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<?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">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
<refentry id="dnssec-trust-anchors.d" conditional='ENABLE_RESOLVE'
xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<title>dnssec-trust-anchors.d</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>dnssec-trust-anchors.d</refentrytitle>
<manvolnum>5</manvolnum>
</refmeta>
<refnamediv>
<refname>dnssec-trust-anchors.d</refname>
<refname>systemd.positive</refname>
<refname>systemd.negative</refname>
<refpurpose>DNSSEC trust anchor configuration files</refpurpose>
</refnamediv>
<refsynopsisdiv>
<para><filename>/etc/dnssec-trust-anchors.d/*.positive</filename></para>
<para><filename>/run/dnssec-trust-anchors.d/*.positive</filename></para>
<para><filename>/usr/lib/dnssec-trust-anchors.d/*.positive</filename></para>
<para><filename>/etc/dnssec-trust-anchors.d/*.negative</filename></para>
<para><filename>/run/dnssec-trust-anchors.d/*.negative</filename></para>
<para><filename>/usr/lib/dnssec-trust-anchors.d/*.negative</filename></para>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>The DNSSEC trust anchor configuration files define positive
and negative trust anchors
<citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
bases DNSSEC integrity proofs on.</para>
</refsect1>
<refsect1>
<title>Positive Trust Anchors</title>
<para>Positive trust anchor configuration files contain <constant class='dns'>DNSKEY</constant> and
<constant class='dns'>DS</constant> resource record definitions to use as base for DNSSEC integrity
proofs. See <ulink url="https://tools.ietf.org/html/rfc4035#section-4.4">RFC 4035, Section 4.4</ulink>
for more information about DNSSEC trust anchors.</para>
<para>Positive trust anchors are read from files with the suffix
<filename>.positive</filename> located in
<filename>/etc/dnssec-trust-anchors.d/</filename>,
<filename>/run/dnssec-trust-anchors.d/</filename> and
<filename>/usr/lib/dnssec-trust-anchors.d/</filename>. These
directories are searched in the specified order, and a trust
anchor file of the same name in an earlier path overrides a trust
anchor files in a later path. To disable a trust anchor file
shipped in <filename>/usr/lib/dnssec-trust-anchors.d/</filename>
it is sufficient to provide an identically-named file in
<filename>/etc/dnssec-trust-anchors.d/</filename> or
<filename>/run/dnssec-trust-anchors.d/</filename> that is either
empty or a symlink to <filename>/dev/null</filename> ("masked").</para>
<para>Positive trust anchor files are simple text files resembling DNS zone files, as documented in
<ulink url="https://tools.ietf.org/html/rfc1035#section-5">RFC 1035, Section 5</ulink>. One <constant
class='dns'>DS</constant> or <constant class='dns'>DNSKEY</constant> resource record may be listed per
line. Empty lines and lines starting with <literal>#</literal> or <literal>;</literal> are ignored, which
may be used for commenting. A <constant class='dns'>DS</constant> resource record is specified like in the
following example:</para>
<programlisting>. IN DS 19036 8 2 49aac11d7b6f6446702e54a1607371607a1a41855200fd2ce1cdde32f24e8fb5</programlisting>
<para>The first word specifies the domain, use
<literal>.</literal> for the root domain. The domain may be
specified with or without trailing dot, which is considered
equivalent. The second word must be <literal>IN</literal> the
third word <literal>DS</literal>. The following words specify the
key tag, signature algorithm, digest algorithm, followed by the
hex-encoded key fingerprint. See <ulink
url="https://tools.ietf.org/html/rfc4034#section-5">RFC 4034,
Section 5</ulink> for details about the precise syntax and meaning
of these fields.</para>
<para>Alternatively, <constant class='dns'>DNSKEY</constant> resource records may be used to define trust
anchors, like in the following example:</para>
