man/systemd.network.xml

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  10   Copyright 2013 Tom Gundersen
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  25
  26 <refentry id="systemd.network" conditional='ENABLE_NETWORKD'>
  27
  28   <refentryinfo>
  29     <title>systemd.network</title>
  30     <productname>systemd</productname>
  31
  32     <authorgroup>
  33       <author>
  34         <contrib>Developer</contrib>
  35         <firstname>Tom</firstname>
  36         <surname>Gundersen</surname>
  37         <email>teg@jklm.no</email>
  38       </author>
  39     </authorgroup>
  40   </refentryinfo>
  41
  42   <refmeta>
  43     <refentrytitle>systemd.network</refentrytitle>
  44     <manvolnum>5</manvolnum>
  45   </refmeta>
  46
  47   <refnamediv>
  48     <refname>systemd.network</refname>
  49     <refpurpose>Network configuration</refpurpose>
  50   </refnamediv>
  51
  52   <refsynopsisdiv>
  53     <para><filename><replaceable>network</replaceable>.network</filename></para>
  54   </refsynopsisdiv>
  55
  56   <refsect1>
  57     <title>Description</title>
  58
  59     <para>Network setup is performed by
  60     <citerefentry><refentrytitle>systemd-networkd</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
  61     </para>
  62
  63     <para>The main network file must have the extension <filename>.network</filename>; other
  64     extensions are ignored. Networks are applied to links whenever the links appear.</para>
  65
  66     <para>The <filename>.network</filename> files are read from the files located in the system
  67     network directory <filename>/usr/lib/systemd/network</filename>, the volatile runtime network
  68     directory <filename>/run/systemd/network</filename> and the local administration network
  69     directory <filename>/etc/systemd/network</filename>. All configuration files are collectively
  70     sorted and processed in lexical order, regardless of the directories in which they live.
  71     However, files with identical filenames replace each other. Files in <filename>/etc</filename>
  72     have the highest priority, files in <filename>/run</filename> take precedence over files with
  73     the same name in <filename>/usr/lib</filename>. This can be used to override a system-supplied
  74     configuration file with a local file if needed. As a special case, an empty file (file size 0)
  75     or symlink with the same name pointing to <filename>/dev/null</filename> disables the
  76     configuration file entirely (it is "masked").</para>
  77
  78     <para>Along with the network file <filename>foo.network</filename>, a "drop-in" directory
  79     <filename>foo.network.d/</filename> may exist. All files with the suffix
  80     <literal>.conf</literal> from this directory will be parsed after the file itself is
  81     parsed. This is useful to alter or add configuration settings, without having to modify the main
  82     configuration file. Each drop-in file must have appropriate section headers.</para>
  83
  84     <para>In addition to <filename>/etc/systemd/network</filename>, drop-in <literal>.d</literal>
  85     directories can be placed in <filename>/usr/lib/systemd/network</filename> or
  86     <filename>/run/systemd/network</filename> directories. Drop-in files in
  87     <filename>/etc</filename> take precedence over those in <filename>/run</filename> which in turn
  88     take precedence over those in <filename>/usr/lib</filename>. Drop-in files under any of these
  89     directories take precedence over the main netdev file wherever located. (Of course, since
  90     <filename>/run</filename> is temporary and <filename>/usr/lib</filename> is for vendors, it is
  91     unlikely drop-ins should be used in either of those places.)</para>
  92
  93     <para>Note that an interface without any static IPv6 addresses configured, and neither DHCPv6
  94     nor IPv6LL enabled, shall be considered to have no IPv6 support. IPv6 will be automatically
  95     disabled for that interface by writing "1" to
  96     <filename>/proc/sys/net/ipv6/conf/<replaceable>ifname</replaceable>/disable_ipv6</filename>.
  97     </para>
  98   </refsect1>
  99
 100   <refsect1>
 101     <title>[Match] Section Options</title>
 102
 103       <para>The network file contains a <literal>[Match]</literal>
 104       section, which determines if a given network file may be applied
 105       to a given device; and a <literal>[Network]</literal> section
 106       specifying how the device should be configured. The first (in
 107       lexical order) of the network files that matches a given device
 108       is applied, all later files are ignored, even if they match as
 109       well.</para>
 110
 111       <para>A network file is said to match a device if each of the
 112       entries in the <literal>[Match]</literal> section matches, or if
 113       the section is empty. The following keys are accepted:</para>
 114
 115       <variablelist class='network-directives'>
 116         <varlistentry>
 117           <term><varname>MACAddress=</varname></term>
 118           <listitem>
 119             <para>The hardware address of the interface (use full colon-delimited hexadecimal, e.g.,
 120             01:23:45:67:89:ab).</para>
 121           </listitem>
 122         </varlistentry>
 123         <varlistentry>
 124           <term><varname>Path=</varname></term>
 125           <listitem>
 126             <para>A whitespace-separated list of shell-style globs
 127             matching the persistent path, as exposed by the udev
 128             property <literal>ID_PATH</literal>. If the list is
 129             prefixed with a "!", the test is inverted; i.e. it is
 130             true when <literal>ID_PATH</literal> does not match any
 131             item in the list.</para>
 132           </listitem>
 133         </varlistentry>
 134         <varlistentry>
 135           <term><varname>Driver=</varname></term>
 136           <listitem>
 137             <para>A whitespace-separated list of shell-style globs
 138             matching the driver currently bound to the device, as
 139             exposed by the udev property <literal>DRIVER</literal>
 140             of its parent device, or if that is not set the driver
 141             as exposed by <literal>ethtool -i</literal> of the
 142             device itself. If the list is prefixed with a "!", the
 143             test is inverted.</para>
 144           </listitem>
 145         </varlistentry>
 146         <varlistentry>
 147           <term><varname>Type=</varname></term>
 148           <listitem>
 149             <para>A whitespace-separated list of shell-style globs
 150             matching the device type, as exposed by the udev property
 151             <literal>DEVTYPE</literal>. If the list is prefixed with
 152             a "!", the test is inverted.</para>
 153           </listitem>
 154         </varlistentry>
 155         <varlistentry>
 156           <term><varname>Name=</varname></term>
 157           <listitem>
 158             <para>A whitespace-separated list of shell-style globs
 159             matching the device name, as exposed by the udev property
 160             <literal>INTERFACE</literal>. If the list is prefixed
 161             with a "!", the test is inverted.</para>
 162           </listitem>
 163         </varlistentry>
 164         <varlistentry>
 165           <term><varname>Host=</varname></term>
 166           <listitem>
 167             <para>Matches against the hostname or machine ID of the
 168             host. See <literal>ConditionHost=</literal> in
 169             <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 170             for details.
 171             </para>
 172           </listitem>
 173         </varlistentry>
 174         <varlistentry>
 175           <term><varname>Virtualization=</varname></term>
 176           <listitem>
 177             <para>Checks whether the system is executed in a virtualized
 178             environment and optionally test whether it is a specific
 179             implementation. See <literal>ConditionVirtualization=</literal> in
 180             <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 181             for details.
 182             </para>
 183           </listitem>
 184         </varlistentry>
 185         <varlistentry>
 186           <term><varname>KernelCommandLine=</varname></term>
 187           <listitem>
 188             <para>Checks whether a specific kernel command line option is
 189             set (or if prefixed with the exclamation mark unset). See
 190             <literal>ConditionKernelCommandLine=</literal> in
 191             <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 192             for details.
 193             </para>
 194           </listitem>
 195         </varlistentry>
 196         <varlistentry>
 197           <term><varname>KernelVersion=</varname></term>
 198           <listitem>
 199             <para>Checks whether the kernel version (as reported by <command>uname -r</command>) matches a certain
 200             expression (or if prefixed with the exclamation mark does not match it). See
 201             <literal>ConditionKernelVersion=</literal> in
 202             <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
 203             details.
 204             </para>
 205           </listitem>
 206         </varlistentry>
 207         <varlistentry>
 208           <term><varname>Architecture=</varname></term>
 209           <listitem>
 210             <para>Checks whether the system is running on a specific
 211             architecture. See <literal>ConditionArchitecture=</literal> in
 212             <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 213             for details.
 214             </para>
 215           </listitem>
 216         </varlistentry>
 217       </variablelist>
 218
 219   </refsect1>
 220
 221   <refsect1>
 222     <title>[Link] Section Options</title>
 223
 224     <para> The <literal>[Link]</literal> section accepts the following keys:</para>
 225
 226     <variablelist class='network-directives'>
 227       <varlistentry>
 228         <term><varname>MACAddress=</varname></term>
 229         <listitem>
 230           <para>The hardware address to set for the device.</para>
 231         </listitem>
 232       </varlistentry>
 233       <varlistentry>
 234         <term><varname>MTUBytes=</varname></term>
 235         <listitem>
 236           <para>The maximum transmission unit in bytes to set for the
 237           device. The usual suffixes K, M, G, are supported and are
 238           understood to the base of 1024.</para>
 239           <para>Note that if IPv6 is enabled on the interface, and the MTU is chosen
 240           below 1280 (the minimum MTU for IPv6) it will automatically be increased to this value.</para>
 241         </listitem>
 242       </varlistentry>
 243       <varlistentry>
 244         <term><varname>ARP=</varname></term>
 245         <listitem>
 246           <para> A boolean. Enables or disables the ARP (low-level Address Resolution Protocol)
 247           for this interface. Defaults to unset, which means that the kernel default will be used.</para>
 248           <para> For example, disabling ARP is useful when creating multiple MACVLAN or VLAN virtual
 249           interfaces atop a single lower-level physical interface, which will then only serve as a
 250           link/"bridge" device aggregating traffic to the same physical link and not participate in
 251           the network otherwise.</para>
 252         </listitem>
 253       </varlistentry>
 254       <varlistentry>
 255         <term><varname>Unmanaged=</varname></term>
 256         <listitem>
 257           <para>A boolean. When <literal>yes</literal>, no attempts are
 258           made to bring up or configure matching links, equivalent to
 259           when there are no matching network files. Defaults to
 260           <literal>no</literal>.</para>
 261           <para>This is useful for preventing later matching network
 262           files from interfering with certain interfaces that are fully
 263           controlled by other applications.</para>
 264         </listitem>
 265       </varlistentry>
 266       <varlistentry>
 267         <term><varname>RequiredForOnline=</varname></term>
 268         <listitem>
 269           <para>A boolean. When <literal>yes</literal>, the network is deemed
 270           required when determining whether the system is online when running
 271           <literal>systemd-networkd-wait-online</literal>.
