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     disable 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>Please note that by default the domain name
 231             specified through DHCP is not used for name resolution.
 232             See option <option>UseDomains=</option> below.</para>
 233           </listitem>
 234         </varlistentry>
 235         <varlistentry>
 236           <term><varname>DHCPServer=</varname></term>
 237           <listitem>
 238             <para>A boolean. Enables DHCPv4 server support. Defaults
 239             to <literal>no</literal>. Further settings for the DHCP
 240             server may be set in the <literal>[DHCPServer]</literal>
 241             section described below.</para>
 242           </listitem>
 243         </varlistentry>
 244         <varlistentry>
 245           <term><varname>LinkLocalAddressing=</varname></term>
 246           <listitem>
 247             <para>Enables link-local address autoconfiguration. Accepts
 248             <literal>yes</literal>, <literal>no</literal>,
 249             <literal>ipv4</literal>, or <literal>ipv6</literal>. Defaults to
 250             <literal>ipv6</literal>.</para>
 251           </listitem>
 252         </varlistentry>
 253         <varlistentry>
 254           <term><varname>IPv4LLRoute=</varname></term>
 255           <listitem>
 256             <para>A boolean. When true, sets up the route needed for
 257             non-IPv4LL hosts to communicate with IPv4LL-only hosts. Defaults
 258             to false.
 259             </para>
 260           </listitem>
 261         </varlistentry>
 262         <varlistentry>
 263           <term><varname>IPv6Token=</varname></term>
 264           <listitem>
 265             <para>An IPv6 address with the top 64 bits unset. When set, indicates the
 266             64 bits interface part of SLAAC IPv6 addresses for this link. By default
 267             it is autogenerated.</para>
 268           </listitem>
 269         </varlistentry>
 270         <varlistentry>
 271           <term><varname>LLMNR=</varname></term>
 272           <listitem>
 273             <para>A boolean or <literal>resolve</literal>. When true, enables
 274             Link-Local Multicast Name Resolution on the link, when set to
 275             <literal>resolve</literal> only resolution is enabled, but not
 276             announcement. Defaults to true.</para>
 277           </listitem>
 278         </varlistentry>
 279         <varlistentry>
 280           <term><varname>LLDP=</varname></term>
 281           <listitem>
 282             <para>A boolean. When true, enables LLDP link receive support.
 283             </para>
 284           </listitem>
 285         </varlistentry>
 286         <varlistentry>
 287           <term><varname>BindCarrier=</varname></term>
 288           <listitem>
 289             <para>A port or a list of ports. When set, controls the
 290             behavior of the current interface. When all ports in the list
 291             are in an operational down state, the current interface is brought
 292             down. When at least one port has carrier, the current interface
 293             is brought up.
 294             </para>
 295           </listitem>
 296         </varlistentry>
 297         <varlistentry>
 298           <term><varname>Address=</varname></term>
 299           <listitem>
 300             <para>A static IPv4 or IPv6 address and its prefix length,
 301             separated by a <literal>/</literal> character. Specify
 302             this key more than once to configure several addresses.
 303             The format of the address must be as described in
 304             <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 305             This is a short-hand for an [Address] section only
 306             containing an Address key (see below). This option may be
 307             specified more than once.
