) setting for the interface.
 420           When unset, the kernel default is used, and router
 421           advertisements are accepted only when local forwarding
 422           is disabled for that interface.
 423           When router advertisements are accepted, they will
 424           trigger the start of the DHCPv6 client if the relevant
 425           flags are passed, or if no routers are found on the link.
 426           Takes a boolean. If true, router advertisements are
 427           accepted, when false, router advertisements are ignored,
 428           independently of the local forwarding state.</para>
 429
 430           <para>See
 431           <ulink url="https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt">ip-sysctl.txt</ulink>
 432           in the kernel documentation, but note that systemd's
 433           setting of <constant>1</constant> corresponds to
 434           kernel's setting of <constant>2</constant>.</para>
 435         </listitem>
 436         </varlistentry>
 437         <varlistentry>
 438           <term><varname>IPv6DuplicateAddressDetection=</varname></term>
 439           <listitem><para>Configures the amount of IPv6 Duplicate
 440           Address Detection (DAD) probes to send. Defaults to unset.
 441         </para></listitem>
 442         </varlistentry>
 443         <varlistentry>
 444           <term><varname>IPv6HopLimit=</varname></term>
 445           <listitem><para>Configures IPv6 Hop Limit. For each router that
 446           forwards the packet, the hop limit is decremented by 1. When the
 447           hop limit field reaches zero, the packet is discarded.
 448           Defaults to unset.
 449         </para></listitem>
 450         </varlistentry>
 451         <varlistentry>
 452           <term><varname>Bridge=</varname></term>
 453           <listitem>
 454             <para>The name of the bridge to add the link to.</para>
 455           </listitem>
 456         </varlistentry>
 457         <varlistentry>
 458           <term><varname>Bond=</varname></term>
 459           <listitem>
 460             <para>The name of the bond to add the link to.</para>
 461           </listitem>
 462         </varlistentry>
 463         <varlistentry>
 464           <term><varname>VLAN=</varname></term>
 465           <listitem>
 466             <para>The name of a VLAN to create on the link. This
 467             option may be specified more than once.</para>
 468           </listitem>
 469         </varlistentry>
 470         <varlistentry>
 471           <term><varname>MACVLAN=</varname></term>
 472           <listitem>
 473             <para>The name of a MACVLAN to create on the link. This
 474             option may be specified more than once.</para>
 475           </listitem>
 476         </varlistentry>
 477         <varlistentry>
 478           <term><varname>VXLAN=</varname></term>
 479           <listitem>
 480             <para>The name of a VXLAN to create on the link. This
 481             option may be specified more than once.</para>
 482           </listitem>
 483         </varlistentry>
 484         <varlistentry>
 485           <term><varname>Tunnel=</varname></term>
 486           <listitem>
 487             <para>The name of a Tunnel to create on the link. This
 488             option may be specified more than once.</para>
 489           </listitem>
 490         </varlistentry>
 491       </variablelist>
 492
 493   </refsect1>
 494
 495   <refsect1>
 496     <title>[Address] Section Options</title>
 497
 498       <para>An <literal>[Address]</literal> section accepts the
 499       following keys. Specify several <literal>[Address]</literal>
 500       sections to configure several addresses.</para>
 501
 502       <variablelist class='network-directives'>
 503         <varlistentry>
 504           <term><varname>Address=</varname></term>
 505           <listitem>
 506             <para>As in the <literal>[Network]</literal> section. This
 507             key is mandatory.</para>
 508           </listitem>
 509         </varlistentry>
 510         <varlistentry>
 511           <term><varname>Peer=</varname></term>
 512           <listitem>
 513             <para>The peer address in a point-to-point connection.