 272           When <literal>no</literal>, the network is ignored when checking for
 273           online state. Defaults to <literal>yes</literal>.</para>
 274           <para>The network will be brought up normally in all cases, but in
 275           the event that there is no address being assigned by DHCP or the
 276           cable is not plugged in, the link will simply remain offline and be
 277           skipped automatically by <literal>systemd-networkd-wait-online</literal>
 278           if <literal>RequiredForOnline=true</literal>.</para>
 279         </listitem>
 280       </varlistentry>
 281     </variablelist>
 282   </refsect1>
 283
 284   <refsect1>
 285     <title>[Network] Section Options</title>
 286
 287       <para>The <literal>[Network]</literal> section accepts the following keys:</para>
 288
 289       <variablelist class='network-directives'>
 290         <varlistentry>
 291           <term><varname>Description=</varname></term>
 292           <listitem>
 293             <para>A description of the device. This is only used for
 294             presentation purposes.</para>
 295           </listitem>
 296         </varlistentry>
 297         <varlistentry>
 298           <term><varname>DHCP=</varname></term>
 299           <listitem>
 300             <para>Enables DHCPv4 and/or DHCPv6 client support. Accepts
 301             <literal>yes</literal>, <literal>no</literal>,
 302             <literal>ipv4</literal>, or <literal>ipv6</literal>. Defaults
 303             to <literal>no</literal>.</para>
 304
 305             <para>Note that DHCPv6 will by default be triggered by Router
 306             Advertisement, if that is enabled, regardless of this parameter.
 307             By enabling DHCPv6 support explicitly, the DHCPv6 client will
 308             be started regardless of the presence of routers on the link,
 309             or what flags the routers pass. See
 310             <literal>IPv6AcceptRA=</literal>.</para>
 311
 312             <para>Furthermore, note that by default the domain name
 313             specified through DHCP is not used for name resolution.
 314             See option <option>UseDomains=</option> below.</para>
 315
 316             <para>See the <literal>[DHCP]</literal> section below for further configuration options for the DHCP client
 317             support.</para>
 318           </listitem>
 319         </varlistentry>
 320         <varlistentry>
 321           <term><varname>DHCPServer=</varname></term>
 322           <listitem>
 323             <para>A boolean. Enables DHCPv4 server support. Defaults
 324             to <literal>no</literal>. Further settings for the DHCP
 325             server may be set in the <literal>[DHCPServer]</literal>
 326             section described below.</para>
 327           </listitem>
 328         </varlistentry>
 329         <varlistentry>
 330           <term><varname>LinkLocalAddressing=</varname></term>
 331           <listitem>
 332             <para>Enables link-local address autoconfiguration. Accepts
 333             <literal>yes</literal>, <literal>no</literal>,
 334             <literal>ipv4</literal>, or <literal>ipv6</literal>. Defaults to
 335             <literal>ipv6</literal>.</para>
 336           </listitem>
 337         </varlistentry>
 338         <varlistentry>
 339           <term><varname>IPv4LLRoute=</varname></term>
 340           <listitem>
 341             <para>A boolean. When true, sets up the route needed for
 342             non-IPv4LL hosts to communicate with IPv4LL-only hosts. Defaults
 343             to false.
 344             </para>
 345           </listitem>
 346         </varlistentry>
 347         <varlistentry>
 348           <term><varname>IPv6Token=</varname></term>
 349           <listitem>
 350             <para>An IPv6 address with the top 64 bits unset. When set, indicates the
 351             64-bit interface part of SLAAC IPv6 addresses for this link. Note that
 352             the token is only ever used for SLAAC, and not for DHCPv6 addresses, even
 353             in the case DHCP is requested by router advertisement. By default, the
 354             token is autogenerated.</para>
 355           </listitem>
 356         </varlistentry>
 357         <varlistentry>
 358           <term><varname>LLMNR=</varname></term>
 359           <listitem>
 360             <para>A boolean or <literal>resolve</literal>. When true,
 361             enables <ulink
 362             url="https://tools.ietf.org/html/rfc4795">Link-Local
 363             Multicast Name Resolution</ulink> on the link. When set to
 364             <literal>resolve</literal>, only resolution is enabled,
 365             but not host registration and announcement. Defaults to
 366             true. This setting is read by
 367             <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 368           </listitem>
 369         </varlistentry>
 370         <varlistentry>
 371           <term><varname>MulticastDNS=</varname></term>
 372           <listitem>
 373             <para>A boolean or <literal>resolve</literal>. When true,
 374             enables <ulink
 375             url="https://tools.ietf.org/html/rfc6762">Multicast
 376             DNS</ulink> support on the link. When set to
 377             <literal>resolve</literal>, only resolution is enabled,
 378             but not host or service registration and
 379             announcement. Defaults to false. This setting is read by
 380             <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 381           </listitem>
 382         </varlistentry>
 383         <varlistentry>
 384           <term><varname>DNSSEC=</varname></term>
 385           <listitem>
 386             <para>A boolean or
 387             <literal>allow-downgrade</literal>. When true, enables
 388             <ulink
 389             url="https://tools.ietf.org/html/rfc4033">DNSSEC</ulink>
 390             DNS validation support on the link. When set to
 391             <literal>allow-downgrade</literal>, compatibility with
 392             non-DNSSEC capable networks is increased, by automatically
 393             turning off DNSSEC in this case. This option defines a
 394             per-interface setting for
 395             <citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>'s
 396             global <varname>DNSSEC=</varname> option. Defaults to
 397             false. This setting is read by
 398             <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 399           </listitem>
 400         </varlistentry>
 401         <varlistentry>
 402           <term><varname>DNSSECNegativeTrustAnchors=</varname></term>
 403           <listitem><para>A space-separated list of DNSSEC negative
 404           trust anchor domains. If specified and DNSSEC is enabled,
 405           look-ups done via the interface's DNS server will be subject
 406           to the list of negative trust anchors, and not require
 407           authentication for the specified domains, or anything below
 408           it. Use this to disable DNSSEC authentication for specific
 409           private domains, that cannot be proven valid using the
 410           Internet DNS hierarchy. Defaults to the empty list. This
 411           setting is read by
 412           <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 413           </listitem>
 414         </varlistentry>
 415         <varlistentry>
 416           <term><varname>LLDP=</varname></term>
 417           <listitem>
 418             <para>Controls support for Ethernet LLDP packet reception. LLDP is a link-layer protocol commonly
 419             implemented on professional routers and bridges which announces which physical port a system is connected
 420             to, as well as other related data. Accepts a boolean or the special value
 421             <literal>routers-only</literal>. When true, incoming LLDP packets are accepted and a database of all LLDP
 422             neighbors maintained. If <literal>routers-only</literal> is set only LLDP data of various types of routers
 423             is collected and LLDP data about other types of devices ignored (such as stations, telephones and
 424             others). If false, LLDP reception is disabled. Defaults to <literal>routers-only</literal>. Use
 425             <citerefentry><refentrytitle>networkctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> to query the
 426             collected neighbor data. LLDP is only available on Ethernet links. See <varname>EmitLLDP=</varname> below
 427             for enabling LLDP packet emission from the local system.
 428             </para>
 429           </listitem>
 430         </varlistentry>
 431         <varlistentry>
 432           <term><varname>EmitLLDP=</varname></term>
 433           <listitem>
 434             <para>Controls support for Ethernet LLDP packet emission. Accepts a boolean parameter or the special values
 435             <literal>nearest-bridge</literal>, <literal>non-tpmr-bridge</literal> and
 436             <literal>customer-bridge</literal>.  Defaults to false, which turns off LLDP packet emission. If not false,
 437             a short LLDP packet with information about the local system is sent out in regular intervals on the
 438             link. The LLDP packet will contain information about the local host name, the local machine ID (as stored
 439             in <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>) and the
 440             local interface name, as well as the pretty hostname of the system (as set in
 441             <citerefentry><refentrytitle>machine-info</refentrytitle><manvolnum>5</manvolnum></citerefentry>). LLDP
 442             emission is only available on Ethernet links. Note that this setting passes data suitable for
 443             identification of host to the network and should thus not be enabled on untrusted networks, where such
 444             identification data should not be made available. Use this option to permit other systems to identify on
 445             which interfaces they are connected to this system. The three special values control propagation of the
 446             LLDP packets. The <literal>nearest-bridge</literal> setting permits propagation only to the nearest
 447             connected bridge, <literal>non-tpmr-bridge</literal> permits propagation across Two-Port MAC Relays, but
 448             not any other bridges, and <literal>customer-bridge</literal> permits propagation until a customer bridge
 449             is reached. For details about these concepts, see <ulink
 450             url="http://standards.ieee.org/getieee802/download/802.1AB-2009.pdf">IEEE 802.1AB-2009</ulink>. Note that
 451             configuring this setting to true is equivalent to <literal>nearest-bridge</literal>, the recommended and
 452             most restricted level of propagation. See <varname>LLDP=</varname> above for an option to enable LLDP
 453             reception.</para>
 454           </listitem>
 455         </varlistentry>
 456         <varlistentry>
 457           <term><varname>BindCarrier=</varname></term>
 458           <listitem>
 459             <para>A link name or a list of link names. When set, controls the behavior of the current
 460             link. When all links in the list are in an operational down state, the current link is brought
 461             down. When at least one link has carrier, the current interface is brought up.
 462             </para>
 463           </listitem>
 464         </varlistentry>
 465         <varlistentry>
 466           <term><varname>Address=</varname></term>
 467           <listitem>
 468             <para>A static IPv4 or IPv6 address and its prefix length,
 469             separated by a <literal>/</literal> character. Specify
 470             this key more than once to configure several addresses.
 471             The format of the address must be as described in
 472             <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 473             This is a short-hand for an [Address] section only
 474             containing an Address key (see below). This option may be
 475             specified more than once.