 308             </para>
 309
 310             <para>If the specified address is 0.0.0.0 (for IPv4) or
 311             [::] (for IPv6), a new address range of the requested size
 312             is automatically allocated from a system-wide pool of
 313             unused ranges. The allocated range is checked against all
 314             current network interfaces and all known network
 315             configuration files to avoid address range conflicts. The
 316             default system-wide pool consists of 192.168.0.0/16,
 317             172.16.0.0/12 and 10.0.0.0/8 for IPv4, and fc00::/7 for
 318             IPv6. This functionality is useful to manage a large
 319             number of dynamically created network interfaces with the
 320             same network configuration and automatic address range
 321             assignment.</para>
 322
 323           </listitem>
 324         </varlistentry>
 325         <varlistentry>
 326           <term><varname>Gateway=</varname></term>
 327           <listitem>
 328             <para>The gateway address, which must be in the format
 329             described in
 330             <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 331             This is a short-hand for a [Route] section only containing
 332             a Gateway key. This option may be specified more than
 333             once.</para>
 334           </listitem>
 335         </varlistentry>
 336         <varlistentry>
 337           <term><varname>DNS=</varname></term>
 338           <listitem>
 339             <para>A DNS server address, which must be in the format
 340             described in
 341             <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 342             This option may be specified more than once.</para>
 343           </listitem>
 344         </varlistentry>
 345         <varlistentry>
 346           <term><varname>Domains=</varname></term>
 347           <listitem>
 348             <para>The domains used for DNS resolution over this link.</para>
 349           </listitem>
 350         </varlistentry>
 351         <varlistentry>
 352           <term><varname>NTP=</varname></term>
 353           <listitem>
 354             <para>An NTP server address. This option may be specified more than once.</para>
 355           </listitem>
 356         </varlistentry>
 357         <varlistentry>
 358           <term><varname>IPForward=</varname></term>
 359           <listitem><para>Configures IP forwarding for the network
 360           interface. If enabled incoming packets on the network
 361           interface will be forwarded to other interfaces according to
 362           the routing table. Takes either a boolean argument, or the
 363           values <literal>ipv4</literal> or <literal>ipv6</literal>,
 364           which only enables IP forwarding for the specified address
 365           family, or <literal>kernel</literal>, which preserves existing sysctl settings.
 366           This controls the
 367           <filename>net.ipv4.conf.&lt;interface&gt;.forwarding</filename>
 368           and
 369           <filename>net.ipv6.conf.&lt;interface&gt;.forwarding</filename>
 370           sysctl options of the network interface (see <ulink
 371           url="https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt">ip-sysctl.txt</ulink>
 372           for details about sysctl options). Defaults to
 373           <literal>no</literal>.</para>
 374
 375          <para>Note: unless this option is turned on, or set to <literal>kernel</literal>,
 376           no IP forwarding is done on this interface, even if this is
 377           globally turned on in the kernel, with the
 378           <filename>net.ipv4.ip_forward</filename>,
 379           <filename>net.ipv4.conf.all.forwarding</filename>, and
 380           <filename>net.ipv6.conf.all.forwarding</filename> sysctl
 381           options.</para>
 382           </listitem>
 383         </varlistentry>
 384         <varlistentry>
 385           <term><varname>IPMasquerade=</varname></term>
 386           <listitem><para>Configures IP masquerading for the network
 387           interface. If enabled packets forwarded from the network
 388           interface will be appear as coming from the local host.
 389           Takes a boolean argument. Implies
 390           <varname>IPForward=ipv4</varname>. Defaults to
 391           <literal>no</literal>.</para></listitem>
 392         </varlistentry>
 393         <varlistentry>
 394           <term><varname>IPv6PrivacyExtensions=</varname></term>
 395           <listitem><para>Configures use of stateless temporary
 396           addresses that change over time (see <ulink
 397           url="https://tools.ietf.org/html/rfc4941">RFC 4941</ulink>,
 398           Privacy Extensions for Stateless Address Autoconfiguration
 399           in IPv6). Takes a boolean or the special values
 400           <literal>prefer-public</literal> and
 401           <literal>kernel</literal>. When true enables the privacy
 402           extensions and prefers temporary addresses over public
 403           addresses. When <literal>prefer-public</literal> enables the
 404           privacy extensions, but prefers public addresses over
 405           temporary addresses. When false, the privacy extensions
 406           remain disabled. When <literal>kernel</literal> the kernel's
 407           default setting will be left in place.  Defaults to
 408           <literal>no</literal>.</para></listitem>
 409         </varlistentry>
 410         <varlistentry>
 411           <term><varname>IPv6AcceptRouterAdvertisements=</varname></term>
 412           <listitem><para>Configures Accept Router Advertisements.
