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Versions: (draft-livingood-dnsop-negative-trust-anchors) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 RFC 7646

Domain Name System Operations                                P. Ebersman
Internet-Draft                                                   Comcast
Intended status: Informational                                 W. Kumari
Expires: February 25, 2016                                        Google
                                                            C. Griffiths
                                                                 Nominet
                                                            J. Livingood
                                                                 Comcast
                                                                R. Weber
                                                                 Nominum
                                                         August 24, 2015


          Definition and Use of DNSSEC Negative Trust Anchors
               draft-ietf-dnsop-negative-trust-anchors-13

Abstract

   DNS Security Extensions (DNSSEC) is now entering widespread
   deployment.  However, domain signing tools and processes are not yet
   as mature and reliable as those for non-DNSSEC-related domain
   administration tools and processes.  This document defines Negative
   Trust Anchors which can be used to mitigate DNSSEC validation
   failures by disabling DNSSEC validation at specified domains.

   [RFC Editor: Please remove this before publication.  This document is
   being stored in github at https://github.com/wkumari/draft-livingood-
   dnsop-negative-trust-anchors . Authors accept pull requests, and keep
   the latest (edit buffer) versions there, so commenters can follow
   along at home.]

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 February 25, 2016.




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Copyright Notice

   Copyright (c) 2015 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
   (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
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction and motivation . . . . . . . . . . . . . . . . .   3
     1.1.  Definition of a Negative Trust Anchor . . . . . . . . . .   3
     1.2.  Motivations for Negative Trust Anchors  . . . . . . . . .   4
       1.2.1.  Mitigating Domain Validation Failures . . . . . . . .   4
       1.2.2.  Improving End User Experience . . . . . . . . . . . .   4
       1.2.3.  Avoiding Switching to a Non-Validating Resolver . . .   5
   2.  Use of a Negative Trust Anchor  . . . . . . . . . . . . . . .   5
     2.1.  Applicability of Negative Trust Anchors . . . . . . . . .   6
   3.  Managing Negative Trust Anchors . . . . . . . . . . . . . . .   7
     3.1.  Alerting Users to Negative Trust Anchor Use . . . . . . .   7
   4.  Removal of a Negative Trust Anchor  . . . . . . . . . . . . .   7
   5.  Comparison to Other DNS Misconfigurations . . . . . . . . . .   8
   6.  Intentionally Broken Domains  . . . . . . . . . . . . . . . .   8
   7.  Discovering broken domains  . . . . . . . . . . . . . . . . .   9
   8.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  11
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  11
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  12
     12.2.  Informative References . . . . . . . . . . . . . . . . .  12
   Appendix A.  Configuration Examples . . . . . . . . . . . . . . .  13
     A.1.  NLNet Labs Unbound  . . . . . . . . . . . . . . . . . . .  13
     A.2.  ISC BIND  . . . . . . . . . . . . . . . . . . . . . . . .  14
     A.3.  Nominum Vantio  . . . . . . . . . . . . . . . . . . . . .  14
   Appendix B.  Document Change Log  . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  18







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1.  Introduction and motivation

   DNSSEC has now entered widespread deployment.  However, the DNSSEC
   signing tools and processes are less mature and reliable than those
   for non-DNSSEC-related administration.  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 to interpret this as a failure
   of their ISP or resolver operator, 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.  Without
   the techniques in this document, this pressure may cause the resolver
   operator to disable (or simply not deploy) DNSSEC validation.

   This document defines the Negative Trust Anchor (NTA), which can be
   used during the transition to ubiquitous DNSSEC deployment.  NTAs are
   configured locally on a validating DNS recursive resolver to shield
   end users from DNSSEC-related authoritative name server operational
   errors.  NTAs are intended to be temporary, and only implemented by
   the organization requiring an NTA (and not distributed by any
   organizations outside of the administrative boundary).  Finally, NTAs
   pertain only to DNSSEC and not to Public Key Infrastructures (PKI)
   such as X.509.

   Use of an NTA to temporarily disable DNSSEC validation for a specific
   misconfigured domain name immediately restores access for end users.
   This allows the domain's administrators to fix their
   misconfiguration, while also allowing the organization using the NTA
   to keep DNSSEC validation enabled and still reach the misconfigured
   domain.

