man/systemd.network.xml

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