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173 lines
8.7 KiB
XML
173 lines
8.7 KiB
XML
<?xml version='1.0'?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="dnssec-trust-anchors.d" conditional='ENABLE_RESOLVE'
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xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>dnssec-trust-anchors.d</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>dnssec-trust-anchors.d</refentrytitle>
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<manvolnum>5</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>dnssec-trust-anchors.d</refname>
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<refname>systemd.positive</refname>
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<refname>systemd.negative</refname>
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<refpurpose>DNSSEC trust anchor configuration files</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<para><filename>/etc/dnssec-trust-anchors.d/*.positive</filename></para>
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<para><filename>/run/dnssec-trust-anchors.d/*.positive</filename></para>
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<para><filename>/usr/lib/dnssec-trust-anchors.d/*.positive</filename></para>
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<para><filename>/etc/dnssec-trust-anchors.d/*.negative</filename></para>
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<para><filename>/run/dnssec-trust-anchors.d/*.negative</filename></para>
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<para><filename>/usr/lib/dnssec-trust-anchors.d/*.negative</filename></para>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para>The DNSSEC trust anchor configuration files define positive
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and negative trust anchors
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<citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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bases DNSSEC integrity proofs on.</para>
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</refsect1>
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<refsect1>
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<title>Positive Trust Anchors</title>
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<para>Positive trust anchor configuration files contain <constant class='dns'>DNSKEY</constant> and
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<constant class='dns'>DS</constant> resource record definitions to use as base for DNSSEC integrity
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proofs. See <ulink url="https://tools.ietf.org/html/rfc4035#section-4.4">RFC 4035, Section 4.4</ulink>
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for more information about DNSSEC trust anchors.</para>
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<para>Positive trust anchors are read from files with the suffix
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<filename>.positive</filename> located in
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<filename>/etc/dnssec-trust-anchors.d/</filename>,
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<filename>/run/dnssec-trust-anchors.d/</filename> and
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<filename>/usr/lib/dnssec-trust-anchors.d/</filename>. These
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directories are searched in the specified order, and a trust
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anchor file of the same name in an earlier path overrides a trust
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anchor files in a later path. To disable a trust anchor file
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shipped in <filename>/usr/lib/dnssec-trust-anchors.d/</filename>
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it is sufficient to provide an identically-named file in
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<filename>/etc/dnssec-trust-anchors.d/</filename> or
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<filename>/run/dnssec-trust-anchors.d/</filename> that is either
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empty or a symlink to <filename>/dev/null</filename> ("masked").</para>
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<para>Positive trust anchor files are simple text files resembling DNS zone files, as documented in
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<ulink url="https://tools.ietf.org/html/rfc1035#section-5">RFC 1035, Section 5</ulink>. One <constant
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class='dns'>DS</constant> or <constant class='dns'>DNSKEY</constant> resource record may be listed per
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line. Empty lines and lines starting with <literal>#</literal> or <literal>;</literal> are ignored, which
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may be used for commenting. A <constant class='dns'>DS</constant> resource record is specified like in the
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following example:</para>
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<programlisting>. IN DS 19036 8 2 49aac11d7b6f6446702e54a1607371607a1a41855200fd2ce1cdde32f24e8fb5</programlisting>
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<para>The first word specifies the domain, use
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<literal>.</literal> for the root domain. The domain may be
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specified with or without trailing dot, which is considered
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equivalent. The second word must be <literal>IN</literal> the
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third word <literal>DS</literal>. The following words specify the
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key tag, signature algorithm, digest algorithm, followed by the
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hex-encoded key fingerprint. See <ulink
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url="https://tools.ietf.org/html/rfc4034#section-5">RFC 4034,
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Section 5</ulink> for details about the precise syntax and meaning
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of these fields.</para>
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<para>Alternatively, <constant class='dns'>DNSKEY</constant> resource records may be used to define trust
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anchors, like in the following example:</para>
