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Domain Name System Operations                               J. Livingood
Internet-Draft                                              C. Griffiths
Intended status: Informational                                   Comcast
Expires: September 28, 2012                               March 27, 2012


          Definition and Use of DNSSEC Negative Trust Anchors
               draft-livingood-negative-trust-anchors-01

Abstract

   DNS Security Extensions (DNSSEC) is now entering widespread
   deployment.  However, domain signing tools and processes are not yet
   as mature and reliable as is the case for non-DNSSEC-related domain
   administration tools and processes.  One potential technique to
   mitigate this is to use a Negative Trust Anchor, which is defined in
   this document.

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
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on September 28, 2012.

Copyright Notice

   Copyright (c) 2012 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
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as



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   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Domain Validation Failures . . . . . . . . . . . . . . . . . .  3
   3.  End User Reaction  . . . . . . . . . . . . . . . . . . . . . .  4
   4.  Switching to a Non-Validating Resolver is Not Recommended  . .  5
   5.  Responsibility for Failures  . . . . . . . . . . . . . . . . .  5
   6.  Definition of a Negative Trust Anchor  . . . . . . . . . . . .  6
   7.  Use of a Negative Trust Anchor . . . . . . . . . . . . . . . .  6
   8.  Managing Negative Trust Anchors  . . . . . . . . . . . . . . .  7
   9.  Comparison to Other DNS Misconfigurations  . . . . . . . . . .  8
   10. Other Considerations . . . . . . . . . . . . . . . . . . . . .  8
     10.1.  Security Considerations . . . . . . . . . . . . . . . . .  8
     10.2.  Privacy Considerations  . . . . . . . . . . . . . . . . .  8
     10.3.  IANA Considerations . . . . . . . . . . . . . . . . . . .  8
   11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . .  8
   12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  9
   13. References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     13.1.  Normative References  . . . . . . . . . . . . . . . . . .  9
     13.2.  Informative References  . . . . . . . . . . . . . . . . . 10
   Appendix A.  Document Change Log . . . . . . . . . . . . . . . . . 10
   Appendix B.  Open Issues . . . . . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10

























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1.  Introduction

   The Domain Name System (DNS), DNS Security Extensions (DNSSEC), and
   related operational practices are defined extensively [RFC1034]
   [RFC1035] [RFC4033] [RFC4034] [RFC4035] [RFC4398] [RFC4509] [RFC4641]
   [RFC5155].

   DNSSEC has now entered widespread deployment.  However, domain
   signing tools and processes are not yet as mature and reliable as is
   the case for non-DNSSEC-related domain administration tools and
   processes.  As a result, operators of DNS recursive resolvers, such
   as Internet Service Providers (ISPs), occasionally observe domains
   incorrectly managing DNSSEC-related resource records.  This
   mismanagement triggers DNSSEC validation failures, and then causes
   large numbers of end users to be unable to reach a domain.  Many end
   users tend interpret this as a failure of their DNS servers, and may
   switch to a non-validating resolver or contact their ISP to complain,
   rather than seeing this as a failure on the part of the domain they
   wanted to reach.

   In the short-term, one potential way to address this is for DNS
   operators to use a Negative Trust Anchor to temporarily disable
   DNSSEC validation for a specific misconfigured domain name.  This
   immediately restore access for end users while that domain's
   administrators fix their misconfiguration.  While DNS operators
   likely prefer not to use this tool, during the global transition to
   DNSSEC it seems some tool is needed to reduce the negative impact on
   such operators.

   A Negative Trust Anchor should be considered a transitional and
   temporary tactic which is not particularly scalable and should not be
   used in the long-term.  Over time, however, the use of Negative Trust
   Anchors will become less necessary as DNSSEC-related domain
   administration becomes more resilient.


2.  Domain Validation Failures

   A domain name can fail validation for two general reasons, a
   legitimate security failure such as due to an attack or compromise of
   some sort, or as a result of misconfiguration on the part of an
   domain administrator.  As domains transition to DNSSEC the most
   likely reason for a validation failure will be due to
   misconfiguration.  Thus, domain administrators should be sure to read
   [RFC4641] in full.  They should also pay special attention to Section
   4.2, pertaining to key rollovers, which appears to be the cause of
   many recent validation failures.




