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Merge pull request #17415 from keszybz/logind-resolved-docs 

A bunch of updates to logind and resolved man pages
This commit is contained in:
Lennart Poettering 2020-10-22 13:44:17 +02:00 committed by GitHub
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230
man/org.freedesktop.resolve1.xml
View File

@ -156,12 +156,6 @@ node /org/freedesktop/resolve1 {
};
</programlisting>
<!--method SetLinkDNSEx is not documented!-->
<!--method SetLinkDefaultRoute is not documented!-->
<!--method SetLinkDNSOverTLS is not documented!-->
<!--method RegisterService is not documented!-->
<!--method UnregisterService is not documented!-->
@ -170,28 +164,8 @@ node /org/freedesktop/resolve1 {
<!--method ResetServerFeatures is not documented!-->
<!--property LLMNR is not documented!-->
<!--property MulticastDNS is not documented!-->
<!--property DNSOverTLS is not documented!-->
<!--property DNSEx is not documented!-->
<!--property FallbackDNS is not documented!-->
<!--property FallbackDNSEx is not documented!-->
<!--property CurrentDNSServer is not documented!-->
<!--property CurrentDNSServerEx is not documented!-->
<!--property DNSSEC is not documented!-->
<!--property DNSSECNegativeTrustAnchors is not documented!-->
<!--property DNSStubListener is not documented!-->
<!--Autogenerated cross-references for systemd.directives, do not edit-->
<variablelist class="dbus-interface" generated="True" extra-ref="org.freedesktop.resolve1.Manager"/>
@ -281,26 +255,28 @@ node /org/freedesktop/resolve1 {
<refsect2>
<title>Methods</title>
<para><function>ResolveHostname()</function> takes a hostname and resolves it to one or more IP addresses.
As parameters it takes the Linux network interface index to execute the query on, or 0 if it may be
done on any suitable interface. The <varname>name</varname> parameter specifies the hostname to
resolve. Note that if required, IDNA conversion is applied to this name unless it is resolved via LLMNR or MulticastDNS. The <varname>family</varname> parameter
limits the results to a specific address family. It may be <constant>AF_INET</constant>,
<constant>AF_INET6</constant> or <constant>AF_UNSPEC</constant>. If <constant>AF_UNSPEC</constant> is specified (recommended), both kinds are retrieved, subject
to local network configuration (i.e. if no local, routable IPv6 address is found, no IPv6 address is
retrieved; and similarly for IPv4). A 64-bit <varname>flags</varname> field may be used to alter the
behaviour of the resolver operation (see below). The method returns an array of address records. Each
address record consists of the interface index the address belongs to, an address family as well as a
byte array with the actual IP address data (which either has 4 or 16 elements, depending on the address
family). The returned address family will be one of <constant>AF_INET</constant> or
<constant>AF_INET6</constant>. For IPv6, the returned address interface index should be used to
initialize the .sin6_scope_id field of a <structname>struct sockaddr_in6</structname> instance to permit
support for resolution to link-local IP addresses. The address array is followed by the canonical name
of the host, which may or may not be identical to the resolved hostname. Finally, a 64-bit
<varname>flags</varname> field is returned that is defined similarly to the <varname>flags</varname>
field that was passed in, but contains information about the resolved data (see below). If the hostname
passed in is an IPv4 or IPv6 address formatted as string, it is parsed, and the result is returned. In
this case, no network communication is done.</para>
<para><function>ResolveHostname()</function> takes a hostname and resolves it to one or more IP
addresses. As parameters it takes the Linux network interface index to execute the query on, or 0 if
it may be done on any suitable interface. The <varname>name</varname> parameter specifies the hostname
to resolve. Note that if required, IDNA conversion is applied to this name unless it is resolved via
