Network Working Group                                            P. Koch
Internet-Draft                                                   M. Sanz
Intended status: Informational                                  DENIC eG
Expires: January 16, 2014                              A.L.J. Verschuren
                                                               SIDN Labs
                                                           July 15, 2013

             Changing DNS Operators for DNSSEC signed Zones


   Changing the DNS delegation for a DNS zone is quite involved if done
   by the books, but most often handled pragmatically in today's
   operational practice at the top level with registries and registrars.
   This document describes a delegation change procedure that maintains
   consistency and validation under DNSSEC.

Status of This Memo

   This Internet-Draft is submitted 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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   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   ( in effect on the date of
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   described in the Simplified BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Purpose of this Document  . . . . . . . . . . . . . . . .   3
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements and Assumptions for Seamless Operator Change . .   4
     2.1.  Requirements for Seamless Operator Change . . . . . . . .   4
     2.2.  Assumptions for Seamless Operator Change  . . . . . . . .   5
   3.  Executing the Change  . . . . . . . . . . . . . . . . . . . .   6
     3.1.  Changing DNS operator only  . . . . . . . . . . . . . . .   7
     3.2.  Changing DNS operator and registrar . . . . . . . . . . .   9
     3.3.  Losing operator not participating . . . . . . . . . . . .   9
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Appendix A.  Document Revision History  . . . . . . . . . . . . .  11
     A.1.  -00 . . . . . . . . . . . . . . . . . . . . . . . . . . .  11
     A.2.  -01 . . . . . . . . . . . . . . . . . . . . . . . . . . .  11
     A.3.  -02 . . . . . . . . . . . . . . . . . . . . . . . . . . .  11
     A.4.  -03 . . . . . . . . . . . . . . . . . . . . . . . . . . .  12
     A.5.  -04 . . . . . . . . . . . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   When the NS RRSet in a DNS delegation is to be changed from one to a
   disjoint other, the most conservative approach would be to add the
   new servers as (stealth) secondary servers, then add them to the NS
   RRSet, change the primary master (that is, change the AXFR/IXFR
   source for all the secondary servers), remove the old name servers'
   names from the NS RRSet and finally cease service on those former
   name servers.  This would involve two changes to the zone file for
   the apex NS RRSet and in turn two interactions with the parent zone
   (the registry) for the delegation NS RRSet.  Another procedure would
   at least see the old name servers acquire the new data by transfer
   and then publish it until the NS records' time to live (TTL) values

   Operational practice deviates from this in many cases, especially
   where there is a combined role of the registrar as registrar, DNS
   operator and web hoster.  Often the new infrastructure is set up
   independent of and in parallel to the old one and there is only one
   delegation change.  Resolvers will access either version of the DNS
   zone and the inconsistency in DNS data and even at the application

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   layer will be tolerated as long as the end user gets to see any
   result at all.

   DNSSEC [RFC4033][RFC4034][RFC4035] is less tolerant to this
   inconsistency, and the challenge is that access to and validation of
   DNS data will involve multiple steps.  The resolver might access DNS
   data through one (say, the old) name server infrastructure and DNS
   key material (the apex DNSKEY RRSet) through the other.  A hard
   switch would increase the likelyhood of a validation failure, should
   the signature over some RRSet not match any key in the DNSKEY RRSet.

1.1.  Purpose of this Document

   This document attempts to list requirements for a seamless change of
   DNS operators in a registry/registrar environment.  It then suggests
   a procedure that should work in an automated environment even for
   large numbers of DNS operator changes.  It is meant as a supplement
   or contribution to the updated version of [RFC4641], as currently
   expressed in [I-D.ietf-dnsop-rfc4641bis], section 4.3.5.

1.2.  Terminology

   The change of DNS infrastructure involves multiple parties.  We are
   using the following terms throughout the document.

   registrar The entity that can change entries in a DNS registry
   database, usually, but not restricted to, by means of a realtime
   provisioning protocol like EPP [RFC5730].  NB: the procedure
   described in this document does not require a strict registry-
   registrar-registrant separation.  Where the registrant can directly
   interact with the registry they are considered filling the registrar

   DNS operator provides the DNS infrastructure for a given DNS zone
   (delegated domain).  This party may or may not be identical to the
   registrant or the registrar.  The details of provisioning the DNS
   data into the DNS zone are beyond the scope of this document.

   losing DNS operator is the party that controls zone content and DNS
   infrastructure at the beginning of a DNS operator change.

   gaining DNS operator denotes the party that will control zone content
   and DNS infrastructure after the successful DNS operator change.

