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RFC 7646

Informational
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Definition and Use of DNSSEC Negative Trust Anchors

 


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Internet Engineering Task Force (IETF)                       P. Ebersman
Request for Comments: 7646                                       Comcast
Category: Informational                                        W. Kumari
ISSN: 2070-1721                                                   Google
                                                            C. Griffiths
                                                                 Nominet
                                                            J. Livingood
                                                                 Comcast
                                                                R. Weber
                                                                 Nominum
                                                          September 2015


          Definition and Use of DNSSEC Negative Trust Anchors

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 (NTAs), which can be used to mitigate DNSSEC validation
   failures by disabling DNSSEC validation at specified domains.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7646.

Page 2 
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. Security Considerations ........................................11
   9. References .....................................................11
      9.1. Normative References ......................................11
      9.2. Informative References ....................................12
   Appendix A.  Configuration Examples ...............................13
     A.1.  NLnet Labs Unbound ........................................13
     A.2.  Internet System Consortium (ISC) BIND .....................14
     A.3.  Nominum Vantio ............................................14
   Acknowledgements ..................................................15
   Authors' Addresses ................................................15

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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 they 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 Negative Trust Anchors (NTAs), 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 (PKIs)
   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.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   [RFC2119].

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 Authentic Data (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

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   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 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 (e.g., 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 pay special attention to Section 4.2 of [RFC6781], which
   pertains to key rollovers, as these 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 about 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.

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   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; 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.

   The following text from [RFC4033] is worth noting: "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, and 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.

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   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).

   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 Top-
   Level Domain (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

   An 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

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   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.

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 that 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 resource record (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.  Therefore, implementors should consider
   transparently disclosing NTAs that 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 8, 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

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   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.

   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
   Start of Authority (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), 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 [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

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   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.

   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 a result of an operator
   error instead of an attack is not trivial, and the examples here
   should be vetted by an experienced professional before making the
   decision to implement an NTA.

   One of the key things to look for when looking at a DNSSEC broken
   domain is consistency and history.  Therefore, it 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 and associated answers
   (this is often referred to as a "passive DNS database").  Another
   invaluable tool is DNSViz (http://dnsviz.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, several tools that do this are available,
   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)

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   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.
   Use DNS Tools (dig) or DNS looking glasses to verify this.  An error
   that is consistently the same is more likely to be caused by an
   operator rather than by 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 EDNS0
   client subnet [CLIENT-SUBNET] is 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 a 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 it yourself, use dig
      +multiline so that you can see the key id of a DNSKEY.  Common
      variations of this can be:

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      *  DS pointing to a non-existent key in the child zone.  Questions
         for consideration here include the following.  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
         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.  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 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 applications that require
   DNSSEC for a domain will perform their own validation, so this should
   not be a major issue.

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

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   [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>.

9.2.  Informative References

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

   [CLIENT-SUBNET]
              Contavalli, C., van der Gaast, W., Lawrence, D., and W.
              Kumari, "Client Subnet in DNS Queries", Work in Progress,
              draft-ietf-dnsop-edns-client-subnet-03, August 2015.

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

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

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

   [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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Appendix A.  Configuration Examples

   The section contains example configurations to achieve NTA
   functionality for the zone foo.example.com.

   Note: These are simply examples -- name server 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 [Unbound-Config] 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 NTAs
   without restarting the name server.

      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-Config].

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A.2.  Internet System Consortium (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.

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Acknowledgements

   Several people made contributions to this document and/or played an
   important role in the development and evolution of it.  In some
   cases, this included performing a detailed review 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, Tony Finch, Chris Ganster,
   Olafur Gudmundsson, Peter Hagopian, Wes Hardaker, Paul Hoffman,
   Christer Holmberg, Shane Kerr, Murray Kucherawy, Rick Lamb, Marc
   Lampo, Ted Lemon, Scott Rose, A. Schulze, Wendy Seltzer, Antoin
   Verschuren, Paul Vixie, Patrik Wallstrom, Nick Weaver,
   W.C.A. Wijngaards, and Suzanne Woolf.

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

Authors' Addresses

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

   Email: ebersman-ietf@dragon.net


   Warren Kumari
   Google
   1600 Amphitheatre Parkway
   Mountain View, CA  94043
   United States

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

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   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/


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

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


   Ralf Weber
   Nominum

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