LLMNR or MulticastDNS. The <varname>family</varname> parameter limits the results to a specific address
family. It may be <constant>AF_INET</constant>, <constant>AF_INET6</constant> or
<constant>AF_UNSPEC</constant>. If <constant>AF_UNSPEC</constant> is specified (recommended), both
kinds are retrieved, subject to local network configuration (i.e. if no local, routable IPv6 address is
found, no IPv6 address is retrieved; and similarly for IPv4). A 64-bit <varname>flags</varname> field
may be used to alter the behaviour of the resolver operation (see below). The method returns an array
of address records. Each address record consists of the interface index the address belongs to, an
address family as well as a byte array with the actual IP address data (which either has 4 or 16
elements, depending on the address family). The returned address family will be one of
<constant>AF_INET</constant> or <constant>AF_INET6</constant>. For IPv6, the returned address interface
index should be used to initialize the .sin6_scope_id field of a
<structname>struct sockaddr_in6</structname> instance to permit support for resolution to link-local IP
addresses. The address array is followed by the canonical name of the host, which may or may not be
identical to the resolved hostname. Finally, a 64-bit <varname>flags</varname> field is returned that
is defined similarly to the <varname>flags</varname> field that was passed in, but contains information
about the resolved data (see below). If the hostname passed in is an IPv4 or IPv6 address formatted as
string, it is parsed, and the result is returned. In this case, no network communication is
done.</para>
<para><function>ResolveAddress()</function> executes the reverse operation: it takes an IP address and
acquires one or more hostnames for it. As parameters it takes the interface index to execute the query
@ -387,15 +363,19 @@ node /org/freedesktop/resolve1 {
<constant>AF_INET6</constant>), followed by a 4-byte or 16-byte array with the raw address data. This
method is a one-step shortcut for retrieving the Link object for a network interface using
<function>GetLink()</function> (see above) and then invoking the <function>SetDNS()</function> method
(see below) on it.
(see below) on it.</para>
<para><function>SetLinkDNSEx()</function> is similar to <function>SetLinkDNS()</function>, but allows
an IP port (instead of the default 53) and DNS name to be specified for each DNS server. The server
name is used for Server Name Indication (SNI), which is useful when DNS-over-TLS is
used. C.f. <varname>DNS=</varname> in
<citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
</para>
<para>Network management software integrating with <filename>systemd-resolved</filename> should
call this method (and the five below) after the interface appeared in the kernel (and thus after a
network interface index has been assigned), but before the network interfaces is activated
(<constant>IFF_UP</constant> set) so that all settings take effect during the full time the network
interface is up. It is safe to alter settings while the interface is up, however. Use
<function>RevertLink()</function> (described below) to reset all per-interface settings.</para>
<para><function>SetLinkDefaultRoute()</function> specifies whether the link shall be used as the
default route for name queries. See the description of name routing in
<citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
for details.</para>
<para>The <function>SetLinkDomains()</function> method sets the search and routing domains to use on a
specific network interface for DNS look-ups. It takes a network interface index and an array of domains,
@ -432,8 +412,22 @@ node /org/freedesktop/resolve1 {
Negative Trust Anchors (NTAs) for a specific network interface. It takes a network interface index and a
list of domains as arguments.</para>
<para>The <function>RevertLink()</function> method may be used to revert all per-link settings done with
the six methods described above to the defaults again.</para>
<para>The <function>SetLinkDNSOverTLS()</function> method enables or disables DNS-over-TLS.