 476             </para>
 477
 478             <para>If the specified address is 0.0.0.0 (for IPv4) or
 479             [::] (for IPv6), a new address range of the requested size
 480             is automatically allocated from a system-wide pool of
 481             unused ranges. The allocated range is checked against all
 482             current network interfaces and all known network
 483             configuration files to avoid address range conflicts. The
 484             default system-wide pool consists of 192.168.0.0/16,
 485             172.16.0.0/12 and 10.0.0.0/8 for IPv4, and fc00::/7 for
 486             IPv6. This functionality is useful to manage a large
 487             number of dynamically created network interfaces with the
 488             same network configuration and automatic address range
 489             assignment.</para>
 490
 491           </listitem>
 492         </varlistentry>
 493         <varlistentry>
 494           <term><varname>Gateway=</varname></term>
 495           <listitem>
 496             <para>The gateway address, which must be in the format
 497             described in
 498             <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 499             This is a short-hand for a [Route] section only containing
 500             a Gateway key. This option may be specified more than
 501             once.</para>
 502           </listitem>
 503         </varlistentry>
 504         <varlistentry>
 505           <term><varname>DNS=</varname></term>
 506           <listitem>
 507             <para>A DNS server address, which must be in the format
 508             described in
 509             <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 510             This option may be specified more than once. This setting is read by
 511             <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 512           </listitem>
 513         </varlistentry>
 514         <varlistentry>
 515           <term><varname>Domains=</varname></term>
 516           <listitem>
 517             <para>A list of domains which should be resolved using the DNS servers on this link. Each item in the list
 518             should be a domain name, optionally prefixed with a tilde (<literal>~</literal>). The domains with the
 519             prefix are called "routing-only domains". The domains without the prefix are called "search domains" and
 520             are first used as search suffixes for extending single-label host names (host names containing no dots) to
 521             become fully qualified domain names (FQDNs). If a single-label host name is resolved on this interface,
 522             each of the specified search domains are appended to it in turn, converting it into a fully qualified
 523             domain name, until one of them may be successfully resolved.</para>
 524
 525             <para>Both "search" and "routing-only" domains are used for routing of DNS queries: look-ups for host names
 526             ending in those domains (hence also single label names, if any "search domains" are listed), are routed to
 527             the DNS servers configured for this interface. The domain routing logic is particularly useful on
 528             multi-homed hosts with DNS servers serving particular private DNS zones on each interface.</para>
 529
 530             <para>The "routing-only" domain <literal>~.</literal> (the tilde indicating definition of a routing domain,
 531             the dot referring to the DNS root domain which is the implied suffix of all valid DNS names) has special
 532             effect. It causes all DNS traffic which does not match another configured domain routing entry to be routed
 533             to DNS servers specified for this interface. This setting is useful to prefer a certain set of DNS servers
 534             if a link on which they are connected is available.</para>
 535
 536             <para>This setting is read by
 537             <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
 538             "Search domains" correspond to the <varname>domain</varname> and <varname>search</varname> entries in
 539             <citerefentry project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 540             Domain name routing has no equivalent in the traditional glibc API, which has no concept of domain
 541             name servers limited to a specific link.</para>
 542           </listitem>
 543         </varlistentry>
 544         <varlistentry>
 545           <term><varname>NTP=</varname></term>
 546           <listitem>
 547             <para>An NTP server address. This option may be specified more than once. This setting is read by
 548             <citerefentry><refentrytitle>systemd-timesyncd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 549           </listitem>
 550         </varlistentry>
 551         <varlistentry>
 552           <term><varname>IPForward=</varname></term>
 553           <listitem><para>Configures IP packet forwarding for the
 554           system. If enabled, incoming packets on any network
 555           interface will be forwarded to any other interfaces
 556           according to the routing table. Takes either a boolean
 557           argument, or the values <literal>ipv4</literal> or
 558           <literal>ipv6</literal>, which only enable IP packet
 559           forwarding for the specified address family.  This controls
 560           the <filename>net.ipv4.ip_forward</filename> and
 561           <filename>net.ipv6.conf.all.forwarding</filename> sysctl
 562           options of the network interface (see <ulink
 563           url="https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt">ip-sysctl.txt</ulink>
 564           for details about sysctl options). Defaults to
 565           <literal>no</literal>.</para>
 566
 567           <para>Note: this setting controls a global kernel option,
 568           and does so one way only: if a network that has this setting
 569           enabled is set up the global setting is turned on.  However,
 570           it is never turned off again, even after all networks with
 571           this setting enabled are shut down again.</para>
 572
 573           <para>To allow IP packet forwarding only between specific
 574           network interfaces use a firewall.</para>
 575           </listitem>
 576         </varlistentry>
 577         <varlistentry>
 578           <term><varname>IPMasquerade=</varname></term>
 579           <listitem><para>Configures IP masquerading for the network
 580           interface. If enabled, packets forwarded from the network
 581           interface will be appear as coming from the local host.
 582           Takes a boolean argument. Implies
 583           <varname>IPForward=ipv4</varname>. Defaults to
 584           <literal>no</literal>.</para></listitem>
 585         </varlistentry>
 586         <varlistentry>
 587           <term><varname>IPv6PrivacyExtensions=</varname></term>
 588           <listitem><para>Configures use of stateless temporary
 589           addresses that change over time (see <ulink
 590           url="https://tools.ietf.org/html/rfc4941">RFC 4941</ulink>,
 591           Privacy Extensions for Stateless Address Autoconfiguration
 592           in IPv6). Takes a boolean or the special values
 593           <literal>prefer-public</literal> and
 594           <literal>kernel</literal>. When true, enables the privacy
 595           extensions and prefers temporary addresses over public
 596           addresses. When <literal>prefer-public</literal>, enables the
 597           privacy extensions, but prefers public addresses over
 598           temporary addresses. When false, the privacy extensions
 599           remain disabled. When <literal>kernel</literal>, the kernel's
 600           default setting will be left in place.  Defaults to
 601           <literal>no</literal>.</para></listitem>
 602         </varlistentry>
 603         <varlistentry>
 604           <term><varname>IPv6AcceptRA=</varname></term>
 605           <listitem><para>Enable or disable IPv6 Router Advertisement (RA) reception support for the interface.  Takes
 606           a boolean parameter. If true, RAs are accepted; if false, RAs are ignored, independently of the local
 607           forwarding state. When not set, the kernel default is used, and RAs are accepted only when local forwarding
 608           is disabled for that interface.  When RAs are accepted, they may trigger the start of the DHCPv6 client if
 609           the relevant flags are set in the RA data, or if no routers are found on the link.</para>
 610
 611           <para>Further settings for the IPv6 RA support may be configured in the
 612           <literal>[IPv6AcceptRA]</literal> section, see below.</para>
 613
 614           <para>Also see <ulink
 615           url="https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt">ip-sysctl.txt</ulink> in the kernel
 616           documentation regarding <literal>accept_ra</literal>, but note that systemd's setting of
 617           <constant>1</constant> (i.e. true) corresponds to kernel's setting of <constant>2</constant>.</para>
 618         </listitem>
 619         </varlistentry>
 620         <varlistentry>
 621           <term><varname>IPv6DuplicateAddressDetection=</varname></term>
 622           <listitem><para>Configures the amount of IPv6 Duplicate
 623           Address Detection (DAD) probes to send. Defaults to unset.
 624         </para></listitem>
 625         </varlistentry>
 626         <varlistentry>
 627           <term><varname>IPv6HopLimit=</varname></term>
 628           <listitem><para>Configures IPv6 Hop Limit. For each router that
 629           forwards the packet, the hop limit is decremented by 1. When the
 630           hop limit field reaches zero, the packet is discarded.
 631           Defaults to unset.
 632         </para></listitem>
 633         </varlistentry>
 634         <varlistentry>
 635           <term><varname>IPv4ProxyARP=</varname></term>
 636           <listitem><para>A boolean. Configures proxy ARP for IPv4. Proxy ARP is the technique in which one host,
 637           usually a router, answers ARP requests intended for another machine. By "faking" its identity,
 638           the router accepts responsibility for routing packets to the "real" destination. (see <ulink
 639           url="https://tools.ietf.org/html/rfc1027">RFC 1027</ulink>.
 640           Defaults to unset.
 641         </para></listitem>
 642         </varlistentry>
 643         <varlistentry>
 644           <term><varname>IPv6ProxyNDP=</varname></term>
 645           <listitem><para>A boolean. Configures proxy NDP for IPv6. Proxy NDP (Neighbor Discovery
 646           Protocol) is a technique for IPv6 to allow routing of addresses to a different
 647           destination when peers expect them to be present on a certain physical link.
 648           In this case a router answers Neighbour Advertisement messages intended for
 649           another machine by offering its own MAC address as destination.
 650           Unlike proxy ARP for IPv4, it is not enabled globally, but will only send Neighbour
 651           Advertisement messages for addresses in the IPv6 neighbor proxy table,
 652           which can also be shown by <command>ip -6 neighbour show proxy</command>.
 653           systemd-networkd will control the per-interface `proxy_ndp` switch for each configured
 654           interface depending on this option.
 655           Defautls to unset.
 656         </para></listitem>
 657         </varlistentry>
 658         <varlistentry>
 659           <term><varname>IPv6ProxyNDPAddress=</varname></term>
 660           <listitem><para>An IPv6 address, for which Neighbour Advertisement messages will be
 661           proxied. This option may be specified more than once. systemd-networkd will add the
 662           <option>IPv6ProxyNDPAddress=</option> entries to the kernel's IPv6 neighbor proxy table.
 663           This option implies <option>IPv6ProxyNDP=true</option> but has no effect if
 664           <option>IPv6ProxyNDP</option> has been set to false. Defaults to unset.
 665         </para></listitem>
 666         </varlistentry>
 667         <varlistentry>
 668           <term><varname>IPv6PrefixDelegation=</varname></term>
 669           <listitem><para>Whether to enable or disable Router Advertisement sending on a link.
 670           Defaults to <literal>false</literal>. See the <literal>[IPv6PrefixDelegation]</literal>
 671           and the <literal>[IPv6Prefix]</literal> sections for configuration options.
