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