C.f. <varname>DNSOverTLS=</varname> in
<citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
for details.</para>
<para>Network management software integrating with <filename>systemd-resolved</filename> should call
<function>SetLinkDNS()</function> or <function>SetLinkDNSEx()</function>,
<function>SetLinkDefaultRoute()</function>, <function>SetLinkDomains()</function> and others after the
interface appeared in the kernel (and thus after a network interface index has been assigned), but
before the network interfaces is activated (<constant>IFF_UP</constant> set) so that all settings take
effect during the full time the network interface is up. It is safe to alter settings while the
interface is up, however. Use <function>RevertLink()</function> (described below) to reset all
per-interface settings.</para>
<para>The <function>RevertLink()</function> method may be used to revert all per-link settings
described above to the defaults.</para>
<refsect3>
<title>The Flags Parameter</title>
@ -458,11 +452,11 @@ node /org/freedesktop/resolve1 {
classic unicast DNS, LLMNR via IPv4/UDP and IPv6/UDP respectively, as well as MulticastDNS via
IPv4/UDP and IPv6/UDP. If all of these five bits are off on input (which is strongly recommended) the
look-up will be done via all suitable protocols for the specific look-up. Note that these flags
operate as filter only, but cannot force a look-up to be done via a protocol. Specifically, <filename>systemd-resolved</filename>
will only route look-ups within the .local TLD to MulticastDNS (plus some reverse look-up address
domains), and single-label names to LLMNR (plus some reverse address lookup domains). It will route
neither of these to Unicast DNS servers. Also, it will do LLMNR and Multicast DNS only on interfaces
suitable for multicast.</para>
operate as filter only, but cannot force a look-up to be done via a protocol. Specifically,
<filename>systemd-resolved</filename> will only route look-ups within the .local TLD to MulticastDNS
(plus some reverse look-up address domains), and single-label names to LLMNR (plus some reverse
address lookup domains). It will route neither of these to Unicast DNS servers. Also, it will do
LLMNR and Multicast DNS only on interfaces suitable for multicast.</para>
<para>On output, these five flags indicate which protocol was used to execute the operation, and hence
where the data was found.</para>
@ -498,34 +492,50 @@ node /org/freedesktop/resolve1 {
the data is "rightfully" unauthenticated (which includes cases where the underlying protocol or server
does not support authenticating data).</para>
</refsect3>
</refsect2>
</refsect2>
<refsect2>
<title>Properties</title>
<para>The <varname>LLMNR</varname> and <varname>MulticastDNS</varname> properties report whether LLMNR
and MulticastDNS are (globally) enabled. Each may be one of <literal>yes</literal>,
<literal>no</literal>, and <literal>resolve</literal>. See <function>SetLinkLLMNR()</function>
and <function>SetLinkMulticastDNS()</function> above.</para>
<para><varname>LLMNRHostname</varname> contains the hostname currently exposed on the network via
LLMNR. It usually follows the system hostname as may be queried via
<citerefentry project="man-pages"><refentrytitle>gethostname</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
but may differ if a conflict is detected on the network.</para>
<para><varname>DNS</varname> contains an array of all DNS servers currently used by
<filename>systemd-resolved</filename>. It contains similar information as the DNS server data written to
/run/systemd/resolve/resolv.conf. Each structure in the array consists of a numeric network interface
index, an address family, and a byte array containing the DNS server address (either 4 bytes in length
for IPv4 or 16 bytes in lengths for IPv6). The array contains DNS servers configured system-wide,
including those possibly read from a foreign <filename>/etc/resolv.conf</filename> or the
<varname>DNS=</varname> setting in <filename>/etc/systemd/resolved.conf</filename>, as well as
per-interface DNS server information either retrieved from
<para><varname>DNS</varname> and <varname>DNSEx</varname> contain arrays of all DNS servers currently
used by <filename>systemd-resolved</filename>. <varname>DNS</varname> contains information similar to
the DNS server data in <filename>/run/systemd/resolve/resolv.conf</filename>. Each structure in the
array consists of a numeric network interface index, an address family, and a byte array containing the
DNS server address (either 4 bytes in length for IPv4 or 16 bytes in lengths for IPv6).
