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>.</para>
 127           </listitem>
 128         </varlistentry>
 129         <varlistentry>
 130           <term><varname>Driver=</varname></term>
 131           <listitem>
 132             <para>A whitespace-separated list of shell-style globs
 133             matching the driver currently bound to the device, as
 134             exposed by the udev property <literal>DRIVER</literal>
 135             of its parent device, or if that is not set the driver
 136             as exposed by <literal>ethtool -i</literal> of the
 137             device itself.</para>
 138           </listitem>
 139         </varlistentry>
 140         <varlistentry>
 141           <term><varname>Type=</varname></term>
 142           <listitem>
 143             <para>A whitespace-separated list of shell-style globs
 144             matching the device type, as exposed by the udev property
 145             <literal>DEVTYPE</literal>.</para>
 146           </listitem>
 147         </varlistentry>
 148         <varlistentry>
 149           <term><varname>Name=</varname></term>
 150           <listitem>
 151             <para>A whitespace-separated list of shell-style globs
 152             matching the device name, as exposed by the udev property
 153             <literal>INTERFACE</literal>.</para>
 154           </listitem>
 155         </varlistentry>
 156         <varlistentry>
 157           <term><varname>Host=</varname></term>
 158           <listitem>
 159             <para>Matches against the hostname or machine ID of the
 160             host. See <literal>ConditionHost=</literal> in
 161             <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 162             for details.
 163             </para>
 164           </listitem>
 165         </varlistentry>
 166         <varlistentry>
 167           <term><varname>Virtualization=</varname></term>
 168           <listitem>
 169             <para>Checks whether the system is executed in a virtualized
 170             environment and optionally test whether it is a specific
 171             implementation. See <literal>ConditionVirtualization=</literal> in
 172             <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 173             for details.
 174             </para>
 175           </listitem>
 176         </varlistentry>
 177         <varlistentry>
 178           <term><varname>KernelCommandLine=</varname></term>
 179           <listitem>
 180             <para>Checks whether a specific kernel command line option is
 181             set (or if prefixed with the exclamation mark unset). See
 182             <literal>ConditionKernelCommandLine=</literal> in
 183             <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 184             for details.
 185             </para>
 186           </listitem>
 187         </varlistentry>
 188         <varlistentry>
 189           <term><varname>Architecture=</varname></term>
 190           <listitem>
 191             <para>Checks whether the system is running on a specific
 192             architecture. See <literal>ConditionArchitecture=</literal> in
 193             <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 194             for details.
 195             </para>
 196           </listitem>
 197         </varlistentry>
 198       </variablelist>
 199
 200   </refsect1>
 201
 202   <refsect1>
 203     <title>[Link] Section Options</title>
 204
 205     <para> The <literal>[Link]</literal> section accepts the following keys:</para>
 206
 207     <variablelist class='network-directives'>
 208       <varlistentry>
 209         <term><varname>MACAddress=</varname></term>
 210         <listitem>
 211           <para>The hardware address to set for the device.</para>
 212         </listitem>
 213       </varlistentry>
 214       <varlistentry>
 215         <term><varname>MTUBytes=</varname></term>
 216         <listitem>
 217           <para>The maximum transmission unit in bytes to set for the
 218           device. The usual suffixes K, M, G, are supported and are
 219           understood to the base of 1024.</para>
 220           <para>Note that if IPv6 is enabled on the interface, and the MTU is chosen
 221           below 1280 (the minimum MTU for IPv6) it will automatically be increased to this value.</para>
 222         </listitem>
 223       </varlistentry>
 224       <varlistentry>
 225         <term><varname>ARP=</varname></term>
 226         <listitem>
 227           <para> A boolean. Enables or disables the ARP (low-level Address Resolution Protocol)
 228           for this interface. Defaults to unset, which means that the kernel default will be used.</para>
 229           <para> For example, disabling ARP is useful when creating multiple MACVLAN or VLAN virtual
 230           interfaces atop a single lower-level physical interface, which will then only serve as a
 231           link/"bridge" device aggregating traffic to the same physical link and not participate in
 232           the network otherwise.</para>
 233         </listitem>
 234       </varlistentry>
 235     </variablelist>
 236   </refsect1>
 237
 238   <refsect1>
 239     <title>[Network] Section Options</title>
 240
 241       <para>The <literal>[Network]</literal> section accepts the following keys:</para>
 242
 243       <variablelist class='network-directives'>
 244         <varlistentry>
 245           <term><varname>Description=</varname></term>
 246           <listitem>
 247             <para>A description of the device. This is only used for
 248             presentation purposes.</para>
 249           </listitem>
 250         </varlistentry>
 251         <varlistentry>
 252           <term><varname>DHCP=</varname></term>
 253           <listitem>
 254             <para>Enables DHCPv4 and/or DHCPv6 client support. Accepts
 255             <literal>yes</literal>, <literal>no</literal>,
 256             <literal>ipv4</literal>, or <literal>ipv6</literal>.</para>
 257
 258             <para>Note that DHCPv6 will by default be triggered by Router
 259             Advertisement, if that is enabled, regardless of this parameter.
 260             By enabling DHCPv6 support explicitly, the DHCPv6 client will
 261             be started regardless of the presence of routers on the link,
 262             or what flags the routers pass. See
 263             <literal>IPv6AcceptRA=</literal>.</para>
 264
 265             <para>Furthermore, note that by default the domain name
 266             specified through DHCP is not used for name resolution.
 267             See option <option>UseDomains=</option> below.</para>
 268
 269             <para>See the <literal>[DHCP]</literal> section below for further configuration options for the DHCP client
 270             support.</para>
 271           </listitem>
 272         </varlistentry>
 273         <varlistentry>
 274           <term><varname>DHCPServer=</varname></term>
 275           <listitem>
 276             <para>A boolean. Enables DHCPv4 server support. Defaults
 277             to <literal>no</literal>. Further settings for the DHCP
 278             server may be set in the <literal>[DHCPServer]</literal>
 279             section described below.</para>
 280           </listitem>
 281         </varlistentry>
 282         <varlistentry>
 283           <term><varname>LinkLocalAddressing=</varname></term>
 284           <listitem>
 285             <para>Enables link-local address autoconfiguration. Accepts
 286             <literal>yes</literal>, <literal>no</literal>,
 287             <literal>ipv4</literal>, or <literal>ipv6</literal>. Defaults to
 288             <literal>ipv6</literal>.</para>
 289           </listitem>
 290         </varlistentry>
 291         <varlistentry>
 292           <term><varname>IPv4LLRoute=</varname></term>
 293           <listitem>
 294             <para>A boolean. When true, sets up the route needed for
 295             non-IPv4LL hosts to communicate with IPv4LL-only hosts. Defaults
 296             to false.