 672           </para></listitem>
 673         </varlistentry>
 674         <varlistentry>
 675           <term><varname>Bridge=</varname></term>
 676           <listitem>
 677             <para>The name of the bridge to add the link to. See
 678             <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 679             </para>
 680           </listitem>
 681         </varlistentry>
 682         <varlistentry>
 683           <term><varname>Bond=</varname></term>
 684           <listitem>
 685             <para>The name of the bond to add the link to. See
 686             <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 687             </para>
 688           </listitem>
 689         </varlistentry>
 690         <varlistentry>
 691           <term><varname>VRF=</varname></term>
 692           <listitem>
 693             <para>The name of the VRF to add the link to. See
 694             <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 695             </para>
 696           </listitem>
 697         </varlistentry>
 698         <varlistentry>
 699           <term><varname>VLAN=</varname></term>
 700           <listitem>
 701             <para>The name of a VLAN to create on the link. See
 702             <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 703             This option may be specified more than once.</para>
 704           </listitem>
 705         </varlistentry>
 706         <varlistentry>
 707           <term><varname>MACVLAN=</varname></term>
 708           <listitem>
 709             <para>The name of a MACVLAN to create on the link. See
 710             <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 711             This option may be specified more than once.</para>
 712           </listitem>
 713         </varlistentry>
 714         <varlistentry>
 715           <term><varname>VXLAN=</varname></term>
 716           <listitem>
 717             <para>The name of a VXLAN to create on the link. See
 718             <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 719             This option may be specified more than once.</para>
 720           </listitem>
 721         </varlistentry>
 722         <varlistentry>
 723           <term><varname>Tunnel=</varname></term>
 724           <listitem>
 725             <para>The name of a Tunnel to create on the link. See
 726             <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 727             This option may be specified more than once.</para>
 728           </listitem>
 729         </varlistentry>
 730       <varlistentry>
 731         <term><varname>ActiveSlave=</varname></term>
 732         <listitem>
 733           <para>A boolean. Specifies the new active slave. The <literal>ActiveSlave=</literal>
 734           option is only valid for following modes:
 735           <literal>active-backup</literal>,
 736           <literal>balance-alb</literal> and
 737           <literal>balance-tlb</literal>. Defaults to false.
 738           </para>
 739         </listitem>
 740       </varlistentry>
 741       <varlistentry>
 742         <term><varname>PrimarySlave=</varname></term>
 743         <listitem>
 744           <para>A boolean. Specifies which slave is the primary device. The specified
 745           device will always be the active slave while it is available. Only when the
 746           primary is off-line will alternate devices be used.  This is useful when
 747           one slave is preferred over another, e.g. when one slave has higher throughput
 748           than another. The <literal>PrimarySlave=</literal> option is only valid for
 749           following modes:
 750           <literal>active-backup</literal>,
 751           <literal>balance-alb</literal> and
 752           <literal>balance-tlb</literal>. Defaults to false.
 753           </para>
 754         </listitem>
 755       </varlistentry>
 756       <varlistentry>
 757         <term><varname>ConfigureWithoutCarrier=</varname></term>
 758         <listitem>
 759           <para>A boolean. Allows networkd to configure a specific link even if it has no carrier.
 760           Defaults to false.
 761           </para>
 762         </listitem>
 763       </varlistentry>
 764       </variablelist>
 765
 766   </refsect1>
 767
 768   <refsect1>
 769     <title>[Address] Section Options</title>
 770
 771       <para>An <literal>[Address]</literal> section accepts the
 772       following keys. Specify several <literal>[Address]</literal>
 773       sections to configure several addresses.</para>
 774
 775       <variablelist class='network-directives'>
 776         <varlistentry>
 777           <term><varname>Address=</varname></term>
 778           <listitem>
 779             <para>As in the <literal>[Network]</literal> section. This
 780             key is mandatory.</para>
 781           </listitem>
 782         </varlistentry>
 783         <varlistentry>
 784           <term><varname>Peer=</varname></term>
 785           <listitem>
 786             <para>The peer address in a point-to-point connection.
 787             Accepts the same format as the <literal>Address</literal>
 788             key.</para>
 789           </listitem>
 790         </varlistentry>
 791         <varlistentry>
 792           <term><varname>Broadcast=</varname></term>
 793           <listitem>
 794             <para>The broadcast address, which must be in the format
 795             described in
 796             <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 797             This key only applies to IPv4 addresses. If it is not
 798             given, it is derived from the <literal>Address</literal>
 799             key.</para>
 800           </listitem>
 801         </varlistentry>
 802         <varlistentry>
 803           <term><varname>Label=</varname></term>
 804           <listitem>
 805             <para>An address label.</para>
 806           </listitem>
 807         </varlistentry>
 808         <varlistentry>
 809           <term><varname>PreferredLifetime=</varname></term>
 810           <listitem>
 811             <para>Allows the default "preferred lifetime" of the address to be overridden.
 812             Only three settings are accepted: <literal>forever</literal> or <literal>infinity</literal>
 813             which is the default and means that the address never expires, and <literal>0</literal> which means
 814             that the address is considered immediately "expired" and will not be used,
 815             unless explicitly requested. A setting of PreferredLifetime=0 is useful for
 816             addresses which are added to be used only by a specific application,
 817             which is then configured to use them explicitly.</para>
 818           </listitem>
 819         </varlistentry>
 820         <varlistentry>
 821           <term><varname>Scope=</varname></term>
 822           <listitem>
 823             <para>The scope of the address, which can be <literal>global</literal>,
 824             <literal>link</literal> or <literal>host</literal> or an unsigned integer ranges 0 to 255.
 825             Defaults to <literal>global</literal>.</para>
 826           </listitem>
 827         </varlistentry>
 828         <varlistentry>
 829           <term><varname>HomeAddress=</varname></term>
 830           <listitem>
 831             <para>Takes a boolean argument. Designates this address the "home address" as defined in
 832             <ulink url="https://tools.ietf.org/html/rfc6275">RFC 6275</ulink>.
 833             Supported only on IPv6. Defaults to false.</para>
 834           </listitem>
 835         </varlistentry>
 836         <varlistentry>
 837           <term><varname>DuplicateAddressDetection=</varname></term>
 838           <listitem>
 839             <para>Takes a boolean argument. Do not perform Duplicate Address Detection
 840             <ulink url="https://tools.ietf.org/html/rfc4862">RFC 4862</ulink> when adding this address.
 841             Supported only on IPv6. Defaults to false.</para>
 842           </listitem>
 843         </varlistentry>
 844         <varlistentry>
 845           <term><varname>ManageTemporaryAddress=</varname></term>
 846           <listitem>
 847             <para>Takes a boolean argument. If true the kernel manage temporary addresses created
 848             from this one as template on behalf of Privacy Extensions
 849             <ulink url="https://tools.ietf.org/html/rfc3041">RFC 3041</ulink>.  For this to become
 850             active, the use_tempaddr sysctl setting has to be set to a value greater than zero.
 851             The given address needs to have a prefix length of 64. This flag allows to use privacy
 852             extensions in a manually configured network, just like if stateless auto-configuration
 853             was active. Defaults to false. </para>
 854           </listitem>
 855         </varlistentry>
 856         <varlistentry>
 857           <term><varname>PrefixRoute=</varname></term>
 858           <listitem>
 859             <para>Takes a boolean argument. When adding or modifying an IPv6 address, the userspace
 860             application needs a way to suppress adding a prefix route. This is for example relevant
 861             together with IFA_F_MANAGERTEMPADDR, where userspace creates autoconf generated addresses,
 862             but depending on on-link, no route for the prefix should be added. Defaults to false.</para>
 863           </listitem>
 864         </varlistentry>
 865         <varlistentry>
 866           <term><varname>AutoJoin=</varname></term>
 867           <listitem>
 868             <para>Takes a boolean argument. Joining multicast group on ethernet level via
 869             <command>ip maddr</command> command would not work if we have an Ethernet switch that does
 870             IGMP snooping since the switch would not replicate multicast packets on  ports that did not
 871             have IGMP reports for the multicast addresses. Linux vxlan interfaces created via
 872             <command>ip link add vxlan</command> or networkd's netdev kind vxlan have the group option
 873             that enables then to do the required join. By extending ip address command with option
 874             <literal>autojoin</literal> we can get similar functionality for openvswitch (OVS) vxlan
 875             interfaces as well as other tunneling mechanisms that need to receive multicast traffic.
 876             Defaults to <literal>no</literal>.</para>
 877           </listitem>
 878         </varlistentry>
 879       </variablelist>
 880   </refsect1>
 881
 882     <refsect1>
 883     <title>[IPv6AddressLabel] Section Options</title>
 884
 885       <para>An <literal>[IPv6AddressLabel]</literal> section accepts the
 886       following keys. Specify several <literal>[IPv6AddressLabel]</literal>
 887       sections to configure several address labels. IPv6 address labels are
 888       used for address selection. See <ulink url="https://tools.ietf.org/html/rfc3484">RFC 3484</ulink>.
 889       Precedence is managed by userspace, and only the label itself is stored in the kernel</para>
 890
 891       <variablelist class='network-directives'>
 892         <varlistentry>
 893           <term><varname>Label=</varname></term>
 894           <listitem>
 895             <para> The label for the prefix (an unsigned integer) ranges 0 to 4294967294.
 896             0xffffffff is reserved. This key is mandatory.</para>
 897           </listitem>
 898         </varlistentry>
 899         <varlistentry>
 900           <term><varname>Prefix=</varname></term>
 901           <listitem>
 902             <para>IPv6 prefix is an address with a prefix length, separated by a slash <literal>/</literal> character.
