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diff --git a/man/resolved.conf.xml b/man/resolved.conf.xml new file mode 100644 index 0000000..d153865 --- /dev/null +++ b/man/resolved.conf.xml @@ -0,0 +1,406 @@ +<?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" [ +<!ENTITY % entities SYSTEM "custom-entities.ent" > +%entities; +]> +<!-- SPDX-License-Identifier: LGPL-2.1-or-later --> + +<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 [Resolve] 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. 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. 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> + + <xi:include href="version-info.xml" xpointer="v213"/></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. Please see + <varname>DNS=</varname> for acceptable format of addresses. 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> + + <xi:include href="version-info.xml" xpointer="v216"/></listitem> + </varlistentry> + + <varlistentry> + <term><varname>Domains=</varname></term> + <listitem><para>A space-separated list of domains, optionally prefixed with <literal>~</literal>, + used for two distinct purposes described below. Defaults to the empty list.</para> + + <para>Any domains <emphasis>not</emphasis> prefixed with <literal>~</literal> are used as search + suffixes when resolving single-label hostnames (domain names which contain no dot), in order to + qualify them into fully-qualified domain names (FQDNs). These "search domains" are strictly processed + in the order they are specified in, 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> with the <varname>search</varname> keyword are used instead, if + that file exists and any domains are configured in it.</para> + + <para>The domains prefixed with <literal>~</literal> are called "route-only domains". All domains + listed here (<emphasis>both search domains and route-only domains</emphasis> after removing the + <literal>~</literal> prefix) define a search path that preferably directs DNS queries to this + interface. This search path has an effect only when suitable per-link DNS servers are known. Such + servers may be defined through the <varname>DNS=</varname> setting (see above) and dynamically at run + time, for example from DHCP leases. If no per-link DNS servers are known, route-only domains have no + effect.</para> + + <para>Use the construct <literal>~.</literal> (which is composed from <literal>~</literal> to + indicate a route-only domain and <literal>.</literal> to indicate the DNS root domain that is the + implied suffix of all DNS domains) to use the DNS servers defined for this link preferably for all + domains.</para> + + <para>See "Protocols and Routing" in + <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry> + for details of how search and route-only domains are used.</para> + + <para>Note that configuring the MulticastDNS domain <literal>local</literal> as search or routing + domain has the effect of routing lookups for this domain to classic unicast DNS. This may be used to + provide compatibility with legacy installations that use this domain in a unicast DNS context, + against the IANA assignment of this domain to pure MulticastDNS purposes. Search and routing domains + are a unicast DNS concept, they <emphasis>cannot</emphasis> be used to resolve single-label lookups + via MulticastDNS.</para> + + <xi:include href="version-info.xml" xpointer="v229"/> + </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> + + <xi:include href="version-info.xml" xpointer="v216"/></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> + + <xi:include href="version-info.xml" xpointer="v234"/></listitem> + </varlistentry> + + <varlistentry> + <term><varname>DNSSEC=</varname></term> + <listitem><para>Takes a boolean argument or <literal>allow-downgrade</literal>.</para> + + <para>If set to 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.</para> + + <para>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.</para> + + <para>If set to false, DNS lookups are not DNSSEC validated. In this mode, or when set to + <literal>allow-downgrade</literal> and the downgrade has happened, the resolver becomes + security-unaware and all forwarded queries have DNSSEC OK (DO) bit unset.</para> + + <para>Note that DNSSEC validation requires retrieval of additional DNS data, and thus results in a + small DNS lookup 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>&DEFAULT_DNSSEC_MODE;</literal>.</para> + + <xi:include href="version-info.xml" xpointer="v229"/> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>DNSOverTLS=</varname></term> + <listitem> + <para>Takes a boolean argument or <literal>opportunistic</literal>. If + true all connections to the server will be encrypted. Note that this + mode requires a DNS server that supports DNS-over-TLS and has a valid + certificate. If the hostname was specified in <varname>DNS=</varname> + by using the format <literal>address#server_name</literal> it + is used to validate its certificate and also to enable Server Name + Indication (SNI) when opening a TLS connection. Otherwise + the certificate is checked against the server's IP. + If the DNS server does not support DNS-over-TLS all DNS requests will fail.</para> + + <para>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 that in <literal>opportunistic</literal> mode the + resolver is not capable of authenticating the server, so it is + vulnerable to "man-in-the-middle" attacks.</para> + + <para>In addition to this global <varname>DNSOverTLS=</varname> setting + <citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry> + also maintains per-link <varname>DNSOverTLS=</varname> settings. For system DNS servers (see above), only the global + <varname>DNSOverTLS=</varname> 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 <literal>&DEFAULT_DNS_OVER_TLS_MODE;</literal>.