Adding upstream version 241.upstream/241upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 272 insertions, 0 deletions

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+<?xml version='1.0'?>
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+
+<!--
+  SPDX-License-Identifier: LGPL-2.1+
+-->
+
+<refentry id="resolved.conf" conditional='ENABLE_RESOLVE'
+    xmlns:xi="http://www.w3.org/2001/XInclude">
+  <refentryinfo>
+    <title>resolved.conf</title>
+    <productname>systemd</productname>
+  </refentryinfo>
+
+  <refmeta>
+    <refentrytitle>resolved.conf</refentrytitle>
+    <manvolnum>5</manvolnum>
+  </refmeta>
+
+  <refnamediv>
+    <refname>resolved.conf</refname>
+    <refname>resolved.conf.d</refname>
+    <refpurpose>Network Name Resolution configuration files</refpurpose>
+  </refnamediv>
+
+  <refsynopsisdiv>
+    <para><filename>/etc/systemd/resolved.conf</filename></para>
+    <para><filename>/etc/systemd/resolved.conf.d/*.conf</filename></para>
+    <para><filename>/run/systemd/resolved.conf.d/*.conf</filename></para>
+    <para><filename>/usr/lib/systemd/resolved.conf.d/*.conf</filename></para>
+  </refsynopsisdiv>
+
+  <refsect1>
+    <title>Description</title>
+
+    <para>These configuration files control local DNS and LLMNR
+    name resolution.</para>
+
+  </refsect1>
+
+  <xi:include href="standard-conf.xml" xpointer="main-conf" />
+
+  <refsect1>
+    <title>Options</title>
+
+    <para>The following options are available in the <literal>[Resolve]</literal> section:</para>
+
+    <variablelist class='network-directives'>
+
+      <varlistentry>
+        <term><varname>DNS=</varname></term>
+        <listitem><para>A space-separated list of IPv4 and IPv6 addresses to use as system DNS servers. DNS requests
+        are sent to one of the listed DNS servers in parallel to suitable per-link DNS servers acquired from
+        <citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry> or
+        set at runtime by external applications.  For compatibility reasons, if this setting is not specified, the DNS
+        servers listed in <filename>/etc/resolv.conf</filename> are used instead, if that file exists and any servers
+        are configured in it. This setting defaults to the empty list.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>FallbackDNS=</varname></term>
+        <listitem><para>A space-separated list of IPv4 and IPv6 addresses to use as the fallback DNS servers. Any
+        per-link DNS servers obtained from
+        <citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+        take precedence over this setting, as do any servers set via <varname>DNS=</varname> above or
+        <filename>/etc/resolv.conf</filename>. This setting is hence only used if no other DNS server information is
+        known. If this option is not given, a compiled-in list of DNS servers is used instead.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>Domains=</varname></term>
+        <listitem><para>A space-separated list of domains. These domains are used as search suffixes when resolving
+        single-label host names (domain names which contain no dot), in order to qualify them into fully-qualified
+        domain names (FQDNs). Search domains are strictly processed in the order they are specified, until the name
+        with the suffix appended is found. For compatibility reasons, if this setting is not specified, the search
+        domains listed in <filename>/etc/resolv.conf</filename> are used instead, if that file exists and any domains
+        are configured in it. This setting defaults to the empty list.</para>
+
+        <para>Specified domain names may optionally be prefixed with <literal>~</literal>. In this case they do not
+        define a search path, but preferably direct DNS queries for the indicated domains to the DNS servers configured
+        with the system <varname>DNS=</varname> setting (see above), in case additional, suitable per-link DNS servers
+        are known. If no per-link DNS servers are known using the <literal>~</literal> syntax has no effect. Use the
+        construct <literal>~.</literal> (which is composed of <literal>~</literal> to indicate a routing domain and
+        <literal>.</literal> to indicate the DNS root domain that is the implied suffix of all DNS domains) to use the
+        system DNS server defined with <varname>DNS=</varname> preferably for all domains.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>LLMNR=</varname></term>
+        <listitem><para>Takes a boolean argument or
+        <literal>resolve</literal>. Controls Link-Local Multicast Name
+        Resolution support (<ulink
+        url="https://tools.ietf.org/html/rfc4795">RFC 4795</ulink>) on
+        the local host. If true, enables full LLMNR responder and
+        resolver support. If false, disables both. If set to
+        <literal>resolve</literal>, only resolution support is enabled,
+        but responding is disabled. Note that
+        <citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+        also maintains per-link LLMNR settings. LLMNR will be
+        enabled on a link only if the per-link and the
+        global setting is on.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>MulticastDNS=</varname></term>