 413           This is enabled if local forwarding is disabled.
 414           Disabled if local forwarding is enabled.
 415           Takes a boolean. Defaults to unset.
 416         </para></listitem>
 417         </varlistentry>
 418         <varlistentry>
 419           <term><varname>Bridge=</varname></term>
 420           <listitem>
 421             <para>The name of the bridge to add the link to.</para>
 422           </listitem>
 423         </varlistentry>
 424         <varlistentry>
 425           <term><varname>Bond=</varname></term>
 426           <listitem>
 427             <para>The name of the bond to add the link to.</para>
 428           </listitem>
 429         </varlistentry>
 430         <varlistentry>
 431           <term><varname>VLAN=</varname></term>
 432           <listitem>
 433             <para>The name of a VLAN to create on the link. This
 434             option may be specified more than once.</para>
 435           </listitem>
 436         </varlistentry>
 437         <varlistentry>
 438           <term><varname>MACVLAN=</varname></term>
 439           <listitem>
 440             <para>The name of a MACVLAN to create on the link. This
 441             option may be specified more than once.</para>
 442           </listitem>
 443         </varlistentry>
 444         <varlistentry>
 445           <term><varname>VXLAN=</varname></term>
 446           <listitem>
 447             <para>The name of a VXLAN to create on the link. This
 448             option may be specified more than once.</para>
 449           </listitem>
 450         </varlistentry>
 451         <varlistentry>
 452           <term><varname>Tunnel=</varname></term>
 453           <listitem>
 454             <para>The name of a Tunnel to create on the link. This
 455             option may be specified more than once.</para>
 456           </listitem>
 457         </varlistentry>
 458       </variablelist>
 459
 460   </refsect1>
 461
 462   <refsect1>
 463     <title>[Address] Section Options</title>
 464
 465       <para>An <literal>[Address]</literal> section accepts the
 466       following keys. Specify several <literal>[Address]</literal>
 467       sections to configure several addresses.</para>
 468
 469       <variablelist class='network-directives'>
 470         <varlistentry>
 471           <term><varname>Address=</varname></term>
 472           <listitem>
 473             <para>As in the <literal>[Network]</literal> section. This
 474             key is mandatory.</para>
 475           </listitem>
 476         </varlistentry>
 477         <varlistentry>
 478           <term><varname>Peer=</varname></term>
 479           <listitem>
 480             <para>The peer address in a point-to-point connection.
 481             Accepts the same format as the <literal>Address</literal>
 482             key.</para>
 483           </listitem>
 484         </varlistentry>
 485         <varlistentry>
 486           <term><varname>Broadcast=</varname></term>
 487           <listitem>
 488             <para>The broadcast address, which must be in the format
 489             described in
 490             <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 491             This key only applies to IPv4 addresses. If it is not
 492             given, it is derived from the <literal>Address</literal>
 493             key.</para>
 494           </listitem>
 495         </varlistentry>
 496         <varlistentry>
 497           <term><varname>Label=</varname></term>
 498           <listitem>
 499             <para>An address label.</para>
 500           </listitem>
 501         </varlistentry>
 502       </variablelist>
 503   </refsect1>
 504
 505   <refsect1>
 506     <title>[Route] Section Options</title>
 507       <para>The <literal>[Route]</literal> section accepts the
 508       following keys. Specify several <literal>[Route]</literal>
 509       sections to configure several routes.</para>
 510
 511       <variablelist class='network-directives'>
 512         <varlistentry>
 513           <term><varname>Gateway=</varname></term>
 514           <listitem>
 515             <para>As in the <literal>[Network]</literal> section.</para>
 516           </listitem>
 517         </varlistentry>
 518         <varlistentry>
 519           <term><varname>Destination=</varname></term>
 520           <listitem>
 521             <para>The destination prefix of the route. Possibly
 522             followed by a slash and the prefixlength. If omitted, a
 523             full-length host route is assumed.</para>
 524           </listitem>
 525         </varlistentry>
 526         <varlistentry>
 527           <term><varname>Source=</varname></term>
 528           <listitem>
 529             <para>The source prefix of the route. Possibly followed by
 530             a slash and the prefixlength. If omitted, a full-length
 531             host route is assumed.</para>
 532           </listitem>
 533         </varlistentry>
 534         <varlistentry>
 535           <term><varname>Metric=</varname></term>
