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systemd.network.xml
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systemd.network.xml
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<?xml version='1.0'?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
<refentry id="systemd.network" conditional='ENABLE_NETWORKD'
xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<title>systemd.network</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>systemd.network</refentrytitle>
<manvolnum>5</manvolnum>
</refmeta>
<refnamediv>
<refname>systemd.network</refname>
<refpurpose>Network configuration</refpurpose>
</refnamediv>
<refsynopsisdiv>
<para><filename><replaceable>network</replaceable>.network</filename></para>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>A plain ini-style text file that encodes network configuration for matching network interfaces,
used by
<citerefentry><refentrytitle>systemd-networkd</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
See <citerefentry><refentrytitle>systemd.syntax</refentrytitle><manvolnum>7</manvolnum></citerefentry>
for a general description of the syntax.</para>
<para>The main network file must have the extension <filename>.network</filename>; other
extensions are ignored. Networks are applied to links whenever the links appear.</para>
<para>The <filename>.network</filename> files are read from the files located in the system network
directories <filename>/usr/lib/systemd/network</filename> and
<filename>/usr/local/lib/systemd/network</filename>, the volatile runtime network directory
<filename>/run/systemd/network</filename> and the local administration network directory
<filename>/etc/systemd/network</filename>. All configuration files are collectively sorted and processed
in lexical order, regardless of the directories in which they live. However, files with identical
filenames replace each other. Files in <filename>/etc/</filename> have the highest priority, files in
<filename>/run/</filename> take precedence over files with the same name under
<filename>/usr/</filename>. This can be used to override a system-supplied configuration file with a local
file if needed. As a special case, an empty file (file size 0) or symlink with the same name pointing to
<filename>/dev/null</filename> disables the configuration file entirely (it is "masked").</para>
<para>Along with the network file <filename>foo.network</filename>, a "drop-in" directory
<filename>foo.network.d/</filename> may exist. All files with the suffix
<literal>.conf</literal> from this directory will be merged in the alphanumeric order and parsed
after the main file itself has been parsed. This is useful to alter or add configuration settings,
without having to modify the main configuration file. Each drop-in file must have appropriate
section headers.</para>
<para>In addition to <filename>/etc/systemd/network</filename>, drop-in <literal>.d</literal>
directories can be placed in <filename>/usr/lib/systemd/network</filename> or
<filename>/run/systemd/network</filename> directories. Drop-in files in
<filename>/etc/</filename> take precedence over those in <filename>/run/</filename> which in turn
take precedence over those in <filename>/usr/lib/</filename>. Drop-in files under any of these
directories take precedence over the main network file wherever located.</para>
</refsect1>
<refsect1>
<title>[Match] Section Options</title>
<para>The network file contains a [Match] section, which determines if a given network file may be
applied to a given device; and a [Network] section specifying how the device should be configured. The
first (in lexical order) of the network files that matches a given device is applied, all later files
are ignored, even if they match as well.</para>
<para>A network file is said to match a network interface if all matches specified by the [Match]
section are satisfied. When a network file does not contain valid settings in [Match] section, then the
file will match all interfaces and <command>systemd-networkd</command> warns about that. Hint: to avoid
the warning and to make it clear that all interfaces shall be matched, add the following:
<programlisting>Name=*</programlisting> The following keys are accepted:</para>
<variablelist class='network-directives'>
<xi:include href="systemd.link.xml" xpointer="mac-address" />
<xi:include href="systemd.link.xml" xpointer="permanent-mac-address" />
<xi:include href="systemd.link.xml" xpointer="path" />
<xi:include href="systemd.link.xml" xpointer="driver" />
<xi:include href="systemd.link.xml" xpointer="type" />
<xi:include href="systemd.link.xml" xpointer="property" />
<varlistentry>
<term><varname>Name=</varname></term>
<listitem>
<para>A whitespace-separated list of shell-style globs matching the device name, as exposed
by the udev property <literal>INTERFACE</literal>, or device's alternative names. If the
list is prefixed with a "!", the test is inverted.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>WLANInterfaceType=</varname></term>
<listitem>
<para>A whitespace-separated list of wireless network type. Supported values are
<literal>ad-hoc</literal>, <literal>station</literal>, <literal>ap</literal>,
<literal>ap-vlan</literal>, <literal>wds</literal>, <literal>monitor</literal>,
<literal>mesh-point</literal>, <literal>p2p-client</literal>, <literal>p2p-go</literal>,
<literal>p2p-device</literal>, <literal>ocb</literal>, and <literal>nan</literal>. If the
list is prefixed with a "!", the test is inverted.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>SSID=</varname></term>
<listitem>
<para>A whitespace-separated list of shell-style globs matching the SSID of the currently
connected wireless LAN. If the list is prefixed with a "!", the test is inverted.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>BSSID=</varname></term>
<listitem>
<para>A whitespace-separated list of hardware address of the currently connected wireless
LAN. Use full colon-, hyphen- or dot-delimited hexadecimal. See the example in
<varname>MACAddress=</varname>. This option may appear more than once, in which case the
lists are merged. If the empty string is assigned to this option, the list is reset.</para>
</listitem>
</varlistentry>
<xi:include href="systemd.link.xml" xpointer="host" />
<xi:include href="systemd.link.xml" xpointer="virtualization" />
<xi:include href="systemd.link.xml" xpointer="kernel-command-line" />
<xi:include href="systemd.link.xml" xpointer="kernel-version" />
<xi:include href="systemd.link.xml" xpointer="architecture" />
</variablelist>
</refsect1>
<refsect1>
<title>[Link] Section Options</title>
<para> The [Link] section accepts the following keys:</para>
<variablelist class='network-directives'>
