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Internet Engineering Task Force A.Durand
INTERNET-DRAFT SUN Microsystems,inc.
November, 24, 2003 J. Ihren
Expires May 25, 2004 Autonomica
DNS IPv6 transport operational guidelines
Status of this Memo
This memo provides information to the Internet community. It does not
specify an Internet standard of any kind. This memo is in full
conformance with all provisions of Section 10 of RFC2026
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."
The list of current Internet-Drafts can be accessed at
The list of Internet-Draft Shadow Directories can be accessed at
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
This memo provides guidelines and Best Current Practice to operate
DNS in a world where queries and responses are carried in a mixed
environment of IPv4 and IPv6 networks.
This document is the result of many conversations that happened in
the DNS community at IETF and elsewhere since 2001. During that
period of time, a number of Internet drafts have been published to
clarify various aspects of the issues at stake. This document focuses
on the conclusion of those discussions.
The authors would like to acknowledge the role of Pekka Savola in his
thorough review of the document.
1. Terminology
The phrase "IPv4 name server" indicates a name server available over
IPv4 transport. It does not imply anything about what DNS data is
served. Likewise, "IPv6 name server" indicates a name server
available over IPv6 transport. The phrase "dual-stack DNS server"
indicates a DNS server that is actually configured to run both
protocols, IPv4 and IPv6, and not merely a server running on a system
capable of running both but actually configured to run only one.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
document are to be interpreted as described in [2119].
2. Introduction to the Problem of Name Space Fragmentation:
following the referral chain
The caching resolver that tries to look up a name starts out at the
root, and follows referrals until it is referred to a nameserver that
is authoritative for the name. If somewhere down the chain of
referrals it is referred to a nameserver that is only accessible over
an unavailable type of transport, a traditional nameserver is unable
to finish the task.
When the Internet moves from IPv4 to a mixture of IPv4 and IPv6 it is
only a matter of time until this starts to happen. The complete DNS
hierarchy then starts to fragment into a graph where authoritative
nameservers for certain nodes are only accessible over a certain
transport. What is feared is that a node using only a particular
version of IP, querying information about another node using the same
version of IP can not do it because, somewhere in the chain of
servers accessed during the resolution process, one or more of them
will only be accessible with the other version of IP.
With all DNS data only available over IPv4 transport everything is
simple. IPv4 resolvers can use the intended mechanism of following
referrals from the root and down while IPv6 resolvers have to work
through a "translator", i.e. they have to use a second name server on
a so-called "dual stack" host as a "forwarder" since they cannot
access the DNS data directly.
With all DNS data only available over IPv6 transport everything would
be equally simple, with the exception of old legacy IPv4 name servers
having to switch to a forwarding configuration.
However, the second situation will not arise in a foreseeable time.
Instead, it is expected that the transition will be from IPv4 only to
a mixture of IPv4 and IPv6, with DNS data of theoretically three
categories depending on whether it is available only over IPv4
transport, only over IPv6 or both.
Having DNS data available on both transports is the best situation.
The major question is how to ensure that it as quickly as possible
becomes the norm. However, while it is obvious that some DNS data
will only be available over v4 transport for a long time it is also
obvious that it is important to avoid fragmenting the name space
available to IPv4 only hosts. I.e. during transition it is not
acceptable to break the name space that we presently have available
for IPv4-only hosts.
3. Policy Based Avoidance of Name Space Fragmentation
Today there are only a few DNS "zones" on the public Internet that
are available over IPv6 transport, and most of them can be regarded
as "experimental". However, as soon as the root and top level domains
are available over IPv6 transport, it is reasonable to expect that it
will become more common to have zones served by IPv6 servers.
Having those zones served only by IPv6-only name server would not be
a good development, since this will fragment the previously
unfragmented IPv4 name space and there are strong reasons to find a
mechanism to avoid it.
The RECOMMENDED approach to maintain name space continuity is to use
administrative policies, as described in the next section.
4. DNS IPv6 Transport RECOMMENDED Guidelines
In order to preserve name space continuity, the following administrative
policies are RECOMMENDED:
- every recursive DNS server SHOULD be either IPv4-only or dual
- every single DNS zone SHOULD be served by at least one IPv4
reachable DNS server.
