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<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!--
This file is part of systemd.
Copyright 2014 Tom Gundersen
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->
<refentry id="systemd-resolved.service" conditional='ENABLE_RESOLVED'>
<refentryinfo>
<title>systemd-resolved.service</title>
<productname>systemd</productname>
<authorgroup>
<author>
<contrib>Developer</contrib>
<firstname>Tom</firstname>
<surname>Gundersen</surname>
<email>teg@jklm.no</email>
</author>
</authorgroup>
</refentryinfo>
<refmeta>
<refentrytitle>systemd-resolved.service</refentrytitle>
<manvolnum>8</manvolnum>
</refmeta>
<refnamediv>
<refname>systemd-resolved.service</refname>
<refname>systemd-resolved</refname>
<refpurpose>Network Name Resolution manager</refpurpose>
</refnamediv>
<refsynopsisdiv>
<para><filename>systemd-resolved.service</filename></para>
<para><filename>/usr/lib/systemd/systemd-resolved</filename></para>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><command>systemd-resolved</command> is a system service that
manages network name resolution. It implements a caching DNS stub
resolver and an LLMNR resolver and responder. It also generates
<filename>/run/systemd/resolve/resolv.conf</filename> for
compatibility which may be symlinked from
<filename>/etc/resolv.conf</filename>. The glibc NSS module
<citerefentry><refentrytitle>nss-resolve</refentrytitle><manvolnum>8</manvolnum></citerefentry>
is necessary to allow libc's NSS resolver functions to resolve
host names via <command>systemd-resolved</command>.</para>
<para>The DNS servers contacted are determined from the global
settings in <filename>/etc/systemd/resolved.conf</filename>, the
per-link static settings in <filename>/etc/systemd/network/*.network</filename> files,
and the per-link dynamic settings received over DHCP. See
<citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
and
<citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for details. To improve compatibility,
<filename>/etc/resolv.conf</filename> is read in order to discover
configured system DNS servers, however only if it is not a symlink
to <filename>/run/systemd/resolve/resolv.conf</filename> (see above).</para>
<para><command>systemd-resolved</command> synthesizes DNS RRs for the following cases:</para>
<itemizedlist>
<listitem><para>The local, configured hostname is resolved to
all locally configured IP addresses ordered by their scope, or
— if none are configured — the IPv4 address 127.0.0.2 (which
is on the local loopback) and the IPv6 address ::1 (which is the
local host).</para></listitem>
<listitem><para>The hostname <literal>localhost</literal> is
resolved to the IP addresses 127.0.0.1 and
::1.</para></listitem>
<listitem><para>The hostname <literal>gateway</literal> is
resolved to all current default routing gateway addresses,
ordered by their metric. This assigns a stable hostname to the
current gateway, useful for referencing it independently of the
current network configuration state.</para></listitem>
</itemizedlist>
<para>Lookup requests are routed to the available DNS servers
and LLMNR interfaces according to the following rules:</para>
<itemizedlist>
<listitem><para>Lookups for the special hostname
<literal>localhost</literal> are never routed to the
network.</para></listitem>
<listitem><para>Single-label names are routed to all local
interfaces capable of IP multicasting, using the LLMNR
protocol. Lookups for IPv4 addresses are only sent via LLMNR on
IPv4, and lookups for IPv6 addresses are only sent via LLMNR on
IPv6. Lookups for the locally configured host name and the
<literal>gateway</literal> host name are never routed to
LLMNR.</para></listitem>
<listitem><para>Multi-label names are routed to all local
interfaces that have a DNS sever configured, plus the globally
configured DNS server if there is one. Address lookups from the
link-local addres range are never routed to
DNS.</para></listitem>
</itemizedlist>
<para>If lookups are routed to multiple interfaces, the first
successful response is returned (thus effectively merging the
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>Note that
<filename>/run/systemd/resolve/resolv.conf</filename> should not
be used directly, but only through a symlink from
<filename>/etc/resolv.conf</filename>.</para>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>nss-resolve</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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