<programlisting>. IN DNSKEY 257 3 8 AwEAAagAIKlVZrpC6Ia7gEzahOR+9W29euxhJhVVLOyQbSEW0O8gcCjFFVQUTf6v58fLjwBd0YI0EzrAcQqBGCzh/RStIoO8g0NfnfL2MTJRkxoXbfDaUeVPQuYEhg37NZWAJQ9VnMVDxP/VHL496M/QZxkjf5/Efucp2gaDX6RS6CXpoY68LsvPVjR0ZSwzz1apAzvN9dlzEheX7ICJBBtuA6G3LQpzW5hOA2hzCTMjJPJ8LbqF6dsV6DoBQzgul0sGIcGOYl7OyQdXfZ57relSQageu+ipAdTTJ25AsRTAoub8ONGcLmqrAmRLKBP1dfwhYB4N7knNnulqQxA+Uk1ihz0=</programlisting>
<para>The first word specifies the domain again, the second word must be <literal>IN</literal>, followed
by <literal>DNSKEY</literal>. The subsequent words encode the <constant class='dns'>DNSKEY</constant>
flags, protocol and algorithm fields, followed by the key data encoded in Base64. See <ulink
url="https://tools.ietf.org/html/rfc4034#section-2">RFC 4034, Section 2</ulink> for details about the
precise syntax and meaning of these fields.</para>
<para>If multiple <constant class='dns'>DS</constant> or <constant class='dns'>DNSKEY</constant> records
are defined for the same domain (possibly even in different trust anchor files), all keys are used and
are considered equivalent as base for DNSSEC proofs.</para>
<para>Note that <filename>systemd-resolved</filename> will
automatically use a built-in trust anchor key for the Internet
root domain if no positive trust anchors are defined for the root
domain. In most cases it is hence unnecessary to define an
explicit key with trust anchor files. The built-in key is disabled
as soon as at least one trust anchor key for the root domain is
defined in trust anchor files.</para>
<para>It is generally recommended to encode trust anchors in <constant class='dns'>DS</constant> resource
records, rather than <constant class='dns'>DNSKEY</constant> resource records.</para>
<para>If a trust anchor specified via a <constant class='dns'>DS</constant> record is found revoked it is
automatically removed from the trust anchor database for the runtime. See <ulink
url="https://tools.ietf.org/html/rfc5011">RFC 5011</ulink> for details about revoked trust anchors. Note
that <filename>systemd-resolved</filename> will not update its trust anchor database from DNS servers
automatically. Instead, it is recommended to update the resolver software or update the new trust anchor
via adding in new trust anchor files.</para>
<para>The current DNSSEC trust anchor for the Internet's root
domain is available at the <ulink
url="https://data.iana.org/root-anchors/root-anchors.xml">IANA
Trust Anchor and Keys</ulink> page.</para>
</refsect1>
<refsect1>
<title>Negative Trust Anchors</title>
<para>Negative trust anchors define domains where DNSSEC validation shall be turned
off. Negative trust anchor files are found at the same location as positive trust anchor files,
and follow the same overriding rules. They are text files with the
<filename>.negative</filename> suffix. Empty lines and lines whose first character is
<literal>;</literal> are ignored. Each line specifies one domain name which is the root of a DNS
subtree where validation shall be disabled. For example:</para>
<programlisting># Reverse IPv4 mappings
10.in-addr.arpa
16.172.in-addr.arpa
168.192.in-addr.arpa
...
# Some custom domains
prod
stag
</programlisting>
<para>Negative trust anchors are useful to support private DNS
subtrees that are not referenced from the Internet DNS hierarchy,
and not signed.</para>
<para><ulink url="https://tools.ietf.org/html/rfc7646">RFC
7646</ulink> for details on negative trust anchors.</para>
<para>If no negative trust anchor files are configured a built-in
set of well-known private DNS zone domains is used as negative
trust anchors.</para>
<para>It is also possibly to define per-interface negative trust
anchors using the <varname>DNSSECNegativeTrustAnchors=</varname>
setting in
<citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry>
files.</para>
</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>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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