<varname>DNSEx</varname> is similar, but additionally contains the IP port and server name (used for
Server Name Indication, SNI). Both arrays contain DNS servers configured system-wide, including those
possibly read from a foreign <filename>/etc/resolv.conf</filename> or the <varname>DNS=</varname>
setting in <filename>/etc/systemd/resolved.conf</filename>, as well as per-interface DNS server
information either retrieved from
<citerefentry><refentrytitle>systemd-networkd</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
or configured by external software via <function>SetLinkDNS()</function> (see above). The network
interface index will be 0 for the system-wide configured services and non-zero for the per-link
servers.</para>
or configured by external software via <function>SetLinkDNS()</function> or
<function>SetLinkDNSEx()</function> (see above). The network interface index will be 0 for the
system-wide configured services and non-zero for the per-link servers.</para>
<para>Similarly, the <varname>Domains</varname> property contains an array of all search and
routing domains currently used by <filename>systemd-resolved</filename>. Each entry consists of a network interface index (again, 0
encodes system-wide entries), the actual domain name, and whether the entry is used only for routing
(true) or for both routing and searching (false).</para>
<para><varname>FallbackDNS</varname> and <varname>FallbackDNSEx</varname> contain arrays of all DNS
servers configured as fallback servers, if any, using the same format as <varname>DNS</varname> and
<varname>DNSEx</varname> described above. See the description of <varname>FallbackDNS=</varname> in
<citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
the description of when those servers are used.</para>
<para><varname>CurrentDNSServer</varname> and <varname>CurrentDNSServerEx</varname> specify the server
that is currently used for query resolution, in the same format as a single entry in the
<varname>DNS</varname> and <varname>DNSEx</varname> arrays described above.</para>
<para>Similarly, the <varname>Domains</varname> property contains an array of all search and routing
domains currently used by <filename>systemd-resolved</filename>. Each entry consists of a network
interface index (again, 0 encodes system-wide entries), the actual domain name, and whether the entry
is used only for routing (true) or for both routing and searching (false).</para>
<para>The <varname>TransactionStatistics</varname> property contains information about the number of
transactions <filename>systemd-resolved</filename> has processed. It contains a pair of unsigned 64-bit counters, the first
@ -540,7 +550,14 @@ node /org/freedesktop/resolve1 {
operations so far. It exposes three 64-bit counters: the first being the total number of current cache
entries (both positive and negative), the second the number of cache hits, and the third the number of
cache misses. The latter counters may be reset using <function>ResetStatistics()</function> (see
above). </para>
above).</para>
<para>The <varname>DNSSEC</varname> property specifies current status of DNSSEC validation. It is one
of <literal>yes</literal> (validation is enforced), <literal>no</literal> (no validation is done),
<literal>allow-downgrade</literal> (validation is done if the current DNS server supports it). See the
description of <varname>DNSSEC=</varname> in
<citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
</para>
<para>The <varname>DNSSECStatistics</varname> property contains information about the DNSSEC
validations executed so far. It contains four 64-bit counters: the number of secure, insecure, bogus,
@ -559,12 +576,20 @@ node /org/freedesktop/resolve1 {
DNSSEC is supported by DNS servers until it verifies that this is not the case. Thus, the reported
value may initially be true, until the first transactions are executed.</para>
<para>The <varname>DNSOverTLS</varname> boolean property reports whether DNS-over-TLS is enabled.
