1DNSSEC-CDS(8)                       BIND 9                       DNSSEC-CDS(8)
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NAME

6       dnssec-cds - change DS records for a child zone based on CDS/CDNSKEY
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SYNOPSIS

9       dnssec-cds  [-a alg...] [-c class] [-D] {-d dsset-file} {-f child-file}
10       [-i**[extension]] [-s** start-time] [-T ttl] [-u] [-v level] [-V]  {do‐
11       main}
12

DESCRIPTION

14       The  dnssec-cds  command changes DS records at a delegation point based
15       on CDS or CDNSKEY records published in the child zone. If both CDS  and
16       CDNSKEY  records  are  present in the child zone, the CDS is preferred.
17       This enables a child zone to inform its parent of upcoming  changes  to
18       its  key-signing  keys (KSKs); by polling periodically with dnssec-cds,
19       the parent can keep the DS  records  up-to-date  and  enable  automatic
20       rolling of KSKs.
21
22       Two input files are required. The -f child-file option specifies a file
23       containing the child's CDS  and/or  CDNSKEY  records,  plus  RRSIG  and
24       DNSKEY  records  so  that they can be authenticated. The -d path option
25       specifies the location of a file containing the current DS records. For
26       example,  this  could be a dsset- file generated by dnssec-signzone, or
27       the output of dnssec-dsfromkey, or the output  of  a  previous  run  of
28       dnssec-cds.
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30       The  dnssec-cds  command uses special DNSSEC validation logic specified
31       by RFC 7344. It requires that the CDS and/or CDNSKEY records be validly
32       signed  by  a key represented in the existing DS records. This is typi‐
33       cally the pre-existing KSK.
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35       For protection against replay attacks,  the  signatures  on  the  child
36       records  must  not  be  older  than  they  were  on  a  previous run of
37       dnssec-cds. Their age is obtained from the modification time of the ds‐
38       set- file, or from the -s option.
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40       To protect against breaking the delegation, dnssec-cds ensures that the
41       DNSKEY RRset can be verified by every  key  algorithm  in  the  new  DS
42       RRset,  and  that  the  same set of keys are covered by every DS digest
43       type.
44
45       By default, replacement DS records are written to the standard  output;
46       with the -i option the input file is overwritten in place. The replace‐
47       ment DS records are the same as the existing records, when no change is
48       required.  The  output  can be empty if the CDS/CDNSKEY records specify
49       that the child zone wants to be insecure.
50
51       WARNING:
52          Be careful not to delete the DS records when dnssec-cds fails!
53
54       Alternatively, dnssec-cds -u writes an nsupdate script to the  standard
55       output. The -u and -i options can be used together to maintain a dsset-
56       file as well as emit an nsupdate script.
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OPTIONS

59       -a algorithm
60              This option specifies a digest algorithm to use when  converting
61              CDNSKEY  records  to DS records. This option can be repeated, so
62              that multiple DS records are created for  each  CDNSKEY  record.
63              This option has no effect when using CDS records.
64
65              The  algorithm  must be one of SHA-1, SHA-256, or SHA-384. These
66              values are case-insensitive, and the hyphen may be  omitted.  If
67              no algorithm is specified, the default is SHA-256.
68
69       -c class
70              This option specifies the DNS class of the zones.
71
72       -D     This  option  generates  DS records from CDNSKEY records if both
73              CDS and CDNSKEY records are present in the child  zone.  By  de‐
74              fault CDS records are preferred.
75
76       -d path
77              This  specifies  the location of the parent DS records. The path
78              can be the name of a file containing the DS records; if it is  a
79              directory, dnssec-cds looks for a dsset- file for the domain in‐
80              side the directory.
81
82              To protect against replay attacks, child records are rejected if
83              they  were  signed earlier than the modification time of the ds‐
84              set- file. This can be adjusted with the -s option.
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86       -f child-file
87              This option specifies the file containing the child's CDS and/or
88              CDNSKEY  records, plus its DNSKEY records and the covering RRSIG
89              records, so that they can be authenticated.
90
91              The examples below describe how to generate this file.
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93       -iextension
94              This option updates the dsset- file in place, instead of writing
95              DS records to the standard output.
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97              There  must  be no space between the -i and the extension. If no
98              extension is provided, the old dsset- is discarded. If an exten‐
99              sion  is  present,  a backup of the old dsset- file is kept with
100              the extension appended to its filename.
101
102              To protect against replay attacks, the modification time of  the
103              dsset-  file is set to match the signature inception time of the
104              child records, provided that it is later than the file's current
105              modification time.
106
107       -s start-time
108              This  option  specifies  the  date  and  time  after which RRSIG
109              records become acceptable. This can be either an absolute  or  a
110              relative  time.  An absolute start time is indicated by a number
111              in YYYYMMDDHHMMSS notation; 20170827133700 denotes 13:37:00  UTC
112              on  August 27th, 2017. A time relative to the dsset- file is in‐
113              dicated with -N, which is N seconds before the file modification
114              time.  A  time  relative  to  the current time is indicated with
115              now+N.
116
117              If no start-time is specified, the modification time of the  ds‐
118              set- file is used.
119
120       -T ttl This  option  specifies  a TTL to be used for new DS records. If
121              not specified, the default is the TTL of the old DS records.  If
122              they  had  no  explicit TTL, the new DS records also have no ex‐
123              plicit TTL.
124
125       -u     This option writes an nsupdate script to  the  standard  output,
126              instead of printing the new DS reords. The output is empty if no
127              change is needed.
128
129              Note: The TTL of new records needs to be specified:  it  can  be
130              done  in  the original dsset- file, with the -T option, or using
131              the nsupdate ttl command.
132
133       -V     This option prints version information.
134
135       -v level
136              This option sets the debugging level. Level 1 is intended to  be
137              usefully  verbose  for general users; higher levels are intended
138              for developers.
139
140       domain This indicates the name of the delegation point/child zone apex.
141

EXIT STATUS

143       The dnssec-cds command exits 0 on success, or non-zero if an error  oc‐
144       curred.
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146       If successful, the DS records may or may not need to be changed.
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EXAMPLES

149       Before   running  dnssec-signzone,  ensure  that  the  delegations  are
150       up-to-date by running dnssec-cds on every dsset- file.
151
152       To fetch the child records required by dnssec-cds, invoke dig as in the
153       script  below. It is acceptable if the dig fails, since dnssec-cds per‐
154       forms all the necessary checking.
155
156          for f in dsset-*
157          do
158              d=${f#dsset-}
159              dig +dnssec +noall +answer $d DNSKEY $d CDNSKEY $d CDS |
160              dnssec-cds -i -f /dev/stdin -d $f $d
161          done
162
163       When the parent zone is automatically signed by named,  dnssec-cds  can
164       be  used with nsupdate to maintain a delegation as follows.  The dsset-
165       file allows the script to avoid having to fetch and validate the parent
166       DS records, and it maintains the replay attack protection time.
167
168          dig +dnssec +noall +answer $d DNSKEY $d CDNSKEY $d CDS |
169          dnssec-cds -u -i -f /dev/stdin -d $f $d |
170          nsupdate -l
171

SEE ALSO

173       dig(1),  dnssec-settime(8), dnssec-signzone(8), nsupdate(1), BIND 9 Ad‐
174       ministrator Reference Manual, RFC 7344.
175

AUTHOR

177       Internet Systems Consortium
178
180       2021, Internet Systems Consortium
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1859.16.23-RH                                                       DNSSEC-CDS(8)
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