dnssec-cds(8) BIND 9 dnssec-cds(8)
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] {domain}
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; by polling periodically with dnssec-cds, the par-
ent 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 RFC 7344. It requires that the CDS and/or CDNSKEY records are
validly signed by a key represented in the existing DS records. This
will typically be the pre-existing key-signing key (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. This time is obtained from the modification time of the
dsset- 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 will be the same as the existing records when no change
is required. The output can be empty if the CDS / CDNSKEY records spec-
ify that the child zone wants to go insecure.
Warning: Be careful not to delete the DS records when dnssec-cds fails!
Alternatively, dnssec-cds -u writes an nsupdate script to the standard
output. You can use the -u and -i options together to maintain a dsset-
file as well as emit an nsupdate script.
OPTIONS
-a algorithm
Specify a digest algorithm to use when converting CDNSKEY
records to DS records. This option can be repeated, so that mul-
tiple DS records are created for each CDNSKEY record. This
option has no effect when using CDS 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.
-c class
Specifies the DNS class of the zones.
-D Generate 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
Location of the parent DS records. The path can be the name of a
file containing the DS records, or if it is a directory,
dnssec-cds looks for a dsset- file for the domain inside 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
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.
-iextension
Update 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 you
provide no extension then the old dsset- is discarded. If an
extension 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 is later than the file's current
modification time.
-s start-time
Specify the date and time after which RRSIG records become
acceptable. This can be either an absolute or relative time. An
absolute start time is indicated by a number in YYYYMMDDHHMMSS
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
dsset- file is used.
-T ttl 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 then the new DS records also have no explicit TTL.
-u Write an nsupdate script to the standard output, instead of
printing the new DS reords. The output will be empty if no
change is needed.
Note: The TTL of new records needs to be specified, either in
the original dsset- file, or with the -T option, or using the
nsupdate ttl command.
-V Print version information.
-v level
Sets the debugging level. Level 1 is intended to be usefully
verbose for general users; higher levels are intended for devel-
opers.
domain 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
occurred.
In the success case, the DS records might or might not need to be
changed.
EXAMPLES
Before running dnssec-signzone, you can 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 you can invoke dig as
in the script below. It's okay 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, you can use
dnssec-cds 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 keeps 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
Administrator Reference Manual, RFC 7344.
AUTHOR
Internet Systems Consortium
COPYRIGHT
2020, Internet Systems Consortium
9.16.4 2020-06-10 dnssec-cds(8)
bind 9.16.4 - Generated Fri Jun 19 08:54:20 CDT 2020