 536           <listitem>
 537             <para>The metric of the route. An unsigned integer</para>
 538           </listitem>
 539         </varlistentry>
 540         <varlistentry>
 541           <term><varname>Scope=</varname></term>
 542           <listitem>
 543             <para>The scope of the route. One of the values <literal>global</literal>,
 544             <literal>link</literal> or <literal>host</literal>. Defaults to
 545             <literal>global</literal>.</para>
 546           </listitem>
 547         </varlistentry>
 548         <varlistentry>
 549           <term><varname>PreferredSource=</varname></term>
 550           <listitem>
 551             <para>The preferred source address of the route. The address
 552             must be in the format described in
 553             <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
 554           </listitem>
 555         </varlistentry>
 556       </variablelist>
 557   </refsect1>
 558
 559   <refsect1>
 560     <title>[DHCP] Section Options</title>
 561       <para>The <literal>[DHCP]</literal> section configures the
 562       DHCPv4 and DHCP6 client, if it is enabled with the
 563       <varname>DHCP=</varname> setting described above:</para>
 564
 565       <variablelist class='network-directives'>
 566         <varlistentry>
 567           <term><varname>UseDNS=</varname></term>
 568           <listitem>
 569             <para>When true (the default), the DNS servers received
 570             from the DHCP server will be used and take precedence over
 571             any statically configured ones.</para>
 572
 573             <para>This corresponds to the <option>nameserver</option>
 574             option in <citerefentry
 575             project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
 576           </listitem>
 577         </varlistentry>
 578         <varlistentry>
 579           <term><varname>UseNTP=</varname></term>
 580           <listitem>
 581             <para>When true (the default), the NTP servers received
 582             from the DHCP server will be used by systemd-timesyncd
 583             and take precedence over any statically configured ones.</para>
 584           </listitem>
 585         </varlistentry>
 586         <varlistentry>
 587           <term><varname>UseMTU=</varname></term>
 588           <listitem>
 589             <para>When true, the interface maximum transmission unit
 590             from the DHCP server will be used on the current link.
 591             Defaults to false.</para>
 592           </listitem>
 593         </varlistentry>
 594         <varlistentry>
 595           <term><varname>SendHostname=</varname></term>
 596           <listitem>
 597             <para>When true (the default), the machine's hostname will
 598             be sent to the DHCP server.</para>
 599           </listitem>
 600         </varlistentry>
 601         <varlistentry>
 602           <term><varname>UseHostname=</varname></term>
 603           <listitem>
 604             <para>When true (the default), the hostname received from
 605             the DHCP server will be set as the transient hostname of the system
 606             </para>
 607           </listitem>
 608         </varlistentry>
 609         <varlistentry>
 610         <term><varname>Hostname=</varname></term>
 611         <listitem>
 612           <para>Use this value for the hostname which is sent to the
 613           DHCP server, instead of machine's hostname.</para>
 614         </listitem>
 615       </varlistentry>
 616         <varlistentry>
 617           <term><varname>UseDomains=</varname></term>
 618           <listitem>
 619             <para>When true (not the default), the domain name
 620             received from the DHCP server will be used for DNS
 621             resolution over this link. When a name cannot be resolved
 622             as specified, the domain name will be used a suffix and
 623             name resolution of that will be attempted.</para>
 624
 625             <para>This corresponds to the <option>domain</option>
 626             option in <citerefentry project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 627             and should not be enabled on untrusted networks.</para>
 628           </listitem>
 629         </varlistentry>
 630         <varlistentry>
 631           <term><varname>UseRoutes=</varname></term>
 632           <listitem>
 633             <para>When true (the default), the static routes will be
 634             requested from the DHCP server and added to the routing
 635             table with metric of 1024.</para>
 636           </listitem>
 637         </varlistentry>
 638
 639         <varlistentry>
 640           <term><varname>UseTimezone=</varname></term>
 641
 642           <listitem><para>When true, the timezone received from the
 643           DHCP server will be set as as timezone of the local
 644           system. Defaults to <literal>no</literal>.</para></listitem>
 645         </varlistentry>
 646
 647         <varlistentry>