</para> + + <xi:include href="version-info.xml" xpointer="v239"/> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>Cache=</varname></term> + <listitem><para>Takes a boolean or <literal>no-negative</literal> as 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. If <literal>no-negative</literal>, only positive answers are cached.</para> + + <para>Note that caching is turned off by default for host-local DNS servers. + See <varname>CacheFromLocalhost=</varname> for details.</para> + + <xi:include href="version-info.xml" xpointer="v231"/></listitem> + </varlistentry> + + <varlistentry> + <term><varname>CacheFromLocalhost=</varname></term> + <listitem><para>Takes a boolean as argument. If <literal>no</literal> (the default), and response cames from + host-local IP address (such as 127.0.0.1 or ::1), the result wouldn't be cached in order to avoid + potential duplicate local caching.</para> + + <xi:include href="version-info.xml" xpointer="v248"/> + </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 addresses 127.0.0.53 and 127.0.0.54, port 53. If <literal>tcp</literal>, the stub will listen for + TCP requests on the same addresses 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> + + <xi:include href="systemd-resolved.service.xml" xpointer="proxy-stub" /> + + <para>Note that the DNS stub listener is turned off implicitly when its listening address and port are already + in use.</para> + + <xi:include href="version-info.xml" xpointer="v232"/></listitem> + </varlistentry> + + <varlistentry> + <term><varname>DNSStubListenerExtra=</varname></term> + <listitem><para>Takes an IPv4 or IPv6 address to listen on. The address may be optionally + prefixed with a protocol name (<literal>udp</literal> or <literal>tcp</literal>) separated with + <literal>:</literal>. If the protocol is not specified, the service will listen on both UDP and + TCP. It may be also optionally suffixed by a numeric port number with separator + <literal>:</literal>. When an IPv6 address is specified with a port number, then the address + must be in the square brackets. If the port is not specified, then the service uses port 53. + Note that this is independent of the primary DNS stub configured with + <varname>DNSStubListener=</varname>, and only configures <emphasis>additional</emphasis> + sockets to listen on. This option can be specified multiple times. If an empty string is + assigned, then the all previous assignments are cleared. Defaults to unset.</para> + + <para>Examples: + <programlisting>DNSStubListenerExtra=192.168.10.10 +DNSStubListenerExtra=2001:db8:0:f102::10 +DNSStubListenerExtra=192.168.10.11:9953 +DNSStubListenerExtra=[2001:db8:0:f102::11]:9953 +DNSStubListenerExtra=tcp:192.168.10.12 +DNSStubListenerExtra=udp:2001:db8:0:f102::12 +DNSStubListenerExtra=tcp:192.168.10.13:9953 +DNSStubListenerExtra=udp:[2001:db8:0:f102::13]:9953</programlisting> + </para> + + <xi:include href="version-info.xml" xpointer="v247"/></listitem> + </varlistentry> + + <varlistentry> + <term><varname>ReadEtcHosts=</varname></term> + <listitem><para>Takes a boolean argument. If <literal>yes</literal> (the default), + <command>systemd-resolved</command> 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> + + <xi:include href="version-info.xml" xpointer="v240"/></listitem> + </varlistentry> + + <varlistentry> + <term><varname>ResolveUnicastSingleLabel=</varname></term> + <listitem><para>Takes a boolean argument. When false (the default), + <command>systemd-resolved</command> will not resolve A and AAAA queries for single-label names over + classic DNS. Note that such names may still be resolved if search domains are specified (see + <varname>Domains=</varname> above), or using other mechanisms, in particular via LLMNR or from + <filename>/etc/hosts</filename>. When true, queries for single-label names will be forwarded to + global DNS servers even if no search domains are defined. + </para> + + <para>This option is provided for compatibility with configurations where <emphasis>public DNS + servers are not used</emphasis>. Forwarding single-label names to servers not under your control is + not standard-conformant, see <ulink + url="https://www.iab.org/documents/correspondence-reports-documents/2013-2/iab-statement-dotless-domains-considered-harmful/">IAB + Statement</ulink>, and may create a privacy and security risk.</para> + + <xi:include href="version-info.xml" xpointer="v246"/></listitem> + </varlistentry> + <varlistentry> + <term>StaleRetentionSec=<replaceable>SECONDS</replaceable></term> + <listitem><para>Takes a duration value, which determines the length of time DNS resource records can + be retained in the cache beyond their Time To Live (TTL). This allows these records to be returned as + stale records. By default, this value is set to zero, meaning that DNS resource records are not + stored in the cache after their TTL expires.</para> + + <para>This is useful when a DNS server failure occurs or becomes unreachable. In such cases, + <citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry> + continues to use the stale records to answer DNS queries, particularly when no valid response can be + obtained from the upstream DNS servers. However, this doesn't apply to NXDOMAIN responses, as those + are still perfectly valid responses. This feature enhances resilience against DNS infrastructure + failures and outages.</para> + + <para><command>systemd-resolved</command> always attempts to reach the upstream DNS servers first, + before providing the client application with any stale data. If this feature is enabled, cache will + not be flushed when changing servers.</para> + + <xi:include href="version-info.xml" xpointer="v254"/> + </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>5</manvolnum></citerefentry> + </para> + </refsect1> + +</refentry> |