+        <listitem><para>Takes a boolean argument or
+        <literal>resolve</literal>. Controls Multicast DNS support (<ulink
+        url="https://tools.ietf.org/html/rfc6762">RFC 6762</ulink>) on
+        the local host. If true, enables full Multicast DNS responder and
+        resolver support. If false, disables both. If set to
+        <literal>resolve</literal>, only resolution support is enabled,
+        but responding is disabled. Note that
+        <citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+        also maintains per-link Multicast DNS settings. Multicast DNS will be
+        enabled on a link only if the per-link and the
+        global setting is on.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>DNSSEC=</varname></term>
+        <listitem><para>Takes a boolean argument or
+        <literal>allow-downgrade</literal>. If true all DNS lookups are
+        DNSSEC-validated locally (excluding LLMNR and Multicast
+        DNS). If the response to a lookup request is detected to be invalid
+        a lookup failure is returned to applications. Note that
+        this mode requires a DNS server that supports DNSSEC. If the
+        DNS server does not properly support DNSSEC all validations
+        will fail. If set to <literal>allow-downgrade</literal> DNSSEC
+        validation is attempted, but if the server does not support
+        DNSSEC properly, DNSSEC mode is automatically disabled. Note
+        that this mode makes DNSSEC validation vulnerable to
+        "downgrade" attacks, where an attacker might be able to
+        trigger a downgrade to non-DNSSEC mode by synthesizing a DNS
+        response that suggests DNSSEC was not supported. If set to
+        false, DNS lookups are not DNSSEC validated.</para>
+
+        <para>Note that DNSSEC validation requires retrieval of
+        additional DNS data, and thus results in a small DNS look-up
+        time penalty.</para>
+
+        <para>DNSSEC requires knowledge of "trust anchors" to prove
+        data integrity. The trust anchor for the Internet root domain
+        is built into the resolver, additional trust anchors may be
+        defined with
+        <citerefentry><refentrytitle>dnssec-trust-anchors.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
+        Trust anchors may change at regular intervals, and old trust
+        anchors may be revoked. In such a case DNSSEC validation is
+        not possible until new trust anchors are configured locally or
+        the resolver software package is updated with the new root
+        trust anchor. In effect, when the built-in trust anchor is
+        revoked and <varname>DNSSEC=</varname> is true, all further
+        lookups will fail, as it cannot be proved anymore whether
+        lookups are correctly signed, or validly unsigned. If
+        <varname>DNSSEC=</varname> is set to
+        <literal>allow-downgrade</literal> the resolver will
+        automatically turn off DNSSEC validation in such a case.</para>
+
+        <para>Client programs looking up DNS data will be informed
+        whether lookups could be verified using DNSSEC, or whether the
+        returned data could not be verified (either because the data
+        was found unsigned in the DNS, or the DNS server did not
+        support DNSSEC or no appropriate trust anchors were known). In
+        the latter case it is assumed that client programs employ a
+        secondary scheme to validate the returned DNS data, should
+        this be required.</para>
+
+        <para>It is recommended to set <varname>DNSSEC=</varname> to
+        true on systems where it is known that the DNS server supports
+        DNSSEC correctly, and where software or trust anchor updates
+        happen regularly. On other systems it is recommended to set
+        <varname>DNSSEC=</varname> to
+        <literal>allow-downgrade</literal>.</para>
+
+        <para>In addition to this global DNSSEC setting
+        <citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+        also maintains per-link DNSSEC settings. For system DNS
+        servers (see above), only the global DNSSEC setting is in
+        effect. For per-link DNS servers the per-link
+        setting is in effect, unless it is unset in which case the
+        global setting is used instead.</para>
+
+        <para>Site-private DNS zones generally conflict with DNSSEC
+        operation, unless a negative (if the private zone is not
+        signed) or positive (if the private zone is signed) trust
+        anchor is configured for them. If
+        <literal>allow-downgrade</literal> mode is selected, it is
+        attempted to detect site-private DNS zones using top-level
+        domains (TLDs) that are not known by the DNS root server. This
+        logic does not work in all private zone setups.</para>
+
+        <para>Defaults to <literal>allow-downgrade</literal></para>
+        </listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>DNSOverTLS=</varname></term>
+        <listitem>
+        <para>Takes false or
+        <literal>opportunistic</literal>. When set to <literal>opportunistic</literal>
+        DNS request are attempted to send encrypted with DNS-over-TLS.