</para>
<para>The <varname>ResolvConfMode</varname> property exposes how <filename>/etc/resolv.conf</filename>
is managed on the host. Currently, the values <literal>uplink</literal>, <literal>stub</literal>,
<literal>static</literal> (these three correspond to the three different files
<filename>systemd-resolved.service</filename> provides), <literal>foreign</literal> (the file is
managed by admin or another service, <filename>systemd-resolved.service</filename> just consumes it),
<literal>missing</literal> (<filename>/etc/resolv.conf</filename> is missing).</para>
<para>The <varname>DNSStubListener</varname> property reports whether the stub listener on port 53 is
enabled. Possible values are <literal>yes</literal> (enabled), <literal>no</literal> (disabled),
<literal>udp</literal> (only the UDP listener is enabled), and <literal>tcp</literal> (only the TCP
listener is enabled).</para>
</refsect2>
</refsect1>
@ -619,40 +644,6 @@ node /org/freedesktop/resolve1/link/_1 {
};
</programlisting>
<!--method SetDNSEx is not documented!-->
<!--method SetDomains is not documented!-->
<!--method SetDefaultRoute is not documented!-->
<!--method SetLLMNR is not documented!-->
<!--method SetMulticastDNS is not documented!-->
<!--method SetDNSOverTLS is not documented!-->
<!--method SetDNSSEC is not documented!-->
<!--method SetDNSSECNegativeTrustAnchors is not documented!-->
<!--method Revert is not documented!-->
<!--property DNSEx is not documented!-->
<!--property CurrentDNSServer is not documented!-->
<!--property CurrentDNSServerEx is not documented!-->
<!--property DefaultRoute is not documented!-->
<!--property LLMNR is not documented!-->
<!--property MulticastDNS is not documented!-->
<!--property DNSOverTLS is not documented!-->
<!--property DNSSEC is not documented!-->
<!--property DNSSECNegativeTrustAnchors is not documented!-->
<!--Autogenerated cross-references for systemd.directives, do not edit-->
@ -721,8 +712,13 @@ node /org/freedesktop/resolve1/link/_1 {
<function>SetLinkDNS()</function> on the Manager object, the main difference being that the later
expects an interface index to be specified. Invoking the methods on the Manager interface has the
benefit of reducing roundtrips, as it is not necessary to first request the Link object path via
<function>GetLink()</function> before invoking the methods. For further details on these methods see
the <interfacename>Manager</interfacename> documentation above.</para>
<function>GetLink()</function> before invoking the methods. The same relationship holds for
<function>SetDNSEx()</function>, <function>SetDomains()</function>,
<function>SetDefaultRoute()</function>, <function>SetLLMNR()</function>,
<function>SetMulticastDNS()</function>, <function>SetDNSOverTLS()</function>,
<function>SetDNSSEC()</function>, <function>SetDNSSECNegativeTrustAnchors()</function>, and
<function>Revert()</function>. For further details on these methods see the
<interfacename>Manager</interfacename> documentation above.</para>
</refsect2>
<refsect2>
@ -744,8 +740,12 @@ node /org/freedesktop/resolve1/link/_1 {
assumed available until it is detected that the configured server does not actually support it. Thus,
this property may initially report that DNSSEC is supported on an interface.</para>
<para><varname>DefaultRoute</varname> exposes a boolean field that indicates whether the interface will
be used as default route for name queries. See <function>SetLinkDefaultRoute()</function> above.</para>
<para>The other properties reflect the state of the various configuration settings for the link which
may be set with the various methods calls such as SetDNS() or SetLLMNR().</para>
may be set with the various methods calls such as <function>SetDNS()</function> or
<function>SetLLMNR()</function>.</para>
</refsect2>
</refsect1>

197
man/systemd-resolved.service.xml
View File

@ -87,17 +87,17 @@
<refsect1>
<title>Synthetic Records</title>
<para><command>systemd-resolved</command> synthesizes DNS resource records (RRs) for the following
<para><command>systemd-resolved</command> synthetizes DNS resource records (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>
loopback interface) and the IPv6 address ::1 (which is the local host).</para></listitem>
<listitem><para>The hostnames <literal>localhost</literal> and <literal>localhost.localdomain</literal>
(as well as any hostname ending in <literal>.localhost</literal> or
<literal>.localhost.localdomain</literal>) are resolved to the IP addresses 127.0.0.1 and ::1.
as well as any hostname ending in <literal>.localhost</literal> or
<literal>.localhost.localdomain</literal> are 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
@ -119,104 +119,162 @@
according to the following rules:</para>
<itemizedlist>
<listitem><para>Names for which synthetic records are generated (as listed in the previous section) are
never routed to the network and a reply is sent immediately. In particular this means that lookups for
<literal>localhost</literal> are never routed to the network.</para></listitem>
<listitem><para>Names for which synthetic records are generated (the local hostname,
<literal>localhost</literal> and <literal>localdomain</literal>, local gateway, as listed in the
previous section) and addresses configured in <filename>/etc/hosts</filename> are never routed to the
network and a reply is sent immediately.</para></listitem>
<listitem><para>Single-label names are routed to all local interfaces capable of IP multicasting, where
LLMNR is not disabled, 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 hostname and the <literal>_gateway</literal> hostname are never routed to LLMNR.
