DNSSEC-CDS(1) BIND 9 DNSSEC-CDS(1)
NAME
dnssec-cds - change DS records for a child zone based on CDS/CDNSKEY
SYNOPSIS
dnssec-cds [-a alg...] [-c class] [-D] {-d dsset-file} {-f child-file}
[-i**[extension]] [-s** start-time] [-T ttl] [-u] [-v level] [-V] {do-
main}
DESCRIPTION
The dnssec-cds command changes DS records at a delegation point based on
CDS or CDNSKEY records published in the child zone. If both CDS and
CDNSKEY records are present in the child zone, the CDS is preferred.
This enables a child zone to inform its parent of upcoming changes to
its key-signing keys (KSKs); by polling periodically with dnssec-cds,
the parent can keep the DS records up-to-date and enable automatic
rolling of KSKs.
Two input files are required. The -f child-file option specifies a file
containing the child's CDS and/or CDNSKEY records, plus RRSIG and DNSKEY
records so that they can be authenticated. The -d path option specifies
the location of a file containing the current DS records. For example,
this could be a dsset- file generated by dnssec-signzone, or the output
of dnssec-dsfromkey, or the output of a previous run of dnssec-cds.
The dnssec-cds command uses special DNSSEC validation logic specified by
]8;;https://datatracker.ietf.org/doc/html/rfc7344.html\RFC 7344]8;;\. It requires that the CDS and/or CDNSKEY records be validly
signed by a key represented in the existing DS records. This is typi-
cally the pre-existing KSK.
For protection against replay attacks, the signatures on the child
records must not be older than they were on a previous run of
dnssec-cds. Their age is obtained from the modification time of the ds-
set- file, or from the -s option.
To protect against breaking the delegation, dnssec-cds ensures that the
DNSKEY RRset can be verified by every key algorithm in the new DS RRset,
and that the same set of keys are covered by every DS digest type.
By default, replacement DS records are written to the standard output;
with the -i option the input file is overwritten in place. The replace-
ment DS records are the same as the existing records, when no change is
required. The output can be empty if the CDS/CDNSKEY records specify
that the child zone wants to be insecure.
WARNING:
Be careful not to delete the DS records when dnssec-cds fails!
Alternatively, :option`dnssec-cds -u` writes an nsupdate script to the
standard output. The -u and -i options can be used together to maintain
a dsset- file as well as emit an nsupdate script.
OPTIONS
-a algorithm
When converting CDS records to DS records, this option specifies
the acceptable digest algorithms. This option can be repeated, so
that multiple digest types are allowed. If none of the CDS
records use an acceptable digest type, dnssec-cds will try to use
CDNSKEY records instead; if there are no CDNSKEY records, it re-
ports an error.
When converting CDNSKEY records to DS records, this option speci-
fies the digest algorithm to use. It can be repeated, so that
multiple DS records are created for each CDNSKEY records.
The algorithm must be one of SHA-1, SHA-256, or SHA-384. These
values are case-insensitive, and the hyphen may be omitted. If no
algorithm is specified, the default is SHA-256 only.
-c class
This option specifies the DNS class of the zones.
-D This option generates DS records from CDNSKEY records if both CDS
and CDNSKEY records are present in the child zone. By default CDS
records are preferred.
-d path
This specifies the location of the parent DS records. The path
can be the name of a file containing the DS records; if it is a
directory, dnssec-cds looks for a dsset- file for the domain in-
side the directory.
To protect against replay attacks, child records are rejected if
they were signed earlier than the modification time of the dsset-
file. This can be adjusted with the -s option.
-f child-file
This option specifies the file containing the child's CDS and/or
CDNSKEY records, plus its DNSKEY records and the covering RRSIG
records, so that they can be authenticated.
The examples below describe how to generate this file.
-i extension
This option updates the dsset- file in place, instead of writing
DS records to the standard output.
There must be no space between the -i and the extension. If no
extension is provided, the old dsset- is discarded. If an exten-
sion is present, a backup of the old dsset- file is kept with the
extension appended to its filename.
To protect against replay attacks, the modification time of the
dsset- file is set to match the signature inception time of the
child records, provided that it is later than the file's current
modification time.
-s start-time
This option specifies the date and time after which RRSIG records
become acceptable. This can be either an absolute or a relative
time. An absolute start time is indicated by a number in YYYYMMD-
DHHMMSS notation; 20170827133700 denotes 13:37:00 UTC on August
27th, 2017. A time relative to the dsset- file is indicated with
-N, which is N seconds before the file modification time. A time
relative to the current time is indicated with now+N.
If no start-time is specified, the modification time of the ds-
set- file is used.
-T ttl This option specifies a TTL to be used for new DS records. If not
specified, the default is the TTL of the old DS records. If they
had no explicit TTL, the new DS records also have no explicit
TTL.
-u This option writes an nsupdate script to the standard output, in-
stead of printing the new DS reords. The output is empty if no
change is needed.
Note: The TTL of new records needs to be specified: it can be
done in the original dsset- file, with the -T option, or using
the nsupdate ttl command.
-V This option prints version information.
-v level
This option sets the debugging level. Level 1 is intended to be
usefully verbose for general users; higher levels are intended
for developers.
domain This indicates the name of the delegation point/child zone apex.
EXIT STATUS
The dnssec-cds command exits 0 on success, or non-zero if an error oc-
curred.
If successful, the DS records may or may not need to be changed.
EXAMPLES
Before running dnssec-signzone, ensure that the delegations are
up-to-date by running dnssec-cds on every dsset- file.
To fetch the child records required by dnssec-cds, invoke dig as in the
script below. It is acceptable if the dig fails, since dnssec-cds per-
forms all the necessary checking.
for f in dsset-*
do
d=${f#dsset-}
dig +dnssec +noall +answer $d DNSKEY $d CDNSKEY $d CDS |
dnssec-cds -i -f /dev/stdin -d $f $d
done
When the parent zone is automatically signed by named, dnssec-cds can be
used with nsupdate to maintain a delegation as follows. The dsset- file
allows the script to avoid having to fetch and validate the parent DS
records, and it maintains the replay attack protection time.
dig +dnssec +noall +answer $d DNSKEY $d CDNSKEY $d CDS |
dnssec-cds -u -i -f /dev/stdin -d $f $d |
nsupdate -l
SEE ALSO
dig(1), dnssec-settime(8), dnssec-signzone(8), nsupdate(1), BIND 9 Ad-
ministrator Reference Manual, ]8;;https://datatracker.ietf.org/doc/html/rfc7344.html\RFC 7344]8;;\.
AUTHOR
Internet Systems Consortium
COPYRIGHT
2025, Internet Systems Consortium
9.20.15-1~deb13u1-Debian 2025-10-18 DNSSEC-CDS(1)
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