<varlistentry>
<term><varname>MACAddress=</varname></term>
<listitem>
<para>The hardware address to set for the device.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>MTUBytes=</varname></term>
<listitem>
<para>The maximum transmission unit in bytes to set for the
device. The usual suffixes K, M, G, are supported and are
understood to the base of 1024.</para>
<para>Note that if IPv6 is enabled on the interface, and the MTU is chosen
below 1280 (the minimum MTU for IPv6) it will automatically be increased to this value.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>ARP=</varname></term>
<listitem>
<para>Takes a boolean. If set to true, the ARP (low-level Address Resolution Protocol)
for this interface is enabled. When unset, the kernel's default will be used.</para>
<para> For example, disabling ARP is useful when creating multiple MACVLAN or VLAN virtual
interfaces atop a single lower-level physical interface, which will then only serve as a
link/"bridge" device aggregating traffic to the same physical link and not participate in
the network otherwise. Defaults to unset.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>Multicast=</varname></term>
<listitem>
<para>Takes a boolean. If set to true, the multicast flag on the device is enabled. Defaults to unset.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>AllMulticast=</varname></term>
<listitem>
<para>Takes a boolean. If set to true, the driver retrieves all multicast packets from the network.
This happens when multicast routing is enabled. Defaults to unset.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>Promiscuous=</varname></term>
<listitem>
<para>Takes a boolean. If set to true, promiscuous mode of the interface is enabled.
Defaults to unset.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>Unmanaged=</varname></term>
<listitem>
<para>Takes a boolean. When <literal>yes</literal>, no attempts are
made to bring up or configure matching links, equivalent to
when there are no matching network files. Defaults to
<literal>no</literal>.</para>
<para>This is useful for preventing later matching network
files from interfering with certain interfaces that are fully
controlled by other applications.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>Group=</varname></term>
<listitem>
<para>Link groups are similar to port ranges found in managed switches. When network interfaces
are added to a numbered group, operations on all the interfaces from that group can be
performed at once. Takes an unsigned integer in the range 0…4294967295. Defaults to unset.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>RequiredForOnline=</varname></term>
<listitem>
<para>Takes a boolean or a minimum operational state and an optional maximum operational state.
Please see <citerefentry><refentrytitle>networkctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
for possible operational states. When <literal>yes</literal>, the network is deemed required when
determining whether the system is online (including when running
<command>systemd-networkd-wait-online</command>). When <literal>no</literal>, the network is ignored
when determining the online state. When a minimum operational state and an optional maximum operational
state are set, <literal>yes</literal> is implied, and this controls the minimum and maximum
operational state required for the network interface to be considered online.</para>
<para>Defaults to <literal>yes</literal> when <varname>ActivationPolicy=</varname> is not set,
or set to <literal>up</literal>, <literal>always-up</literal>, or <literal>bound</literal>.
Defaults to <literal>no</literal> when <varname>ActivationPolicy=</varname> is set to
<literal>manual</literal> or <literal>down</literal>. This is forced to <literal>no</literal>
when <varname>ActivationPolicy=</varname> is set to <literal>always-down</literal>.</para>
<para>The network will be brought up normally (as configured by <varname>ActivationPolicy=</varname>),
but in the event that there is no address being assigned by DHCP or the
cable is not plugged in, the link will simply remain offline and be
skipped automatically by <command>systemd-networkd-wait-online</command>
if <literal>RequiredForOnline=no</literal>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>RequiredFamilyForOnline=</varname></term>
<listitem>
<para>Takes an address family. When specified, an IP address in the given family is deemed required
when determining whether the link is online (including when running
<command>systemd-networkd-wait-online</command>). Takes one of <literal>ipv4</literal>,
<literal>ipv6</literal>, <literal>both</literal>, or <literal>any</literal>. Defaults to
<literal>any</literal>. Note that this option has no effect if
<literal>RequiredForOnline=no</literal>, or if <literal>RequiredForOnline=</literal> specifies a
minimum operational state below <literal>degraded</literal>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>ActivationPolicy=</varname></term>
<listitem>
<para>Specifies the policy for <command>systemd-networkd</command> managing the link
administrative state. Specifically, this controls how <command>systemd-networkd</command>
changes the network device's <literal>IFF_UP</literal> flag, which is sometimes
controlled by system administrators by running e.g., <command>ip set dev eth0 up</command>
or <command>ip set dev eth0 down</command>, and can also be changed with
<command>networkctl up eth0</command> or <command>networkctl down eth0</command>.</para>
<para>Takes one of <literal>up</literal>, <literal>always-up</literal>,
<literal>manual</literal>, <literal>always-down</literal>, <literal>down</literal>,
or <literal>bound</literal>. When <literal>manual</literal>, <command>systemd-networkd</command>
will not change the link's admin state automatically; the system administrator must bring the
interface up or down manually, as desired. When <literal>up</literal> (the default) or
<literal>always-up</literal>, or <literal>down</literal> or <literal>always-down</literal>,
<command>systemd-networkd</command> will set the link up or down, respectively,
when the interface is (re)configured. When <literal>always-up</literal> or
<literal>always-down</literal>, <command>systemd-networkd</command> will set the link up
or down, respectively, any time <command>systemd-networkd</command> detects a change in
the administrative state. When <varname>BindCarrier=</varname> is also set, this is
automatically set to <literal>bound</literal> and any other value is ignored.</para>
<para>When the policy is set to <literal>down</literal> or <literal>manual</literal>,
the default value of <varname>RequiredForOnline=</varname> is <literal>no</literal>.