</para></listitem>
<listitem><para>Single-label names are resolved using LLMNR on all local interfaces where LLMNR is
enabled. Lookups for IPv4 addresses are only sent via LLMNR on IPv4, and lookups for IPv6 addresses are
only sent via LLMNR on IPv6. Note that lookups for single-label synthetized names are not routed to
LLMNR, MulticastDNS or unicast DNS.</para></listitem>
<listitem><para>Multi-label names with the domain suffix <literal>.local</literal> are routed to all
local interfaces capable of IP multicasting, where MulticastDNS is not disabled, using the MulticastDNS
protocol. As with LLMNR, IPv4 address lookups are sent via IPv4 and IPv6 address lookups are sent via
IPv6.</para></listitem>
<listitem><para>Queries for the address records (A and AAAA) of single-label non-synthetized names are
resolved via unicast DNS using search domains. For any interface which defines search domains, such
look-ups are routed to that interface, suffixed with each of the search domains defined on that
interface in turn. When global search domains are defined, such look-ups are routed to all interfaces,
suffixed by each of the global search domains in turn. Additionally, lookup of single-label names via
unicast DNS may be enabled with the <varname>ResolveUnicastSingleLabel=yes</varname> setting. The
details of which servers are queried and how the final reply is chosen are described below. Note that
this means that address queries for single-label names are never sent out to remote DNS servers by
default, and resoulution is only possible if search domains are defined.</para></listitem>
<listitem><para>Resolution of address records (A and AAAA) via unicast DNS (i.e. not LLMNR or
MulticastDNS) for non-synthesized single-label names is allowed for non-top-level domains. This means
that such records can be resolved when search domains are defined. For any interface which defines
search domains, such look-ups are routed to that interface, suffixed with each of the search domains
defined on that interface in turn. When global search domains are defined, such look-ups are routed to
all interfaces, suffixed by each of the global search domains in turn. Additionally, lookup of
single-label names via unicast DNS may be enabled with the
<varname>ResolveUnicastSingleLabel=yes</varname> setting. The details of which servers are queried and
how the final reply is chosen are described below. Note that this means that address queries for
single-label names are never sent out to remote DNS servers by default, and if no search domains are
defined, resolution will fail.</para></listitem>
<listitem><para>Multi-label names with the domain suffix <literal>.local</literal> are resolved using
MulticastDNS on all local interfaces where MulticastDNS is enabled. As with LLMNR, IPv4 address lookups
are sent via IPv4 and IPv6 address lookups are sent via IPv6.</para></listitem>
<listitem><para>Other multi-label names are routed to all local interfaces that have a DNS server
configured, plus the globally configured DNS servers if there are any. Note that by default, lookups for
domains with the <literal>.local</literal> suffix are not routed to DNS servers, unless the domain is
specified explicitly as routing or search domain for the DNS server and interface. This means that on
networks where the <literal>.local</literal> domain is defined in a site-specific DNS server, explicit
search or routing domains need to be configured to make lookups within this DNS domain work. Note that
these days, it's generally recommended to avoid defining <literal>.local</literal> in a DNS server, as
<ulink url="https://tools.ietf.org/html/rfc6762">RFC6762</ulink> reserves this domain for exclusive
<listitem><para>Queries for multi-label names are routed via unicast DNS on local interfaces that have
a DNS server configured, plus the globally configured DNS servers if there are any. Which interfaces
are used is determined by the routing logic based on search and route-only domains, described below.