 903             This key is mandatory. </para>
 904           </listitem>
 905         </varlistentry>
 906       </variablelist>
 907   </refsect1>
 908
 909  <refsect1>
 910     <title>[RoutingPolicyRule] Section Options</title>
 911
 912       <para>An <literal>[RoutingPolicyRule]</literal> section accepts the
 913       following keys. Specify several <literal>[RoutingPolicyRule]</literal>
 914       sections to configure several rules.</para>
 915
 916       <variablelist class='network-directives'>
 917         <varlistentry>
 918           <term><varname>TypeOfService=</varname></term>
 919           <listitem>
 920             <para>Specifies the type of service to match a number between 0 to 255.</para>
 921           </listitem>
 922         </varlistentry>
 923         <varlistentry>
 924           <term><varname>From=</varname></term>
 925           <listitem>
 926             <para>Specifies the source address prefix to match. Possibly followed by a slash and the prefix length.</para>
 927           </listitem>
 928         </varlistentry>
 929         <varlistentry>
 930           <term><varname>To=</varname></term>
 931           <listitem>
 932             <para>Specifies the destination address prefix to match. Possibly followed by a slash and the prefix length.</para>
 933           </listitem>
 934         </varlistentry>
 935         <varlistentry>
 936           <term><varname>FirewallMark=</varname></term>
 937           <listitem>
 938             <para>Specifies the iptables firewall mark value to match (a number between 1 and 4294967295).</para>
 939           </listitem>
 940         </varlistentry>
 941         <varlistentry>
 942           <term><varname>Table=</varname></term>
 943           <listitem>
 944             <para>Specifies the routing table identifier to lookup if the rule
 945             selector matches. The table identifier for a route (a number between 1 and 4294967295).</para>
 946           </listitem>
 947         </varlistentry>
 948         <varlistentry>
 949           <term><varname>Priority=</varname></term>
 950           <listitem>
 951             <para>Specifies the priority of this rule. <varname>Priority=</varname> is an unsigned
 952             integer. Higher number means lower priority, and rules get processed in order of increasing number.</para>
 953           </listitem>
 954         </varlistentry>
 955         <varlistentry>
 956           <term><varname>IncomingInterface=</varname></term>
 957           <listitem>
 958             <para>Specifies incoming device to match. If the interface is loopback, the rule only matches packets originating from this host.</para>
 959           </listitem>
 960         </varlistentry>
 961         <varlistentry>
 962           <term><varname>OutgoingInterface=</varname></term>
 963           <listitem>
 964             <para>Specifies the outgoing device to match. The outgoing interface is only available for packets originating from local sockets that are bound to a device.</para>
 965           </listitem>
 966         </varlistentry>
 967       </variablelist>
 968   </refsect1>
 969
 970   <refsect1>
 971     <title>[Route] Section Options</title>
 972       <para>The <literal>[Route]</literal> section accepts the
 973       following keys. Specify several <literal>[Route]</literal>
 974       sections to configure several routes.</para>
 975
 976       <variablelist class='network-directives'>
 977         <varlistentry>
 978           <term><varname>Gateway=</varname></term>
 979           <listitem>
 980             <para>As in the <literal>[Network]</literal> section.</para>
 981           </listitem>
 982         </varlistentry>
 983          <varlistentry>
 984            <term><varname>GatewayOnlink=</varname></term>
 985            <listitem>
 986              <para>The <literal>GatewayOnlink</literal> option tells the kernel that it does not have
 987              to check if the gateway is reachable directly by the current machine (i.e., the kernel does
 988              not need to check if the gateway is attached to the local network), so that we can insert the
 989              route in the kernel table without it being complained about. A boolean, defaults to <literal>no</literal>.
 990              </para>
 991            </listitem>
 992          </varlistentry>
 993         <varlistentry>
 994           <term><varname>Destination=</varname></term>
 995           <listitem>
 996             <para>The destination prefix of the route. Possibly
 997             followed by a slash and the prefix length. If omitted, a
 998             full-length host route is assumed.</para>
 999           </listitem>
1000         </varlistentry>
1001         <varlistentry>
1002           <term><varname>Source=</varname></term>
1003           <listitem>
1004             <para>The source prefix of the route. Possibly followed by
1005             a slash and the prefix length. If omitted, a full-length
1006             host route is assumed.</para>
1007           </listitem>
1008         </varlistentry>
1009         <varlistentry>
1010           <term><varname>Metric=</varname></term>
1011           <listitem>
1012             <para>The metric of the route (an unsigned integer).</para>
1013           </listitem>
1014         </varlistentry>
1015         <varlistentry>
1016           <term><varname>IPv6Preference=</varname></term>
1017           <listitem>
1018             <para>Specifies the route preference as defined in <ulink
1019             url="https://tools.ietf.org/html/rfc4191">RFC4191</ulink> for Router Discovery messages.
1020             Which can be one of <literal>low</literal> the route has a lowest priority,
1021             <literal>medium</literal> the route has a default priority or
1022             <literal>high</literal> the route has a highest priority.</para>
1023           </listitem>
1024         </varlistentry>
1025         <varlistentry>
1026           <term><varname>Scope=</varname></term>
1027           <listitem>
1028             <para>The scope of the route, which can be <literal>global</literal>,
1029             <literal>link</literal> or <literal>host</literal>. Defaults to
1030             <literal>global</literal>.</para>
1031           </listitem>
1032         </varlistentry>
1033         <varlistentry>
1034           <term><varname>PreferredSource=</varname></term>
1035           <listitem>
1036             <para>The preferred source address of the route. The address
1037             must be in the format described in
1038             <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
1039           </listitem>
1040         </varlistentry>
1041         <varlistentry>
1042           <term><varname>Table=<replaceable>num</replaceable></varname></term>
1043           <listitem>
1044           <para>The table identifier for the route (a number between 1 and 4294967295, or 0 to unset).
1045           The table can be retrieved using <command>ip route show table <replaceable>num</replaceable></command>.
1046           </para>
1047           </listitem>
1048         </varlistentry>
1049         <varlistentry>
1050           <term><varname>Protocol=</varname></term>
1051           <listitem>
1052             <para>The Protocol identifier for the route. Takes a number between 0 and 255 or the special values
1053             <literal>kernel</literal>, <literal>boot</literal> and <literal>static</literal>. Defaults to
1054             <literal>static</literal>.
1055             </para>
1056           </listitem>
1057         </varlistentry>
1058         <varlistentry>
1059           <term><varname>Type=</varname></term>
1060           <listitem>
1061             <para>The Type identifier for special route types, which can be
1062             <literal>unicast</literal> route to a destination network address which describes the path to the destination,
1063             <literal>blackhole</literal> packets are discarded silently,
1064             <literal>unreachable</literal> packets are discarded and the ICMP message host unreachable is generated,
1065             <literal>prohibit</literal> packets are discarded and the ICMP message communication administratively
1066             prohibited is generated. Defaults to <literal>unicast</literal>.
1067             </para>
1068           </listitem>
1069         </varlistentry>
1070         <varlistentry>
1071           <term><varname>InitialCongestionWindow=</varname></term>
1072           <listitem>
1073             <para>The TCP initial congestion window or <literal>InitialCongestionWindow</literal>  is used during the start
1074             of a TCP connection. During the start of a TCP session, when a client requests for a resource, the server's initial congestion window
1075             determines how many data packets will be sent during the initial burst of data. Takes a number between between 1 and 4294967295 (2^32 - 1).
1076             Defaults to unset.
1077             </para>
1078           </listitem>
1079         </varlistentry>
1080         <varlistentry>
1081           <term><varname>InitialAdvertisedReceiveWindow=</varname></term>
1082           <listitem>
1083             <para>The TCP receive window size or <literal>InitialAdvertisedReceiveWindow</literal> is the amount of receive data (in bytes)
1084             that can be buffered at one time on a connection. The sending host can send only that amount of data before waiting for
1085             an acknowledgment and window update from the receiving host. Takes a number between 1 and 4294967295 (2^32 - 1). Defaults to unset.
1086             </para>
1087           </listitem>
1088         </varlistentry>
1089
1090       </variablelist>
1091   </refsect1>
1092
1093   <refsect1>
1094     <title>[DHCP] Section Options</title>
1095       <para>The <literal>[DHCP]</literal> section configures the
1096       DHCPv4 and DHCP6 client, if it is enabled with the
1097       <varname>DHCP=</varname> setting described above:</para>
1098
1099       <variablelist class='network-directives'>
1100         <varlistentry>
1101           <term><varname>UseDNS=</varname></term>
1102           <listitem>
1103             <para>When true (the default), the DNS servers received
1104             from the DHCP server will be used and take precedence over
1105             any statically configured ones.</para>
1106
1107             <para>This corresponds to the <option>nameserver</option>
1108             option in <citerefentry
1109             project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
1110           </listitem>
1111         </varlistentry>
1112         <varlistentry>
1113           <term><varname>UseNTP=</varname></term>
1114           <listitem>
1115             <para>When true (the default), the NTP servers received
1116             from the DHCP server will be used by systemd-timesyncd
1117             and take precedence over any statically configured ones.</para>
1118           </listitem>
1119         </varlistentry>
1120         <varlistentry>
1121           <term><varname>UseMTU=</varname></term>
1122           <listitem>
1123             <para>When true, the interface maximum transmission unit
1124             from the DHCP server will be used on the current link.
1125             Defaults to false.</para>
1126           </listitem>
1127         </varlistentry>
1128         <varlistentry>
1129           <term><varname>Anonymize=</varname></term>
1130           <listitem>
1131             <para>Takes a boolean argument. When true, the options sent to the DHCP server will
1132             follow the <ulink url="https://tools.ietf.org/html/rfc7844">RFC 7844</ulink>
1133             (Anonymity Profiles for DHCP Clients) to minimize disclosure of identifying information.
1134             Defaults to false.</para>
1135
1136             <para>This option should only be set to true when
1137             <varname>MACAddressPolicy=</varname> is set to <literal>random</literal>
1138             (see <citerefentry
1139             project='man-pages'><refentrytitle>systemd.link</refentrytitle><manvolnum>5</manvolnum></citerefentry>).</para>
1140
1141             <para>Note that this configuration will overwrite others.