 648           <term><varname>CriticalConnection=</varname></term>
 649           <listitem>
 650             <para>When true, the connection will never be torn down
 651             even if the DHCP lease expires. This is contrary to the
 652             DHCP specification, but may be the best choice if, say,
 653             the root filesystem relies on this connection. Defaults to
 654             false.</para>
 655           </listitem>
 656         </varlistentry>
 657         <varlistentry>
 658           <term><varname>ClientIdentifier=</varname></term>
 659           <listitem>
 660             <para>DHCP client identifier to use. Either <literal>mac</literal>
 661             to use the MAC address of the link or <literal>duid</literal>
 662             (the default) to use a RFC4361-compliant Client ID.</para>
 663           </listitem>
 664         </varlistentry>
 665         <varlistentry>
 666           <term><varname>VendorClassIdentifier=</varname></term>
 667           <listitem>
 668             <para>The vendor class identifier used to identify vendor
 669             type and configuration.</para>
 670           </listitem>
 671         </varlistentry>
 672         <varlistentry>
 673           <term><varname>RequestBroadcast=</varname></term>
 674           <listitem>
 675             <para>Request the server to use broadcast messages before
 676             the IP address has been configured. This is necessary for
 677             devices that cannot receive RAW packets, or that cannot
 678             receive packets at all before an IP address has been
 679             configured. On the other hand, this must not be enabled on
 680             networks where broadcasts are filtered out.</para>
 681           </listitem>
 682         </varlistentry>
 683         <varlistentry>
 684           <term><varname>RouteMetric=</varname></term>
 685           <listitem>
 686             <para>Set the routing metric for routes specified by the
 687             DHCP server.</para>
 688           </listitem>
 689         </varlistentry>
 690       </variablelist>
 691
 692   </refsect1>
 693
 694   <refsect1>
 695     <title>[DHCPServer] Section Options</title>
 696     <para>The <literal>[DHCPServer]</literal> section contains
 697     settings for the DHCP server, if enabled via the
 698     <varname>DHCPServer=</varname> option described above:</para>
 699
 700     <variablelist class='network-directives'>
 701
 702       <varlistentry>
 703         <term><varname>PoolOffset=</varname></term>
 704         <term><varname>PoolSize=</varname></term>
 705
 706         <listitem><para>Configures the pool of addresses to hand out. The pool
 707         is a contiguous sequence of IP addresses in the subnet configured for
 708         the server address, which does not include the subnet nor the broadcast
 709         address. <varname>PoolOffset=</varname> takes the offset of the pool
 710         from the start of subnet, or zero to use the default value.
 711         <varname>PoolSize=</varname> takes the number of IP addresses in the
 712         pool or zero to use the default value. By default the pool starts at
 713         the first address after the subnet address and takes up the rest of
 714         the subnet, excluding the broadcast address. If the pool includes
 715         the server address (the default), this is reserved and not handed
 716         out to clients.</para></listitem>
 717       </varlistentry>
 718
 719       <varlistentry>
 720         <term><varname>DefaultLeaseTimeSec=</varname></term>
 721         <term><varname>MaxLeaseTimeSec=</varname></term>
 722
 723         <listitem><para>Control the default and maximum DHCP lease
 724         time to pass to clients. These settings take time values in seconds or
 725         another common time unit, depending on the suffix. The default
 726         lease time is used for clients that did not ask for a specific
 727         lease time. If a client asks for a lease time longer than the
 728         maximum lease time it is automatically shortened to the
 729         specified time. The default lease time defaults to 1h, the
 730         maximum lease time to 12h. Shorter lease times are beneficial
 731         if the configuration data in DHCP leases changes frequently
 732         and clients shall learn the new settings with shorter
 733         latencies. Longer lease times reduce the generated DHCP
 734         network traffic.</para></listitem>
 735       </varlistentry>
 736
 737       <varlistentry>
 738         <term><varname>EmitDNS=</varname></term>
 739         <term><varname>DNS=</varname></term>
 740
 741         <listitem><para>Configures whether the DHCP leases handed out
 742         to clients shall contain DNS server information. The
 743         <varname>EmitDNS=</varname> setting takes a boolean argument
 744         and defaults to <literal>yes</literal>. The DNS servers to
 745         pass to clients may be configured with the
