dnssec-trust-anchors.d(5) — Linux manual page

NAME \| SYNOPSIS \| DESCRIPTION \| POSITIVE TRUST ANCHORS \| NEGATIVE TRUST ANCHORS \| SEE ALSO \| NOTES \| COLOPHON

DNSSEC-TRUST-ANCHORS.D(5) dnssec-trust-anchors.dDNSSEC-TRUST-ANCHORS.D(5)

NAME top

       dnssec-trust-anchors.d, systemd.positive, systemd.negative -
       DNSSEC trust anchor configuration files

SYNOPSIS top

           /etc/dnssec-trust-anchors.d/*.positive
           /run/dnssec-trust-anchors.d/*.positive
           /usr/local/lib/dnssec-trust-anchors.d/*.positive
           /usr/lib/dnssec-trust-anchors.d/*.positive
           /etc/dnssec-trust-anchors.d/*.negative
           /run/dnssec-trust-anchors.d/*.negative
           /usr/local/lib/dnssec-trust-anchors.d/*.negative
           /usr/lib/dnssec-trust-anchors.d/*.negative

DESCRIPTION top

       The DNSSEC trust anchor configuration files define positive and
       negative trust anchors systemd-resolved.service(8) bases DNSSEC
       integrity proofs on.

POSITIVE TRUST ANCHORS top

Positive trust anchor configuration files contain DNSKEY and DS
resource record definitions to use as base for DNSSEC integrity
proofs. See RFC 4035, Section 4.4[1] for more information about
DNSSEC trust anchors.

Positive trust anchors are read from files with the suffix
.positive located in /etc/dnssec-trust-anchors.d/,
/run/dnssec-trust-anchors.d/ and /usr/lib/dnssec-trust-anchors.d/.
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 /usr/lib/dnssec-trust-anchors.d/ it is sufficient to
provide an identically-named file in /etc/dnssec-trust-anchors.d/
or /run/dnssec-trust-anchors.d/ that is either empty or a symlink
to /dev/null ("masked").

Positive trust anchor files are simple text files resembling DNS
zone files, as documented in RFC 1035, Section 5[2]. One DS or
DNSKEY resource record may be listed per line. Empty lines and
lines starting with "#" or ";" are ignored, which may be used for
commenting. A DS resource record is specified like in the
following example:

. IN DS 19036 8 2 49aac11d7b6f6446702e54a1607371607a1a41855200fd2ce1cdde32f24e8fb5

The first word specifies the domain, use "." for the root domain.
The domain may be specified with or without trailing dot, which is
considered equivalent. The second word must be "IN" the third word
"DS". The following words specify the key tag, signature
algorithm, digest algorithm, followed by the hex-encoded key
fingerprint. See RFC 4034, Section 5[3] for details about the
precise syntax and meaning of these fields.

Alternatively, DNSKEY resource records may be used to define trust
anchors, like in the following example:

. IN DNSKEY 257 3 8 AwEAAagAIKlVZrpC6Ia7gEzahOR+9W29euxhJhVVLOyQbSEW0O8gcCjFFVQUTf6v58fLjwBd0YI0EzrAcQqBGCzh/RStIoO8g0NfnfL2MTJRkxoXbfDaUeVPQuYEhg37NZWAJQ9VnMVDxP/VHL496M/QZxkjf5/Efucp2gaDX6RS6CXpoY68LsvPVjR0ZSwzz1apAzvN9dlzEheX7ICJBBtuA6G3LQpzW5hOA2hzCTMjJPJ8LbqF6dsV6DoBQzgul0sGIcGOYl7OyQdXfZ57relSQageu+ipAdTTJ25AsRTAoub8ONGcLmqrAmRLKBP1dfwhYB4N7knNnulqQxA+Uk1ihz0=

The first word specifies the domain again, the second word must be
"IN", followed by "DNSKEY". The subsequent words encode the DNSKEY
flags, protocol and algorithm fields, followed by the key data
encoded in Base64. See RFC 4034, Section 2[4] for details about
the precise syntax and meaning of these fields.

If multiple DS or DNSKEY 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.

Note that systemd-resolved 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.

It is generally recommended to encode trust anchors in DS resource
records, rather than DNSKEY resource records.

If a trust anchor specified via a DS record is found revoked it is
automatically removed from the trust anchor database for the
runtime. See RFC 5011[5] for details about revoked trust anchors.
Note that systemd-resolved 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.

The current DNSSEC trust anchor for the Internet's root domain is
available at the IANA Trust Anchor and Keys[6] page.

NEGATIVE TRUST ANCHORS top

       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 .negative suffix.
       Empty lines and lines whose first character is ";" are ignored.
       Each line specifies one domain name which is the root of a DNS
       subtree where validation shall be disabled. For example:

           # Reverse IPv4 mappings
           10.in-addr.arpa
           16.172.in-addr.arpa
           168.192.in-addr.arpa
           ...
           # Some custom domains
           prod
           stag

       Negative trust anchors are useful to support private DNS subtrees
       that are not referenced from the Internet DNS hierarchy, and not
       signed.

       RFC 7646[7] for details on negative trust anchors.

       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.

       It is also possibly to define per-interface negative trust anchors
       using the DNSSECNegativeTrustAnchors= setting in
       systemd.network(5) files.

NOTES top

        1. RFC 4035, Section 4.4
           https://tools.ietf.org/html/rfc4035#section-4.4

        2. RFC 1035, Section 5
           https://tools.ietf.org/html/rfc1035#section-5

        3. RFC 4034, Section 5
           https://tools.ietf.org/html/rfc4034#section-5

        4. RFC 4034, Section 2
           https://tools.ietf.org/html/rfc4034#section-2

        5. RFC 5011
           https://tools.ietf.org/html/rfc5011

        6. IANA Trust Anchor and Keys
           https://data.iana.org/root-anchors/root-anchors.xml

        7. RFC 7646
           https://tools.ietf.org/html/rfc7646

COLOPHON top

       This page is part of the systemd (systemd system and service
       manager) project.  Information about the project can be found at
       ⟨http://www.freedesktop.org/wiki/Software/systemd⟩.  If you have a
       bug report for this manual page, see
       ⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
       This page was obtained from the project's upstream Git repository
       ⟨https://github.com/systemd/systemd.git⟩ on 2025-08-11.  (At that
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       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

systemd 258~rc2                                 DNSSEC-TRUST-ANCHORS.D(5)

Pages that refer to this page: resolved.conf(5), systemd.directives(7), systemd.index(7), systemd-resolved.service(8)