 297             </para>
 298           </listitem>
 299         </varlistentry>
 300         <varlistentry>
 301           <term><varname>IPv6Token=</varname></term>
 302           <listitem>
 303             <para>An IPv6 address with the top 64 bits unset. When set, indicates the
 304             64-bit interface part of SLAAC IPv6 addresses for this link. Note that
 305             the token is only ever used for SLAAC, and not for DHCPv6 addresses, even
 306             in the case DHCP is requested by router advertisement. By default, the
 307             token is autogenerated.</para>
 308           </listitem>
 309         </varlistentry>
 310         <varlistentry>
 311           <term><varname>LLMNR=</varname></term>
 312           <listitem>
 313             <para>A boolean or <literal>resolve</literal>. When true,
 314             enables <ulink
 315             url="https://tools.ietf.org/html/rfc4795">Link-Local
 316             Multicast Name Resolution</ulink> on the link. When set to
 317             <literal>resolve</literal>, only resolution is enabled,
 318             but not host registration and announcement. Defaults to
 319             true. This setting is read by
 320             <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 321           </listitem>
 322         </varlistentry>
 323         <varlistentry>
 324           <term><varname>MulticastDNS=</varname></term>
 325           <listitem>
 326             <para>A boolean or <literal>resolve</literal>. When true,
 327             enables <ulink
 328             url="https://tools.ietf.org/html/rfc6762">Multicast
 329             DNS</ulink> support on the link. When set to
 330             <literal>resolve</literal>, only resolution is enabled,
 331             but not host or service registration and
 332             announcement. Defaults to false. This setting is read by
 333             <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 334           </listitem>
 335         </varlistentry>
 336         <varlistentry>
 337           <term><varname>DNSSEC=</varname></term>
 338           <listitem>
 339             <para>A boolean or
 340             <literal>allow-downgrade</literal>. When true, enables
 341             <ulink
 342             url="https://tools.ietf.org/html/rfc4033">DNSSEC</ulink>
 343             DNS validation support on the link. When set to
 344             <literal>allow-downgrade</literal>, compatibility with
 345             non-DNSSEC capable networks is increased, by automatically
 346             turning off DNSEC in this case. This option defines a
 347             per-interface setting for
 348             <citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>'s
 349             global <varname>DNSSEC=</varname> option. Defaults to
 350             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>DNSSECNegativeTrustAnchors=</varname></term>
 356           <listitem><para>A space-separated list of DNSSEC negative
 357           trust anchor domains. If specified and DNSSEC is enabled,
 358           look-ups done via the interface's DNS server will be subject
 359           to the list of negative trust anchors, and not require
 360           authentication for the specified domains, or anything below
 361           it. Use this to disable DNSSEC authentication for specific
 362           private domains, that cannot be proven valid using the
 363           Internet DNS hierarchy. Defaults to the empty list. This
 364           setting is read by
 365           <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 366           </listitem>
 367         </varlistentry>
 368         <varlistentry>
 369           <term><varname>LLDP=</varname></term>
 370           <listitem>
 371             <para>Controls support for Ethernet LLDP packet reception. LLDP is a link-layer protocol commonly
 372             implemented on professional routers and bridges which announces which physical port a system is connected
 373             to, as well as other related data. Accepts a boolean or the special value
 374             <literal>routers-only</literal>. When true, incoming LLDP packets are accepted and a database of all LLDP
 375             neighbors maintained. If <literal>routers-only</literal> is set only LLDP data of various types of routers
 376             is collected and LLDP data about other types of devices ignored (such as stations, telephones and
 377             others). If false, LLDP reception is disabled. Defaults to <literal>routers-only</literal>. Use
 378             <citerefentry><refentrytitle>networkctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> to query the
 379             collected neighbor data. LLDP is only available on Ethernet links. See <varname>EmitLLDP=</varname> below
 380             for enabling LLDP packet emission from the local system.
 381             </para>
 382           </listitem>
 383         </varlistentry>
 384         <varlistentry>
 385           <term><varname>EmitLLDP=</varname></term>
 386           <listitem>
 387             <para>Controls support for Ethernet LLDP packet emission. Accepts a boolean parameter or the special values
 388             <literal>nearest-bridge</literal>, <literal>non-tpmr-bridge</literal> and
 389             <literal>customer-bridge</literal>.  Defaults to false, which turns off LLDP packet emission. If not false,
 390             a short LLDP packet with information about the local system is sent out in regular intervals on the
 391             link. The LLDP packet will contain information about the local host name, the local machine ID (as stored
 392             in <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>) and the
 393             local interface name, as well as the pretty hostname of the system (as set in
 394             <citerefentry><refentrytitle>machine-info</refentrytitle><manvolnum>5</manvolnum></citerefentry>). LLDP
 395             emission is only available on Ethernet links. Note that this setting passes data suitable for
 396             identification of host to the network and should thus not be enabled on untrusted networks, where such
 397             identification data should not be made available. Use this option to permit other systems to identify on
 398             which interfaces they are connected to this system. The three special values control propagation of the
 399             LLDP packets. The <literal>nearest-bridge</literal> setting permits propagation only to the nearest
 400             connected bridge, <literal>non-tpmr-bridge</literal> permits propagation across Two-Port MAC Relays, but
 401             not any other bridges, and <literal>customer-bridge</literal> permits propagation until a customer bridge
 402             is reached. For details about these concepts, see <ulink
 403             url="http://standards.ieee.org/getieee802/download/802.1AB-2009.pdf">IEEE 802.1AB-2009</ulink>. Note that
 404             configuring this setting to true is equivalent to <literal>nearest-bridge</literal>, the recommended and
 405             most restricted level of propagation. See <varname>LLDP=</varname> above for an option to enable LLDP
 406             reception.</para>
 407           </listitem>
 408         </varlistentry>
 409         <varlistentry>
 410           <term><varname>BindCarrier=</varname></term>
 411           <listitem>
 412             <para>A link name or a list of link names. When set, controls the behavior of the current
 413             link. When all links in the list are in an operational down state, the current link is brought
 414             down. When at least one link has carrier, the current interface is brought up.
 415             </para>
 416           </listitem>
 417         </varlistentry>
 418         <varlistentry>
 419           <term><varname>Address=</varname></term>
 420           <listitem>
 421             <para>A static IPv4 or IPv6 address and its prefix length,
 422             separated by a <literal>/</literal> character. Specify
 423             this key more than once to configure several addresses.
 424             The format of the address must be as described in
 425             <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 426             This is a short-hand for an [Address] section only
 427             containing an Address key (see below). This option may be
 428             specified more than once.