When the policy is set to <literal>always-down</literal>, the value of
<varname>RequiredForOnline=</varname> forced to <literal>no</literal>.</para>
<para>The administrative state is not the same as the carrier state, so using
<literal>always-up</literal> does not mean the link will never lose carrier. The link
carrier depends on both the administrative state as well as the network device's physical
connection. However, to avoid reconfiguration failures, when using <literal>always-up</literal>,
<varname>IgnoreCarrierLoss=</varname> is forced to true.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>[SR-IOV] Section Options</title>
<para>The [SR-IOV] section accepts the following keys. Specify several [SR-IOV] sections to configure
several SR-IOVs. SR-IOV provides the ability to partition a single physical PCI resource into virtual
PCI functions which can then be injected into a VM. In the case of network VFs, SR-IOV improves
north-south network performance (that is, traffic with endpoints outside the host machine) by allowing
traffic to bypass the host machine’s network stack.</para>
<variablelist class='network-directives'>
<varlistentry>
<term><varname>VirtualFunction=</varname></term>
<listitem>
<para>Specifies a Virtual Function (VF), lightweight PCIe function designed solely to move data
in and out. Takes an unsigned integer in the range 0…2147483646. This option is compulsory.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>VLANId=</varname></term>
<listitem>
<para>Specifies VLAN ID of the virtual function. Takes an unsigned integer in the range 1…4095.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>QualityOfService=</varname></term>
<listitem>
<para>Specifies quality of service of the virtual function. Takes an unsigned integer in the range 1…4294967294.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>VLANProtocol=</varname></term>
<listitem>
<para>Specifies VLAN protocol of the virtual function. Takes <literal>802.1Q</literal> or
<literal>802.1ad</literal>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>MACSpoofCheck=</varname></term>
<listitem>
<para>Takes a boolean. Controls the MAC spoof checking. When unset, the kernel's default will be used.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>QueryReceiveSideScaling=</varname></term>
<listitem>
<para>Takes a boolean. Toggle the ability of querying the receive side scaling (RSS)
configuration of the virtual function (VF). The VF RSS information like RSS hash key may be
considered sensitive on some devices where this information is shared between VF and the
physical function (PF). When unset, the kernel's default will be used.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>Trust=</varname></term>
<listitem>
<para>Takes a boolean. Allows to set trust mode of the virtual function (VF). When set, VF
users can set a specific feature which may impact security and/or performance. When unset,
the kernel's default will be used.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>LinkState=</varname></term>
<listitem>
<para>Allows to set the link state of the virtual function (VF). Takes a boolean or a
special value <literal>auto</literal>. Setting to <literal>auto</literal> means a
reflection of the physical function (PF) link state, <literal>yes</literal> lets the VF to
communicate with other VFs on this host even if the PF link state is down,
<literal>no</literal> causes the hardware to drop any packets sent by the VF. When unset,
the kernel's default will be used.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>MACAddress=</varname></term>
<listitem>
<para>Specifies the MAC address for the virtual function.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>[Network] Section Options</title>
<para>The [Network] section accepts the following keys:</para>
<variablelist class='network-directives'>
<varlistentry>
<term><varname>Description=</varname></term>
<listitem>
<para>A description of the device. This is only used for
presentation purposes.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>DHCP=</varname></term>
<listitem>
<para>Enables DHCPv4 and/or DHCPv6 client support. Accepts
<literal>yes</literal>, <literal>no</literal>,
<literal>ipv4</literal>, or <literal>ipv6</literal>. Defaults
to <literal>no</literal>.</para>
<para>Note that DHCPv6 will by default be triggered by Router
Advertisement, if that is enabled, regardless of this parameter.
By enabling DHCPv6 support explicitly, the DHCPv6 client will
be started regardless of the presence of routers on the link,
or what flags the routers pass. See
<literal>IPv6AcceptRA=</literal>.</para>
<para>Furthermore, note that by default the domain name
specified through DHCP is not used for name resolution.