This rules out IPv6-only DNS servers performing full recursion and
DNS zones served only by IPv6-only DNS servers. However, one could
very well design a configuration where a chain of IPv6 only DNS
servers forward queries to a set of dual stack DNS servers actually
performing those recursive queries. This approach could be revisited
if/when translation techniques between IPv4 and IPv6 were to be
widely deployed.
In order to help enforcing the second point, the optional operational
zone validation processes SHOULD ensure that there is at least one
IPv4 address record available for the name servers of any child
delegations within the zone.
5. Security Considerations
Being a critical piece of the Internet infrastructure, the DNS is a
potential value target and thus should be protected. Great care
should be taken not to weaken the security of DNS while introducing
IPv6 operation.
Keeping the DNS name space from fragmenting is a critical thing for
the availability and the operation of the Internet; this memo
addresses this issue by clear and simple operational guidelines.
The RECOMMENDED guidelines are compatible with the operation of
DNSSEC and do not introduce any new security issues.
6. Author Addresses
Alain Durand
SUN Microsystems, Inc
17 Network circle UMPK17-202
Menlo Park, CA, 94025
Johan Ihren
Bellmansgatan 30
SE-118 47 Stockholm, Sweden
7. Normative References
[2119] Bradner, S., "Key Words for Use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
8. Full Copyright Statement
"Copyright (C) The Internet Society (2003). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
Funding for the RFC Editor function is currently provided by the
Internet Society.
DNSOP G. Guette
Internet-Draft IRISA/INRIA Rennes
Expires: August 8, 2004 O. Courtay
February 8, 2004
Requirements for Automated Key Rollover in DNSsec
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as
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."
The list of current Internet-Drafts can be accessed at http://
The list of Internet-Draft Shadow Directories can be accessed at
This Internet-Draft will expire on August 8, 2004.
Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
This document describes problems that appear during an automated
rollover and gives the requirements for the design of communication
between parent zone and child zone in an automated rollover process.
This document is essentially about key rollover, the rollover of
one other Resource Record present at delegation point (NS RR) is
also discussed.
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1. Introduction
The DNS security extensions (DNSsec) [1] uses public-key cryptography
and digital signatures. It stores the public keys in KEY Resource
Records (RRs). Because old keys and frequently used keys are
vulnerable, they must be changed periodically. In DNSsec this is the
case for Zone Signing Keys (ZSKs) and Key Signing Keys (KSKs) [2, 4].
Automation of key rollover process is necessary for large zones
because inside a large zone, there are too many changes to handle for
a single administrator.
Let us consider for example a zone with one million child zones among
which only 10% of secured child zones. If the child zones change their
keys once a year on average, that implies 300 changes per day for the
parent zone. All these changes are hard to manage manually.
Automated rollover is optional and resulting from an agreement
between the administrator of the parent zone and the administrator of
the child zone. Of course, key rollover can also be done manually by
This document describes the requirements for the design of messages
of automated key rollover process.
2. The Key Rollover Process
Key rollover consists in replacing the DNSsec keys used to sign
resource records in a given DNS zone file. There are two types of
rollover, ZSK rollover and KSK rollover.
In ZSK rollover, all changes are local to the zone that changes its
key: there is no need to contact other zones (e.g. parent zone) to
propagate the performed changes because this type of key have no
associated DS records in the parent zone.
In KSK rollover, new DS RR(s) MUST be created and stored in the
parent zone. In consequence, the child zone MUST contact its parent
zone and notify it about the KSK change(s).
Manual key rollover exists and works [3]. The key rollover is built
from two parts of different nature:
- An algorithm that generates new keys. It could be local to the
- The interaction between parent and child zone
In this document we focus on the interaction between parent and
child zone servers.
One example of manual key rollover is:
Child zone creates a new KSK, waiting for the creation of the DS
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record in its parent zone and then child zone deletes old key.
In manual rollover, communications are managed by the zone
administrators and the security of these communications is out of
scope of DNSsec.
Automated key rollover MUST use a secure communication between parent
and child zone. In this document we concentrate our efforts on
defining interactions between entities present in key rollover
process that are not explicitly defined in manual key rollover
3. Basic Requirements
The main constraint to respect during a key rollover is that the
chain of trust MUST be preserved. Even if a resolver retrieve some RRs
from recursive name server. Every RR MUST be verifiable at any time,
every message exchanged during rollover MUST be authenticated and
data integrity MUST be guaranteed.