 429             </para>
 430
 431             <para>If the specified address is 0.0.0.0 (for IPv4) or
 432             [::] (for IPv6), a new address range of the requested size
 433             is automatically allocated from a system-wide pool of
 434             unused ranges. The allocated range is checked against all
 435             current network interfaces and all known network
 436             configuration files to avoid address range conflicts. The
 437             default system-wide pool consists of 192.168.0.0/16,
 438             172.16.0.0/12 and 10.0.0.0/8 for IPv4, and fc00::/7 for
 439             IPv6. This functionality is useful to manage a large
 440             number of dynamically created network interfaces with the
 441             same network configuration and automatic address range
 442             assignment.</para>
 443
 444           </listitem>
 445         </varlistentry>
 446         <varlistentry>
 447           <term><varname>Gateway=</varname></term>
 448           <listitem>
 449             <para>The gateway address, which must be in the format
 450             described in
 451             <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 452             This is a short-hand for a [Route] section only containing
 453             a Gateway key. This option may be specified more than
 454             once.</para>
 455           </listitem>
 456         </varlistentry>
 457         <varlistentry>
 458           <term><varname>DNS=</varname></term>
 459           <listitem>
 460             <para>A DNS server address, which must be in the format
 461             described in
 462             <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 463             This option may be specified more than once. This setting is read by
 464             <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 465           </listitem>
 466         </varlistentry>
 467         <varlistentry>
 468           <term><varname>Domains=</varname></term>
 469           <listitem>
 470             <para>A list of domains which should be resolved using the DNS servers on this link. Each item in the list
 471             should be a domain name, optionally prefixed with a tilde (<literal>~</literal>). The domains with the
 472             prefix are called "routing-only domains". The domains without the prefix are called "search domains" and
 473             are first used as search suffixes for extending single-label host names (host names containing no dots) to
 474             become fully qualified domain names (FQDNs). If a single-label host name is resolved on this interface,
 475             each of the specified search domains are appended to it in turn, converting it into a fully qualified
 476             domain name, until one of them may be successfully resolved.</para>
 477
 478             <para>Both "search" and "routing-only" domains are used for routing of DNS queries: look-ups for host names
 479             ending in those domains (hence also single label names, if any "search domains" are listed), are routed to
 480             the DNS servers configured for this interface. The domain routing logic is particularly useful on
 481             multi-homed hosts with DNS servers serving particular private DNS zones on each interface.</para>
 482
 483             <para>The "routing-only" domain <literal>~.</literal> (the tilde indicating definition of a routing domain,
 484             the dot referring to the DNS root domain which is the implied suffix of all valid DNS names) has special
 485             effect. It causes all DNS traffic which does not match another configured domain routing entry to be routed
 486             to DNS servers specified for this interface. This setting is useful to prefer a certain set of DNS servers
 487             if a link on which they are connected is available.</para>
 488
 489             <para>This setting is read by
 490             <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
 491             "Search domains" correspond to the <varname>domain</varname> and <varname>search</varname> entries in
 492             <citerefentry><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 493             Domain name routing has no equivalent in the traditional glibc API, which has no concept of domain
 494             name servers limited to a specific link.</para>
 495           </listitem>
 496         </varlistentry>
 497         <varlistentry>
 498           <term><varname>NTP=</varname></term>
 499           <listitem>
 500             <para>An NTP server address. This option may be specified more than once. This setting is read by
 501             <citerefentry><refentrytitle>systemd-timesyncd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 502           </listitem>
 503         </varlistentry>
 504         <varlistentry>
 505           <term><varname>IPForward=</varname></term>
 506           <listitem><para>Configures IP packet forwarding for the
 507           system. If enabled, incoming packets on any network
 508           interface will be forwarded to any other interfaces
 509           according to the routing table. Takes either a boolean
 510           argument, or the values <literal>ipv4</literal> or
 511           <literal>ipv6</literal>, which only enable IP packet
 512           forwarding for the specified address family.  This controls
 513           the <filename>net.ipv4.ip_forward</filename> and
 514           <filename>net.ipv6.conf.all.forwarding</filename> sysctl
 515           options of the network interface (see <ulink
 516           url="https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt">ip-sysctl.txt</ulink>
 517           for details about sysctl options). Defaults to
 518           <literal>no</literal>.</para>
 519
 520           <para>Note: this setting controls a global kernel option,
 521           and does so one way only: if a network that has this setting
 522           enabled is set up the global setting is turned on.  However,
 523           it is never turned off again, even after all networks with
 524           this setting enabled are shut down again.</para>
 525
 526           <para>To allow IP packet forwarding only between specific
 527           network interfaces use a firewall.</para>
 528           </listitem>
 529         </varlistentry>
 530         <varlistentry>
 531           <term><varname>IPMasquerade=</varname></term>
 532           <listitem><para>Configures IP masquerading for the network
 533           interface. If enabled, packets forwarded from the network
 534           interface will be appear as coming from the local host.
 535           Takes a boolean argument. Implies
 536           <varname>IPForward=ipv4</varname>. Defaults to
 537           <literal>no</literal>.</para></listitem>
 538         </varlistentry>
 539         <varlistentry>
 540           <term><varname>IPv6PrivacyExtensions=</varname></term>
 541           <listitem><para>Configures use of stateless temporary
 542           addresses that change over time (see <ulink
 543           url="https://tools.ietf.org/html/rfc4941">RFC 4941</ulink>,
 544           Privacy Extensions for Stateless Address Autoconfiguration
 545           in IPv6). Takes a boolean or the special values
 546           <literal>prefer-public</literal> and
 547           <literal>kernel</literal>. When true, enables the privacy
 548           extensions and prefers temporary addresses over public
 549           addresses. When <literal>prefer-public</literal>, enables the
 550           privacy extensions, but prefers public addresses over
 551           temporary addresses. When false, the privacy extensions
 552           remain disabled. When <literal>kernel</literal>, the kernel's
 553           default setting will be left in place.  Defaults to
 554           <literal>no</literal>.</para></listitem>
 555         </varlistentry>
 556         <varlistentry>
 557           <term><varname>IPv6AcceptRA=</varname></term>
 558           <listitem><para>Enable or disable IPv6 Router Advertisement (RA) reception support for the interface.  Takes
 559           a boolean parameter. If true, RAs are accepted; if false, RAs are ignored, independently of the local
 560           forwarding state. When not set, the kernel default is used, and RAs are accepted only when local forwarding
 561           is disabled for that interface.  When RAs are accepted, they may trigger the start of the DHCPv6 client if
 562           the relevant flags are set in the RA data, or if no routers are found on the link.</para>
 563
 564           <para>Further settings for the IPv6 RA support may be configured in the
 565           <literal>[IPv6AcceptRA]</literal> section, see below.</para>
 566
 567           <para>Also see <ulink
 568           url="https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt">ip-sysctl.txt</ulink> in the kernel
 569           documentation regarding <literal>accept_ra</literal>, but note that systemd's setting of
 570           <constant>1</constant> (i.e. true) corresponds to kernel's setting of <constant>2</constant>.</para>
 571         </listitem>
 572         </varlistentry>
 573         <varlistentry>
 574           <term><varname>IPv6DuplicateAddressDetection=</varname></term>
 575           <listitem><para>Configures the amount of IPv6 Duplicate
 576           Address Detection (DAD) probes to send. Defaults to unset.
 577         </para></listitem>
 578         </varlistentry>
 579         <varlistentry>
 580           <term><varname>IPv6HopLimit=</varname></term>
 581           <listitem><para>Configures IPv6 Hop Limit. For each router that
 582           forwards the packet, the hop limit is decremented by 1. When the
 583           hop limit field reaches zero, the packet is discarded.