   [ ED NOTE: Don't forget to insert 2119 boilerplate - not doing now,
   to avoid messing up section numbers... ]

1.1.  Definition of a Negative Trust Anchor

   Trust Anchors are defined in [RFC5914].  A trust anchor is used by a
   validating caching resolver as a starting point for building the
   authentication chain for a signed DNS response.  By way of analogy,
   NTAs stop validation of the authentication chain.  Instead, the
   validator treats any upstream responses as if the zone is unsigned
   and does not set the AD bit in responses it sends to clients.  Note
   that this is a behavior, and not a separate resource record.  This
   NTA can potentially be implemented at any level within the chain of
   trust and would stop validation from that point in the chain down.
   Validation starts again if there is a positive trust anchor further



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   down in the chain.  For example, if there is an NTA at example.com,
   and a positive trust anchor at foo.bar.example.com, then validation
   resumes for foo.bar.example.com and anything below it.

1.2.  Motivations for Negative Trust Anchors

1.2.1.  Mitigating 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 a zone
   administrator.  As domains transition to DNSSEC, the most common
   reason for a validation failure has been misconfiguration.  Thus,
   domain administrators should be sure to read [RFC6781] in full.  They
   should also pay special attention to Section 4.2, pertaining to key
   rollovers, which appear to be the cause of many recent validation
   failures.

   It is also possible that some DNSSEC validation failures could arise
   due to differences in how different software developers interpret
   DNSSEC standards and/or how those developers choose to implement
   support for DNSSEC.  For example, it is conceivable that a domain may
   be DNSSEC signed properly, and one vendor's DNS recursive resolvers
   will validate the domain but other vendors' software may fail to
   validate the domain.

1.2.2.  Improving End User Experience

   End users generally do not know of, understand, or care about the
   resolution process that causes connections to happen.  This is by
   design: the point of the DNS is to insulate users from having to
   remember IP addresses through a friendlier way of naming systems.  It
   follows from this that end users do not, and should not, be expected
   to know about DNSSEC, validation, or anything of the sort.  As a
   result, end users may misinterpret the failure to reach a domain due
   to DNSSEC-related misconfiguration . They may (incorrectly) assume
   that their ISP is purposely blocking access to the domain or that it
   is a performance failure on the part of their ISP (especially of the
   ISP's DNS servers).  They may contact their ISP to complain, which
   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



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   recursive resolver operator is actually doing exactly what they are
   supposed to do in failing to resolve a domain name; this is the
   expected result when a domain can no longer be validated and it
   protects end users from a potential security threat.  Use of an NTA
   would allow the ISP to specifically remedy the failure to reach that
   domain, without compromising security for other sites.  This would
   result in a satisfied end user, with minimal impact to the ISP, while
   maintaining the security of DNSSEC for correctly maintained domains.

   It is worth noting the following text from [RFC4033] - "In the final
   analysis, however, authenticating both DNS keys and data is a matter
   of local policy, which may extend or even override the protocol
   extensions defined in this document set."  A responsibility (one of
   many) of a caching server operator is to "protect the integrity of
   the cache."

1.2.3.  Avoiding Switching to a Non-Validating Resolver

   As noted in Section 1.2.2, 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.  Domains that fail DNSSEC for legitimate reasons
   (versus misconfiguration) 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.

2.  Use of a Negative Trust Anchor

   Technical personnel trained in the operation of DNS servers must
   confirm that a DNSSEC validation 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.
   They should also confirm that the domain is not intentionally broken,
   such as for testing purposes as noted in Section 6.  Finally, they
   should make a reasonable attempt to contact the domain owner of the
   misconfigured zone, preferably prior to implementing the NTA.
   Involving trained technical personnel is costly, but operational
   experience suggests that this is a very rare event, usually on the
   order of once per quarter (or even less).




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   It is important for the resolver operator to confirm that the domain
   is still under the ownership / control of the legitimate owner of the
   domain in order to ensure that disabling validation for a specific
   domain does not direct users to an address under an attacker's
   control.  Contacting the domain owner and telling them the DNSSEC
   records that the resolver operator is seeing allows the resolver
   operator to determine if the issue is a DNSSEC misconfiguration or an
   attack.

