<?xml version='1.0'?>

<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"

"http://www.oasis-open.org/docbook/xml/4.5/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><simplelist>

<member><filename>/etc/dnssec-trust-anchors.d/*.positive</filename></member>

<member><filename>/run/dnssec-trust-anchors.d/*.positive</filename></member>

<member><filename>/usr/local/lib/dnssec-trust-anchors.d/*.positive</filename></member>

<member><filename>/usr/lib/dnssec-trust-anchors.d/*.positive</filename></member>

<member><filename>/etc/dnssec-trust-anchors.d/*.negative</filename></member>

<member><filename>/run/dnssec-trust-anchors.d/*.negative</filename></member>

<member><filename>/usr/local/lib/dnssec-trust-anchors.d/*.negative</filename></member>

<member><filename>/usr/lib/dnssec-trust-anchors.d/*.negative</filename></member>

</simplelist></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><simplelist type="inline">

<member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>

<member><citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>

<member><citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>

<member><citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>

</simplelist></para>

</refsect1>

</refentry>