 584           Defaults to unset.
 585         </para></listitem>
 586         </varlistentry>
 587         <varlistentry>
 588           <term><varname>ProxyARP=</varname></term>
 589           <listitem><para>A boolean. Configures proxy ARP. Proxy ARP is the technique in which one host,
 590           usually a router, answers ARP requests intended for another machine. By "faking" its identity,
 591           the router accepts responsibility for routing packets to the "real" destination. (see <ulink
 592           url="https://tools.ietf.org/html/rfc1027">RFC 1027</ulink>.
 593           Defaults to unset.
 594         </para></listitem>
 595         </varlistentry>
 596         <varlistentry>
 597           <term><varname>Bridge=</varname></term>
 598           <listitem>
 599             <para>The name of the bridge to add the link to.</para>
 600           </listitem>
 601         </varlistentry>
 602         <varlistentry>
 603           <term><varname>Bond=</varname></term>
 604           <listitem>
 605             <para>The name of the bond to add the link to.</para>
 606           </listitem>
 607         </varlistentry>
 608         <varlistentry>
 609           <term><varname>VRF=</varname></term>
 610           <listitem>
 611             <para>The name of the VRF to add the link to.</para>
 612           </listitem>
 613         </varlistentry>
 614         <varlistentry>
 615           <term><varname>VLAN=</varname></term>
 616           <listitem>
 617             <para>The name of a VLAN to create on the link. This
 618             option may be specified more than once.</para>
 619           </listitem>
 620         </varlistentry>
 621         <varlistentry>
 622           <term><varname>MACVLAN=</varname></term>
 623           <listitem>
 624             <para>The name of a MACVLAN to create on the link. This
 625             option may be specified more than once.</para>
 626           </listitem>
 627         </varlistentry>
 628         <varlistentry>
 629           <term><varname>VXLAN=</varname></term>
 630           <listitem>
 631             <para>The name of a VXLAN to create on the link. This
 632             option may be specified more than once.</para>
 633           </listitem>
 634         </varlistentry>
 635         <varlistentry>
 636           <term><varname>Tunnel=</varname></term>
 637           <listitem>
 638             <para>The name of a Tunnel to create on the link. This
 639             option may be specified more than once.</para>
 640           </listitem>
 641         </varlistentry>
 642       </variablelist>
 643
 644   </refsect1>
 645
 646   <refsect1>
 647     <title>[Address] Section Options</title>
 648
 649       <para>An <literal>[Address]</literal> section accepts the
 650       following keys. Specify several <literal>[Address]</literal>
 651       sections to configure several addresses.</para>
 652
 653       <variablelist class='network-directives'>
 654         <varlistentry>
 655           <term><varname>Address=</varname></term>
 656           <listitem>
 657             <para>As in the <literal>[Network]</literal> section. This
 658             key is mandatory.</para>
 659           </listitem>
 660         </varlistentry>
 661         <varlistentry>
 662           <term><varname>Peer=</varname></term>
 663           <listitem>
 664             <para>The peer address in a point-to-point connection.
 665             Accepts the same format as the <literal>Address</literal>
 666             key.</para>
 667           </listitem>
 668         </varlistentry>
 669         <varlistentry>
 670           <term><varname>Broadcast=</varname></term>
 671           <listitem>
 672             <para>The broadcast address, which must be in the format
 673             described in
 674             <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 675             This key only applies to IPv4 addresses. If it is not
 676             given, it is derived from the <literal>Address</literal>
 677             key.</para>
 678           </listitem>
 679         </varlistentry>
 680         <varlistentry>
 681           <term><varname>Label=</varname></term>
 682           <listitem>
 683             <para>An address label.</para>
 684           </listitem>
 685         </varlistentry>
 686         <varlistentry>
 687           <term><varname>PreferredLifetime=</varname></term>
 688           <listitem>
 689             <para>Allows the default "preferred lifetime" of the address to be overridden.
 690             Only three settings are accepted: <literal>forever</literal> or <literal>infinity</literal>
 691             which is the default and means that the address never expires, and <literal>0</literal> which means
 692             that the address is considered immediately "expired" and will not be used,
 693             unless explicitly requested. A setting of PreferredLifetime=0 is useful for
 694             addresses which are added to be used only by a specific application,
 695             which is then configured to use them explicitly.</para>
 696           </listitem>
 697         </varlistentry>
 698         <varlistentry>
 699           <term><varname>HomeAddress=</varname></term>
 700           <listitem>
 701             <para>Takes a boolean argument. Designates this address the "home address" as defined in
 702             <ulink url="https://tools.ietf.org/html/rfc6275">RFC 6275</ulink>.
 703             Supported only on IPv6. Defaults to false.</para>
 704           </listitem>
 705         </varlistentry>
 706         <varlistentry>
 707           <term><varname>DuplicateAddressDetection=</varname></term>
 708           <listitem>
 709             <para>Takes a boolean argument. Do not perform Duplicate Address Detection
 710             <ulink url="https://tools.ietf.org/html/rfc4862">RFC 4862</ulink> when adding this address.
 711             Supported only on IPv6. Defaults to false.</para>
 712           </listitem>
 713         </varlistentry>
 714         <varlistentry>
 715           <term><varname>ManageTemporaryAddress=</varname></term>
 716           <listitem>
 717             <para>Takes a boolean argument. If true the kernel manage temporary addresses created
 718             from this one as template on behalf of Privacy Extensions
 719             <ulink url="https://tools.ietf.org/html/rfc3041">RFC 3041</ulink>.  For this to become
 720             active, the use_tempaddr sysctl setting has to be set to a value greater than zero.