+        If the DNS server does not support TLS, DNS-over-TLS is disabled.
+        Note that this mode makes DNS-over-TLS vulnerable to "downgrade"
+        attacks, where an attacker might be able to trigger a downgrade
+        to non-encrypted mode by synthesizing a response that suggests
+        DNS-over-TLS was not supported. If set to false, DNS lookups
+        are send over UDP.</para>
+
+        <para>Note that DNS-over-TLS requires additional data to be
+        send for setting up an encrypted connection, and thus results
+        in a small DNS look-up time penalty.</para>
+
+        <para>Note as the resolver is not capable of authenticating
+        the server, it is vulnerable for "man-in-the-middle" attacks.</para>
+
+        <para>In addition to this global DNSOverTLS setting
+        <citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+        also maintains per-link DNSOverTLS settings. For system DNS
+        servers (see above), only the global DNSOverTLS setting is in
+        effect. For per-link DNS servers the per-link
+        setting is in effect, unless it is unset in which case the
+        global setting is used instead.</para>
+
+        <para>Defaults to off.</para>
+        </listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>Cache=</varname></term>
+        <listitem><para>Takes a boolean argument. If <literal>yes</literal> (the default), resolving a domain name
+        which already got queried earlier will return the previous result as long as it is still valid, and thus does
+        not result in a new network request. Be aware that turning off caching comes at a performance penalty, which
+        is particularly high when DNSSEC is used.</para>
+
+        <para>Note that caching is turned off implicitly if the configured DNS server is on a host-local IP address
+        (such as 127.0.0.1 or ::1), in order to avoid duplicate local caching.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>DNSStubListener=</varname></term>
+        <listitem><para>Takes a boolean argument or one of <literal>udp</literal> and <literal>tcp</literal>. If
+        <literal>udp</literal>, a DNS stub resolver will listen for UDP requests on address 127.0.0.53
+        port 53. If <literal>tcp</literal>, the stub will listen for TCP requests on the same address and port. If
+        <literal>yes</literal> (the default), the stub listens for both UDP and TCP requests.  If <literal>no</literal>, the stub
+        listener is disabled.</para>
+
+        <para>Note that the DNS stub listener is turned off implicitly when its listening address and port are already
+        in use.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>ReadEtcHosts=</varname></term>
+        <listitem><para>Takes a boolean argument. If <literal>yes</literal> (the default), the DNS stub resolver will read
+        <filename>/etc/hosts</filename>, and try to resolve hosts or address by using the entries in the file before
+        sending query to DNS servers.</para></listitem>
+      </varlistentry>
+
+    </variablelist>
+  </refsect1>
+
+  <refsect1>
+      <title>See Also</title>
+      <para>
+      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>dnssec-trust-anchors.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>4</manvolnum></citerefentry>
+      </para>
+  </refsect1>
+
+</refentry>