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resolved: document .local domain routing a bit more in detail 

Inspired by the discussions in #8851, even though the issue appears to
be entirely unrelated to the .local domain in the end.
This commit is contained in:
Lennart Poettering 2018-06-08 11:36:11 +02:00 committed by Zbigniew Jędrzejewski-Szmek
parent 0323073878
commit 6cdf635de0
1 changed files with 27 additions and 21 deletions
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48
man/systemd-resolved.service.xml
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@ -46,8 +46,8 @@
<title>Description</title>
<para><command>systemd-resolved</command> is a system service that provides network name resolution to local
applications. It implements a caching and validating DNS/DNSSEC stub resolver, as well as an LLMNR resolver and
responder. Local applications may submit network name resolution requests via three interfaces:</para>
applications. It implements a caching and validating DNS/DNSSEC stub resolver, as well as an LLMNR and MulticastDNS
resolver and responder. Local applications may submit network name resolution requests via three interfaces:</para>
<itemizedlist>
<listitem><para>The native, fully-featured API <command>systemd-resolved</command> exposes on the bus. See the
@ -77,8 +77,10 @@
<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, the per-link dynamic settings received over DHCP and any
DNS server information made available by other system services. See
<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
<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,
@ -111,27 +113,31 @@
non-address types (like MX).</para></listitem>
</itemizedlist>
<para>Lookup requests are routed to the available DNS servers
and LLMNR interfaces according to the following rules:</para>
<para>Lookup requests are routed to the available DNS servers, LLMNR and MulticastDNS interfaces according to the
following rules:</para>
<itemizedlist>
<listitem><para>Lookups for the special hostname
<literal>localhost</literal> are never routed to the
network. (A few other, special domains are handled the same way.)</para></listitem>
<listitem><para>Lookups for the special hostname <literal>localhost</literal> are never routed to the network. (A
few other, special domains are handled the same way.)</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>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 server configured, plus the globally
configured DNS server if there is one. Address lookups from the
link-local address range are never routed to
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, 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>Other multi-label names are routed to all local interfaces that have a DNS server configured,
plus the globally configured DNS server if there is one. Address lookups from the link-local address range are
never routed to DNS. 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 today 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>
</itemizedlist>
<para>If lookups are routed to multiple interfaces, the first