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<refentry xmlns:db="http://docbook.org/ns/docbook" version="5.0" xml:id="man.dnssec-cds">
<info>
<date>2017-10-02</date>
</info>
<refentryinfo>
<corpname>ISC</corpname>
<corpauthor>Internet Systems Consortium, Inc.</corpauthor>
<author>
<personname>Tony Finch</personname>
<email>dot@dotat.at</email>
<email>fanf2@cam.ac.uk</email>
<affiliation>Cambridge University Information Services</affiliation>
<personblurb></personblurb>
</author>
</refentryinfo>
<refmeta>
<refentrytitle><application>dnssec-cds</application></refentrytitle>
<manvolnum>8</manvolnum>
<refmiscinfo>BIND9</refmiscinfo>
</refmeta>
<refnamediv>
<refname><application>dnssec-cds</application></refname>
<refpurpose>change DS records for a child zone based on CDS/CDNSKEY</refpurpose>
</refnamediv>
<docinfo>
<copyright>
<year>2017</year>
<year>2018</year>
<year>2019</year>
<holder>Internet Systems Consortium, Inc. ("ISC")</holder>
</copyright>
</docinfo>
<refsynopsisdiv>
<cmdsynopsis sepchar=" ">
<command>dnssec-cds</command>
<arg choice="opt" rep="repeat"><option>-a <replaceable class="parameter">alg</replaceable></option></arg>
<arg choice="opt" rep="norepeat"><option>-c <replaceable class="parameter">class</replaceable></option></arg>
<arg choice="opt" rep="norepeat"><option>-D</option></arg>
<arg choice="req" rep="norepeat"><option>-d <replaceable class="parameter">dsset-file</replaceable></option></arg>
<arg choice="req" rep="norepeat"><option>-f <replaceable class="parameter">child-file</replaceable></option></arg>
<arg choice="opt" rep="norepeat"><option>-i</option><arg choice="opt" rep="norepeat"><replaceable class="parameter">extension</replaceable></arg></arg>
<arg choice="opt" rep="norepeat"><option>-s <replaceable class="parameter">start-time</replaceable></option></arg>
<arg choice="opt" rep="norepeat"><option>-T <replaceable class="parameter">ttl</replaceable></option></arg>
<arg choice="opt" rep="norepeat"><option>-u</option></arg>
<arg choice="opt" rep="norepeat"><option>-v <replaceable class="parameter">level</replaceable></option></arg>
<arg choice="opt" rep="norepeat"><option>-V</option></arg>
<arg choice="req" rep="norepeat">domain</arg>
</cmdsynopsis>
</refsynopsisdiv>
<refsection><info><title>DESCRIPTION</title></info>
<para>
The <command>dnssec-cds</command> 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 <command>dnssec-cds</command>, the
parent can keep the DS records up to date and enable automatic
rolling of KSKs.
</para>
<para>
Two input files are required. The
<option>-f <replaceable class="parameter">child-file</replaceable></option>
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
<option>-d <replaceable class="parameter">path</replaceable></option>
option specifies the location of a file containing the current DS
records. For example, this could be a <filename>dsset-</filename>
file generated by <command>dnssec-signzone</command>, or the output of
<command>dnssec-dsfromkey</command>, or the output of a previous
run of <command>dnssec-cds</command>.
</para>
<para>
The <command>dnssec-cds</command> 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 typicially be the pre-existing
key-signing key (KSK).
</para>
<para>
For protection against replay attacks, the signatures on the
child records must not be older than they were on a previous run
of <command>dnssec-cds</command>. This time is obtained from the
modification time of the <filename>dsset-</filename> file, or
from the <option>-s</option> option.
</para>
<para>
To protect against breaking the delegation,
<command>dnssec-cds</command> 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.
</para>
<para>
By default, replacement DS records are written to the standard
output; with the <option>-i</option> option the input file is
overwritten in place. The replacement 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 specify that
the child zone wants to go insecure.
</para>
<para>
Warning: Be careful not to delete the DS records
when <command>dnssec-cds</command> fails!
</para>
<para>
Alternatively, <command>dnssec-cds -u</command> writes
an <command>nsupdate</command> script to the standard output.
You can use the <option>-u</option> and <option>-i</option>
options together to maintain a <filename>dsset-</filename> file
as well as emit an <command>nsupdate</command> script.
</para>
</refsection>
<refsection><info><title>OPTIONS</title></info>
<variablelist>
<varlistentry>
<term>-a <replaceable class="parameter">algorithm</replaceable></term>
<listitem>
<para>
Specify 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.
