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Versions: 00 01 02                                                      
Domain Name System Operations Working Group                   G. Barwood
Intended status: Standards Track                            03 July 2010

                            DNS Transport


   This document describes a new resource record type that allows a
   child zone to publish the DS RRset for a DNS zone.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on January 3, 2011.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors. All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   (http://trustee.ietf.org/license-info) in effect on the date of
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1.  Introduction

  This document defines a new resource record that may be used to
  publish the DS RRset [RFC4034] in the child zone. A new resource
  record type is needed, because the DS RR appears only on the upper
  (parental) side of a delegation.

  The mnenomic for the new resource record type is "CDS", which is
  intended to stand for "Child DS".

  The DNSSEC DS RRset for a zone is defined by the child zone but stored
  in the parent zone. After creating a new key signing key, the child
  zone needs to update the parent zone.

  There is currently no DNS protocol mechanism for accomplishing this.
  It is assumed that the DS RRset is transferred by some out-of-band

  In particular the CDS RR MAY be used to securely automate the rollover
  of the key signing key for a zone.

  A new resource record type is preferred to using flags in the DNSKEY
  RRset. It allows the DS to be published without revealing the public
  key, delaying the time at which an attacker can start cryptanalysis;
  the size of the DNSKEY RRset is not changed, which avoids potential
  transport problems with large responses; and it allows arbitrary DS
  records to be published which may have no corresponding DNSKEY, which
  might be useful in future for defining transport parameters.

2.  Definitions

  The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
  document are to be interpreted as described in [RFC2119].

3.  Resource Record Format

  The wire and presentation format is identical to the DS record.

  However no special processing is performed by servers or clients when
  serving or resolving.

  The CDS record MUST be signed with a key that has the Secure Entry
  Point flag set.

3.  Usage

  The CDS RRset MAY be used by the parent zone to create or update the
  DS RRset. The parent zone MAY periodically check the child zone to see
  if the CDS RRset has changed. The child zone MAY send a NOTIFY message
  [RFC1996] to a name server for the parent zone to expidite the

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  The parent zone SHOULD attempt to authenticate [RFC4033] the CDS
  RRset. If the authentication succeeds or yields Insecure, extra
  security checks are not normally necessary, but MAY be performed
  according to the parent zone policy. If the authentication fails (the
  result is  Bogus), no action is taken, other than appropriate alerts
  to inform operators or administrators that there is a problem.

  The parent zone SHOULD check that the signing key(s) have the Secure
  Entry Point flag set.

  The parent zone SHOULD ensure that old versions of the CDS RRset do
  not overwrite newer versions, which can occur if there is a delay
  updating secondary name servers for the child zone. This MAY be
  accomplished by checking that the signature inception in the RRSIG has

  If the CDS RRset does not exist, the parent MUST take no action.
  Specifically it MUST NOT delete the existing DS RRset.

  If the child zone loses the secret key(s) for the zone, and needs to
  reset the parent DS RRset, this must be accomplished by an out-of-band
  mechanism not defined here.

  To mitigate situations where a key signing key has been compromised,
  the parent zone MAY take extra security measures, for example
  informing ( by email or other methods ) the zone administrator of the
  change,  and delaying the acceptance of the new DS RRset for some
  period of time. However the precise out-of-band measures that a parent
  zone SHOULD take are outside the scope of this document.

4.  IANA Considerations

  IANA is requested to assign the DNS Resource Record Type code for
  the CDS record.

5.  Security considerations

  This document is entirely concerned with security considerations.

6.  Acknowledgements

  This document was created following discussion on automation of KSK
  rollover on the DNS Operations Working Group mailing list.

  Thanks to the people who provided review and suggestions:
  Mark Andrews, Richard Doty, Olafur Gudmundsson, Shane Kerr,
  Stephan Lagerholm, Chris Thompson.

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7.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC1996]  Vixie, P., "A Mechanism for Prompt Notification of Zone
              Changes (DNS NOTIFY)", RFC 1996, August 1996.

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements", RFC
              4033, March 2005.

   [RFC4034]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Resource Records for the DNS Security Extensions",
              RFC 4034, March 2005.

Author's Address

   George Barwood
   33 Sandpiper Close
   GL2 4LZ
   United Kingdom

   EMail: george.barwood@blueyonder.co.uk

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