See option <option>UseDomains=</option> below.</para>
<para>See the [DHCPv4] or [DHCPv6] sections below for further configuration options for the DHCP
client support.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>DHCPServer=</varname></term>
<listitem>
<para>Takes a boolean. If set to <literal>yes</literal>, DHCPv4 server will be started. Defaults
to <literal>no</literal>. Further settings for the DHCP server may be set in the [DHCPServer]
section described below.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>LinkLocalAddressing=</varname></term>
<listitem>
<para>Enables link-local address autoconfiguration. Accepts <option>yes</option>,
<option>no</option>, <option>ipv4</option>, and <option>ipv6</option>. An IPv6 link-local address
is configured when <option>yes</option> or <option>ipv6</option>. An IPv4 link-local address is
configured when <option>yes</option> or <option>ipv4</option> and when DHCPv4 autoconfiguration
has been unsuccessful for some time. (IPv4 link-local address autoconfiguration will usually
happen in parallel with repeated attempts to acquire a DHCPv4 lease).</para>
<para>Defaults to <option>no</option> when <varname>Bridge=yes</varname> is set, and
<option>ipv6</option> otherwise.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>IPv6LinkLocalAddressGenerationMode=</varname></term>
<listitem>
<para>Specifies how IPv6 link local address is generated. Takes one of
<literal>eui64</literal>, <literal>none</literal>, <literal>stable-privacy</literal> and
<literal>random</literal>. When unset, <literal>stable-privacy</literal> is used if
<varname>IPv6StableSecretAddress=</varname> is specified, and if not,
<literal>eui64</literal> is used. Note that if <varname>LinkLocalAddressing=</varname> is
<literal>no</literal> or <literal>ipv4</literal>, then
<varname>IPv6LinkLocalAddressGenerationMode=</varname> will be ignored. Also, even if
<varname>LinkLocalAddressing=</varname> is <literal>yes</literal> or
<literal>ipv6</literal>, setting <varname>IPv6LinkLocalAddressGenerationMode=none</varname>
disables to configure an IPv6 link-local address.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>IPv6StableSecretAddress=</varname></term>
<listitem>
<para>Takes an IPv6 address. The specified address will be used as a stable secret for
generating IPv6 link-local address. If this setting is specified, and
<varname>IPv6LinkLocalAddressGenerationMode=</varname> is unset, then
<varname>IPv6LinkLocalAddressGenerationMode=stable-privacy</varname> is implied.
If this setting is not specified, and <literal>stable-privacy</literal> is set to
<varname>IPv6LinkLocalAddressGenerationMode=</varname>,
then a stable secret address will be generated from the local machine ID and the interface
name.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>IPv4LLRoute=</varname></term>
<listitem>
<para>Takes a boolean. If set to true, sets up the route needed for
non-IPv4LL hosts to communicate with IPv4LL-only hosts. Defaults
to false.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>DefaultRouteOnDevice=</varname></term>
<listitem>
<para>Takes a boolean. If set to true, sets up the default route bound to the interface.
Defaults to false. This is useful when creating routes on point-to-point interfaces.
This is equivalent to e.g. the following,
<programlisting>ip route add default dev veth99</programlisting>
or,
<programlisting>[Route]
Gateway=0.0.0.0</programlisting></para>
<para>Currently, there are no way to specify e.g., the table for the route configured by
this setting. To configure the default route with such an additional property, please use
the following instead:
<programlisting>[Route]
Gateway=0.0.0.0
Table=1234</programlisting></para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>IPv6Token=</varname></term>
<listitem>
<para>Specifies an optional address generation mode for the Stateless Address
Autoconfiguration (SLAAC). Supported modes are <literal>prefixstable</literal> and
<literal>static</literal>.</para>
<para>When the mode is set to <literal>static</literal>, an IPv6 address must be
specified after a colon (<literal>:</literal>), and the lower bits of the supplied
address are combined with the upper bits of a prefix received in a Router Advertisement
(RA) message to form a complete address. Note that if multiple prefixes are received in an
RA message, or in multiple RA messages, addresses will be formed from each of them using
the supplied address. This mode implements SLAAC but uses a static interface identifier
instead of an identifier generated by using the EUI-64 algorithm. Because the interface
identifier is static, if Duplicate Address Detection detects that the computed address is a
duplicate (in use by another node on the link), then this mode will fail to provide an
address for that prefix. If an IPv6 address without mode is specified, then
<literal>static</literal> mode is assumed.</para>
<para>When the mode is set to <literal>prefixstable</literal> the
<ulink url="https://tools.ietf.org/html/rfc7217">RFC 7217</ulink> algorithm for generating
interface identifiers will be used. This mode can optionally take an IPv6 address separated
with a colon (<literal>:</literal>). If an IPv6 address is specified, then an interface
identifier is generated only when a prefix received in an RA message matches the supplied
address.</para>
<para>If no address generation mode is specified (which is the default), or a received
prefix does not match any of the addresses provided in <literal>prefixstable</literal>
mode, then the EUI-64 algorithm will be used to form an interface identifier for that
prefix. This mode is also SLAAC, but with a potentially stable interface identifier which
does not directly map to the interface's hardware address.</para>
<para>Note that the <literal>prefixstable</literal> algorithm uses both the interface
name and MAC address as input to the hash to compute the interface identifier, so if either
of those are changed the resulting interface identifier (and address) will change, even if
the prefix received in the RA message has not changed.</para>
<para>This setting can be specified multiple times. If an empty string is assigned, then
the all previous assignments are cleared.</para>
<para>Examples:
<programlisting>IPv6Token=::1a:2b:3c:4d
IPv6Token=static:::1a:2b:3c:4d
IPv6Token=prefixstable