 514             Accepts the same format as the <literal>Address</literal>
 515             key.</para>
 516           </listitem>
 517         </varlistentry>
 518         <varlistentry>
 519           <term><varname>Broadcast=</varname></term>
 520           <listitem>
 521             <para>The broadcast address, which must be in the format
 522             described in
 523             <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 524             This key only applies to IPv4 addresses. If it is not
 525             given, it is derived from the <literal>Address</literal>
 526             key.</para>
 527           </listitem>
 528         </varlistentry>
 529         <varlistentry>
 530           <term><varname>Label=</varname></term>
 531           <listitem>
 532             <para>An address label.</para>
 533           </listitem>
 534         </varlistentry>
 535       </variablelist>
 536   </refsect1>
 537
 538   <refsect1>
 539     <title>[Route] Section Options</title>
 540       <para>The <literal>[Route]</literal> section accepts the
 541       following keys. Specify several <literal>[Route]</literal>
 542       sections to configure several routes.</para>
 543
 544       <variablelist class='network-directives'>
 545         <varlistentry>
 546           <term><varname>Gateway=</varname></term>
 547           <listitem>
 548             <para>As in the <literal>[Network]</literal> section.</para>
 549           </listitem>
 550         </varlistentry>
 551         <varlistentry>
 552           <term><varname>Destination=</varname></term>
 553           <listitem>
 554             <para>The destination prefix of the route. Possibly
 555             followed by a slash and the prefix length. If omitted, a
 556             full-length host route is assumed.</para>
 557           </listitem>
 558         </varlistentry>
 559         <varlistentry>
 560           <term><varname>Source=</varname></term>
 561           <listitem>
 562             <para>The source prefix of the route. Possibly followed by
 563             a slash and the prefix length. If omitted, a full-length
 564             host route is assumed.</para>
 565           </listitem>
 566         </varlistentry>
 567         <varlistentry>
 568           <term><varname>Metric=</varname></term>
 569           <listitem>
 570             <para>The metric of the route (an unsigned integer).</para>
 571           </listitem>
 572         </varlistentry>
 573         <varlistentry>
 574           <term><varname>Scope=</varname></term>
 575           <listitem>
 576             <para>The scope of the route, which can be <literal>global</literal>,
 577             <literal>link</literal> or <literal>host</literal>. Defaults to
 578             <literal>global</literal>.</para>
 579           </listitem>
 580         </varlistentry>
 581         <varlistentry>
 582           <term><varname>PreferredSource=</varname></term>
 583           <listitem>
 584             <para>The preferred source address of the route. The address
 585             must be in the format described in
 586             <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
 587           </listitem>
 588         </varlistentry>
 589       </variablelist>
 590   </refsect1>
 591
 592   <refsect1>
 593     <title>[DHCP] Section Options</title>
 594       <para>The <literal>[DHCP]</literal> section configures the
 595       DHCPv4 and DHCP6 client, if it is enabled with the
 596       <varname>DHCP=</varname> setting described above:</para>
 597
 598       <variablelist class='network-directives'>
 599         <varlistentry>
 600           <term><varname>UseDNS=</varname></term>
 601           <listitem>
 602             <para>When true (the default), the DNS servers received
 603             from the DHCP server will be used and take precedence over
 604             any statically configured ones.</para>
 605
 606             <para>This corresponds to the <option>nameserver</option>
 607             option in <citerefentry
 608             project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
 609           </listitem>
 610         </varlistentry>
 611         <varlistentry>
 612           <term><varname>UseNTP=</varname></term>
 613           <listitem>
 614             <para>When true (the default), the NTP servers received
 615             from the DHCP server will be used by systemd-timesyncd
 616             and take precedence over any statically configured ones.</para>
 617           </listitem>
 618         </varlistentry>
 619         <varlistentry>
 620           <term><varname>UseMTU=</varname></term>
 621           <listitem>
 622             <para>When true, the interface maximum transmission unit
 623             from the DHCP server will be used on the current link.
 624             Defaults to false.</para>
 625           </listitem>
 626         </varlistentry>
 627         <varlistentry>
 628           <term><varname>SendHostname=</varname></term>
 629           <listitem>
 630             <para>When true (the default), the machine's hostname will
 631             be sent to the DHCP server.</para>
 632           </listitem>