   The terms Zone Signing Key (ZSK) and Key Signing Key (KSK) are
   defined in section 2 of [RFC4033].

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   Domain names and IP addresses herein are for explanatory purposes
   only and should not be expected to lead to useful information in real
   life [RFC2606],[RFC5735].

2.  Requirements and Assumptions for Seamless Operator Change

   Regardless of the the particular registry provisioning protocol
   (e.g., EPP, [RFC5730], [RFC5731]) DNS registries usually provide for
   a method to transfer a domain name between different registrars.
   However, from this angle there is no separate role for the DNS
   operator, the entity that is responsible for the DNS infrastructure
   and/or the content of the DNS zone.  This entity may be identical to
   the registrar, the registrant, or neither.  From the DNSSEC
   perspective it is important to consider the entity controlling the
   ZSK and KSK in any transfer that involves changing the NS RRSet to a
   disjoint set (as opposed to simple additions to or removals from the
   NS RRSet).

   The change of a registrar is of limited effect from the DNSSEC
   perspective.  The discussion of the ability of the gaining registrar
   to accept DNSSEC information within a domain object is beyond the
   scope of this document.  The focus is kept on the change of the DNS
   operator.  There are two cases: ideally, the losing operator will be
   able to incorporate data generated by the gaining operator into their
   version of the DNS zone.  However, the proposed solution should also
   be able to cover the case where this cooperation cannot be relied

2.1.  Requirements for Seamless Operator Change

   This is a list of requirements for the operator change:

   no validation failures During the operator change, as in normal
   operations, DNSSEC validation failures, resulting from unavailable or
   outdated key or signature material, must be avoided.

   validation failures worse than insecure Where there is the choice
   between DNSSEC validation failures and an insecure state, the latter
   is to be preferred, although its extent still ought to be kept to a
   necessary minimum.

   no private keys Private cryptographic keys will not be exchanged
   between the losing and the gaining operator.  Scenarios in which this
   would be feasible would not pose the challenges addressed in this

   no use of foreign RRSIG information The process of signing a zone is
   usually done in one of three ways: The zone is signed completely as a

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   file, then loaded into a name server, the signer is a "bump in the
   wire" solution or the name server combines signing and serving on the
   primary master.  Adding foreign signatures into a zone is not easily
   achieved in any of these setups, so it ought to be avoided.  It also
   helps contain the effect of changes to an RRSet locally, as no
   signatures have to be generated remotely with subsequent re-import.

   little interaction To ease automation the number of interactions
   between registry, registrar or registrars and operators should be

   little overhead for losing operator Whenever interaction or action
   cannot be avoided, the losing operator should be involved as little
   as possible to avoid overhead for the leaving customer.  In turn,
   this suggests the gaining operator should be in control of the

2.2.  Assumptions for Seamless Operator Change

   This is a list of assumptions for the operator change:

   no direct communication channel between operators We do not assume
   the existence of a direct, confidential, authenticated communication
   channel between the losing and the gaining operator.  On an abstract
   level, the registrant could be viewed as an indirect channel, but
   involving the registrant is not necessarily easily automated.

   secure communication channel between operator, registrar, and
   registry We do, though, assume the existence of a direct,
   confidential, authenticated communication channel between an operator
   and their registrar as well as between the registrar and the

   incorporation of foreign DNSKEY RRs To achieve a symmetric validation
   chain along the DS/KSK/ZSK of both the losing and the gaining DNS
   operator it is assumed that either operator can, technically,
   incorporate DNSKEY RRs into their apex DNSKEY RRSet.  This includes
   the ability to subsequently properly sign the DNSKEY RRSet.

   ability to store and retrieve DNSKEY RRs We assume that registrars
   are able to store in and retrieve from the registry DNSKEY RRs or
   equivalent information.  This can be achieved by the registry using
   DNSKEY RRs as key material (as opposed to or in addition to DS RRs)
   or by the ability to insert DNSKEY data in free text or remarks
   fields within or associated with the domain object.

   no algorithm rollover Current reading is that an algorithm rollover
   requires a full validation with all algorithms involved, whereas a

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   key rollover will work whenever data can be validated using either
   key ([RFC4035], section 2.2).  Therefore, it is assumed that both
   operators utilize the same DNSSEC key algorithm during the transfer.
   This does neither preclude the use of different key sizes nor the
   change of key algorithms after the DNS operator change.