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   In one recent example [DNSSEC Validation Failure Analysis], a
   specific domain name failed to validate.  An investigation revealed
   that the domain's administrators performed a Key Signing Key (KSK)
   rollover by (1) generating a new key and (2) signing the domain with
   the new key.  However, they did not use a double-signing procedure
   for the KSK and a pre-publish procedure for the ZSK.  Double-signing
   refers to signing a zone with two KSKs and then updating the parent
   zone with the new DS record so that both keys are valid at the same
   time.  This meant that the domain name was signed with the new KSK,
   but it was not double-signed with the old KSK.  So, the new key was
   used for signing the zone but the old key was not.  As a result, the
   domain could not be trusted and returned an error when trying to
   reach the domain.  Thus, the domain was in a situation where the
   DNSSEC chain of trust was broken because the Delegation Signer (DS)
   record pointed to the old KSK, which was no longer used for signing
   the zone.  (A DS record provides a link in the chain of trust for
   DNSSEC from the parent zone to the child zone - in this case between
   TLD and domain name.)


3.  End User Reaction

   End users generally do not know what DNSSEC is, nor should they be
   expected to at the current time (especially absent widespread
   integration of DNSSEC indicators in end user software such as web
   browsers).  As a result, end users may incorrectly interpret the
   failure to reach a domain due to DNSSEC-related misconfiguration as
   their ISP purposely blocking access to the domain or as a performance
   failure on the part of their ISP (especially of the ISP's DNS
   servers).  End users may feel less satisfied with their ISP's
   service, which may make them more likely to switch to a competing
   ISP.  They may also contact their ISP to complain, which of course
   will incur cost for their ISP.  In addition, they may use online
   tools and sites to complain of this problem, such as via a blog, web
   forum, or social media site, which may lead to dissatisfaction on the
   part of other end users or general criticism of an ISP or operator of
   a DNS recursive resolver.

   As end users publicize these failures, others may recommend they
   switch from security-aware DNS resolvers to resolvers not performing
   DNSSEC validation.  This is a shame since the ISP or other DNS
   recursive resolver operator is actually doing exactly what they are
   supposed to do in failing to resolve a domain name, as this is the
   expected result when a domain can no longer be validated, protecting
   end users from a potential security threat.






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4.  Switching to a Non-Validating Resolver is Not Recommended

   As noted in Section 3 some people may consider switching to an
   alternative, non-validating resolver themselves, or may recommend
   that others do so.  But if a domain fails DNSSEC validation and is
   inaccessible, this could very well be due to a security-related
   issue.  In order to be as safe and secure as possible, end users
   should not change to DNS servers that do not perform DNSSEC
   validation as a workaround, and people should not recommend that
   others do so either.  Even if a website in a domain seems to look
   "normal" and valid, according to the DNSSEC protocol, that domain is
   not secure.  Domains that fail DNSSEC for legitimate reasons may be
   in control of hackers or there could be other significant security
   issues with the domain.

   Thus, switching to a non-validating resolver to restore access to a
   domain that fails DNSSEC validation is not a recommended practice, is
   bad advice to others, is potentially harmful to end user security,
   and is potentially harmful to DNSSEC adoption.


5.  Responsibility for Failures

   A domain administrator is solely and completely responsible for
   managing their domain name(s) and DNS resource records.  This
   includes complete responsibility for the correctness of those
   resource records, the proper functioning of their DNS authoritative
   servers, and the correctness of DNS records linking their domain to a
   top-level domain (TLD) or other higher level domain.  Even in cases
   where some error may be introduced by a third party, whether that is
   due to an authoritative server software vendor, software tools
   vendor, domain name registrar, or other organization, these are all
   parties that the domain administrator has selected and is responsible
   for managing successfully.

   There are some cases where the domain administrator is different than
   the domain owner.  In those cases, a domain owner has delegated
   operational responsibility to the domain administrator.  So no matter
   whether a domain owner is also the domain administrator or not, the
   domain administrator is nevertheless operationally responsible for
   the proper configuration operation of the domain.