   In the case of a validation failure due to misconfiguration of a TLD
   or popular domain name (such as a top 100 website), content or
   services in the affected TLD or domain could be inaccessible for a
   large number of users.  In such cases, it may be appropriate to use
   an NTA as soon as the misconfiguration is confirmed.  An example of a
   list of "top N" websites is the "Alexa Top 500 Sites on the Web"
   [Alexa], , or a list of the of the most-accessed names in the
   resolver's cache.

   Once a domain has been confirmed to fail DNSSEC validation due to a
   DNSSEC-related misconfiguration, an ISP or other DNS recursive
   resolver operator may elect to use an NTA for that domain or sub-
   domain.  This instructs their DNS recursive resolver to temporarily
   NOT perform DNSSEC validation at or in the misconfigured domain.
   This immediately restores access to the domain for end users while
   the domain's administrator corrects the misconfiguration(s).  It does
   not and should not involve turning off validation more broadly.

2.1.  Applicability of Negative Trust Anchors

   A NTA MUST only be used for a limited duration.  Implementors SHOULD
   allow the operator using the NTA to set an end time and date
   associated with any NTA.  Optimally, this time and date is set in a
   DNS recursive resolver's configuration, though in the short-term this
   may also be achieved via other systems or supporting processes.  Use
   of an NTA MUST NOT be automatic.

   Finally, an NTA SHOULD be used only in a specific domain or sub-
   domain and MUST NOT affect validation of other names up the
   authentication chain.  For example, an NTA for zone1.example.com
   would affect only names at or below zone1.example.com, and validation
   would still be performed on example.com, .com, and the root (".").
   This NTA also SHOULD NOT affect names in another branch of the tree
   (such as example.net).  In another example, an NTA for example.com
   would affect only names within example.com, and validation would
   still be performed on .com, and the root (".").  In this scenario, if
   there is a (probably manually configured) trust anchor for
   zone1.example.com, validation would be performed for
   zone1.example.com and subdomains of zone1.example.com.



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3.  Managing Negative Trust Anchors

   While NTAs 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.

   Most current implementations of DNS validating resolvers currently
   follow [RFC4033] on configuring a Trust Anchor using either a public
   key as in a DNSKEY RR or a hash of a public key as in a DS RR.

   Different DNS validators may have different configuration names for
   an NTA.  For examples see Appendix A.

   An NTA placed at a node where there is a configured positive trust
   anchor MUST take precedence over that trust anchor, effectively
   disabling it.  Implementations MAY issue a warning or informational
   message when this occurs, so that operators are not surprised when
   this happens.

3.1.  Alerting Users to Negative Trust Anchor Use

   End users of a DNS recursive resolver or other people may wonder why
   a domain that fails DNSSEC validation resolves with a supposedly
   validating resolver.  As a result, implementors should consider
   transparently disclosing those NTAs which are currently in place or
   were in place in the past, such as on a website [Disclosure-Example].

   This is particularly important since there is currently no special
   DNS query response code that could indicate to end users or
   applications that an NTA is in place.  Such disclosures should
   optimally include both the data and time that the NTA was put in
   place and when it was removed.

4.  Removal of a Negative Trust Anchor

   As explored in Section 10, using an NTA once the zone correctly
   validates can have security considerations.  It is therefore
   RECOMMENDED that NTA implementors should periodically attempt to
   validate the domain in question, for the period of time that the NTA
   is in place, until such validation is again successful.  NTAs MUST
   expire automatically when their configured lifetime ends.  The
   lifetime SHOULD NOT exceed a week.  There is limited experience with
   what this value should be, but at least one large vendor has
   documented customer feedback suggesting that a week is reasonable
   based on expectations of how long failures take to fix or to be
   forgotten.  Operational experience may further refine these
   expectations.




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   Before removing the NTA, all authoritative resolvers listed in the
   zone should be checked (due to anycast and load balancers it may not
   be possible to check all instances).

   Once all testing succeeds, an NTA should be removed as soon as is
   reasonably possible.  One possible method to automatically determine
   when the NTA can be removed is to send a periodic query for type SOA
   at the NTA node; if it gets a response that it can validate (whether
   the response was an actual SOA answer or a NOERROR/NODATA with
   appropriate NSEC/NSEC3 records), the NTA is presumed no longer to be
   necessary and is removed.  Implementations SHOULD, by default,
   perform this operation.  Note that under some circumstances this is
   undesirable behavior (for example, if www.example.com has a bad
   signature, but example.com/SOA is fine) and so implementations may
   wish to allow the operator to override this spot-check / behavior.