   ZSK/KSK separation This document assumes a key separation between
   Zone Signing Key (ZSK) and Key Signing Key (KSK) as per [RFC4641].
   Where a zone maintainer decides to use only a single key [I-D.ietf-
   dnsop-rfc4641bis] the process layout will remain the same, details of
   differences to be explored in a future update of this draft.

   no ZSK/KSK rollover in progress Since no private keys will change
   hands, the operator change implies a key rollover from the losing to
   the gaining operator.  A progressing rollover of the ZSK or KSK at
   the losing DNS operator would add complexity due to more possible
   validation paths.  While both a rollover and a DNS

   operator change can be combined, we will, for the sake of
   simplicty, assume they will not.  How to implement this business
   constraint is beyond the scope of this document.  Since the DNS
   zone at the gaining DNS operator will be set up from scratch, it
   is assumed there is no rollover in progress, either.

   resolver does not indefinitely prolongate retention of cached data
   Some resolvers are known to refresh the TTL of an NS RRSet of a zone
   upon every authoritative response they receive that carries this NS
   RRSet in the authority section.  This is partly in the spirit of
   [RFC2181] in that this source (the authoritative child) is more
   credible than the NS RRSet in a referral, but independent of DNSSEC
   this behaviour leads to an undesired side effect.  These 'sticky'
   resolvers will never learn of a redelegation if that happens by
   switching between two non-overlapping sets of name servers, which is
   current practice in many environments.  Therefore the process for
   operator change does not have to take this behaviour into account but
   may assume benign resolver operation.

3.  Executing the Change

   The challenge to face is that during the DNS operator change
   resolvers may see an NS RRSet pointing to either the losing or the
   gaining operator's name servers.  They may also have cached DNS data
   and corresponding signatures from either source and this may in
   particular mean that the apex DNSKEY RRSet and its signature or
   signatures have a different origin than some other to-be-validated

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   To prevent validation failures, resolvers need, through careful
   timing, be given the chance to acquire the necessary DNSKEY data that
   allows them to validate signed DNS data from either source.
   Therefore the DNSKEY RRSets originating from either infrastructure or
   a limited time window need to have a non zero intersection set that
   will be covered by both the old an the new trust anchor (or KSK).

   Changing the DNS operator will be a three step process involving both
   the gaining and the losing DNS operator.  For the sake of simplicity,
   the first case will not cover a registrar change.

3.1.  Changing DNS operator only

   At the beginning, there is a delegation to the losing operator's name
   servers and a DS RR pointing to a KSK controlled by that losing
   registrar in the parent zone.  As a first step, the gaining operator
   will obtain through the DNS the ZSK(!) from the losing operator's
   version of the zone, validate it using the publicly available DNS
   information, add it to its apex DNSKEY RRSet and re-sign that RRSet.
   At this point, the new infrastructure will not yet be queried, but it
   would provide a validation path through the new KSK for signatures
   generated with the old ZSK.  To achieve symmetry, the new ZSK needs
   to be incorporated into the old apex DNSKEY RRSet.  Since a (trusted,
   validatable) path to that information is not available in the DNS,
   yet and no direct communication path between the losing and the
   gaining operator is assumed, the registry will act as a dropbox.
   Again, for the sake of simplicity, we assume that the registry
   accepts key material in the form DNSKEY rather than DS resource

   The first change to the registration data, to be initiated by the
   gaining operator will add the new KSK and the new ZSK to the domain
   object.  This way, the parent zone can publish two (or three, taking
   into account the ZSK) DS RRs, one for either KSK.  At the same time,
   the registry can make available the new ZSK to the losing operator.
   No change is initiated yet to the parent zone NS RRSet.