 746         <varname>DNS=</varname> option, which takes a list of IPv4
 747         addresses. If the <varname>EmitDNS=</varname> option is
 748         enabled but no servers configured the servers are
 749         automatically propagated from an "uplink" interface that has
 750         appropriate servers set. The "uplink" interface is determined
 751         by the default route of the system with the highest
 752         priority. Note that this information is acquired at the time
 753         the lease is handed out, and does not take uplink interfaces
 754         into account that acquire DNS or NTP server information at a
 755         later point. DNS server propagation does not take
 756         <filename>/etc/resolv.conf</filename> into account. Also, note
 757         that the leases are not refreshed if uplink network
 758         configuration changes. To ensure clients regularly acquire the
 759         most current uplink DNS server information it is thus
 760         advisable to shorten the DHCP lease time via
 761         <varname>MaxLeaseTimeSec=</varname> described
 762         above.</para></listitem>
 763       </varlistentry>
 764
 765       <varlistentry>
 766         <term><varname>EmitNTP=</varname></term>
 767         <term><varname>NTP=</varname></term>
 768
 769         <listitem><para>Similar to the <varname>EmitDNS=</varname> and
 770         <varname>DNS=</varname> settings described above these
 771         settings configure whether and what NTP server information
 772         shall be emitted as part of the DHCP lease. The same syntax,
 773         propagation semantics and defaults apply as for
 774         <varname>EmitDNS=</varname> and
 775         <varname>DNS=</varname>.</para></listitem>
 776       </varlistentry>
 777
 778       <varlistentry>
 779         <term><varname>EmitTimezone=</varname></term>
 780         <term><varname>Timezone=</varname></term>
 781
 782         <listitem><para>Configures whether the DHCP leases handed out
 783         to clients shall contain timezone information. The
 784         <varname>EmitTimezone=</varname> setting takes a boolean
 785         argument and defaults to <literal>yes</literal>. The
 786         <varname>Timezone=</varname> setting takes a timezone string
 787         (such as <literal>Europe/Berlin</literal> or
 788         <literal>UTC</literal>) to pass to clients. If no explicit
 789         timezone is set the system timezone of the local host is
 790         propagated, as determined by the
 791         <filename>/etc/localtime</filename> symlink.</para></listitem>
 792       </varlistentry>
 793
 794     </variablelist>
 795   </refsect1>
 796
 797   <refsect1>
 798     <title>[Bridge] Section Options</title>
 799       <para>The <literal>[Bridge]</literal> section accepts the
 800       following keys.</para>
 801       <variablelist class='network-directives'>
 802         <varlistentry>
 803           <term><varname>UnicastFlood=</varname></term>
 804           <listitem>
 805             <para>A boolean. Controls whether the bridge should flood
 806             traffic for which an FDB entry is missing and the destination
 807             is unknown through this port. Defaults to on.
 808             </para>
 809           </listitem>
 810         </varlistentry>
 811         <varlistentry>
 812           <term><varname>HairPin=</varname></term>
 813           <listitem>
 814             <para>A boolean. Configures whether traffic may be sent back
 815             out of the port on which it was received. By default, this
 816             flag is false, and the bridge will not forward traffic back
 817             out of the receiving port.</para>
 818           </listitem>
 819         </varlistentry>
 820         <varlistentry>
 821           <term><varname>UseBPDU=</varname></term>
 822           <listitem>
 823             <para>A boolean. Configures whether STP Bridge Protocol Data Units will be
 824             processed by the bridge port. Defaults to yes.</para>
 825           </listitem>
 826         </varlistentry>
 827         <varlistentry>
 828           <term><varname>FastLeave=</varname></term>
 829           <listitem>
 830             <para>A boolean. This flag allows the bridge to immediately stop multicast
 831             traffic on a port that receives IGMP Leave message. It is only used with
 832             IGMP snooping if enabled on the bridge. Defaults to off.</para>
 833           </listitem>
 834         </varlistentry>
 835         <varlistentry>
 836           <term><varname>AllowPortToBeRoot=</varname></term>
 837           <listitem>
 838             <para>A boolean. Configures whether a given port is allowed to
 839             become a root port. Only used when STP is enabled on the bridge.
 840             Defaults to on.</para>
 841           </listitem>
 842         </varlistentry>
 843         <varlistentry>
 844           <term><varname>Cost=</varname></term>
 845           <listitem>
 846             <para>Sets the "cost" of sending packets of this interface.