   When removing the NTA, the implementation SHOULD remove all cached
   entries at and below the NTA node.

5.  Comparison to Other DNS Misconfigurations

   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.

   With DNSSEC breakage, it is often possible to tell that there is a
   misconfiguration by looking at the data and not needing to guess what
   it should have been.

6.  Intentionally Broken Domains

   Some domains, such as dnssec-failed.org, have been intentionally
   broken for testing purposes
   [Measuring-DNSSEC-Validation-of-Website-Visitors] [Netalyzr].  For
   example, dnssec-failed.org is a DNSSEC-signed domain that is broken.
   If an end user is querying a validating DNS recursive resolver, then
   this or other similarly intentionally broken domains should fail to
   resolve and should result in a "Server Failure" error (RCODE 2, also
   known as 'SERVFAIL').  If such a domain resolved successfully, then
   it is a sign that the DNS recursive resolver is not fully validating.





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   Organizations that utilize NTAs should not add an NTA for any
   intentionally broken domain.  Such additions are prevented by the
   requirement that the operator attempt to contact the administrators
   for the zone that has broken DNSSEC.

   Organizations operating an intentionally broken domain may wish to
   consider adding a TXT record for the domain to the effect of "This
   domain is purposely DNSSEC broken for testing purposes".

7.  Discovering broken domains

   Discovering that a domain is DNSSEC broken as result of an operator
   error instead of an attack is not trivial, and the examples here
   should be vetted by an experienced professional before taking the
   decision on implementing an NTA.

   One of the key thing to look for when looking at a DNSSEC broken
   domain is consistency and history.  It therefore is good if you have
   the ability to look at the server's DNS traffic over a long period of
   time or have a database that stores DNS names associated answers
   (this is often referred to as a "passive DNS database").  Another
   invaluable tool is dnsviz (http://www.dnsivz.net) which also stores
   DNSSEC related data historically.  The drawback here is that you need
   for it to have tested the domain before the incident occurs.

   The first and easiest thing to check is if the failure of the domain
   is consistent across different software implementations.  If not, you
   want to inform the vendor where it fails so that the vendor can look
   more deeply into the issue.

   The next thing is to figure out what the actual failure mode is.  At
   the time of this writing are several tools to do this, including:

   o  DNSViz (http://dnsviz.net)

   o  Verisign DNSSEC debugger (http://dnssec-debugger.verisignlabs.com)

   o  zonemaster (http://www.zonemaster.fr, https://github.com/dotse/
      zonemaster)

   most of these tools are open source and can be installed locally.
   However, using the tools over the Internet has the advantage of
   providing visibility from a different point.  This is an incomplete
   list, and it is expected that additional tools will be developed over
   time to aid in troubleshooting DNSSEC issues.

   Once you figure out what the error is, you need to check if it shows
   consistently around the world and from all authoritative servers.



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   Use DNS Tools (dig) or DNS looking glasses to verify this.  An error
   that is consistently the same is more likely to be operator caused
   than an attack.  Also if the output from the authoritative server is
   consistently different from the resolvers' output this hints to an
   attack rather then an error, unless there is EDNS0 client subnet
   (draft-ietf-dnsop-edns-client-subnet) applied to the domain.

   A last check is to look at the actual DNS data.  Is the result of the
   query still the same or has it changed?  While a lot of DNSSEC errors
   occur on events that change DNSSEC data, the actual record someone
   wants to go to often stays the same.  If the data is the same, this
   is an indication (not a guarantee) that the error is operator caused.
   Keep in mind that with DNS being used to globally balance traffic the
   data associated to a name might be different in different parts of
   the Internet.