</para>
<para>
The <replaceable>algorithm</replaceable> 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.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-c <replaceable class="parameter">class</replaceable></term>
<listitem>
<para>
Specifies the DNS class of the zones.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-D</term>
<listitem>
<para>
Generate DS records from CDNSKEY records if both CDS and
CDNSKEY records are present in the child zone. By default
CDS records are preferred.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-d <replaceable class="parameter">path</replaceable></term>
<listitem>
<para>
Location of the parent DS records.
The <replaceable>path</replaceable> can be the name of a file
containing the DS records, or if it is a
directory, <command>dnssec-cds</command> looks for
a <filename>dsset-</filename> file for
the <replaceable>domain</replaceable> inside the directory.
</para>
<para>
To protect against replay attacks, child records are
rejected if they were signed earlier than the modification
time of the <filename>dsset-</filename> file. This can be
adjusted with the <option>-s</option> option.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-f <replaceable class="parameter">child-file</replaceable></term>
<listitem>
<para>
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.
</para>
<para>
The EXAMPLES below describe how to generate this file.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-i<arg choice="opt" rep="norepeat"><replaceable class="parameter">extension</replaceable></arg></term>
<listitem>
<para>
Update the <filename>dsset-</filename> file in place,
instead of writing DS records to the standard output.
</para>
<para>
There must be no space between the <option>-i</option> and
the <replaceable>extension</replaceable>. If you provide
no <replaceable>extension</replaceable> then the
old <filename>dsset-</filename> is discarded. If
an <replaceable>extension</replaceable> is present, a
backup of the old <filename>dsset-</filename> file is kept
with the <replaceable>extension</replaceable> appended to
its filename.
</para>
<para>
To protect against replay attacks, the modification time
of the <filename>dsset-</filename> file is set to match
the signature inception time of the child records,
provided that is later than the file's current
modification time.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-s <replaceable class="parameter">start-time</replaceable></term>
<listitem>
<para>
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 <filename>dsset-</filename> 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.
</para>
<para>
If no <replaceable>start-time</replaceable> is specified, the
modification time of the <filename>dsset-</filename> file
is used.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-T <replaceable class="parameter">ttl</replaceable></term>
<listitem>
<para>
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.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-u</term>
<listitem>
<para>
Write an <command>nsupdate</command> script to the
standard output, instead of printing the new DS reords.
The output will be empty if no change is needed.
</para>
<para>
Note: The TTL of new records needs to be specified, either
in the original <filename>dsset-</filename> file, or with
the <option>-T</option> option, or using
the <command>nsupdate</command> <command>ttl</command>
command.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-V</term>
<listitem>
<para>
Print version information.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-v <replaceable class="parameter">level</replaceable></term>
<listitem>
<para>
Sets the debugging level. Level 1 is intended to be
usefully verbose for general users; higher levels are
intended for developers.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable>domain</replaceable></term>
<listitem>
<para>
The name of the delegation point / child zone apex.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsection>
<refsection><info><title>EXIT STATUS</title></info>
<para>
The <command>dnssec-cds</command> command exits 0 on success, or
non-zero if an error occurred.
</para>
<para>
In the success case, the DS records might or might not need
to be changed.
</para>
</refsection>
<refsection><info><title>EXAMPLES</title></info>
<para>
Before running <command>dnssec-signzone</command>, you can ensure
that the delegations are up-to-date by running
<command>dnssec-cds</command> on every <filename>dsset-</filename> file.
</para>
<para>
To fetch the child records required by <command>dnssec-cds</command>
you can invoke <command>dig</command> as in the script below. It's
okay if the <command>dig</command> fails since
<command>dnssec-cds</command> performs all the necessary checking.
</para>
<programlisting>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
</programlisting>
<para>
When the parent zone is automatically signed by
<command>named</command>, you can use <command>dnssec-cds</command>
with <command>nsupdate</command> to maintain a delegation as follows.
The <filename>dsset-</filename> file allows the script to avoid
having to fetch and validate the parent DS records, and it keeps the
replay attack protection time.
</para>
<programlisting>
dig +dnssec +noall +answer $d DNSKEY $d CDNSKEY $d CDS |
dnssec-cds -u -i -f /dev/stdin -d $f $d |
nsupdate -l
</programlisting>
</refsection>
<refsection><info><title>SEE ALSO</title></info>
<para>
<citerefentry>
<refentrytitle>dig</refentrytitle><manvolnum>1</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>dnssec-settime</refentrytitle><manvolnum>8</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>dnssec-signzone</refentrytitle><manvolnum>8</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>nsupdate</refentrytitle><manvolnum>1</manvolnum>
</citerefentry>,
<citetitle>BIND 9 Administrator Reference Manual</citetitle>,
<citetitle>RFC 7344</citetitle>.
</para>
</refsection>
</refentry>