 721             The given address needs to have a prefix length of 64. This flag allows to use privacy
 722             extensions in a manually configured network, just like if stateless auto-configuration
 723             was active. Defaults to false. </para>
 724           </listitem>
 725         </varlistentry>
 726         <varlistentry>
 727           <term><varname>PrefixRoute=</varname></term>
 728           <listitem>
 729             <para>Takes a boolean argument. When adding or modifying an IPv6 address, the userspace
 730             application needs a way to suppress adding a prefix route. This is for example relevant
 731             together with IFA_F_MANAGERTEMPADDR, where userspace creates autoconf generated addresses,
 732             but depending on on-link, no route for the prefix should be added. Defaults to false.</para>
 733           </listitem>
 734         </varlistentry>
 735         <varlistentry>
 736           <term><varname>AutoJoin=</varname></term>
 737           <listitem>
 738             <para>Takes a boolean argument. Joining multicast group on ethernet level via
 739             <command>ip maddr</command> command would not work if we have an Ethernet switch that does
 740             IGMP snooping since the switch would not replicate multicast packets on  ports that did not
 741             have IGMP reports for the multicast addresses. Linux vxlan interfaces created via
 742             <command>ip link add vxlan</command> or networkd's netdev kind vxlan have the group option
 743             that enables then to do the required join. By extending ip address command with option
 744             <literal>autojoin</literal> we can get similar functionality for openvswitch (OVS) vxlan
 745             interfaces as well as other tunneling mechanisms that need to receive multicast traffic.
 746             Defaults to <literal>no</literal>.</para>
 747           </listitem>
 748         </varlistentry>
 749       </variablelist>
 750   </refsect1>
 751
 752   <refsect1>
 753     <title>[Route] Section Options</title>
 754       <para>The <literal>[Route]</literal> section accepts the
 755       following keys. Specify several <literal>[Route]</literal>
 756       sections to configure several routes.</para>
 757
 758       <variablelist class='network-directives'>
 759         <varlistentry>
 760           <term><varname>Gateway=</varname></term>
 761           <listitem>
 762             <para>As in the <literal>[Network]</literal> section.</para>
 763           </listitem>
 764         </varlistentry>
 765         <varlistentry>
 766           <term><varname>Destination=</varname></term>
 767           <listitem>
 768             <para>The destination prefix of the route. Possibly
 769             followed by a slash and the prefix length. If omitted, a
 770             full-length host route is assumed.</para>
 771           </listitem>
 772         </varlistentry>
 773         <varlistentry>
 774           <term><varname>Source=</varname></term>
 775           <listitem>
 776             <para>The source prefix of the route. Possibly followed by
 777             a slash and the prefix length. If omitted, a full-length
 778             host route is assumed.</para>
 779           </listitem>
 780         </varlistentry>
 781         <varlistentry>
 782           <term><varname>Metric=</varname></term>
 783           <listitem>
 784             <para>The metric of the route (an unsigned integer).</para>
 785           </listitem>
 786         </varlistentry>
 787         <varlistentry>
 788           <term><varname>Scope=</varname></term>
 789           <listitem>
 790             <para>The scope of the route, which can be <literal>global</literal>,
 791             <literal>link</literal> or <literal>host</literal>. Defaults to
 792             <literal>global</literal>.</para>
 793           </listitem>
 794         </varlistentry>
 795         <varlistentry>
 796           <term><varname>PreferredSource=</varname></term>
 797           <listitem>
 798             <para>The preferred source address of the route. The address
 799             must be in the format described in
 800             <citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
 801           </listitem>
 802         </varlistentry>
 803         <varlistentry>
 804           <term><varname>Table=<replaceable>num</replaceable></varname></term>
 805           <listitem>
 806           <para>The table identifier for the route (a number between 1 and 4294967295, or 0 to unset).
 807           The table can be retrieved using <command>ip route show table <replaceable>num</replaceable></command>.
 808           </para>
 809           </listitem>
 810         </varlistentry>
 811       </variablelist>
 812   </refsect1>
 813
 814   <refsect1>
 815     <title>[DHCP] Section Options</title>
 816       <para>The <literal>[DHCP]</literal> section configures the
 817       DHCPv4 and DHCP6 client, if it is enabled with the
 818       <varname>DHCP=</varname> setting described above:</para>
 819
 820       <variablelist class='network-directives'>
 821         <varlistentry>
 822           <term><varname>UseDNS=</varname></term>
 823           <listitem>
 824             <para>When true (the default), the DNS servers received
 825             from the DHCP server will be used and take precedence over
 826             any statically configured ones.</para>
 827
 828             <para>This corresponds to the <option>nameserver</option>
 829             option in <citerefentry
 830             project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
 831           </listitem>
 832         </varlistentry>
 833         <varlistentry>
 834           <term><varname>UseNTP=</varname></term>
 835           <listitem>
 836             <para>When true (the default), the NTP servers received
 837             from the DHCP server will be used by systemd-timesyncd
 838             and take precedence over any statically configured ones.</para>
 839           </listitem>
 840         </varlistentry>
 841         <varlistentry>
 842           <term><varname>UseMTU=</varname></term>
 843           <listitem>
 844             <para>When true, the interface maximum transmission unit
 845             from the DHCP server will be used on the current link.