   Upon appearance of the gaining operator's ZSK in the registry
   database the losing operator is supposed to copy this ZSK into its
   version of the apex DNSKEY RRSet and to re-sign the DNSKEY RRSet with
   the old KSK.

   Once that has happened and the TTL value of the (previous, sans new
   ZSK) DNSKEY RRSet has passed, all resolver caches will either have no
   DNSKEY RRSet for this zone or they will have acquired one that has a
   signature made by the old KSK over both the old and the new ZSK.  The
   second precondition for the next step is that no DS RRSets exist
   without reference to the new KSK that was inserted in the previous,

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   first step.  This will be the case after the new DS RRSet will have
   been visible in the DNS and the TTL of the DS RRSet (actually, that
   of the previous instance of that DS RRSet) will have expired.  Both
   expiration intervals may and likely will overlap, but may start at
   different times and are otherwise independent.  The termination of
   the later of the two will determine the earliest point in time for

   The gaining operator can now initiate the second step, changing the
   NS RRSet in the parent to the new name server infrastructure.  At the
   same time, the ZSK can be removed from the domain object since the
   registry has fulfilled its role as a ZSK dropbox.  Note that a hard
   delegation change rather than a multi-step phase-in is part of the
   design to reflect today's operational practice.

   After this second step, the parent zone will contain an NS RRSet
   delegating to the gaining operator's name servers as well as two DS
   records, one referring to the old KSK, the other referring to the new
   KSK.  Due to the two DS RRs, either DNSKEY RRSet can be validated.
   Either path will provide validation for both the old and the new ZSK.
   That enables RRSIG validation on all DNS data independent of its
   origin at the losing or gaining operator's version of the zone.

   The final third step can be started after all instances of DNSKEY
   RRSets containing the old KSK have expired.  This also requires that
   no queries are directed to the name servers of the losing operator.
   The latter can be assumed after the TTL of the (old) NS RRSet at the
   parent has passed (no delegations to old infrastructure) and
   subsequently the TTL of the NS RRSet at the losing operator's zone
   has also passed (no refresh or overwrite of referral data by
   authoritative data from the child zone).  Since a DNSKEY RRSet might
   have been sent as part of a DNS response just before this expiry,
   this DNSKEY RRSet's (originating from the losing operator, containing
   old KSK and new ZSK) TTL must pass, too.  In total, counting from the
   appearance of the new NS RRSet in the parent zone, the sum of the TTL
   of the NS RRSet at the parent, the TTL of the NS RRSet at the child
   (losing operator) and the TTL of the DNSKEY RR at the losing operator
   determines the earliest point in time for proceeding with the next

   The third step will be removing the old KSK from the domain object as
   part of the KSK rollover.  The parent zone will then publish a single
   DS RR pointing to the new KSK only.  As soon as the new DS RRSet will
   be the only one present in caches, the losing operator may cease to
   serve the zone.  The gaining operator, in turn, can remove the old
   ZSK from its apex DNSKEY RRSet, not without re-signing this RRSet

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3.2.  Changing DNS operator and registrar

   Should the DNS operator change involve a registrar change the
   procedure described in the previous paragraph can be followed with
   one minor change.  The first step, adding the new KSK and the new
   ZSK, will be immediately preceded by a transfer initiated by the
   gaining registrar.  Until the second step will have been executed,
   the gaining registrar will be the sponsoring entity for a domain
   object that continues to refer to the losing operator's
   infrastructure and therefore probably also the losing registrar's

3.3.  Losing operator not participating

   The procedure described in the previous sections depends upon the
   losing DNS operator's participation to incorporate the new ZSK into
   their DNSKEY RRSet.  Should the losing operator not participate,
   reasons for this being beyond the scope of this document, the gaining
   operator can notice this after waiting a reasonable amount of time
   after executing the first step.

   The only known working way to avoid validation failures in this case
   is to declare the zone insecure by removing the DS RR from the parent
   zone.  Some timing considerations are still due.  After the parent
   has stopped publishing the DS RRSet, and at least one DS TTL has
   passed, the registered NS RRSet can be changed from the losing
   operator's to the gaining operator's infrastructure.  The gaining
   operator's key material can be registered in a second step only after
   the maximum of the TTL values of the parent's and the (losing
   operator's) child's NS RRSet has passed, again counting from the
   appearance of the NS RRSet in the parent zone.  At this point, the
   zone's security status is back to "secure".