 633         </varlistentry>
 634         <varlistentry>
 635           <term><varname>UseHostname=</varname></term>
 636           <listitem>
 637             <para>When true (the default), the hostname received from
 638             the DHCP server will be set as the transient hostname of the system
 639             </para>
 640           </listitem>
 641         </varlistentry>
 642         <varlistentry>
 643         <term><varname>Hostname=</varname></term>
 644         <listitem>
 645           <para>Use this value for the hostname which is sent to the
 646           DHCP server, instead of machine's hostname.</para>
 647         </listitem>
 648       </varlistentry>
 649         <varlistentry>
 650           <term><varname>UseDomains=</varname></term>
 651           <listitem>
 652             <para>When true (not the default), the domain name
 653             received from the DHCP server will be used for DNS
 654             resolution over this link. When a name cannot be resolved
 655             as specified, the domain name will be used a suffix and
 656             name resolution of that will be attempted.</para>
 657
 658             <para>This corresponds to the <option>domain</option>
 659             option in <citerefentry project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 660             and should not be enabled on untrusted networks.</para>
 661           </listitem>
 662         </varlistentry>
 663         <varlistentry>
 664           <term><varname>UseRoutes=</varname></term>
 665           <listitem>
 666             <para>When true (the default), the static routes will be
 667             requested from the DHCP server and added to the routing
 668             table with a metric of 1024.</para>
 669           </listitem>
 670         </varlistentry>
 671
 672         <varlistentry>
 673           <term><varname>UseTimezone=</varname></term>
 674
 675           <listitem><para>When true, the timezone received from the
 676           DHCP server will be set as as timezone of the local
 677           system. Defaults to <literal>no</literal>.</para></listitem>
 678         </varlistentry>
 679
 680         <varlistentry>
 681           <term><varname>CriticalConnection=</varname></term>
 682           <listitem>
 683             <para>When true, the connection will never be torn down
 684             even if the DHCP lease expires. This is contrary to the
 685             DHCP specification, but may be the best choice if, say,
 686             the root filesystem relies on this connection. Defaults to
 687             false.</para>
 688           </listitem>
 689         </varlistentry>
 690         <varlistentry>
 691           <term><varname>ClientIdentifier=</varname></term>
 692           <listitem>
 693             <para>DHCP client identifier to use. Either <literal>mac</literal>
 694             to use the MAC address of the link or <literal>duid</literal>
 695             (the default) to use a RFC4361-compliant Client ID.</para>
 696           </listitem>
 697         </varlistentry>
 698         <varlistentry>
 699           <term><varname>VendorClassIdentifier=</varname></term>
 700           <listitem>
 701             <para>The vendor class identifier used to identify vendor
 702             type and configuration.</para>
 703           </listitem>
 704         </varlistentry>
 705         <varlistentry>
 706           <term><varname>RequestBroadcast=</varname></term>
 707           <listitem>
 708             <para>Request the server to use broadcast messages before
 709             the IP address has been configured. This is necessary for
 710             devices that cannot receive RAW packets, or that cannot
 711             receive packets at all before an IP address has been
 712             configured. On the other hand, this must not be enabled on
 713             networks where broadcasts are filtered out.</para>
 714           </listitem>
 715         </varlistentry>
 716         <varlistentry>
 717           <term><varname>RouteMetric=</varname></term>
 718           <listitem>
 719             <para>Set the routing metric for routes specified by the
 720             DHCP server.</para>
 721           </listitem>
 722         </varlistentry>
 723       </variablelist>
 724
 725   </refsect1>
 726
 727   <refsect1>
 728     <title>[DHCPServer] Section Options</title>
 729     <para>The <literal>[DHCPServer]</literal> section contains
 730     settings for the DHCP server, if enabled via the
 731     <varname>DHCPServer=</varname> option described above:</para>
 732
 733     <variablelist class='network-directives'>
 734
 735       <varlistentry>
 736         <term><varname>PoolOffset=</varname></term>
 737         <term><varname>PoolSize=</varname></term>
 738
 739         <listitem><para>Configures the pool of addresses to hand out. The pool
 740         is a contiguous sequence of IP addresses in the subnet configured for
 741         the server address, which does not include the subnet nor the broadcast
 742         address. <varname>PoolOffset=</varname> takes the offset of the pool
 743         from the start of subnet, or zero to use the default value.