 846             Defaults to false.</para>
 847           </listitem>
 848         </varlistentry>
 849         <varlistentry>
 850           <term><varname>SendHostname=</varname></term>
 851           <listitem>
 852             <para>When true (the default), the machine's hostname will
 853             be sent to the DHCP server.</para>
 854           </listitem>
 855         </varlistentry>
 856         <varlistentry>
 857           <term><varname>UseHostname=</varname></term>
 858           <listitem>
 859             <para>When true (the default), the hostname received from
 860             the DHCP server will be set as the transient hostname of the system
 861             </para>
 862           </listitem>
 863         </varlistentry>
 864         <varlistentry>
 865         <term><varname>Hostname=</varname></term>
 866         <listitem>
 867           <para>Use this value for the hostname which is sent to the
 868           DHCP server, instead of machine's hostname.</para>
 869         </listitem>
 870       </varlistentry>
 871         <varlistentry>
 872           <term><varname>UseDomains=</varname></term>
 873           <listitem>
 874             <para>Takes a boolean argument, or the special value <literal>route</literal>. When true, the domain name
 875             received from the DHCP server will be used as DNS search domain over this link, similar to the effect of
 876             the <option>Domains=</option> setting. If set to <literal>route</literal>, the domain name received from
 877             the DHCP server will be used for routing DNS queries only, but not for searching, similar to the effect of
 878             the <option>Domains=</option> setting when the argument is prefixed with <literal>~</literal>. Defaults to
 879             false.</para>
 880
 881             <para>It is recommended to enable this option only on trusted networks, as setting this affects resolution
 882             of all host names, in particular of single-label names. It is generally safer to use the supplied domain
 883             only as routing domain, rather than as search domain, in order to not have it affect local resolution of
 884             single-label names.</para>
 885
 886             <para>When set to true, this setting corresponds to the <option>domain</option> option in <citerefentry
 887             project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
 888           </listitem>
 889         </varlistentry>
 890         <varlistentry>
 891           <term><varname>UseRoutes=</varname></term>
 892           <listitem>
 893             <para>When true (the default), the static routes will be
 894             requested from the DHCP server and added to the routing
 895             table with a metric of 1024.</para>
 896           </listitem>
 897         </varlistentry>
 898
 899         <varlistentry>
 900           <term><varname>UseTimezone=</varname></term>
 901
 902           <listitem><para>When true, the timezone received from the
 903           DHCP server will be set as timezone of the local
 904           system. Defaults to <literal>no</literal>.</para></listitem>
 905         </varlistentry>
 906
 907         <varlistentry>
 908           <term><varname>CriticalConnection=</varname></term>
 909           <listitem>
 910             <para>When true, the connection will never be torn down
 911             even if the DHCP lease expires. This is contrary to the
 912             DHCP specification, but may be the best choice if, say,
 913             the root filesystem relies on this connection. Defaults to
 914             false.</para>
 915           </listitem>
 916         </varlistentry>
 917
 918         <varlistentry>
 919           <term><varname>ClientIdentifier=</varname></term>
 920           <listitem>
 921             <para>The DHCPv4 client identifier to use. Either <literal>mac</literal> to use the MAC address of the link
 922             or <literal>duid</literal> (the default, see below) to use an RFC4361-compliant Client ID.</para>
 923           </listitem>
 924         </varlistentry>
 925
 926         <varlistentry>
 927           <term><varname>VendorClassIdentifier=</varname></term>
 928           <listitem>
 929             <para>The vendor class identifier used to identify vendor
 930             type and configuration.</para>
 931           </listitem>
 932         </varlistentry>
 933
 934         <varlistentry>
 935           <term><varname>DUIDType=</varname></term>
 936           <listitem>
 937             <para>Override the global <varname>DUIDType</varname> setting for this network. See
 938             <citerefentry><refentrytitle>networkd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 939             for a description of possible values.</para>
 940           </listitem>
 941         </varlistentry>
 942
 943         <varlistentry>
 944           <term><varname>DUIDRawData=</varname></term>
 945           <listitem>
 946             <para>Override the global <varname>DUIDRawData</varname> setting for this network. See
 947             <citerefentry><refentrytitle>networkd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 948             for a description of possible values.</para>
 949           </listitem>
 950         </varlistentry>
 951
 952         <varlistentry>
 953           <term><varname>IAID=</varname></term>
 954           <listitem>
 955             <para>The DHCP Identity Association Identifier (IAID) for the interface, a 32-bit unsigned integer.</para>
 956           </listitem>
 957         </varlistentry>
 958
 959         <varlistentry>
 960           <term><varname>RequestBroadcast=</varname></term>
 961           <listitem>
 962             <para>Request the server to use broadcast messages before
 963             the IP address has been configured. This is necessary for
 964             devices that cannot receive RAW packets, or that cannot
 965             receive packets at all before an IP address has been
 966             configured. On the other hand, this must not be enabled on
 967             networks where broadcasts are filtered out.</para>
 968           </listitem>
 969         </varlistentry>
 970
 971         <varlistentry>
 972           <term><varname>RouteMetric=</varname></term>
 973           <listitem>
 974             <para>Set the routing metric for routes specified by the
 975             DHCP server.</para>
 976           </listitem>
 977         </varlistentry>
 978
 979         <varlistentry>
 980           <term><varname>RouteTable=<replaceable>num</replaceable></varname></term>
 981           <listitem>
 982             <para>The table identifier for DHCP routes (a number between 1 and 4294967295, or 0 to unset).
 983             The table can be retrieved using <command>ip route show table <replaceable>num</replaceable></command>.
 984             </para>
 985           </listitem>
 986         </varlistentry>
 987       </variablelist>
 988     </refsect1>
 989
 990   <refsect1>
 991     <title>[IPv6AcceptRA] Section Options</title>
 992       <para>The <literal>[IPv6AcceptRA]</literal> section configures the IPv6 Router Advertisement
 993       (RA) client, if it is enabled with the <varname>IPv6AcceptRA=</varname> setting described
 994       above:</para>
 995
 996       <variablelist class='network-directives'>
 997         <varlistentry>
 998           <term><varname>UseDNS=</varname></term>
 999           <listitem>
1000             <para>When true (the default), the DNS servers received in the Router Advertisement will be used and take
1001             precedence over any statically configured ones.</para>
1002
1003             <para>This corresponds to the <option>nameserver</option> option in <citerefentry
1004             project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
1005           </listitem>
1006         </varlistentry>
1007
1008         <varlistentry>
1009           <term><varname>UseDomains=</varname></term>
1010           <listitem>
1011             <para>Takes a boolean argument, or the special value <literal>route</literal>. When true, the domain name
1012             received via IPv6 Router Advertisement (RA) will be used as DNS search domain over this link, similar to
1013             the effect of the <option>Domains=</option> setting. If set to <literal>route</literal>, the domain name
1014             received via IPv6 RA will be used for routing DNS queries only, but not for searching, similar to the
1015             effect of the <option>Domains=</option> setting when the argument is prefixed with
1016             <literal>~</literal>. Defaults to false.</para>
1017
1018             <para>It is recommended to enable this option only on trusted networks, as setting this affects resolution
1019             of all host names, in particular of single-label names. It is generally safer to use the supplied domain
1020             only as routing domain, rather than as search domain, in order to not have it affect local resolution of
1021             single-label names.</para>
1022
1023             <para>When set to true, this setting corresponds to the <option>domain</option> option in <citerefentry
1024             project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
1025           </listitem>
1026         </varlistentry>
1027
1028         <varlistentry>
1029           <term><varname>RouteTable=<replaceable>num</replaceable></varname></term>
1030           <listitem>
1031             <para>The table identifier for the routes received in the Router Advertisement
1032             (a number between 1 and 4294967295, or 0 to unset).
1033             The table can be retrieved using <command>ip route show table <replaceable>num</replaceable></command>.
1034             </para>
1035           </listitem>
1036         </varlistentry>
1037       </variablelist>
1038   </refsect1>
1039
1040
1041   <refsect1>
1042     <title>[DHCPServer] Section Options</title>
1043     <para>The <literal>[DHCPServer]</literal> section contains
1044     settings for the DHCP server, if enabled via the
1045     <varname>DHCPServer=</varname> option described above:</para>
1046
1047     <variablelist class='network-directives'>
1048
1049       <varlistentry>
1050         <term><varname>PoolOffset=</varname></term>
1051         <term><varname>PoolSize=</varname></term>
1052
1053         <listitem><para>Configures the pool of addresses to hand out. The pool
1054         is a contiguous sequence of IP addresses in the subnet configured for
1055         the server address, which does not include the subnet nor the broadcast
1056         address. <varname>PoolOffset=</varname> takes the offset of the pool
1057         from the start of subnet, or zero to use the default value.