IPv6Token=prefixstable:2002:da8:1::</programlisting></para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>LLMNR=</varname></term>
<listitem>
<para>Takes a boolean or <literal>resolve</literal>. When true,
enables <ulink
url="https://tools.ietf.org/html/rfc4795">Link-Local
Multicast Name Resolution</ulink> on the link. When set to
<literal>resolve</literal>, only resolution is enabled,
but not host registration and announcement. Defaults to
true. This setting is read by
<citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>MulticastDNS=</varname></term>
<listitem>
<para>Takes a boolean or <literal>resolve</literal>. When true,
enables <ulink
url="https://tools.ietf.org/html/rfc6762">Multicast
DNS</ulink> support on the link. When set to
<literal>resolve</literal>, only resolution is enabled,
but not host or service registration and
announcement. Defaults to false. This setting is read by
<citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>DNSOverTLS=</varname></term>
<listitem>
<para>Takes a boolean or <literal>opportunistic</literal>.
When true, enables
<ulink
url="https://tools.ietf.org/html/rfc7858">DNS-over-TLS</ulink>
support on the link.
When set to <literal>opportunistic</literal>, compatibility with
non-DNS-over-TLS servers is increased, by automatically
turning off DNS-over-TLS servers in this case.
This option defines a per-interface setting for
<citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>'s
global <varname>DNSOverTLS=</varname> option. Defaults to
false. This setting is read by
<citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>DNSSEC=</varname></term>
<listitem>
<para>Takes a boolean or <literal>allow-downgrade</literal>. When true, enables
<ulink url="https://tools.ietf.org/html/rfc4033">DNSSEC</ulink>
DNS validation support on the link. When set to
<literal>allow-downgrade</literal>, compatibility with
non-DNSSEC capable networks is increased, by automatically
turning off DNSSEC in this case. This option defines a
per-interface setting for
<citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>'s
global <varname>DNSSEC=</varname> option. Defaults to
false. This setting is read by
<citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>DNSSECNegativeTrustAnchors=</varname></term>
<listitem><para>A space-separated list of DNSSEC negative
trust anchor domains. If specified and DNSSEC is enabled,
look-ups done via the interface's DNS server will be subject
to the list of negative trust anchors, and not require
authentication for the specified domains, or anything below
it. Use this to disable DNSSEC authentication for specific
private domains, that cannot be proven valid using the
Internet DNS hierarchy. Defaults to the empty list. This
setting is read by
<citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>LLDP=</varname></term>
<listitem>
<para>Controls support for Ethernet LLDP packet reception. LLDP is a link-layer protocol commonly
implemented on professional routers and bridges which announces which physical port a system is connected
to, as well as other related data. Accepts a boolean or the special value
<literal>routers-only</literal>. When true, incoming LLDP packets are accepted and a database of all LLDP
neighbors maintained. If <literal>routers-only</literal> is set only LLDP data of various types of routers
is collected and LLDP data about other types of devices ignored (such as stations, telephones and
others). If false, LLDP reception is disabled. Defaults to <literal>routers-only</literal>. Use
<citerefentry><refentrytitle>networkctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> to query the
collected neighbor data. LLDP is only available on Ethernet links. See <varname>EmitLLDP=</varname> below
for enabling LLDP packet emission from the local system.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>EmitLLDP=</varname></term>
<listitem>
<para>Controls support for Ethernet LLDP packet emission. Accepts a boolean parameter or the special values
<literal>nearest-bridge</literal>, <literal>non-tpmr-bridge</literal> and
<literal>customer-bridge</literal>. Defaults to false, which turns off LLDP packet emission. If not false,
a short LLDP packet with information about the local system is sent out in regular intervals on the
link. The LLDP packet will contain information about the local hostname, the local machine ID (as stored
in <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>) and the
local interface name, as well as the pretty hostname of the system (as set in
<citerefentry><refentrytitle>machine-info</refentrytitle><manvolnum>5</manvolnum></citerefentry>). LLDP
emission is only available on Ethernet links. Note that this setting passes data suitable for
identification of host to the network and should thus not be enabled on untrusted networks, where such
identification data should not be made available. Use this option to permit other systems to identify on
which interfaces they are connected to this system. The three special values control propagation of the
LLDP packets. The <literal>nearest-bridge</literal> setting permits propagation only to the nearest
connected bridge, <literal>non-tpmr-bridge</literal> permits propagation across Two-Port MAC Relays, but
not any other bridges, and <literal>customer-bridge</literal> permits propagation until a customer bridge
is reached. For details about these concepts, see <ulink
url="https://standards.ieee.org/findstds/standard/802.1AB-2016.html">IEEE 802.1AB-2016</ulink>. Note that
configuring this setting to true is equivalent to <literal>nearest-bridge</literal>, the recommended and
most restricted level of propagation. See <varname>LLDP=</varname> above for an option to enable LLDP
reception.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>BindCarrier=</varname></term>
<listitem>
<para>A link name or a list of link names. When set, controls the behavior of the current
link. When all links in the list are in an operational down state, the current link is brought
down. When at least one link has carrier, the current interface is brought up.</para>
<para>This forces <varname>ActivationPolicy=</varname> to be set to <literal>bound</literal>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>Address=</varname></term>
<listitem>
<para>A static IPv4 or IPv6 address and its prefix length,
separated by a <literal>/</literal> character. Specify
this key more than once to configure several addresses.