 847             Each port in a bridge may have different speed and the cost
 848             is used to decide which link to use. Faster interfaces
 849             should have lower costs.</para>
 850           </listitem>
 851         </varlistentry>
 852       </variablelist>
 853   </refsect1>
 854   <refsect1>
 855     <title>[BridgeFDB] Section Options</title>
 856       <para>The <literal>[BridgeFDB]</literal> section manages the
 857       forwarding database table of a port and accepts the following
 858       keys. Specify several <literal>[BridgeFDB]</literal> sections to
 859       configure several static MAC table entries.</para>
 860
 861       <variablelist class='network-directives'>
 862         <varlistentry>
 863           <term><varname>MACAddress=</varname></term>
 864           <listitem>
 865             <para>As in the <literal>[Network]</literal> section. This
 866             key is mandatory.</para>
 867           </listitem>
 868         </varlistentry>
 869         <varlistentry>
 870           <term><varname>VLANId=</varname></term>
 871           <listitem>
 872             <para>The VLAN Id for the new static MAC table entry. If
 873             omitted, no VLAN Id info is appended to the new static MAC
 874             table entry.</para>
 875           </listitem>
 876         </varlistentry>
 877       </variablelist>
 878   </refsect1>
 879
 880   <refsect1>
 881     <title>Example</title>
 882     <example>
 883       <title>/etc/systemd/network/50-static.network</title>
 884
 885       <programlisting>[Match]
 886 Name=enp2s0
 887
 888 [Network]
 889 Address=192.168.0.15/24
 890 Gateway=192.168.0.1</programlisting>
 891     </example>
 892
 893     <example>
 894       <title>/etc/systemd/network/80-dhcp.network</title>
 895
 896       <programlisting>[Match]
 897 Name=en*
 898
 899 [Network]
 900 DHCP=yes</programlisting>
 901     </example>
 902
 903     <example>
 904       <title>/etc/systemd/network/25-bridge-static.network</title>
 905
 906       <programlisting>[Match]
 907 Name=bridge0
 908
 909 [Network]
 910 Address=192.168.0.15/24
 911 Gateway=192.168.0.1
 912 DNS=192.168.0.1</programlisting>
 913     </example>
 914
 915     <example>
 916       <title>/etc/systemd/network/25-bridge-slave-interface.network</title>
 917
 918       <programlisting>[Match]
 919 Name=enp2s0
 920
 921 [Network]
 922 Bridge=bridge0</programlisting>
 923     </example>
 924     <example>
 925       <title>/etc/systemd/network/25-ipip.network</title>
 926
 927       <programlisting>[Match]
 928 Name=em1
 929
 930 [Network]
 931 Tunnel=ipip-tun</programlisting>
 932     </example>
 933
 934     <example>
 935       <title>/etc/systemd/network/25-sit.network</title>
 936
 937       <programlisting>[Match]
 938 Name=em1
 939
 940 [Network]
 941 Tunnel=sit-tun</programlisting>
 942     </example>
 943
 944     <example>
 945       <title>/etc/systemd/network/25-gre.network</title>
 946
 947       <programlisting>[Match]
 948 Name=em1
 949
 950 [Network]
 951 Tunnel=gre-tun</programlisting>
 952     </example>
 953
 954     <example>
 955       <title>/etc/systemd/network/25-vti.network</title>
 956
 957       <programlisting>[Match]
 958 Name=em1
 959
 960 [Network]
 961 Tunnel=vti-tun</programlisting>
 962     </example>
 963
 964     <example>
 965       <title>/etc/systemd/network/25-bond.network</title>
 966
 967       <programlisting>[Match]
 968 Name=bond1
 969
 970 [Network]
 971 DHCP=yes
 972 </programlisting>
 973     </example>
 974
 975   </refsect1>
 976
 977   <refsect1>
 978     <title>See Also</title>
 979     <para>
 980       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 981       <citerefentry><refentrytitle>systemd-networkd</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 982       <citerefentry><refentrytitle>systemd.link</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 983       <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 984     </para>
 985   </refsect1>
 986
 987 </refentry>