Ubuntu Manpage: dnssec-trust-anchors.d, systemd.positive, systemd.negative

Provided by: systemd_256.5-2ubuntu3.1_amd64

NAME

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

SYNOPSIS

           /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

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

POSITIVE TRUST ANCHORS

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

       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