   So in the case of a domain name failing to successfully validate,
   when this is due to a misconfiguration of the domain, that is the
   sole responsibility of the domain administrator.

   Any assistance or mitigation responses undertaken by other parties to
   mitigate the misconfiguration of a domain name by a domain



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   administrator, especially operators of DNS recursive resolvers, are
   optional and at the pleasure of those parties.


6.  Definition of a Negative Trust Anchor

   Trust Anchors are defined in [RFC5914].  A trust anchor should be
   used by a validating caching resolver as a starting point for
   building the authentication chain for a signed DNS response.  The
   inverse of this is a Negative Trust Anchor, which creates a stopping
   point for a caching resolver to end validation of the authentication
   chain.  This Negative Trust Anchor can potentially be placed at any
   level within the chain of trust and would stop validation at that
   point in the chain.


7.  Use of a Negative Trust Anchor

   When a domain has been confirmed to fail DNSSEC validation due to a
   DNSSEC-related misconfiguration, an ISP or other DNS recursive
   resolver operator may in some cases use a Negative Trust Anchor for a
   domain or sub-domain.  This instructs a DNS recursive resolver to
   temporarily NOT perform DNSSEC validation for a specific domain name.
   This immediately restores access to the domain for end users while
   the domain's administrator corrects the misconfiguration(s).

   In the case of a validation failure due to misconfiguration of a TLD
   or popular domain name (such as a top 100 website), this could make
   content or services in the affected TLD or domain to be inaccessible
   for a large number of users.  A Negative Trust Anchor can therefore
   be useful in the short-term when used on a targeted and time-limited
   basis.  It does not and should not involve turning off validation
   more broadly, and helps during the transition to DNSSEC as
   organizations that are new to signing their domains are still
   maturing their DNSSEC operational practices, alleviating end user
   issues Section 3 and restoring end user access.  However, use of a
   Negative Trust Anchor should not be automatic in any way, and must
   involve investigation by technical personnel trained in the operation
   of DNS servers.  Such an investigation must confirm that a failure is
   due to misconfiguration, as a similar breakage could have occurred if
   an attacker gained access to a domain's authoritative servers and
   modified those records or had the domain pointed to their own rogue
   authoritative servers.  Furthermore, a Negative Trust Anchor should
   be used only for a short duration, perhaps for a day or less.

   Finally, a Negative Trust Anchor is used only in a specific domain or
   sub-domain and would not affect validation at other names up the
   authentication chain.  For example, a Negative Trust Anchor for



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   zone1.example.com would affect only names within zone1.example.com,
   and validation would still be performed on example.com, .com, and the
   root (".").  In another example, a Negative Trust Anchor for
   example.com would affect only names within example.com, and
   validation would still be performed on .com, and the root (".")


         Root (.)              <======
             |                       ||
             |                       ||<======>+----+----+    DNSSEC
             |                       ||        |Recursive|   Validation
         TLD (com)             <=====||        |Resolver |   <========>
             |                        +<------>+---------+
             |                        |                       DNS NTA
             |                        |                    (example.com)
     SUB TLD (example.com)     <------|                     <---------->
             |                        |
             |                        |
             |                        |
             (www.example.com  <-------




                  Figure 1: Negative Trust Anchor Diagram


8.  Managing Negative Trust Anchors

   This tool is unlikely to be and probably should not be used over the
   long-term since DNSSEC-related domain administration practices will
   naturally improve over time.  In addition, however, continued and
   frequent use of Negative Trust Anchors is not scalable since it
   requires investigation by technical personnel and may involve manual
   processes, resulting in increased operational overhead (and therefore
   cost).

   While Negative Trust Anchors have proven useful during the early
   stages of DNSSEC adoption, domain owners are ultimately responsible
   for managing and ensuring their DNS records are configured correctly
   Section 5.

   Most current implementations of DNS validating resolvers currently
   follow [RFC4033] on defining the implementation of Trust Anchor as
   either using Delegation Signer (DS), Key Signing Key (KSK), or Zone
   Signing Key (ZSK).  A Negative Trust Anchor should use domain name
   formatting that signifies where in a delegation a validation process
   should be stopped.