The format of the address must be as described in
<citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
This is a short-hand for an [Address] section only
containing an Address key (see below). This option may be
specified more than once.
</para>
<para>If the specified address is <literal>0.0.0.0</literal> (for IPv4) or <literal>::</literal>
(for IPv6), a new address range of the requested size is automatically allocated from a
system-wide pool of unused ranges. Note that the prefix length must be equal or larger than 8 for
IPv4, and 64 for IPv6. The allocated range is checked against all current network interfaces and
all known network configuration files to avoid address range conflicts. The default system-wide
pool consists of 192.168.0.0/16, 172.16.0.0/12 and 10.0.0.0/8 for IPv4, and fd00::/8 for IPv6.
This functionality is useful to manage a large number of dynamically created network interfaces
with the same network configuration and automatic address range assignment.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>Gateway=</varname></term>
<listitem>
<para>The gateway address, which must be in the format
described in
<citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
This is a short-hand for a [Route] section only containing
a Gateway key. This option may be specified more than
once.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>DNS=</varname></term>
<listitem>
<para>A DNS server address, which must be in the format described in
<citerefentry project='man-pages'><refentrytitle>inet_pton</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
This option may be specified more than once. Each address can optionally take a port number
separated with <literal>:</literal>, a network interface name or index separated with
<literal>%</literal>, and a Server Name Indication (SNI) separated with <literal>#</literal>.
When IPv6 address is specified with a port number, then the address must be in the square
brackets. That is, the acceptable full formats are
<literal>111.222.333.444:9953%ifname#example.com</literal> for IPv4 and
<literal>[1111:2222::3333]:9953%ifname#example.com</literal> for IPv6. If an empty string is
assigned, then the all previous assignments are cleared. This setting is read by
<citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>Domains=</varname></term>
<listitem>
<para>A whitespace-separated list of domains which should be resolved using the DNS servers on
this link. Each item in the list should be a domain name, optionally prefixed with a tilde
(<literal>~</literal>). The domains with the prefix are called "routing-only domains". The
domains without the prefix are called "search domains" and are first used as search suffixes for
extending single-label hostnames (hostnames containing no dots) to become fully qualified
domain names (FQDNs). If a single-label hostname is resolved on this interface, each of the
specified search domains are appended to it in turn, converting it into a fully qualified domain
name, until one of them may be successfully resolved.</para>
<para>Both "search" and "routing-only" domains are used for routing of DNS queries: look-ups for hostnames
ending in those domains (hence also single label names, if any "search domains" are listed), are routed to
the DNS servers configured for this interface. The domain routing logic is particularly useful on
multi-homed hosts with DNS servers serving particular private DNS zones on each interface.</para>
<para>The "routing-only" domain <literal>~.</literal> (the tilde indicating definition of a routing domain,
the dot referring to the DNS root domain which is the implied suffix of all valid DNS names) has special
effect. It causes all DNS traffic which does not match another configured domain routing entry to be routed
to DNS servers specified for this interface. This setting is useful to prefer a certain set of DNS servers
if a link on which they are connected is available.</para>
<para>This setting is read by
<citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
"Search domains" correspond to the <varname>domain</varname> and <varname>search</varname> entries in
<citerefentry project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
Domain name routing has no equivalent in the traditional glibc API, which has no concept of domain
name servers limited to a specific link.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>DNSDefaultRoute=</varname></term>
<listitem>
<para>Takes a boolean argument. If true, this link's configured DNS servers are used for resolving domain
names that do not match any link's configured <varname>Domains=</varname> setting. If false, this link's
configured DNS servers are never used for such domains, and are exclusively used for resolving names that
match at least one of the domains configured on this link. If not specified defaults to an automatic mode:
queries not matching any link's configured domains will be routed to this link if it has no routing-only
domains configured.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>NTP=</varname></term>
<listitem>
<para>An NTP server address (either an IP address, or a hostname). This option may be specified more than once. This setting is read by
<citerefentry><refentrytitle>systemd-timesyncd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>IPForward=</varname></term>
<listitem><para>Configures IP packet forwarding for the
system. If enabled, incoming packets on any network
interface will be forwarded to any other interfaces
according to the routing table. Takes a boolean,
or the values <literal>ipv4</literal> or