Note that by default, lookups for domains with the <literal>.local</literal> suffix are not routed to
DNS servers, unless the domain is specified explicitly as routing or search domain for the DNS server
and interface. This means that on networks where the <literal>.local</literal> domain is defined in a
site-specific DNS server, explicit search or routing domains need to be configured to make lookups work
within this DNS domain. Note that these days, it's generally recommended to avoid defining
<literal>.local</literal> in a DNS server, as <ulink
url="https://tools.ietf.org/html/rfc6762">RFC6762</ulink> reserves this domain for exclusive
MulticastDNS use.</para></listitem>
<listitem><para>Address lookups are routed similarly to multi-label names, with the exception that
addresses from the link-local address range are never routed to unicast DNS and are only resolved using
LLMNR and MulticastDNS (when enabled).</para></listitem>
<listitem><para>Address lookups (reverse lookups) are routed similarly to multi-label names, with the
exception that addresses from the link-local address range are never routed to unicast DNS and are only
resolved using LLMNR and MulticastDNS (when enabled).</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 and other
settings. See
<para>Routing of lookups is determined by the per-interface routing domains (search and route-only) and
global search domains. 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>
<citerefentry><refentrytitle>resolvectl</refentrytitle><manvolnum>1</manvolnum></citerefentry> for a
description how those settings are set dynamically and the discussion of <varname>Domains=</varname> in
<citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry> for a
description of globally configured DNS settings.</para>
<para>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 (see
<citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry>),
or the globally configured DNS settings (see the discussion of <varname>Domains=</varname> in
<citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>),
"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>
configured routing domains (search or route-only) of any link, or the globally configured DNS settings,
"best matching" routing 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" routing domain. (Note that more than one link might have this same "best matching" routing
domain configured, in which case the query is sent to all of them in parallel).</para>
<para>In case of single-label names, when search domains are defined, the same logic applies, except
that the name is first suffixed by the search domain.</para></listitem>
that the name is first suffixed by each of the search domains in turn. Note that this search logic
doesn't apply to any names with at least one dot. Also see the discussion about compatiblity with
the traditional glibc resolver below.</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 a query does not match any configured routing domain (either per-link or global), it
is sent to all DNS servers that are configured on links with the <varname>DefaultRoute=</varname>
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>If there is no link configured as <varname>DefaultRoute=</varname> and no global DNS
server configured, one of the compiled-in fallback DNS servers is used.</para></listitem>
<listitem><para>Otherwise the query is failed as no suitable DNS servers could be determined.
<listitem><para>Otherwise the unicast DNS query fails, as no suitable DNS servers can 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>The <varname>DefaultRoute=</varname> 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 a route-only domain other than
<literal>~.</literal>, it defaults to false, otherwise to true.</para>
<para>Effectively this means: in order to support single-label non-synthetized names, define appropriate
search domains. 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 these queries (unless they too carry such a
route-only domain). In order to route all such DNS queries to a specific link only if no other link
is preferable, set the "DNS default route" option for the link to true and do not configure a
search domains. In order to preferably route all DNS queries not explicitly matched by routing 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 these queries (unless they too carry such a routing
domain). In order to route all such DNS queries to a specific link only if no other link is preferred,
set the <varname>DefaultRoute=</varname> 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>
receives any DNS traffic not matching any of its configured routing domains, set the
<varname>DefaultRoute=</varname> option for it to false.</para>
<para>See
<citerefentry><refentrytitle>org.freedesktop.resolve1</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for information about the D-Bus APIs <filename>systemd-resolved</filename> provides.</para>
</refsect1>
<refsect1>
<title>Compatibility with the traditional glibc stub resolver</title>
<para>This section provides a short summary of differences in the stub resolver implemented by
<citerefentry><refentrytitle>nss-resolve</refentrytitle><manvolnum>8</manvolnum></citerefentry> together
with <command>systemd-resolved</command> and the tranditional stub resolver implemented in
<citerefentry><refentrytitle>nss-dns</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
<itemizedlist>
<listitem><para>Some names are always resolved internally (see Synthetic Records above). Traditionally
they would be resolved by <filename>nss-files</filename>, and only if provided in
<filename>/etc/hosts</filename>.</para></listitem>
<listitem><para>Single-label names are not resolved for A and AAAA records using unicast DNS (unless
overriden with <varname>ResolveUnicastSingleLabel=</varname>, see
<citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>).