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9.  Comparison to Other DNS Misconfigurations

   As noted in Section 5 domain administrators are ultimately
   responsible for managing and ensuring their DNS records are
   configured correctly.  ISPs or other DNS recursive resolver operators
   cannot and should not correct misconfigured A, CNAME, MX, or other
   resource records of domains for which they are not authoritative.
   Expecting non-authoritative entities to protect domain administrators
   from any misconfiguration of resource records is therefore
   unrealistic and unreasonable, and in the long-term is harmful to the
   delegated design of the DNS and could lead to extensive operational
   instability and/or variation.


10.  Other Considerations

10.1.  Security Considerations

   End to end DNSSEC validation will be disabled during the time that a
   Negative Trust Anchor is used.  In addition, the Negative Trust
   Anchor may be in place after the point in time when the DNS
   misconfiguration that caused validation to break has been fixed.
   Thus, there may be a gap between when a domain has have been re-
   secured and when a Negative Trust Anchor is removed.  In addition, a
   Negative Trust Anchor may be put in place by DNS recursive resolver
   operators without the knowledge of the authoritative domain
   administrator for a given domain name.

10.2.  Privacy Considerations

   There are no privacy considerations in this document.

10.3.  IANA Considerations

   There are no IANA considerations in this document.


11.  Contributors

   The following people made significant textual contributions to this
   document and/or played an important role in the development and
   evolution of this document:

   - John Barnitz

   - Tom Creighton

   - Chris Ganster



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12.  Acknowledgements

   The authors and contributors also wish to acknowledge the assistance
   of the following individuals or groups.  Some of these people
   provided helpful and important guidance in the development of this
   document and/or in the development of the concepts covered in this
   document.  Other people assisted by performing a detailed review of
   this document, and then providing feedback and constructive criticism
   for revisions to this document, or engaged in a healthy debate over
   the subject of the document.  All of this was helpful and therefore
   the following individuals merit acknowledgement:

   - Your Name Here!


13.  References

13.1.  Normative 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.

   [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.

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

   [RFC4398]  Josefsson, S., "Storing Certificates in the Domain Name
              System (DNS)", RFC 4398, March 2006.

   [RFC4509]  Hardaker, W., "Use of SHA-256 in DNSSEC Delegation Signer
              (DS) Resource Records (RRs)", RFC 4509, May 2006.

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

   [RFC5155]  Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS
              Security (DNSSEC) Hashed Authenticated Denial of



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              Existence", RFC 5155, March 2008.

   [RFC5914]  Housley, R., Ashmore, S., and C. Wallace, "Trust Anchor
              Format", RFC 5914, June 2010.

13.2.  Informative References

   [DNSSEC Validation Failure Analysis]
              Barnitz, J., Creighton, T., Ganster, C., Griffiths, C.,
              and J. Livingood, "Analysis of DNSSEC Validation Failure -
              NASA.GOV", Comcast , January 2012, <http://
              www.dnssec.comcast.net/
              DNSSEC_Validation_Failure_NASAGOV_20120118_FINAL.pdf>.


Appendix A.  Document Change Log

   [RFC Editor: This section is to be removed before publication]

   -00: First version published as an individual draft.

   -01: Fixed minor typos and grammatical nits.  Closed all open
   editorial items.


Appendix B.  Open Issues

   [RFC Editor: This section is to be removed before publication]

   - Decide whether to include intentionally insecure names in this (per
   Antoin Verschuren and Patrik Wallstrom)


Authors' Addresses

   Jason Livingood
   Comcast Cable Communications
   One Comcast Center
   1701 John F. Kennedy Boulevard
   Philadelphia, PA  19103
   US

   Email: jason_livingood@cable.comcast.com
   URI:   http://www.comcast.com







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   Chris Griffiths
   Comcast Cable Communications
   One Comcast Center
   1701 John F. Kennedy Boulevard
   Philadelphia, PA  19103
   US

   Email: chris_griffiths@cable.comcast.com
   URI:   http://www.comcast.com










































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