4.  Security Considerations

   Since the procedure described in this document is incompatible with a
   DNSKEY algorithm rollover during the operator change, it may
   encourage the use of the same algorithm across all operators
   involved.  This could essentially limit the algorithm agility from an
   operational perspective.  Concerted action might be advised should
   that preferred algorithm no longer be appropriate.

   Preferring insecure state over validation failure is a judgement that
   should be revisited, especially in the light of emerging application
   protocols that will ignore unsigned or unvalidated DNS data.

   As with a regular ZSK key rollover there is an odd chance that RRSets
   with larger TTL values than the DNSKEY and NS RRSets, which dominate

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   the timing considerations, stay in a validator's cache.  Any attempt
   to revalidate these would lead to validation failures due to the
   unavailability of the old ZSK.

5.  IANA Considerations

   This document does not request any IANA action.

6.  Acknowledgements

   The review, comments, and contributions by James Galvin and Paul
   Wouters are much appreciated.  Special thanks go to the authors and
   contributors of [RFC4641] and [I-D.ietf-dnsop-rfc4641bis] for
   detailed work on key rollovers.

7.  References

7.1.  Normative References

   [RFC2606]  Eastlake, D.E. and A. Panitz, "Reserved Top Level DNS
              Names", BCP 32, RFC 2606, June 1999.

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

   [RFC4641]  Kolkman, O. and R. Gieben, "DNSSEC Operational Practices",
              RFC 4641, September 2006.

   [RFC5735]  Cotton, M. and L. Vegoda, "Special Use IPv4 Addresses",
              RFC 5735, January 2010.

   [RFC6781]  Kolkman, O., Mekking, W., and R. Gieben, "DNSSEC
              Operational Practices, Version 2", RFC 6781, December

7.2.  Informative References

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, November 1987.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

   [RFC2181]  Elz, R. and R. Bush, "Clarifications to the DNS
              Specification", RFC 2181, July 1997.

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

   [RFC4035]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Protocol Modifications for the DNS Security
              Extensions", RFC 4035, March 2005.

   [RFC5730]  Hollenbeck, S., "Extensible Provisioning Protocol (EPP)",
              STD 69, RFC 5730, August 2009.

   [RFC5731]  Hollenbeck, S., "Extensible Provisioning Protocol (EPP)
              Domain Name Mapping", STD 69, RFC 5731, August 2009.

   [RFC5910]  Gould, J. and S. Hollenbeck, "Domain Name System (DNS)
              Security Extensions Mapping for the Extensible
              Provisioning Protocol (EPP)", RFC 5910, May 2010.

Appendix A.  Document Revision History

   [This section should be removed by the RFC editor before publishing]

A.1.  -00

   1.  Initial document.

A.2.  -01

   Expanded on the assumptions and requirements.

   Added initial version of the process description.

A.3.  -02

   Split requirements and assumptions.

   Declared sticky resolvers a non-issue.

   Increased level of detail of discussion of TTL expiration between

   Added early security considerations.

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A.4.  -03

   Removed redundant requirement.

   Reclassified 'sticky' resolver issue to assumption.

   Explictly assume secure path between registrar and registry.

   Clarified rollover in progress.

A.5.  -04

   Clarified operational practice in the introduction.

   Added timing considerations for going through insecure.

   Elaborated on combined transfer and operator change.

   Expanded security considerations section.

   Elevated 4033, 4641, and 4641bis to normative references; relaxed
   1034, 1035, and 2181 to informative.

Authors' Addresses

   Peter Koch
   Kaiserstrasse 75-77
   Frankfurt  60329

   Phone: +49 69 27235 0
   Email: pk@DENIC.DE

   Marcos Sanz
   Kaiserstrasse 75-77
   Frankfurt  60329

   Phone: +49 69 27235 0
   Email: sanz@DENIC.DE

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   Antoin Verschuren
   SIDN Labs
   Meander 501
   Arnhem  6825 MD


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