   Here are some examples of common DNSSEC failures that have been seen
   as operator signing errors on the Internet:

   o  RRSIG timing issue.  Each signature has an inception time and
      expiry time, between which it is valid.  Letting this time expire
      without creating a new signature is one of the most common DNSSEC
      errors.  To a lesser extent, this also occurs if signatures were
      made active before the inception time.  For all of these errors
      your primary check is to check on the data.  Signature expiration
      is also about the only error we see on actual data (like
      www.example.com).  All other errors are more or less related to
      dealing with the chain of trust established by DS records in the
      parent zone and DNSKEYs in the child zones.  These mostly occur
      during key rollovers, but are not limited to that.

   o  DNSKEYs in child zone don't match the DS record in the parent
      zone.  There is a big variation of this that can happen at any
      point in the key lifecycle.  DNSViz is the best tool to show
      problems in the chain.  If you debug yourself, use dig +multiline
      so that you can see the key id of a DNSKEY.  Common Variations of
      this can be:

      *  DS pointing to a non existent key in the child zone.  Questions
         for consideration here include: Has there ever been a key (and,
         if so, was it used)?  Has there been a recent change in the
         DNSKEY RRSet (indicating a key rollover)?  Has the actual data
         in the zone changed?  Is the zone DNSSEC signed at all and has
         it been in the past?

      *  DS pointing to an existent key, but no signatures are made with
         the key.  The checks above should be done, with the addition of




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         checking if another key in the DNSKEY RRSet is now used to sign
         the records.

      *  Data in DS or DNSKEY doesn't match the other.  This is more
         common in initial setup when there was a copy and paste error.
         Again checking history on data is the best you can do there.

   All of the above is just a starting point for consideration when
   deciding whether or not to deploy a trust anchor.  It is not possible
   to provide a simple checklist to run through to determine whether a
   domain is broken because of an attack or an operator error.

8.  Privacy Considerations

   There are no privacy considerations in this document.

9.  IANA Considerations

   There are no IANA considerations in this document.

10.  Security Considerations

   End to end DNSSEC validation will be disabled during the time that an
   NTA is used.  In addition, the NTA 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
   been re-secured and when an NTA is removed.  In addition, an NTA may
   be put in place by DNS recursive resolver operators without the
   knowledge of the authoritative domain administrator for a given
   domain name.  However, attempts SHOULD be made to contact and inform
   the domain administrator prior to putting the NTA in place.

   One side effect of implementing an NTA is that it may break client
   applications that assume that a domain is signed and expect an AD bit
   in the response.  It is expected that many application that require
   DNSSEC for a domain will perform their own validation, and so this
   should not be a major issue.

11.  Acknowledgements

   Several people made contributions of text to this document and/or
   played an important role in the development and evolution of this
   document.  This in some cases included performing a detailed review
   of this document and then providing feedback and constructive
   criticism for future revisions, or engaging in a healthy debate over
   the subject of the document.  All of this was helpful and therefore
   the following individuals merit acknowledgement: Joe Abley, John
   Barnitz, Tom Creighton, Marco Davids, Brian Dickson, Patrik Falstrom,



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   Tony Finch, Chris Ganster, Olafur Gudmundsson, Peter Hagopian,
   Christer Holmberg, Wes Hardaker, Paul Hoffman, Shane Kerr, Murray
   Kucherawy, Rick Lamb, Marc Lampo, Scott Rose, Ted Lemon, Wendy
   Seltzer, A.  Schulze, Antoin Verschuren, Paul Vixie, Patrik
   Wallstrom, Nick Weaver, W.C.A.  Wijngaards, Suzanne Woolf.

   Edward Lewis, Evan Hunt, Andrew Sullivan and Tatuya Jinmei provided
   especially large amounts of text and / or detailed review.

12.  References

12.1.  Normative References

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements", RFC
              4033, DOI 10.17487/RFC4033, March 2005,
              <http://www.rfc-editor.org/info/rfc4033>.

   [RFC5914]  Housley, R., Ashmore, S., and C. Wallace, "Trust Anchor
              Format", RFC 5914, DOI 10.17487/RFC5914, June 2010,
              <http://www.rfc-editor.org/info/rfc5914>.

   [RFC6781]  Kolkman, O., Mekking, W., and R. Gieben, "DNSSEC
              Operational Practices, Version 2", RFC 6781, DOI 10.17487/
              RFC6781, December 2012,
              <http://www.rfc-editor.org/info/rfc6781>.

12.2.  Informative References

   [Alexa]    Alexa, an Amazon.com Company, "Alexa "The top 500 sites on
              the web. "", , May 2015, <http://www.alexa.com/topsites>.

   [Disclosure-Example]
              Comcast, "faa.gov Failing DNSSEC Validation (Fixed)",
              Comcast , February 2013,
              <http://dns.comcast.net/index.php/entry/
              faa-gov-failing-dnssec-validation-fixed>.