 744         <varname>PoolSize=</varname> takes the number of IP addresses in the
 745         pool or zero to use the default value. By default, the pool starts at
 746         the first address after the subnet address and takes up the rest of
 747         the subnet, excluding the broadcast address. If the pool includes
 748         the server address (the default), this is reserved and not handed
 749         out to clients.</para></listitem>
 750       </varlistentry>
 751
 752       <varlistentry>
 753         <term><varname>DefaultLeaseTimeSec=</varname></term>
 754         <term><varname>MaxLeaseTimeSec=</varname></term>
 755
 756         <listitem><para>Control the default and maximum DHCP lease
 757         time to pass to clients. These settings take time values in seconds or
 758         another common time unit, depending on the suffix. The default
 759         lease time is used for clients that did not ask for a specific
 760         lease time. If a client asks for a lease time longer than the
 761         maximum lease time, it is automatically shortened to the
 762         specified time. The default lease time defaults to 1h, the
 763         maximum lease time to 12h. Shorter lease times are beneficial
 764         if the configuration data in DHCP leases changes frequently
 765         and clients shall learn the new settings with shorter
 766         latencies. Longer lease times reduce the generated DHCP
 767         network traffic.</para></listitem>
 768       </varlistentry>
 769
 770       <varlistentry>
 771         <term><varname>EmitDNS=</varname></term>
 772         <term><varname>DNS=</varname></term>
 773
 774         <listitem><para>Configures whether the DHCP leases handed out
 775         to clients shall contain DNS server information. The
 776         <varname>EmitDNS=</varname> setting takes a boolean argument
 777         and defaults to <literal>yes</literal>. The DNS servers to
 778         pass to clients may be configured with the
 779         <varname>DNS=</varname> option, which takes a list of IPv4
 780         addresses. If the <varname>EmitDNS=</varname> option is
 781         enabled but no servers configured, the servers are
 782         automatically propagated from an "uplink" interface that has
 783         appropriate servers set. The "uplink" interface is determined
 784         by the default route of the system with the highest
 785         priority. Note that this information is acquired at the time
 786         the lease is handed out, and does not take uplink interfaces
 787         into account that acquire DNS or NTP server information at a
 788         later point. DNS server propagation does not take
 789         <filename>/etc/resolv.conf</filename> into account. Also, note
 790         that the leases are not refreshed if the uplink network
 791         configuration changes. To ensure clients regularly acquire the
 792         most current uplink DNS server information, it is thus
 793         advisable to shorten the DHCP lease time via
 794         <varname>MaxLeaseTimeSec=</varname> described
 795         above.</para></listitem>
 796       </varlistentry>
 797
 798       <varlistentry>
 799         <term><varname>EmitNTP=</varname></term>
 800         <term><varname>NTP=</varname></term>
 801
 802         <listitem><para>Similar to the <varname>EmitDNS=</varname> and
 803         <varname>DNS=</varname> settings described above, these
 804         settings configure whether and what NTP server information
 805         shall be emitted as part of the DHCP lease. The same syntax,
 806         propagation semantics and defaults apply as for
 807         <varname>EmitDNS=</varname> and
 808         <varname>DNS=</varname>.</para></listitem>
 809       </varlistentry>
 810
 811       <varlistentry>
 812         <term><varname>EmitTimezone=</varname></term>
 813         <term><varname>Timezone=</varname></term>
 814
 815         <listitem><para>Configures whether the DHCP leases handed out
 816         to clients shall contain timezone information. The
 817         <varname>EmitTimezone=</varname> setting takes a boolean
 818         argument and defaults to <literal>yes</literal>. The
 819         <varname>Timezone=</varname> setting takes a timezone string
 820         (such as <literal>Europe/Berlin</literal> or
 821         <literal>UTC</literal>) to pass to clients. If no explicit
 822         timezone is set, the system timezone of the local host is
 823         propagated, as determined by the
 824         <filename>/etc/localtime</filename> symlink.</para></listitem>
 825       </varlistentry>
 826
 827     </variablelist>
 828   </refsect1>
 829
 830   <refsect1>
 831     <title>[Bridge] Section Options</title>
 832       <para>The <literal>[Bridge]</literal> section accepts the
 833       following keys.</para>
 834       <variablelist class='network-directives'>
 835         <varlistentry>
 836           <term><varname>UnicastFlood=</varname></term>
 837           <listitem>
 838             <para>A boolean. Controls whether the bridge should flood
 839             traffic for which an FDB entry is missing and the destination
 840             is unknown through this port. Defaults to on.
 841             </para>
 842           </listitem>
 843         </varlistentry>
 844         <varlistentry>
 845           <term><varname>HairPin=</varname></term>
 846           <listitem>
 847             <para>A boolean. Configures whether traffic may be sent back
 848             out of the port on which it was received. By default, this
 849             flag is false, and the bridge will not forward traffic back
 850             out of the receiving port.</para>
 851           </listitem>
 852         </varlistentry>
 853         <varlistentry>
 854           <term><varname>UseBPDU=</varname></term>
 855           <listitem>
 856             <para>A boolean. Configures whether STP Bridge Protocol Data Units will be
 857             processed by the bridge port. Defaults to yes.</para>
 858           </listitem>
 859         </varlistentry>
 860         <varlistentry>
 861           <term><varname>FastLeave=</varname></term>
 862           <listitem>
 863             <para>A boolean. This flag allows the bridge to immediately stop multicast
 864             traffic on a port that receives an IGMP Leave message. It is only used with
 865             IGMP snooping if enabled on the bridge. Defaults to off.</para>
 866           </listitem>
 867         </varlistentry>
 868         <varlistentry>
 869           <term><varname>AllowPortToBeRoot=</varname></term>
 870           <listitem>
 871             <para>A boolean. Configures whether a given port is allowed to
 872             become a root port. Only used when STP is enabled on the bridge.
