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
draft-koch-dnsop-dnssec-operator-change-05
Abstract
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
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
Copyright Notice
Copyright (c) 2013 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
Provisions Relating to IETF Documents
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the Trust Legal Provisions and are provided without warranty as
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
expire.
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
role.
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
upon.
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
document.
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
minimized.
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
process.
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
registry.
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
RRSet.
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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
records.
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
progress.
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
step.
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
afterwards.
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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
data.
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
2012.
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
updates.
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
DENIC eG
Kaiserstrasse 75-77
Frankfurt 60329
DE
Phone: +49 69 27235 0
Email: pk@DENIC.DE
Marcos Sanz
DENIC eG
Kaiserstrasse 75-77
Frankfurt 60329
DE
Phone: +49 69 27235 0
Email: sanz@DENIC.DE
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Antoin Verschuren
SIDN Labs
Meander 501
Arnhem 6825 MD
NL
Email: antoin.verschuren@sidn.nl
URI: https://www.sidn.nl/
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