This is similar to the <option>no-tld-query</option> option being set in
<citerefentry><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
</para></listitem>
<listitem><para>Search domains are not used for <emphasis>suffixing</emphasis> of multi-label names.
(Search domains are nevertheless used for lookup <emphasis>routing</emphasis>, for names that were
originally specified as single-label or multi-label.) Any name with at least one dot is always
interpreted as a FQDN. <filename>nss-dns</filename> would resolve names both as relative (using search
domains) and absolute FQDN names. Some names would be resolved as relative first, and after that query
has failed, as absolute, while other names would be resolved in opposite order. The
<varname>ndots</varname> option in <filename>/etc/resolv.conf</filename> was used to control how many
dots the name needs to have to be resolved as relative first. This stub resolver does not implement
this at all: multi-label names are only resolved as FQDNs. (There are currently more than 1500
top-level domain names defined, and new ones are added regularly, often using "attractive" names that
are also likely to be used locally. Not looking up multi-label names in this fashion avoids fragility
in both directions: a valid global name could be obscured by a local name, and resolution of a relative
local name could suddenly break when a new top-level domain is created, or when a new subdomain of a
top-level domain in registered. Resolving any given name as either relative or absolute avoids this
ambiguity.)</para></listitem>
<listitem><para>This resolver has a notion of the special <literal>.local</literal> domain used for
MulticastDNS, and will not route queries with that suffix to unicast DNS servers unless explicitly
configured, see above. Also, reverse lookups for link-local addresses are not sent to unicast DNS
servers.</para></listitem>
<listitem><para>This resolver reads and caches <filename>/etc/hosts</filename> internally. (In other
words, <filename>nss-resolve</filename> replaces <filename>nss-files</filename> in addition to
<filename>nss-dns</filename>). Entries in <filename>/etc/hosts</filename> have highest priority.</para>
</listitem>
<listitem><para>This resolver also implements LLMNR and MulticastDNS in addition to the classic unicast
DNS protocol, and will resolve single-label names using LLMNR (when enabled) and names ending in
<literal>.local</literal> using MulticastDNS (when enabled).</para></listitem>
<listitem><para>Environment variables <varname>$LOCALDOMAIN</varname> and
<varname>$RES_OPTIONS</varname> described in
<citerefentry><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry> are not
supported currently.</para></listitem>
</itemizedlist>
</refsect1>
<refsect1>
<title><filename>/etc/resolv.conf</filename></title>
@ -303,7 +361,6 @@
synchronous way.</para></listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>

8
src/resolve/resolved-resolv-conf.c
View File

@ -273,8 +273,8 @@ static int write_uplink_resolv_conf_contents(FILE *f, OrderedSet *dns, OrderedSe
}
if (ordered_set_isempty(domains))
fputs("search .", f); /* Make sure that if the local hostname is chosen as fqdn this does not
* imply a search domain */
fputs("search .\n", f); /* Make sure that if the local hostname is chosen as fqdn this does not
* imply a search domain */
else
write_resolv_conf_search(domains, f);
@ -302,8 +302,8 @@ static int write_stub_resolv_conf_contents(FILE *f, OrderedSet *dns, OrderedSet
"options edns0 trust-ad\n", f);
if (ordered_set_isempty(domains))
fputs("search .", f); /* Make sure that if the local hostname is chosen as fqdn this does not
* imply a search domain */
fputs("search .\n", f); /* Make sure that if the local hostname is chosen as fqdn this does not
* imply a search domain */
else
write_resolv_conf_search(domains, f);

1
src/resolve/resolved.conf.in
View File

@ -25,5 +25,6 @@
#LLMNR=@DEFAULT_LLMNR_MODE@
#Cache=yes
#DNSStubListener=yes
#DNSStubListenerExtra=
#ReadEtcHosts=yes
#ResolveUnicastSingleLabel=no