 873             Defaults to on.</para>
 874           </listitem>
 875         </varlistentry>
 876         <varlistentry>
 877           <term><varname>Cost=</varname></term>
 878           <listitem>
 879             <para>Sets the "cost" of sending packets of this interface.
 880             Each port in a bridge may have a different speed and the cost
 881             is used to decide which link to use. Faster interfaces
 882             should have lower costs.</para>
 883           </listitem>
 884         </varlistentry>
 885       </variablelist>
 886   </refsect1>
 887   <refsect1>
 888     <title>[BridgeFDB] Section Options</title>
 889       <para>The <literal>[BridgeFDB]</literal> section manages the
 890       forwarding database table of a port and accepts the following
 891       keys. Specify several <literal>[BridgeFDB]</literal> sections to
 892       configure several static MAC table entries.</para>
 893
 894       <variablelist class='network-directives'>
 895         <varlistentry>
 896           <term><varname>MACAddress=</varname></term>
 897           <listitem>
 898             <para>As in the <literal>[Network]</literal> section. This
 899             key is mandatory.</para>
 900           </listitem>
 901         </varlistentry>
 902         <varlistentry>
 903           <term><varname>VLANId=</varname></term>
 904           <listitem>
 905             <para>The VLAN ID for the new static MAC table entry. If
 906             omitted, no VLAN ID info is appended to the new static MAC
 907             table entry.</para>
 908           </listitem>
 909         </varlistentry>
 910       </variablelist>
 911   </refsect1>
 912
 913   <refsect1>
 914     <title>Example</title>
 915     <example>
 916       <title>/etc/systemd/network/50-static.network</title>
 917
 918       <programlisting>[Match]
 919 Name=enp2s0
 920
 921 [Network]
 922 Address=192.168.0.15/24
 923 Gateway=192.168.0.1</programlisting>
 924     </example>
 925
 926     <example>
 927       <title>/etc/systemd/network/80-dhcp.network</title>
 928
 929       <programlisting>[Match]
 930 Name=en*
 931
 932 [Network]
 933 DHCP=yes</programlisting>
 934     </example>
 935
 936     <example>
 937       <title>/etc/systemd/network/25-bridge-static.network</title>
 938
 939       <programlisting>[Match]
 940 Name=bridge0
 941
 942 [Network]
 943 Address=192.168.0.15/24
 944 Gateway=192.168.0.1
 945 DNS=192.168.0.1</programlisting>
 946     </example>
 947
 948     <example>
 949       <title>/etc/systemd/network/25-bridge-slave-interface.network</title>
 950
 951       <programlisting>[Match]
 952 Name=enp2s0
 953
 954 [Network]
 955 Bridge=bridge0</programlisting>
 956     </example>
 957     <example>
 958       <title>/etc/systemd/network/25-ipip.network</title>
 959
 960       <programlisting>[Match]
 961 Name=em1
 962
 963 [Network]
 964 Tunnel=ipip-tun</programlisting>
 965     </example>
 966
 967     <example>
 968       <title>/etc/systemd/network/25-sit.network</title>
 969
 970       <programlisting>[Match]
 971 Name=em1
 972
 973 [Network]
 974 Tunnel=sit-tun</programlisting>
 975     </example>
 976
 977     <example>
 978       <title>/etc/systemd/network/25-gre.network</title>
 979
 980       <programlisting>[Match]
 981 Name=em1
 982
 983 [Network]
 984 Tunnel=gre-tun</programlisting>
 985     </example>
 986
 987     <example>
 988       <title>/etc/systemd/network/25-vti.network</title>
 989
 990       <programlisting>[Match]
 991 Name=em1
 992
 993 [Network]
 994 Tunnel=vti-tun</programlisting>
 995     </example>
 996
 997     <example>
 998       <title>/etc/systemd/network/25-bond.network</title>
 999
1000       <programlisting>[Match]
1001 Name=bond1
1002
1003 [Network]
1004 DHCP=yes
1005 </programlisting>
1006     </example>
1007
1008   </refsect1>
1009
1010   <refsect1>
1011     <title>See Also</title>
1012     <para>
1013       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1014       <citerefentry><refentrytitle>systemd-networkd</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
1015       <citerefentry><refentrytitle>systemd.link</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1016       <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1017     </para>
1018   </refsect1>
1019
1020 </refentry>