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+.. Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+..
+.. SPDX-License-Identifier: MPL-2.0
+..
+.. This Source Code Form is subject to the terms of the Mozilla Public
+.. License, v. 2.0.  If a copy of the MPL was not distributed with this
+.. file, you can obtain one at https://mozilla.org/MPL/2.0/.
+..
+.. See the COPYRIGHT file distributed with this work for additional
+.. information regarding copyright ownership.
+
+.. highlight: console
+
+.. _man_dnssec-cds:
+
+dnssec-cds - change DS records for a child zone based on CDS/CDNSKEY
+--------------------------------------------------------------------
+
+Synopsis
+~~~~~~~~
+
+:program:`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 (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 :rfc:`7344`. It requires that the CDS and/or CDNSKEY records
+be validly signed by a key represented in the existing DS records. This
+is typically 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
+``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
+replacement 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, ``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``
+   This option specifies a digest algorithm to use when converting CDNSKEY records to
+   DS records. This option can be repeated, so that multiple 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``
+   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 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``
+   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.
+
+``-iextension``
+   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
+   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 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 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``
+   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, instead 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
+occurred.
+
+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`` performs 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
+~~~~~~~~
+
+:manpage:`dig(1)`, :manpage:`dnssec-settime(8)`, :manpage:`dnssec-signzone(8)`, :manpage:`nsupdate(1)`, BIND 9 Administrator
+Reference Manual, :rfc:`7344`.