1142             In concrete, the following variables will be ignored:
1143             <varname>SendHostname=</varname>, <varname>ClientIdentifier=</varname>,
1144             <varname>UseRoutes=</varname>, <varname>SendHostname=</varname>,
1145             <varname>UseMTU=</varname>, <varname>VendorClassIdentifier=</varname>,
1146             <varname>UseTimezone=</varname>.</para>
1147           </listitem>
1148         </varlistentry>
1149         <varlistentry>
1150           <term><varname>SendHostname=</varname></term>
1151           <listitem>
1152             <para>When true (the default), the machine's hostname will
1153             be sent to the DHCP server.</para>
1154           </listitem>
1155         </varlistentry>
1156         <varlistentry>
1157           <term><varname>UseHostname=</varname></term>
1158           <listitem>
1159             <para>When true (the default), the hostname received from
1160             the DHCP server will be set as the transient hostname of the system
1161             </para>
1162           </listitem>
1163         </varlistentry>
1164         <varlistentry>
1165         <term><varname>Hostname=</varname></term>
1166         <listitem>
1167           <para>Use this value for the hostname which is sent to the
1168           DHCP server, instead of machine's hostname.</para>
1169         </listitem>
1170       </varlistentry>
1171         <varlistentry>
1172           <term><varname>UseDomains=</varname></term>
1173           <listitem>
1174             <para>Takes a boolean argument, or the special value <literal>route</literal>. When true, the domain name
1175             received from the DHCP server will be used as DNS search domain over this link, similar to the effect of
1176             the <option>Domains=</option> setting. If set to <literal>route</literal>, the domain name received from
1177             the DHCP server will be used for routing DNS queries only, but not for searching, similar to the effect of
1178             the <option>Domains=</option> setting when the argument is prefixed with <literal>~</literal>. Defaults to
1179             false.</para>
1180
1181             <para>It is recommended to enable this option only on trusted networks, as setting this affects resolution
1182             of all host names, in particular of single-label names. It is generally safer to use the supplied domain
1183             only as routing domain, rather than as search domain, in order to not have it affect local resolution of
1184             single-label names.</para>
1185
1186             <para>When set to true, this setting corresponds to the <option>domain</option> option in <citerefentry
1187             project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
1188           </listitem>
1189         </varlistentry>
1190         <varlistentry>
1191           <term><varname>UseRoutes=</varname></term>
1192           <listitem>
1193             <para>When true (the default), the static routes will be requested from the DHCP server and added to the
1194               routing table with a metric of 1024, and a scope of "global", "link" or "host", depending on the route's
1195               destination and gateway. If the destination is on the local host, e.g., 127.x.x.x, or the same as the
1196               link's own address, the scope will be set to "host". Otherwise if the gateway is null (a direct route), a
1197               "link" scope will be used. For anything else, scope defaults to "global".</para>
1198           </listitem>
1199         </varlistentry>
1200
1201         <varlistentry>
1202           <term><varname>UseTimezone=</varname></term>
1203
1204           <listitem><para>When true, the timezone received from the
1205           DHCP server will be set as timezone of the local
1206           system. Defaults to <literal>no</literal>.</para></listitem>
1207         </varlistentry>
1208
1209         <varlistentry>
1210           <term><varname>CriticalConnection=</varname></term>
1211           <listitem>
1212             <para>When true, the connection will never be torn down
1213             even if the DHCP lease expires. This is contrary to the
1214             DHCP specification, but may be the best choice if, say,
1215             the root filesystem relies on this connection. Defaults to
1216             false.</para>
1217           </listitem>
1218         </varlistentry>
1219
1220         <varlistentry>
1221           <term><varname>ClientIdentifier=</varname></term>
1222           <listitem>
1223             <para>The DHCPv4 client identifier to use. Either <literal>mac</literal> to use the MAC address of the link
1224             or <literal>duid</literal> (the default, see below) to use an RFC4361-compliant Client ID.</para>
1225           </listitem>
1226         </varlistentry>
1227
1228         <varlistentry>
1229           <term><varname>VendorClassIdentifier=</varname></term>
1230           <listitem>
1231             <para>The vendor class identifier used to identify vendor
1232             type and configuration.</para>
1233           </listitem>
1234         </varlistentry>
1235
1236         <varlistentry>
1237           <term><varname>DUIDType=</varname></term>
1238           <listitem>
1239             <para>Override the global <varname>DUIDType</varname> setting for this network. See
1240             <citerefentry><refentrytitle>networkd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1241             for a description of possible values.</para>
1242           </listitem>
1243         </varlistentry>
1244
1245         <varlistentry>
1246           <term><varname>DUIDRawData=</varname></term>
1247           <listitem>
1248             <para>Override the global <varname>DUIDRawData</varname> setting for this network. See
1249             <citerefentry><refentrytitle>networkd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1250             for a description of possible values.</para>
1251           </listitem>
1252         </varlistentry>
1253
1254         <varlistentry>
1255           <term><varname>IAID=</varname></term>
1256           <listitem>
1257             <para>The DHCP Identity Association Identifier (IAID) for the interface, a 32-bit unsigned integer.</para>
1258           </listitem>
1259         </varlistentry>
1260
1261         <varlistentry>
1262           <term><varname>RequestBroadcast=</varname></term>
1263           <listitem>
1264             <para>Request the server to use broadcast messages before
1265             the IP address has been configured. This is necessary for
1266             devices that cannot receive RAW packets, or that cannot
1267             receive packets at all before an IP address has been
1268             configured. On the other hand, this must not be enabled on
1269             networks where broadcasts are filtered out.</para>
1270           </listitem>
1271         </varlistentry>
1272
1273         <varlistentry>
1274           <term><varname>RouteMetric=</varname></term>
1275           <listitem>
1276             <para>Set the routing metric for routes specified by the
1277             DHCP server.</para>
1278           </listitem>
1279         </varlistentry>
1280
1281         <varlistentry>
1282           <term><varname>RouteTable=<replaceable>num</replaceable></varname></term>
1283           <listitem>
1284             <para>The table identifier for DHCP routes (a number between 1 and 4294967295, or 0 to unset).
1285             The table can be retrieved using <command>ip route show table <replaceable>num</replaceable></command>.
1286             </para>
1287             <para>When used in combination with <varname>VRF=</varname> the
1288             VRF's routing table is used unless this parameter is specified.
1289             </para>
1290           </listitem>
1291         </varlistentry>
1292
1293         <varlistentry>
1294           <term><varname>ListenPort=</varname></term>
1295           <listitem>
1296             <para>Allow setting custom port for the DHCP client to listen on.</para>
1297           </listitem>
1298         </varlistentry>
1299       </variablelist>
1300     </refsect1>
1301
1302   <refsect1>
1303     <title>[IPv6AcceptRA] Section Options</title>
1304       <para>The <literal>[IPv6AcceptRA]</literal> section configures the IPv6 Router Advertisement
1305       (RA) client, if it is enabled with the <varname>IPv6AcceptRA=</varname> setting described
1306       above:</para>
1307
1308       <variablelist class='network-directives'>
1309         <varlistentry>
1310           <term><varname>UseDNS=</varname></term>
1311           <listitem>
1312             <para>When true (the default), the DNS servers received in the Router Advertisement will be used and take
1313             precedence over any statically configured ones.</para>
1314
1315             <para>This corresponds to the <option>nameserver</option> option in <citerefentry
1316             project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
1317           </listitem>
1318         </varlistentry>
1319
1320         <varlistentry>
1321           <term><varname>UseDomains=</varname></term>
1322           <listitem>
1323             <para>Takes a boolean argument, or the special value <literal>route</literal>. When true, the domain name
1324             received via IPv6 Router Advertisement (RA) will be used as DNS search domain over this link, similar to
1325             the effect of the <option>Domains=</option> setting. If set to <literal>route</literal>, the domain name
1326             received via IPv6 RA will be used for routing DNS queries only, but not for searching, similar to the
1327             effect of the <option>Domains=</option> setting when the argument is prefixed with
1328             <literal>~</literal>. Defaults to false.</para>
1329
1330             <para>It is recommended to enable this option only on trusted networks, as setting this affects resolution
1331             of all host names, in particular of single-label names. It is generally safer to use the supplied domain
1332             only as routing domain, rather than as search domain, in order to not have it affect local resolution of
1333             single-label names.</para>
1334
1335             <para>When set to true, this setting corresponds to the <option>domain</option> option in <citerefentry
1336             project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
1337           </listitem>
1338         </varlistentry>
1339
1340         <varlistentry>
1341           <term><varname>RouteTable=<replaceable>num</replaceable></varname></term>
1342           <listitem>
1343             <para>The table identifier for the routes received in the Router Advertisement
1344             (a number between 1 and 4294967295, or 0 to unset).
1345             The table can be retrieved using <command>ip route show table <replaceable>num</replaceable></command>.
1346             </para>
1347           </listitem>
1348         </varlistentry>
1349       </variablelist>
1350   </refsect1>
1351
1352
1353   <refsect1>
1354     <title>[DHCPServer] Section Options</title>
1355     <para>The <literal>[DHCPServer]</literal> section contains
1356     settings for the DHCP server, if enabled via the
1357     <varname>DHCPServer=</varname> option described above:</para>
1358
1359     <variablelist class='network-directives'>
1360
1361       <varlistentry>
1362         <term><varname>PoolOffset=</varname></term>
1363         <term><varname>PoolSize=</varname></term>
1364
1365         <listitem><para>Configures the pool of addresses to hand out. The pool
1366         is a contiguous sequence of IP addresses in the subnet configured for
1367         the server address, which does not include the subnet nor the broadcast
1368         address. <varname>PoolOffset=</varname> takes the offset of the pool
1369         from the start of subnet, or zero to use the default value.