<literal>ipv6</literal>, which only enable IP packet
forwarding for the specified address family. This controls
the <filename>net.ipv4.ip_forward</filename> and
<filename>net.ipv6.conf.all.forwarding</filename> sysctl
options of the network interface (see <ulink
url="https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt">ip-sysctl.txt</ulink>
for details about sysctl options). Defaults to
<literal>no</literal>.</para>
<para>Note: this setting controls a global kernel option,
and does so one way only: if a network that has this setting
enabled is set up the global setting is turned on. However,
it is never turned off again, even after all networks with
this setting enabled are shut down again.</para>
<para>To allow IP packet forwarding only between specific
network interfaces use a firewall.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>IPMasquerade=</varname></term>
<listitem><para>Configures IP masquerading for the network interface. If enabled, packets
forwarded from the network interface will be appear as coming from the local host. Takes one
of <literal>ipv4</literal>, <literal>ipv6</literal>, <literal>both</literal>, or
<literal>no</literal>. Defaults to <literal>no</literal>. If enabled, this automatically sets
<varname>IPForward=</varname> to one of <literal>ipv4</literal>, <literal>ipv6</literal> or
<literal>yes</literal>.</para>
<para>Note. Any positive boolean values such as <literal>yes</literal> or
<literal>true</literal> are now deprecated. Please use one of the values in the above.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>IPv6PrivacyExtensions=</varname></term>
<listitem><para>Configures use of stateless temporary
addresses that change over time (see <ulink
url="https://tools.ietf.org/html/rfc4941">RFC 4941</ulink>,
Privacy Extensions for Stateless Address Autoconfiguration
in IPv6). Takes a boolean or the special values
<literal>prefer-public</literal> and
<literal>kernel</literal>. When true, enables the privacy
extensions and prefers temporary addresses over public
addresses. When <literal>prefer-public</literal>, enables the
privacy extensions, but prefers public addresses over
temporary addresses. When false, the privacy extensions
remain disabled. When <literal>kernel</literal>, the kernel's
default setting will be left in place. Defaults to
<literal>no</literal>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>IPv6AcceptRA=</varname></term>
<listitem><para>Takes a boolean. Controls IPv6 Router Advertisement (RA) reception support for the
interface. If true, RAs are accepted; if false, RAs are ignored. When RAs are accepted, they may
trigger the start of the DHCPv6 client if the relevant flags are set in the RA data, or if no
routers are found on the link. The default is to disable RA reception for bridge devices or when IP
forwarding is enabled, and to enable it otherwise. Cannot be enabled on bond devices and when link
local addressing is disabled.</para>
<para>Further settings for the IPv6 RA support may be configured in the [IPv6AcceptRA] section, see
below.</para>
<para>Also see <ulink
url="https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt">ip-sysctl.txt</ulink> in the kernel
documentation regarding <literal>accept_ra</literal>, but note that systemd's setting of
<constant>1</constant> (i.e. true) corresponds to kernel's setting of <constant>2</constant>.</para>
<para>Note that kernel's implementation of the IPv6 RA protocol is always disabled,
regardless of this setting. If this option is enabled, a userspace implementation of the IPv6
RA protocol is used, and the kernel's own implementation remains disabled, since
<command>systemd-networkd</command> needs to know all details supplied in the advertisements,
and these are not available from the kernel if the kernel's own implementation is used.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>IPv6DuplicateAddressDetection=</varname></term>
<listitem><para>Configures the amount of IPv6 Duplicate
Address Detection (DAD) probes to send. When unset, the kernel's default will be used.
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>IPv6HopLimit=</varname></term>
<listitem><para>Configures IPv6 Hop Limit. For each router that
forwards the packet, the hop limit is decremented by 1. When the
hop limit field reaches zero, the packet is discarded.
When unset, the kernel's default will be used.
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>IPv4AcceptLocal=</varname></term>
<listitem><para>Takes a boolean. Accept packets with local source addresses. In combination
with suitable routing, this can be used to direct packets between two local interfaces over
the wire and have them accepted properly. When unset, the kernel's default will be used.
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>IPv4RouteLocalnet=</varname></term>
<listitem><para>Takes a boolean. When true, the kernel does not consider loopback addresses as martian source or destination
while routing. This enables the use of 127.0.0.0/8 for local routing purposes. When unset, the kernel's default will be used.
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>IPv4ProxyARP=</varname></term>
<listitem><para>Takes a boolean. Configures proxy ARP for IPv4. Proxy ARP is the technique in which one host,
usually a router, answers ARP requests intended for another machine. By "faking" its identity,
the router accepts responsibility for routing packets to the "real" destination. See <ulink
url="https://tools.ietf.org/html/rfc1027">RFC 1027</ulink>.
When unset, the kernel's default will be used.