Two entities are present during a KSK rollover: the child zone and
its parent zone. These zones are generally managed by different
administrators. These administrators MUST agree on some parameters
like availability of automated rollover, the maximum delay between
notification of changes in the child zone and the resigning of the
parent zone. The child zone needs to know this delay to schedule its
During an automated rollover process, data are transmitted between
the primary name server of the parent and the the primary name server
of the child zone.
The reason is that the IP address of the primary name server is easy
to obtain.
Other solutions based on machine dedicated to the rollover are not
suitable solutions because of the difficulty to obtain the IP
addresses of the dedicated machine in an automated manner.
4. Messages authentication and information exchanged
Every exchanged message MUST be authenticated and the authentication
tool MUST be a DNSsec tool such as TSIG [5], SIG(0) [6] or DNSsec
request with verifiable SIG records.
Once the changes related to a KSK are made in a child zone, this zone
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MUST notify its parent zone in order to create the new DS RR and
store this DS RR in parent zone file.
The parent zone MUST receive all the child Keys that needs the
creation of an associated DS RRs in the parent zone.
Some errors could occur during transmission between child zone and
parent zone. Key rollover solution MUST be fault tolerant, i.e. at
any time the rollover MUST be in a consistent state and all RRs MUST
be verifiable, even if an error occurs. That is to say that it MUST
remains a valid chain of trust.
5. Emergency Rollover
A key of a zone might be compromised and this key MUST be changed as
soon as possible. Fast changes could break the chain of trust. The
part of DNS tree having this zone as apex can become unverifiable,
but the break of the chain of trust is necessary if we want to no one
can use the compromised key to spoof DNS data.
Parent zone behavior after an emergency rollover in one of its child
zone is an open discussion.
Should we define:
- an EMERGENCY flag. When a child zone does an emergency KSK change,
it uses the EMERGENCY flag to notify its parents that the chain of
trust is broken and will stay broken until right DS creation and a
parent zone resigning.
- a maximum time delay after next parent zone resigning, we ensure
that after this delay the parent zone is resigned and the right DS
is created.
- that no pre-defined behavior for the parent zone is needed
6. Other Resource Record concerned by automatic rollover
NS records are also present at delegation point, so when the child
zone changes some NS records, the corresponding records at
delegation point in parent zone MUST be updated. NS records are
concerned by rollover and this rollover could be automated too. In
this case, when the child zone notifies its parent zone that some NS
records have been changed, the parent zone MUST verify that these NS
records are present in child zone before doing any changes in its own
zone file. This allow to avoid inconsistency between NS records at
delegation point and NS records present in the child zone.
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7. Security consideration
This document describes requirements to design an automated key
rollover in DNSsec based on DNSsec security. In the same way the, as
plain DNSsec, the automatic key rollover contains no mechanism
protecting against denial of service (DoS) resistant. The security
level obtain after an automatic key rollover, is the security level
provided by DNSsec.
8. Acknowledgments
The authors want to acknowledge Mohsen Souissi, Bernard Cousin,
Bertrand Leonard and members of IDsA project for their contribution
to this document.
Normative references
[1] Eastlake, D., "Domain Name System Security Extensions", RFC
2535, March 1999.
[2] Gudmundsson, O., "Delegation Signer Resource Record",
draft-ietf-dnsext-delegation-signer-15 (work in progress),
June 2003.
[3] Kolkman, O. and Gieben, R., "DNSSEC key operations",
draft-ietf-dnsext-operational-practices (work in progress),
June 2003.
[4] Kolkman, O. and Schlyter, J., "KEY RR Secure Entry Point Flag"
draft-ietf-dnsext-keyrr-key-signing-flag-10 (work in progress),
September 2003.
[5] Vixie, P., Gudmundsson, O., Eastlake, D., and Wellington, B.,
"Secret Key Transaction Authentication for DNS (TSIG)", RFC
2845, May 2000.
[6] Eastlake, D., "DNS Request and Transaction Signatures (SIG(0)s)",
RFC 2931, September 2000.
[7] Eastlake, D.,"DNS Security Operational Considerations", RFC
2541, March 1999.
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Author's Addresses
Gilles Guette
Campus Universitaire de Beaulieu
35042 Rennes France
Phone : (33) 02 99 84 71 32
Fax : (33) 02 99 84 25 29
E-mail :
Olivier Courtay
2, rue de la ch‚taigneraie
35512 Cesson C‰vign‰ CEDEX France
Phone : (33) 02 99 84 71 31
Fax : (33) 02 99 84 25 29