1370         <varname>PoolSize=</varname> takes the number of IP addresses in the
1371         pool or zero to use the default value. By default, the pool starts at
1372         the first address after the subnet address and takes up the rest of
1373         the subnet, excluding the broadcast address. If the pool includes
1374         the server address (the default), this is reserved and not handed
1375         out to clients.</para></listitem>
1376       </varlistentry>
1377
1378       <varlistentry>
1379         <term><varname>DefaultLeaseTimeSec=</varname></term>
1380         <term><varname>MaxLeaseTimeSec=</varname></term>
1381
1382         <listitem><para>Control the default and maximum DHCP lease
1383         time to pass to clients. These settings take time values in seconds or
1384         another common time unit, depending on the suffix. The default
1385         lease time is used for clients that did not ask for a specific
1386         lease time. If a client asks for a lease time longer than the
1387         maximum lease time, it is automatically shortened to the
1388         specified time. The default lease time defaults to 1h, the
1389         maximum lease time to 12h. Shorter lease times are beneficial
1390         if the configuration data in DHCP leases changes frequently
1391         and clients shall learn the new settings with shorter
1392         latencies. Longer lease times reduce the generated DHCP
1393         network traffic.</para></listitem>
1394       </varlistentry>
1395
1396       <varlistentry>
1397         <term><varname>EmitDNS=</varname></term>
1398         <term><varname>DNS=</varname></term>
1399
1400         <listitem><para>Configures whether the DHCP leases handed out
1401         to clients shall contain DNS server information. The
1402         <varname>EmitDNS=</varname> setting takes a boolean argument
1403         and defaults to <literal>yes</literal>. The DNS servers to
1404         pass to clients may be configured with the
1405         <varname>DNS=</varname> option, which takes a list of IPv4
1406         addresses. If the <varname>EmitDNS=</varname> option is
1407         enabled but no servers configured, the servers are
1408         automatically propagated from an "uplink" interface that has
1409         appropriate servers set. The "uplink" interface is determined
1410         by the default route of the system with the highest
1411         priority. Note that this information is acquired at the time
1412         the lease is handed out, and does not take uplink interfaces
1413         into account that acquire DNS or NTP server information at a
1414         later point. DNS server propagation does not take
1415         <filename>/etc/resolv.conf</filename> into account. Also, note
1416         that the leases are not refreshed if the uplink network
1417         configuration changes. To ensure clients regularly acquire the
1418         most current uplink DNS server information, it is thus
1419         advisable to shorten the DHCP lease time via
1420         <varname>MaxLeaseTimeSec=</varname> described
1421         above.</para></listitem>
1422       </varlistentry>
1423
1424       <varlistentry>
1425         <term><varname>EmitNTP=</varname></term>
1426         <term><varname>NTP=</varname></term>
1427
1428         <listitem><para>Similar to the <varname>EmitDNS=</varname> and
1429         <varname>DNS=</varname> settings described above, these
1430         settings configure whether and what NTP server information
1431         shall be emitted as part of the DHCP lease. The same syntax,
1432         propagation semantics and defaults apply as for
1433         <varname>EmitDNS=</varname> and
1434         <varname>DNS=</varname>.</para></listitem>
1435       </varlistentry>
1436
1437       <varlistentry>
1438         <term><varname>EmitRouter=</varname></term>
1439
1440         <listitem><para>Similar to the <varname>EmitDNS=</varname>
1441         setting described above, this setting configures whether the
1442         DHCP lease should contain the router option. The same syntax,
1443         propagation semantics and defaults apply as for
1444         <varname>EmitDNS=</varname>.</para></listitem>
1445       </varlistentry>
1446
1447       <varlistentry>
1448         <term><varname>EmitTimezone=</varname></term>
1449         <term><varname>Timezone=</varname></term>
1450
1451         <listitem><para>Configures whether the DHCP leases handed out
1452         to clients shall contain timezone information. The
1453         <varname>EmitTimezone=</varname> setting takes a boolean
1454         argument and defaults to <literal>yes</literal>. The
1455         <varname>Timezone=</varname> setting takes a timezone string
1456         (such as <literal>Europe/Berlin</literal> or
1457         <literal>UTC</literal>) to pass to clients. If no explicit
1458         timezone is set, the system timezone of the local host is
1459         propagated, as determined by the
1460         <filename>/etc/localtime</filename> symlink.</para></listitem>
1461       </varlistentry>
1462
1463     </variablelist>
1464   </refsect1>
1465
1466   <refsect1>
1467     <title>[IPv6PrefixDelegation] Section Options</title>
1468     <para>The <literal>[IPv6PrefixDelegation]</literal> section contains
1469     settings for sending IPv6 Router Advertisements and whether to act as
1470     a router, if enabled via the <varname>IPv6PrefixDelegation=</varname>
1471     option described above. IPv6 network prefixes are defined with one or
1472     more <literal>[IPv6Prefix]</literal> sections.</para>
1473
1474     <variablelist class='network-directives'>
1475
1476       <varlistentry>
1477         <term><varname>Managed=</varname></term>
1478         <term><varname>OtherInformation=</varname></term>
1479
1480         <listitem><para>Controls whether a DHCPv6 server is used to acquire IPv6
1481         addresses on the network link when <varname>Managed=</varname> boolean
1482         is set to <literal>true</literal> or if only additional network
1483         information can be obtained via DHCPv6 for the network link when
1484         <varname>OtherInformation=</varname> boolean is set to
1485         <literal>true</literal>. Both settings default to
1486         <literal>false</literal>, which means that a DHCPv6 server is not being
1487         used.</para></listitem>
1488       </varlistentry>
1489
1490       <varlistentry>
1491         <term><varname>RouterLifetimeSec=</varname></term>
1492
1493         <listitem><para>Configures the IPv6 router lifetime in seconds. If set,
1494         this host also announces itself in Router Advertisements as an IPv6
1495         router for the network link. Defaults to unset, which means the host is
1496         not acting as a router.</para>
1497         </listitem>
1498       </varlistentry>
1499
1500       <varlistentry>
1501         <term><varname>RouterPreference=</varname></term>
1502
1503         <listitem><para>Configures IPv6 router preference if
1504         <varname>RouterLifetimeSec=</varname> is non-zero. Valid values are
1505         <literal>high</literal>, <literal>medium</literal> and
1506         <literal>low</literal>, with <literal>normal</literal> and
1507         <literal>default</literal> added as synonyms for
1508         <literal>medium</literal> just to make configuration easier. See
1509         <ulink url="https://tools.ietf.org/html/rfc4191">RFC 4191</ulink>
1510         for details. Defaults to <literal>medium</literal>.</para></listitem>
1511       </varlistentry>
1512
1513       <varlistentry>
1514         <term><varname>EmitDNS=</varname></term>
1515         <term><varname>DNS=</varname></term>
1516
1517         <listitem><para><varname>DNS=</varname> specifies a list of recursive
1518         DNS server IPv6 addresses that distributed via Router Advertisement
1519         messages when <varname>EmitDNS=</varname> is true. If <varname>DNS=
1520         </varname> is empty, DNS servers are read from the
1521         <literal>[Network]</literal> section. If the
1522         <literal>[Network]</literal> section does not contain any DNS servers
1523         either, DNS servers from the uplink with the highest priority default
1524         route are used. When <varname>EmitDNS=</varname> is false, no DNS server
1525         information is sent in Router Advertisement messages.
1526         <varname>EmitDNS=</varname> defaults to true.
1527         </para></listitem>
1528       </varlistentry>
1529
1530       <varlistentry>
1531         <term><varname>EmitDomains=</varname></term>
1532         <term><varname>Domains=</varname></term>
1533
1534         <listitem><para>A list of DNS search domains distributed via Router
1535         Advertisement messages when <varname>EmitDomains=</varname> is true. If
1536         <varname>Domains=</varname> is empty, DNS search domains are read from the
1537         <literal>[Network]</literal> section. If the <literal>[Network]</literal>
1538         section does not contain any DNS search domains either, DNS search
1539         domains from the uplink with the highest priority default route are
1540         used. When <varname>EmitDomains=</varname> is false, no DNS search domain
1541         information is sent in Router Advertisement messages.
1542         <varname>EmitDomains=</varname> defaults to true.
1543         </para></listitem>
1544       </varlistentry>
1545
1546       <varlistentry>
1547         <term><varname>DNSLifetimeSec=</varname></term>
1548
1549         <listitem><para>Lifetime in seconds for the DNS server addresses listed
1550         in <varname>DNS=</varname> and search domains listed in
1551         <varname>Domains=</varname>.</para></listitem>
1552       </varlistentry>
1553
1554     </variablelist>
1555     </refsect1>
1556
1557       <refsect1>
1558     <title>[IPv6Prefix] Section Options</title>
1559     <para>One or more <literal>[IPv6Prefix]</literal> sections contain the IPv6
1560     prefixes that are announced via Router Advertisements. See
1561     <ulink url="https://tools.ietf.org/html/rfc4861">RFC 4861</ulink>
1562     for further details.</para>
1563
1564     <variablelist class='network-directives'>
1565
1566       <varlistentry>
1567         <term><varname>AddressAutoconfiguration=</varname></term>
1568         <term><varname>OnLink=</varname></term>
1569
1570         <listitem><para>Boolean values to specify whether IPv6 addresses can be
1571         autoconfigured with this prefix and whether the prefix can be used for
1572         onlink determination. Both settings default to <literal>true</literal>
1573         in order to ease configuration.
1574         </para></listitem>
1575       </varlistentry>
1576
1577       <varlistentry>
1578         <term><varname>Prefix=</varname></term>
1579
1580         <listitem><para>The IPv6 prefix that is to be distributed to hosts.
1581         Similarly to configuring static IPv6 addresses, the setting is
1582         configured as an IPv6 prefix and its prefix length, separated by a
1583         <literal>/</literal> character. Use multiple
1584         <literal>[IPv6Prefix]</literal> sections to configure multiple IPv6
1585         prefixes since prefix lifetimes, address autoconfiguration and onlink
1586         status may differ from one prefix to another.</para></listitem>
1587       </varlistentry>
1588
1589       <varlistentry>
1590         <term><varname>PreferredLifetimeSec=</varname></term>
1591         <term><varname>ValidLifetimeSec=</varname></term>
1592
1593         <listitem><para>Preferred and valid lifetimes for the prefix measured in
1594         seconds. <varname>PreferredLifetimeSec=</varname> defaults to 604800
1595         seconds (one week) and <varname>ValidLifetimeSec=</varname> defaults
1596         to 2592000 seconds (30 days).</para></listitem>
1597       </varlistentry>
1598
1599     </variablelist>
1600     </refsect1>
1601
1602     <refsect1>
1603     <title>[Bridge] Section Options</title>
1604       <para>The <literal>[Bridge]</literal> section accepts the
1605       following keys.</para>
1606       <variablelist class='network-directives'>
1607         <varlistentry>
1608           <term><varname>UnicastFlood=</varname></term>
1609           <listitem>
1610             <para>A boolean. Controls whether the bridge should flood
1611             traffic for which an FDB entry is missing and the destination
1612             is unknown through this port. Defaults to on.
1613             </para>
1614           </listitem>
1615         </varlistentry>
1616         <varlistentry>
1617           <term><varname>HairPin=</varname></term>
1618           <listitem>
1619             <para>A boolean. Configures whether traffic may be sent back
1620             out of the port on which it was received. By default, this
1621             flag is false, and the bridge will not forward traffic back
1622             out of the receiving port.</para>
1623           </listitem>
1624         </varlistentry>
1625         <varlistentry>
1626           <term><varname>UseBPDU=</varname></term>
1627           <listitem>
1628             <para>A boolean. Configures whether STP Bridge Protocol Data Units will be
1629             processed by the bridge port. Defaults to yes.</para>
1630           </listitem>
1631         </varlistentry>
1632         <varlistentry>
1633           <term><varname>FastLeave=</varname></term>
1634           <listitem>
1635             <para>A boolean. This flag allows the bridge to immediately stop multicast
1636             traffic on a port that receives an IGMP Leave message. It is only used with
1637             IGMP snooping if enabled on the bridge. Defaults to off.</para>
1638           </listitem>
1639         </varlistentry>
1640         <varlistentry>
1641           <term><varname>AllowPortToBeRoot=</varname></term>
1642           <listitem>
1643             <para>A boolean. Configures whether a given port is allowed to
1644             become a root port. Only used when STP is enabled on the bridge.
1645             Defaults to on.</para>
1646           </listitem>
1647         </varlistentry>
1648         <varlistentry>
1649           <term><varname>Cost=</varname></term>
1650           <listitem>
1651             <para>Sets the "cost" of sending packets of this interface.