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>IPv6ProxyNDP=</varname></term>
<listitem><para>Takes a boolean. Configures proxy NDP for IPv6. Proxy NDP (Neighbor Discovery
Protocol) is a technique for IPv6 to allow routing of addresses to a different
destination when peers expect them to be present on a certain physical link.
In this case a router answers Neighbour Advertisement messages intended for
another machine by offering its own MAC address as destination.
Unlike proxy ARP for IPv4, it is not enabled globally, but will only send Neighbour
Advertisement messages for addresses in the IPv6 neighbor proxy table,
which can also be shown by <command>ip -6 neighbour show proxy</command>.
systemd-networkd will control the per-interface `proxy_ndp` switch for each configured
interface depending on this option.
When unset, the kernel's default will be used.
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>IPv6ProxyNDPAddress=</varname></term>
<listitem><para>An IPv6 address, for which Neighbour Advertisement messages will be
proxied. This option may be specified more than once. systemd-networkd will add the
<option>IPv6ProxyNDPAddress=</option> entries to the kernel's IPv6 neighbor proxy table.
This option implies <option>IPv6ProxyNDP=yes</option> but has no effect if
<option>IPv6ProxyNDP</option> has been set to false. When unset, the kernel's default will be used.
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>IPv6SendRA=</varname></term>
<listitem><para>Whether to enable or disable Router Advertisement sending on a link. Takes a
boolean value. When enabled, prefixes configured in [IPv6Prefix] sections and routes
configured in [IPv6RoutePrefix] sections are distributed as defined in the [IPv6SendRA]
section. If <varname>DHCPv6PrefixDelegation=</varname> is enabled, then the delegated
prefixes are also distributed. See <varname>DHCPv6PrefixDelegation=</varname> setting and the
[IPv6SendRA], [IPv6Prefix], [IPv6RoutePrefix], and [DHCPv6PrefixDelegation] sections for more
configuration options.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>DHCPv6PrefixDelegation=</varname></term>
<listitem><para>Takes a boolean value. When enabled, requests prefixes using a DHCPv6 client
configured on another link. By default, an address within each delegated prefix will be
assigned, and the prefixes will be announced through IPv6 Router Advertisement when
<varname>IPv6SendRA=</varname> is enabled. Such default settings can be configured in
[DHCPv6PrefixDelegation] section. Defaults to disabled.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>IPv6MTUBytes=</varname></term>
<listitem><para>Configures IPv6 maximum transmission unit (MTU).
An integer greater than or equal to 1280 bytes. When unset, the kernel's default will be used.
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>BatmanAdvanced=</varname></term>
<term><varname>Bond=</varname></term>
<term><varname>Bridge=</varname></term>
<term><varname>VRF=</varname></term>
<listitem>
<para>The name of the B.A.T.M.A.N. Advanced, bond, bridge, or VRF interface to add the link
to. See
<citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>IPVLAN=</varname></term>
<term><varname>IPVTAP=</varname></term>
<term><varname>L2TP=</varname></term>
<term><varname>MACsec=</varname></term>
<term><varname>MACVLAN=</varname></term>
<term><varname>MACVTAP=</varname></term>
<term><varname>Tunnel=</varname></term>
<term><varname>VLAN=</varname></term>
<term><varname>VXLAN=</varname></term>
<term><varname>Xfrm=</varname></term>
<listitem>
<para>The name of an IPVLAN, IPVTAP, L2TP, MACsec, MACVLAN, MACVTAP, tunnel, VLAN, VXLAN, or
Xfrm to be created on the link. See
<citerefentry><refentrytitle>systemd.netdev</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
This option may be specified more than once.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>ActiveSlave=</varname></term>
<listitem>
<para>Takes a boolean. Specifies the new active slave. The <literal>ActiveSlave=</literal>
option is only valid for following modes:
<literal>active-backup</literal>,
<literal>balance-alb</literal> and
<literal>balance-tlb</literal>. Defaults to false.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>PrimarySlave=</varname></term>
<listitem>
<para>Takes a boolean. Specifies which slave is the primary device. The specified
device will always be the active slave while it is available. Only when the
primary is off-line will alternate devices be used. This is useful when
one slave is preferred over another, e.g. when one slave has higher throughput
than another. The <literal>PrimarySlave=</literal> option is only valid for
following modes:
<literal>active-backup</literal>,
<literal>balance-alb</literal> and
<literal>balance-tlb</literal>. Defaults to false.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>ConfigureWithoutCarrier=</varname></term>
<listitem>
<para>Takes a boolean. Allows networkd to configure a specific link even if it has no carrier.
Defaults to false. If <option>IgnoreCarrierLoss=</option> is not explicitly set, it will
default to this value.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>IgnoreCarrierLoss=</varname></term>
<listitem>
<para>Takes a boolean. Allows networkd to retain both the static and dynamic configuration
of the interface even if its carrier is lost. When unset, the value specified with
<option>ConfigureWithoutCarrier=</option> is used.
</para>
<para>When <varname>ActivationPolicy=</varname> is set to <literal>always-up</literal>, this
is forced to <literal>true</literal>.
</para>
</listitem>
</varlistentry>