1058         <varname>PoolSize=</varname> takes the number of IP addresses in the
1059         pool or zero to use the default value. By default, the pool starts at
1060         the first address after the subnet address and takes up the rest of
1061         the subnet, excluding the broadcast address. If the pool includes
1062         the server address (the default), this is reserved and not handed
1063         out to clients.</para></listitem>
1064       </varlistentry>
1065
1066       <varlistentry>
1067         <term><varname>DefaultLeaseTimeSec=</varname></term>
1068         <term><varname>MaxLeaseTimeSec=</varname></term>
1069
1070         <listitem><para>Control the default and maximum DHCP lease
1071         time to pass to clients. These settings take time values in seconds or
1072         another common time unit, depending on the suffix. The default
1073         lease time is used for clients that did not ask for a specific
1074         lease time. If a client asks for a lease time longer than the
1075         maximum lease time, it is automatically shortened to the
1076         specified time. The default lease time defaults to 1h, the
1077         maximum lease time to 12h. Shorter lease times are beneficial
1078         if the configuration data in DHCP leases changes frequently
1079         and clients shall learn the new settings with shorter
1080         latencies. Longer lease times reduce the generated DHCP
1081         network traffic.</para></listitem>
1082       </varlistentry>
1083
1084       <varlistentry>
1085         <term><varname>EmitDNS=</varname></term>
1086         <term><varname>DNS=</varname></term>
1087
1088         <listitem><para>Configures whether the DHCP leases handed out
1089         to clients shall contain DNS server information. The
1090         <varname>EmitDNS=</varname> setting takes a boolean argument
1091         and defaults to <literal>yes</literal>. The DNS servers to
1092         pass to clients may be configured with the
1093         <varname>DNS=</varname> option, which takes a list of IPv4
1094         addresses. If the <varname>EmitDNS=</varname> option is
1095         enabled but no servers configured, the servers are
1096         automatically propagated from an "uplink" interface that has
1097         appropriate servers set. The "uplink" interface is determined
1098         by the default route of the system with the highest
1099         priority. Note that this information is acquired at the time
1100         the lease is handed out, and does not take uplink interfaces
1101         into account that acquire DNS or NTP server information at a
1102         later point. DNS server propagation does not take
1103         <filename>/etc/resolv.conf</filename> into account. Also, note
1104         that the leases are not refreshed if the uplink network
1105         configuration changes. To ensure clients regularly acquire the
1106         most current uplink DNS server information, it is thus
1107         advisable to shorten the DHCP lease time via
1108         <varname>MaxLeaseTimeSec=</varname> described
1109         above.</para></listitem>
1110       </varlistentry>
1111
1112       <varlistentry>
1113         <term><varname>EmitNTP=</varname></term>
1114         <term><varname>NTP=</varname></term>
1115
1116         <listitem><para>Similar to the <varname>EmitDNS=</varname> and
1117         <varname>DNS=</varname> settings described above, these
1118         settings configure whether and what NTP server information
1119         shall be emitted as part of the DHCP lease. The same syntax,
1120         propagation semantics and defaults apply as for
1121         <varname>EmitDNS=</varname> and
1122         <varname>DNS=</varname>.</para></listitem>
1123       </varlistentry>
1124
1125       <varlistentry>
1126         <term><varname>EmitRouter=</varname></term>
1127
1128         <listitem><para>Similar to the <varname>EmitDNS=</varname>
1129         setting described above, this setting configures whether the
1130         DHCP lease should contain the router option. The same syntax,
1131         propagation semantics and defaults apply as for
1132         <varname>EmitDNS=</varname>.</para></listitem>
1133       </varlistentry>
1134
1135       <varlistentry>
1136         <term><varname>EmitTimezone=</varname></term>
1137         <term><varname>Timezone=</varname></term>
1138
1139         <listitem><para>Configures whether the DHCP leases handed out
1140         to clients shall contain timezone information. The
1141         <varname>EmitTimezone=</varname> setting takes a boolean
1142         argument and defaults to <literal>yes</literal>. The
1143         <varname>Timezone=</varname> setting takes a timezone string
1144         (such as <literal>Europe/Berlin</literal> or
1145         <literal>UTC</literal>) to pass to clients. If no explicit
1146         timezone is set, the system timezone of the local host is
1147         propagated, as determined by the
1148         <filename>/etc/localtime</filename> symlink.</para></listitem>
1149       </varlistentry>
1150
1151     </variablelist>
1152   </refsect1>
1153
1154   <refsect1>
1155     <title>[Bridge] Section Options</title>
1156       <para>The <literal>[Bridge]</literal> section accepts the
1157       following keys.</para>
1158       <variablelist class='network-directives'>
1159         <varlistentry>
1160           <term><varname>UnicastFlood=</varname></term>
1161           <listitem>
1162             <para>A boolean. Controls whether the bridge should flood
1163             traffic for which an FDB entry is missing and the destination
1164             is unknown through this port. Defaults to on.
1165             </para>
1166           </listitem>
1167         </varlistentry>
1168         <varlistentry>
1169           <term><varname>HairPin=</varname></term>
1170           <listitem>
1171             <para>A boolean. Configures whether traffic may be sent back
1172             out of the port on which it was received. By default, this
1173             flag is false, and the bridge will not forward traffic back
1174             out of the receiving port.</para>
1175           </listitem>
1176         </varlistentry>
1177         <varlistentry>
1178           <term><varname>UseBPDU=</varname></term>
1179           <listitem>
1180             <para>A boolean. Configures whether STP Bridge Protocol Data Units will be
1181             processed by the bridge port. Defaults to yes.</para>
1182           </listitem>
1183         </varlistentry>
1184         <varlistentry>
1185           <term><varname>FastLeave=</varname></term>
1186           <listitem>
1187             <para>A boolean. This flag allows the bridge to immediately stop multicast
1188             traffic on a port that receives an IGMP Leave message. It is only used with
1189             IGMP snooping if enabled on the bridge. Defaults to off.</para>
1190           </listitem>
1191         </varlistentry>
1192         <varlistentry>
1193           <term><varname>AllowPortToBeRoot=</varname></term>
1194           <listitem>
1195             <para>A boolean. Configures whether a given port is allowed to
1196             become a root port. Only used when STP is enabled on the bridge.
1197             Defaults to on.</para>
1198           </listitem>
1199         </varlistentry>
1200         <varlistentry>
1201           <term><varname>Cost=</varname></term>
1202           <listitem>
1203             <para>Sets the "cost" of sending packets of this interface.