   [Measuring-DNSSEC-Validation-of-Website-Visitors]
              Mens, J., "Is my Web site being used via a DNSSEC-
              validator?", July 2012, <http://jpmens.net/2012/07/30/
              is-my-web-site-being-used-via-dnssec-validator/>.









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   [Netalyzr]
              Weaver, N., Kreibich, C., Nechaev, B., and V. Paxson,
              "Implications of Netalyzr's DNS Measurements", Securing
              and Trusting Internet Names, SATIN 2011 SATIN 2011, April
              2011, <http://conferences.npl.co.uk/satin/presentations/
              satin2011slides-Weaver.pdf>.

   [Unbound-Configuration]
              Wijngaards, W., "Unbound: How to Turn Off DNSSEC", June
              2010, <http://unbound.net/documentation/
              howto_turnoff_dnssec.html>.

Appendix A.  Configuration Examples

   The section contains example configurations to achieve Negative Trust
   Anchor functionality for the zone foo.example.com.

   Note: These are simply examples - nameserver operators are expected
   to test and understand the implications of these operations.  Note
   also that some of available implementations may not implement all
   recommended functionality in this document.  In that case it is
   advisable to request the developer or vendor of the implementation to
   support the missing feature, rather than start using the incomplete
   implementation.

A.1.  NLNet Labs Unbound

   Unbound lets us simply disable validation checking for a specific
   zone by adding configuration statements to unbound.conf:

   server:
           domain-insecure: "foo.example.com"

   Using the 'unbound-control' command one can add and remove Negative
   Trust Anchors without restarting the nameserver.

      Using the "unbound-control" command:
           list_insecure                 list domain-insecure zones
           insecure_add zone             add domain-insecure zone
           insecure_remove zone          remove domain-insecure zone

   Items added with the "unbound-control" command are added to the
   running server and are lost when the server is restarted.  Items from
   unbound.conf stay after restart.

   For additional information see [Unbound-Configuration]





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A.2.  ISC BIND

   Use the "rndc" command:

     nta -dump
               List all negative trust anchors.
     nta [-lifetime duration] [-force] domain [view]
               Set a negative trust anchor, disabling DNSSEC validation
               for the given domain.
               Using -lifetime specifies the duration of the NTA, up
               to one week. The default is one hour.
               Using -force prevents the NTA from expiring before its
               full lifetime, even if the domain can validate sooner.
     nta -remove domain [view]
               Remove a negative trust anchor, re-enabling validation
               for the given domain.

A.3.  Nominum Vantio

   **

   *negative-trust-anchors*

   _Format_: name

   _Command Channel_: view.update name=world negative-trust-
   anchors=(foo.example.com)

   _Command Channel_: resolver.update name=res1 negative-trust-
   anchors=(foo.example.com)

   *Description*: Disables DNSSEC validation for a domain, even if the
   domain is under an existing security root.

Appendix B.  Document Change Log

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

   -12 to -13:

   o  ... and add Chris' email address.

   o  Finally incorporate Wendy Seltzer's pull request with tenst fixup
      nits.

   -11 to -12:

   o  Simply updated Chris' affiliation.



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   -10.5 to 11

      Integrated Alissa Cooper's No Objection comments.  Text from Suz
      and Evan.

   -10.4 to 10.5

      Integrated some comments from Ben Campbell's No Objection IESG
      review.

   -10.3 to 10.4

      s/personnel trained in the operation of DNS servers MUST confirm/
      personnel trained in the operation of DNS servers must confirm/ -
      Alissa Cooper,

   -10.2 to 10.3

   o  Integrated comments from Gen-ART review - Christer Holmberg.

   o  Offlist comment from Tony Finch.  Made the "Negative Trust Anchors
      are intended to be temporary," sentence much better.

   -10.1 to 10.2

   o  Incoroprated comments from IETF LC, including:

   o  A.  Schulze - s/Unound/Unbound/

   o  Joe Abley: Tone in into jarring.  S1.2 s/domain administrator/zone
      administrator/, dnscheck -> zonemaster

   -10 to 10.1

   o  Fixed some typos (e.g Anrew -> Andrew)

   -09 to -10

   o  'Implementations MAY issue a warning or informational message when
      this occurs' - changed SHOULD to MAY, per Evan.