1652             Each port in a bridge may have a different speed and the cost
1653             is used to decide which link to use. Faster interfaces
1654             should have lower costs. It is an integer value between 1 and
1655             65535.</para>
1656           </listitem>
1657         </varlistentry>
1658         <varlistentry>
1659           <term><varname>Priority=</varname></term>
1660           <listitem>
1661             <para>Sets the "priority" of sending packets on this interface.
1662             Each port in a bridge may have a different priority which is used
1663             to decide which link to use. Lower value means higher priority.
1664             It is an integer value between 0 to 63. Networkd does not set any
1665             default, meaning the kernel default value of 32 is used.</para>
1666           </listitem>
1667         </varlistentry>
1668       </variablelist>
1669   </refsect1>
1670   <refsect1>
1671     <title>[BridgeFDB] Section Options</title>
1672       <para>The <literal>[BridgeFDB]</literal> section manages the
1673       forwarding database table of a port and accepts the following
1674       keys. Specify several <literal>[BridgeFDB]</literal> sections to
1675       configure several static MAC table entries.</para>
1676
1677       <variablelist class='network-directives'>
1678         <varlistentry>
1679           <term><varname>MACAddress=</varname></term>
1680           <listitem>
1681             <para>As in the <literal>[Network]</literal> section. This
1682             key is mandatory.</para>
1683           </listitem>
1684         </varlistentry>
1685         <varlistentry>
1686           <term><varname>VLANId=</varname></term>
1687           <listitem>
1688             <para>The VLAN ID for the new static MAC table entry. If
1689             omitted, no VLAN ID information is appended to the new static MAC
1690             table entry.</para>
1691           </listitem>
1692         </varlistentry>
1693       </variablelist>
1694   </refsect1>
1695   <refsect1>
1696     <title>[BridgeVLAN] Section Options</title>
1697       <para>The <literal>[BridgeVLAN]</literal> section manages the VLAN ID configuration of a bridge port and accepts
1698       the following keys. Specify several <literal>[BridgeVLAN]</literal> sections to configure several VLAN entries.
1699       The <varname>VLANFiltering=</varname> option has to be enabled, see <literal>[Bridge]</literal> section in
1700       <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
1701
1702       <variablelist class='network-directives'>
1703         <varlistentry>
1704           <term><varname>VLAN=</varname></term>
1705           <listitem>
1706             <para>The VLAN ID allowed on the port. This can be either a single ID or a range M-N. VLAN IDs are valid
1707             from 1 to 4094.</para>
1708           </listitem>
1709         </varlistentry>
1710         <varlistentry>
1711           <term><varname>EgressUntagged=</varname></term>
1712           <listitem>
1713             <para>The VLAN ID specified here will be used to untag frames on egress. Configuring
1714             <varname>EgressUntagged=</varname> implicates the use of <varname>VLAN=</varname> above and will enable the
1715             VLAN ID for ingress as well. This can be either a single ID or a range M-N.</para>
1716           </listitem>
1717         </varlistentry>
1718         <varlistentry>
1719           <term><varname>PVID=</varname></term>
1720           <listitem>
1721             <para>The Port VLAN ID specified here is assigned to all untagged frames at ingress.
1722             <varname>PVID=</varname> can be used only once. Configuring <varname>PVID=</varname> implicates the use of
1723             <varname>VLAN=</varname> above and will enable the VLAN ID for ingress as well.</para>
1724           </listitem>
1725         </varlistentry>
1726       </variablelist>
1727   </refsect1>
1728
1729   <refsect1>
1730     <title>Examples</title>
1731     <example>
1732       <title>Static network configuration</title>
1733
1734       <programlisting># /etc/systemd/network/50-static.network
1735 [Match]
1736 Name=enp2s0
1737
1738 [Network]
1739 Address=192.168.0.15/24
1740 Gateway=192.168.0.1</programlisting>
1741
1742       <para>This brings interface <literal>enp2s0</literal> up with a static address. The
1743       specified gateway will be used for a default route.</para>
1744     </example>
1745
1746     <example>
1747       <title>DHCP on ethernet links</title>
1748
1749       <programlisting># /etc/systemd/network/80-dhcp.network
1750 [Match]
1751 Name=en*
1752
1753 [Network]
1754 DHCP=yes</programlisting>
1755
1756       <para>This will enable DHCPv4 and DHCPv6 on all interfaces with names starting with
1757       <literal>en</literal> (i.e. ethernet interfaces).</para>
1758     </example>
1759
1760     <example>
1761       <title>A bridge with two enslaved links</title>
1762
1763       <programlisting># /etc/systemd/network/25-bridge-static.network
1764 [Match]
1765 Name=bridge0
1766
1767 [Network]
1768 Address=192.168.0.15/24
1769 Gateway=192.168.0.1
1770 DNS=192.168.0.1</programlisting>
1771
1772       <programlisting># /etc/systemd/network/25-bridge-slave-interface-1.network
1773 [Match]
1774 Name=enp2s0
1775
1776 [Network]
1777 Bridge=bridge0</programlisting>
1778
1779       <programlisting># /etc/systemd/network/25-bridge-slave-interface-2.network
1780 [Match]
1781 Name=wlp3s0
1782
1783 [Network]
1784 Bridge=bridge0</programlisting>
1785
1786       <para>This creates a bridge and attaches devices <literal>enp2s0</literal> and
1787       <literal>wlp3s0</literal> to it. The bridge will have the specified static address
1788       and network assigned, and a default route via the specified gateway will be
1789       added. The specified DNS server will be added to the global list of DNS resolvers.
1790       </para>
1791     </example>
1792
1793     <example>
1794       <title></title>
1795
1796       <programlisting>
1797 # /etc/systemd/network/20-bridge-slave-interface-vlan.network
1798 [Match]
1799 Name=enp2s0
1800
1801 [Network]
1802 Bridge=bridge0
1803
1804 [BridgeVLAN]
1805 VLAN=1-32
1806 PVID=42
1807 EgressUntagged=42
1808
1809 [BridgeVLAN]
1810 VLAN=100-200
1811
1812 [BridgeVLAN]
1813 EgressUntagged=300-400</programlisting>
1814
1815     <para>This overrides the configuration specified in the previous example for the
1816     interface <literal>enp2s0</literal>, and enables VLAN on that bridge port. VLAN IDs
1817     1-32, 42, 100-400 will be allowed. Packets tagged with VLAN IDs 42, 300-400 will be
1818     untagged when they leave on this interface. Untagged packets which arrive on this
1819     interface will be assigned VLAN ID 42.</para>
1820     </example>
1821
1822     <example>
1823       <title>Various tunnels</title>
1824
1825       <programlisting>/etc/systemd/network/25-tunnels.network
1826 [Match]
1827 Name=ens1
1828
1829 [Network]
1830 Tunnel=ipip-tun
1831 Tunnel=sit-tun
1832 Tunnel=gre-tun
1833 Tunnel=vti-tun
1834       </programlisting>
1835
1836       <programlisting>/etc/systemd/network/25-tunnel-ipip.netdev
1837 [NetDev]
1838 Name=ipip-tun
1839 Kind=ipip
1840       </programlisting>
1841
1842       <programlisting>/etc/systemd/network/25-tunnel-sit.netdev
1843 [NetDev]
1844 Name=sit-tun
1845 Kind=sit
1846       </programlisting>
1847
1848       <programlisting>/etc/systemd/network/25-tunnel-gre.netdev
1849 [NetDev]
1850 Name=gre-tun
1851 Kind=gre
1852       </programlisting>
1853
1854       <programlisting>/etc/systemd/network/25-tunnel-vti.netdev
1855 [NetDev]
1856 Name=vti-tun
1857 Kind=vti
1858       </programlisting>
1859
1860       <para>This will bring interface <literal>ens1</literal> up and create an IPIP tunnel,
1861       a SIT tunnel, a GRE tunnel, and a VTI tunnel using it.</para>
1862     </example>
1863
1864     <example>
1865       <title>A bond device</title>
1866
1867       <programlisting># /etc/systemd/network/30-bond1.network
1868 [Match]
1869 Name=bond1
1870
1871 [Network]
1872 DHCP=ipv6
1873 </programlisting>
1874
1875       <programlisting># /etc/systemd/network/30-bond1.netdev
1876 [NetDev]
1877 Name=bond1
1878 Kind=bond
1879 </programlisting>
1880
1881       <programlisting># /etc/systemd/network/30-bond1-dev1.network
1882 [Match]
1883 MACAddress=52:54:00:e9:64:41
1884
1885 [Network]
1886 Bond=bond1
1887 </programlisting>
1888
1889       <programlisting># /etc/systemd/network/30-bond1-dev2.network
1890 [Match]
1891 MACAddress=52:54:00:e9:64:42
1892
1893 [Network]
1894 Bond=bond1
1895 </programlisting>
1896
1897     <para>This will create a bond device <literal>bond1</literal> and enslave the two
1898     devices with MAC addresses 52:54:00:e9:64:41 and 52:54:00:e9:64:42 to it. IPv6 DHCP
1899     will be used to acquire an address.</para>
1900     </example>
1901
1902     <example>
1903       <title>Virtual Routing and Forwarding (VRF)</title>
1904       <para>Add the <literal>bond1</literal> interface to the VRF master interface
1905       <literal>vrf1</literal>. This will redirect routes generated on this interface to be
1906       within the routing table defined during VRF creation. For kernels before 4.8 traffic
1907       won't be redirected towards the VRFs routing table unless specific ip-rules are added.
1908       </para>
1909       <programlisting># /etc/systemd/network/25-vrf.network
1910 [Match]
1911 Name=bond1
1912
1913 [Network]
1914 VRF=vrf1
1915 </programlisting>
1916     </example>
1917
1918     <example>
1919       <title>MacVTap</title>
1920       <para>This brings up a network interface <literal>macvtap-test</literal>
1921       and attaches it to <literal>enp0s25</literal>.</para>
1922       <programlisting># /usr/lib/systemd/network/25-macvtap.network
1923 [Match]
1924 Name=enp0s25
1925
1926 [Network]
1927 MACVTAP=macvtap-test
1928 </programlisting>
1929     </example>
1930   </refsect1>
1931
1932   <refsect1>
1933     <title>See Also</title>
1934     <para>
1935       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1936       <citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
1937       <citerefentry><refentrytitle>systemd.link</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1938       <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1939       <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
1940     </para>
1941   </refsect1>
1942
1943 </refentry>