1204             Each port in a bridge may have a different speed and the cost
1205             is used to decide which link to use. Faster interfaces
1206             should have lower costs.</para>
1207           </listitem>
1208         </varlistentry>
1209       </variablelist>
1210   </refsect1>
1211   <refsect1>
1212     <title>[BridgeFDB] Section Options</title>
1213       <para>The <literal>[BridgeFDB]</literal> section manages the
1214       forwarding database table of a port and accepts the following
1215       keys. Specify several <literal>[BridgeFDB]</literal> sections to
1216       configure several static MAC table entries.</para>
1217
1218       <variablelist class='network-directives'>
1219         <varlistentry>
1220           <term><varname>MACAddress=</varname></term>
1221           <listitem>
1222             <para>As in the <literal>[Network]</literal> section. This
1223             key is mandatory.</para>
1224           </listitem>
1225         </varlistentry>
1226         <varlistentry>
1227           <term><varname>VLANId=</varname></term>
1228           <listitem>
1229             <para>The VLAN ID for the new static MAC table entry. If
1230             omitted, no VLAN ID info is appended to the new static MAC
1231             table entry.</para>
1232           </listitem>
1233         </varlistentry>
1234       </variablelist>
1235   </refsect1>
1236   <refsect1>
1237     <title>[BridgeVLAN] Section Options</title>
1238       <para>The <literal>[BridgeVLAN]</literal> section manages the VLAN ID configuration of a bridge port and accepts
1239       the following keys. Specify several <literal>[BridgeVLAN]</literal> sections to configure several VLAN entries.
1240       The <varname>VLANFiltering=</varname> option has to be enabled, see <literal>[Bridge]</literal> section in
1241       <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
1242
1243       <variablelist class='network-directives'>
1244         <varlistentry>
1245           <term><varname>VLAN=</varname></term>
1246           <listitem>
1247             <para>The VLAN ID allowed on the port. This can be either a single ID or a range M-N. VLAN IDs are valid
1248             from 1 to 4094.</para>
1249           </listitem>
1250         </varlistentry>
1251         <varlistentry>
1252           <term><varname>EgressUntagged=</varname></term>
1253           <listitem>
1254             <para>The VLAN ID specified here will be used to untag frames on egress. Configuring
1255             <varname>EgressUntagged=</varname> implicates the use of <varname>VLAN=</varname> above and will enable the
1256             VLAN ID for ingress as well. This can be either a single ID or a range M-N.</para>
1257           </listitem>
1258         </varlistentry>
1259         <varlistentry>
1260           <term><varname>PVID=</varname></term>
1261           <listitem>
1262             <para>The Port VLAN ID specified here is assigned to all untagged frames at ingress.
1263             <varname>PVID=</varname> can be used only once. Configuring <varname>PVID=</varname> implicates the use of
1264             <varname>VLAN=</varname> above and will enable the VLAN ID for ingress as well.</para>
1265           </listitem>
1266         </varlistentry>
1267       </variablelist>
1268   </refsect1>
1269
1270   <refsect1>
1271     <title>Example</title>
1272     <example>
1273       <title>/etc/systemd/network/50-static.network</title>
1274
1275       <programlisting>[Match]
1276 Name=enp2s0
1277
1278 [Network]
1279 Address=192.168.0.15/24
1280 Gateway=192.168.0.1</programlisting>
1281     </example>
1282
1283     <example>
1284       <title>/etc/systemd/network/80-dhcp.network</title>
1285
1286       <programlisting>[Match]
1287 Name=en*
1288
1289 [Network]
1290 DHCP=yes</programlisting>
1291     </example>
1292
1293     <example>
1294       <title>/etc/systemd/network/25-bridge-static.network</title>
1295
1296       <programlisting>[Match]
1297 Name=bridge0
1298
1299 [Network]
1300 Address=192.168.0.15/24
1301 Gateway=192.168.0.1
1302 DNS=192.168.0.1</programlisting>
1303     </example>
1304
1305     <example>
1306       <title>/etc/systemd/network/25-bridge-slave-interface.network</title>
1307
1308       <programlisting>[Match]
1309 Name=enp2s0
1310
1311 [Network]
1312 Bridge=bridge0</programlisting>
1313     </example>
1314     <example>
1315       <title>/etc/systemd/network/25-bridge-slave-interface-vlan.network</title>
1316
1317       <programlisting>[Match]
1318 Name=enp2s0
1319
1320 [Network]
1321 Bridge=bridge0
1322
1323 [BridgeVLAN]
1324 VLAN=1-32
1325 PVID=42
1326 EgressUntagged=42
1327
1328 [BridgeVLAN]
1329 VLAN=100-200
1330
1331 [BridgeVLAN]
1332 EgressUntagged=300-400</programlisting>
1333     </example>
1334     <example>
1335       <title>/etc/systemd/network/25-ipip.network</title>
1336
1337       <programlisting>[Match]
1338 Name=em1
1339
1340 [Network]
1341 Tunnel=ipip-tun</programlisting>
1342     </example>
1343
1344     <example>
1345       <title>/etc/systemd/network/25-sit.network</title>
1346
1347       <programlisting>[Match]
1348 Name=em1
1349
1350 [Network]
1351 Tunnel=sit-tun</programlisting>
1352     </example>
1353
1354     <example>
1355       <title>/etc/systemd/network/25-gre.network</title>
1356
1357       <programlisting>[Match]
1358 Name=em1
1359
1360 [Network]
1361 Tunnel=gre-tun</programlisting>
1362     </example>
1363
1364     <example>
1365       <title>/etc/systemd/network/25-vti.network</title>
1366
1367       <programlisting>[Match]
1368 Name=em1
1369
1370 [Network]
1371 Tunnel=vti-tun</programlisting>
1372     </example>
1373
1374     <example>
1375       <title>/etc/systemd/network/25-bond.network</title>
1376
1377       <programlisting>[Match]
1378 Name=bond1
1379
1380 [Network]
1381 DHCP=yes
1382 </programlisting>
1383     </example>
1384
1385     <example>
1386       <title>/etc/systemd/network/25-vrf.network</title>
1387       <para>Add the bond1 interface to the VRF master interface vrf-test. This will redirect routes generated on this interface to be within the routing table defined during VRF creation. Traffic won't be redirected towards the VRFs routing table unless specific ip-rules are added.</para>
1388       <programlisting>[Match]
1389 Name=bond1
1390
1391 [Network]
1392 VRF=vrf-test
1393 </programlisting>
1394     </example>
1395
1396   </refsect1>
1397
1398   <refsect1>
1399     <title>See Also</title>
1400     <para>
1401       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1402       <citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
1403       <citerefentry><refentrytitle>systemd.link</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1404       <citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1405       <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
1406     </para>
1407   </refsect1>
1408
1409 </refentry>