   -08 to -09

   o  Clarified that an NTA MUST take precedence over a positive, local
      TA.

   -07 to -08




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   o  Added some cleanup from Paul Hoffman and Evan Hunt.

   o  Some better text on how to make Unbound do this, provided by
      W.C.A.  Wijngaards.

   -06 to -07

   o  Addressed a large number of comments from Paul Hoffman, Scott Rose
      and some more from Jinmei.

   -05 to -06

   o  A bunch of comments from Tony Finch.

   -04 to -05

   o  A large bunch of cleanups from Jinmei.  Thanks!

   o  Also clarified that if there is an NTA at foo.bar.baz.example, and
      a positive *trust anchor* at bar.baz.example, the most specific
      wins.  I'm not very happy with this text, any additional text
      gratefully accepted...

   -03 to -04:

   o  Addressed some comment from an email from Jinmei that I had
      missed.  Turns out others had made many of the same comments, and
      so most had already been addressed.

   -02 to -03:

   o  Included text from Ralph into Appendix B

   o  A bunch of comments from Andrew Sullivan ('[DNSOP] negative-trust-
      anchors-02" - Mar 18th)

   o  Updated keywords

   -01 to -02:

   o  Gah!  I forgot to run spell check.  And I type like a chimpanzee
      with bad hand-eye coordination...

   -00 to -01:

   o  Stole chunks of text from Ed Lewis' mailing list "tirade" :-)

   o  New rndc usage text from Evan.



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   o  Deleted the (already resolved) open issues from Appendix C, moved
      the unresolved issues into github, resolved them!

   o  Clarification that automated removal is best removal method, and
      how to implement (Evan Hunt)

   o  Clarify that an NTA is not a RR (Rick Lamb)

   o  Grammar fixes.

   Ind-07 - WG-00:

   o  Simply updated name to reflect WG doc.

   Individual-00: First version published as an individual draft.

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

   Individual-02: Simple date change to keep doc from expiring.
   Substantive updates planned.

   Individual-03: Changes to address feedback from Paul Vixie, by adding
   a new section "Limited Time and Scope of Use".  Changes to address
   issues raised by Antoin Verschuren and Patrik Wallstrom, by adding a
   new section "Intentionally Broken Domains" and added two related
   references.  Added text to address the need for manual investigation,
   as suggested by Patrik Falstrom.  Added a suggestion on notification
   as suggested by Marc Lampo.  Made several additions and changes
   suggested by Ralf Weber, Wes Hardaker, Nick Weaver, Tony Finch, Shane
   Kerr, Joe Abley, Murray Kucherawy, Olafur Gudmundsson.

   Individual-04: Moved the section defining an NTA forward, and added
   new text to the Abstract and Introduction per feedback from Paul
   Hoffman.

   Individual-05: Incorporated feedback from the DNSOP WG list received
   on 2/17/13 and 2/18/13.  This is likely the final version before the
   IETF 86 draft cutoff date.  Updated references to RFC6781 to RFC6781,
   per March Davids.

   Individual-06: Added more OPEN issues to continue tracking WG
   discussion.  No changes in the main document - just expanded issue
   tracking.

   Individual-07: Refresh document - needs revision and rework before
   IETF-91.  Planning to add more contributors.




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   o  Using github issue tracker - go see https://github.com/wkumari/
      draft-livingood-dnsop-negative-trust-anchors for more details.

   o  A bunch of readability improvments.

   o  Issue: Notify the domain owner of the validation failure -
      resolved.

   o  Issue: Make the NTA as specific as possible - resolved.

Authors' Addresses

   Paul Ebersman
   Comcast
   One Comcast Center
   1701 John F. Kennedy Boulevard
   Philadelphia, PA  19103
   US

   Email: ebersman-ietf@dragon.net


   Warren Kumari
   Google
   1600 Amphitheatre Parkway
   Mountain View, CA  94043
   US

   Email: warren@kumari.net
   URI:   http://www.google.com


   Chris Griffiths
   Nominet
   Minerva House
   Edmund Halley Road
   Oxford Science Park
   Oxford  OX4 4DQ
   United Kingdom

   Email: cgriffiths@gmail.com
   URI:   http://www.nominet.org.uk/









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

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


   Ralf Weber
   Nominum

   Email: Ralf.Weber@nominum.com
   URI:   http://www.nominum.com



































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