<?xml version='1.0'?>
-<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+<!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+
--->
+<!-- SPDX-License-Identifier: LGPL-2.1+ -->
<refentry id="systemd-resolved.service" conditional='ENABLE_RESOLVE'>
<filename>/etc/systemd/resolved.conf</filename>, the per-link static settings in
<filename>/etc/systemd/network/*.network</filename> files (in case
<citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry> is
- used), the per-link dynamic settings received over DHCP, and any DNS server information made available by other
- system services. See
+ used), the per-link dynamic settings received over DHCP, user request made via
+ <citerefentry><refentrytitle>resolvectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>, and any DNS server
+ information made available by other system services. See
<citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry> and
<citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry> for details
about systemd's own configuration files for DNS servers. To improve compatibility,
<filename>/etc/resolv.conf</filename> is read in order to discover configured system DNS servers, but only if it is
- not a symlink to <filename>/run/systemd/resolve/stub-resolv.conf</filename> or
- <filename>/run/systemd/resolve/resolv.conf</filename> (see below).</para>
+ not a symlink to <filename>/run/systemd/resolve/stub-resolv.conf</filename>,
+ <filename>/usr/lib/systemd/resolv.conf</filename> or <filename>/run/systemd/resolve/resolv.conf</filename> (see
+ below).</para>
+
+ </refsect1>
+
+ <refsect1>
+ <title>Synthetic Records</title>
<para><command>systemd-resolved</command> synthesizes DNS resource records (RRs) for the following cases:</para>
to their configured addresses and back, but they will not affect lookups for
non-address types (like MX).</para></listitem>
</itemizedlist>
+ </refsect1>
+
+ <refsect1>
+ <title>Protocols and Routing</title>
<para>Lookup requests are routed to the available DNS servers, LLMNR and MulticastDNS interfaces according to the
following rules:</para>
lookup zones on all matching interfaces). If the lookup failed on
all interfaces, the last failing response is returned.</para>
- <para>Routing of lookups may be influenced by configuring
- per-interface domain names. See
- <citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry>
- for details. Lookups for a hostname ending in one of the
- per-interface domains are exclusively routed to the matching
- interfaces.</para>
+ <para>Routing of lookups may be influenced by configuring per-interface domain names and other settings. See
+ <citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry> and
+ <citerefentry><refentrytitle>resolvectl</refentrytitle><manvolnum>1</manvolnum></citerefentry> for details. The
+ following query routing logic applies for unicast DNS traffic:</para>
+
+ <itemizedlist>
+ <listitem><para>If a name to look up matches (that is: is equal to or has as suffix) any of the configured search
+ or route-only domains of any link (or the globally configured DNS settings), the "best matching"
+ search/route-only domain is determined: the matching one with the most labels. The query is then sent to all DNS
+ servers of any links or the globally configured DNS servers associated with this "best matching"
+ search/route-only domain. (Note that more than one link might have this same "best matching" search/route-only
+ domain configured, in which case the query is sent to all of them in parallel).</para></listitem>
+
+ <listitem><para>If a query does not match any configured search/route-only domain (neither per-link nor global),
+ it is sent to all DNS servers that are configured on links with the "DNS default route" option set, as well as
+ the globally configured DNS server.</para></listitem>
+
+ <listitem><para>If there is no link configured as "DNS default route" and no global DNS server configured, the
+ compiled-in fallback DNS server is used.</para></listitem>
+
+ <listitem><para>Otherwise the query is failed as no suitable DNS servers could be determined.</para></listitem>
+ </itemizedlist>
+
+ <para>The "DNS default route" option is a boolean setting configurable with <command>resolvectl</command> or in
+ <filename>.network</filename> files. If not set, it is implicitly determined based on the configured DNS domains
+ for a link: if there's any route-only domain (not matching <literal>~.</literal>) it defaults to false, otherwise
+ to true.</para>
+
+ <para>Effectively this means: in order to preferably route all DNS queries not explicitly matched by
+ search/route-only domain configuration to a specific link, configure a <literal>~.</literal> route-only domain on
+ it. This will ensure that other links will not be considered for the queries (unless they too carry such a
+ route-only domain). In order to route all such DNS queries to a specific link only in case no other link is
+ preferable, then set the "DNS default route" option for the link to true, and do not configure a
+ <literal>~.</literal> route-only domain on it. Finally, in order to ensure that a specific link never receives any
+ DNS traffic not matching any of its configured search/route-only domains, set the "DNS default route" option for it
+ to false.</para>
<para>See the <ulink url="https://www.freedesktop.org/wiki/Software/systemd/resolved"> resolved D-Bus API
Documentation</ulink> for information about the APIs <filename>systemd-resolved</filename> provides.</para>
-
</refsect1>
<refsect1>
<command>systemd-resolved</command> will flush all caches it maintains. Note that it should normally not be
necessary to request this explicitly – except for debugging purposes – as <command>systemd-resolved</command>
flushes the caches automatically anyway any time the host's network configuration changes. Sending this signal
- to <command>systemd-resolved</command> is equivalent to the <command>resolvectl --flush-caches</command>
+ to <command>systemd-resolved</command> is equivalent to the <command>resolvectl flush-caches</command>
command, however the latter is recommended since it operates in a synchronous way.</para></listitem>
</varlistentry>
should normally not be necessary to request this explicitly – except for debugging purposes – as
<command>systemd-resolved</command> automatically forgets learnt information any time the DNS server
configuration changes. Sending this signal to <command>systemd-resolved</command> is equivalent to the
- <command>resolvectl --reset-server-features</command> command, however the latter is recommended since it
+ <command>resolvectl reset-server-features</command> command, however the latter is recommended since it
operates in a synchronous way.</para></listitem>
</varlistentry>
</variablelist>
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