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<programlisting>. IN DNSKEY 257 3 8 AwEAAagAIKlVZrpC6Ia7gEzahOR+9W29euxhJhVVLOyQbSEW0O8gcCjFFVQUTf6v58fLjwBd0YI0EzrAcQqBGCzh/RStIoO8g0NfnfL2MTJRkxoXbfDaUeVPQuYEhg37NZWAJQ9VnMVDxP/VHL496M/QZxkjf5/Efucp2gaDX6RS6CXpoY68LsvPVjR0ZSwzz1apAzvN9dlzEheX7ICJBBtuA6G3LQpzW5hOA2hzCTMjJPJ8LbqF6dsV6DoBQzgul0sGIcGOYl7OyQdXfZ57relSQageu+ipAdTTJ25AsRTAoub8ONGcLmqrAmRLKBP1dfwhYB4N7knNnulqQxA+Uk1ihz0=</programlisting>
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<para>The first word specifies the domain again, the second word must be <literal>IN</literal>, followed
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by <literal>DNSKEY</literal>. The subsequent words encode the <constant class='dns'>DNSKEY</constant>
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flags, protocol and algorithm fields, followed by the key data encoded in Base64. See <ulink
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url="https://tools.ietf.org/html/rfc4034#section-2">RFC 4034, Section 2</ulink> for details about the
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precise syntax and meaning of these fields.</para>
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<para>If multiple <constant class='dns'>DS</constant> or <constant class='dns'>DNSKEY</constant> records
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are defined for the same domain (possibly even in different trust anchor files), all keys are used and
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are considered equivalent as base for DNSSEC proofs.</para>
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<para>Note that <filename>systemd-resolved</filename> will
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automatically use a built-in trust anchor key for the Internet
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root domain if no positive trust anchors are defined for the root
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domain. In most cases it is hence unnecessary to define an
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explicit key with trust anchor files. The built-in key is disabled
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as soon as at least one trust anchor key for the root domain is
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defined in trust anchor files.</para>
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<para>It is generally recommended to encode trust anchors in <constant class='dns'>DS</constant> resource
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records, rather than <constant class='dns'>DNSKEY</constant> resource records.</para>
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<para>If a trust anchor specified via a <constant class='dns'>DS</constant> record is found revoked it is
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automatically removed from the trust anchor database for the runtime. See <ulink
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url="https://tools.ietf.org/html/rfc5011">RFC 5011</ulink> for details about revoked trust anchors. Note
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that <filename>systemd-resolved</filename> will not update its trust anchor database from DNS servers
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automatically. Instead, it is recommended to update the resolver software or update the new trust anchor
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via adding in new trust anchor files.</para>
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<para>The current DNSSEC trust anchor for the Internet's root
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domain is available at the <ulink
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url="https://data.iana.org/root-anchors/root-anchors.xml">IANA
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Trust Anchor and Keys</ulink> page.</para>
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</refsect1>
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<refsect1>
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<title>Negative Trust Anchors</title>
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<para>Negative trust anchors define domains where DNSSEC validation shall be turned
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off. Negative trust anchor files are found at the same location as positive trust anchor files,
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and follow the same overriding rules. They are text files with the
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<filename>.negative</filename> suffix. Empty lines and lines whose first character is
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<literal>;</literal> are ignored. Each line specifies one domain name which is the root of a DNS
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subtree where validation shall be disabled. For example:</para>
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<programlisting># Reverse IPv4 mappings
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10.in-addr.arpa
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16.172.in-addr.arpa
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168.192.in-addr.arpa
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...
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# Some custom domains
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prod
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stag
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</programlisting>
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<para>Negative trust anchors are useful to support private DNS
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subtrees that are not referenced from the Internet DNS hierarchy,
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and not signed.</para>
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<para><ulink url="https://tools.ietf.org/html/rfc7646">RFC
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7646</ulink> for details on negative trust anchors.</para>
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<para>If no negative trust anchor files are configured a built-in
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set of well-known private DNS zone domains is used as negative
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trust anchors.</para>
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<para>It is also possibly to define per-interface negative trust
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anchors using the <varname>DNSSECNegativeTrustAnchors=</varname>
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setting in
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<citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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files.</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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