<pre>Network Working Group                                          R. Arends
Request for Comments: 4035                          Telematica Instituut
Obsoletes: <a href="./rfc2535">2535</a>, <a href="./rfc3008">3008</a>, <a href="./rfc3090">3090</a>, <a href="./rfc3445">3445</a>, <a href="./rfc3655">3655</a>, <a href="./rfc3658">3658</a>,                R. Austein
           <a href="./rfc3755">3755</a>, <a href="./rfc3757">3757</a>, <a href="./rfc3845">3845</a>                                          ISC
Updates: <a href="./rfc1034">1034</a>, <a href="./rfc1035">1035</a>, <a href="./rfc2136">2136</a>, <a href="./rfc2181">2181</a>, <a href="./rfc2308">2308</a>, <a href="./rfc3225">3225</a>,                   M. Larson
         <a href="./rfc3007">3007</a>, <a href="./rfc3597">3597</a>, <a href="./rfc3226">3226</a>                                       VeriSign
Category: Standards Track                                      D. Massey
                                               Colorado State University
                                                                 S. Rose
                                                                    NIST
                                                              March 2005


         <span class="h1">Protocol Modifications for the DNS Security Extensions</span>

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This document is part of a family of documents that describe the DNS
   Security Extensions (DNSSEC).  The DNS Security Extensions are a
   collection of new resource records and protocol modifications that
   add data origin authentication and data integrity to the DNS.  This
   document describes the DNSSEC protocol modifications.  This document
   defines the concept of a signed zone, along with the requirements for
   serving and resolving by using DNSSEC.  These techniques allow a
   security-aware resolver to authenticate both DNS resource records and
   authoritative DNS error indications.

   This document obsoletes <a href="./rfc2535">RFC 2535</a> and incorporates changes from all
   updates to <a href="./rfc2535">RFC 2535</a>.










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Table of Contents

   <a href="#section-1">1</a>.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  <a href="#page-3">3</a>
       <a href="#section-1.1">1.1</a>.  Background and Related Documents . . . . . . . . . . . .  <a href="#page-4">4</a>
       <a href="#section-1.2">1.2</a>.  Reserved Words . . . . . . . . . . . . . . . . . . . . .  <a href="#page-4">4</a>
   <a href="#section-2">2</a>.  Zone Signing . . . . . . . . . . . . . . . . . . . . . . . . .  <a href="#page-4">4</a>
       <a href="#section-2.1">2.1</a>.  Including DNSKEY RRs in a Zone . . . . . . . . . . . . .  <a href="#page-5">5</a>
       <a href="#section-2.2">2.2</a>.  Including RRSIG RRs in a Zone  . . . . . . . . . . . . .  <a href="#page-5">5</a>
       <a href="#section-2.3">2.3</a>.  Including NSEC RRs in a Zone . . . . . . . . . . . . . .  <a href="#page-6">6</a>
       <a href="#section-2.4">2.4</a>.  Including DS RRs in a Zone . . . . . . . . . . . . . . .  <a href="#page-7">7</a>
       2.5.  Changes to the CNAME Resource Record.  . . . . . . . . .  <a href="#page-7">7</a>
       2.6.  DNSSEC RR Types Appearing at Zone Cuts.  . . . . . . . .  <a href="#page-8">8</a>
       <a href="#section-2.7">2.7</a>.  Example of a Secure Zone . . . . . . . . . . . . . . . .  <a href="#page-8">8</a>
   <a href="#section-3">3</a>.  Serving  . . . . . . . . . . . . . . . . . . . . . . . . . . .  <a href="#page-8">8</a>
       <a href="#section-3.1">3.1</a>.  Authoritative Name Servers . . . . . . . . . . . . . . .  <a href="#page-9">9</a>
             <a href="#section-3.1.1">3.1.1</a>.  Including RRSIG RRs in a Response  . . . . . . . <a href="#page-10">10</a>
             <a href="#section-3.1.2">3.1.2</a>.  Including DNSKEY RRs in a Response . . . . . . . <a href="#page-11">11</a>
             <a href="#section-3.1.3">3.1.3</a>.  Including NSEC RRs in a Response . . . . . . . . <a href="#page-11">11</a>
             <a href="#section-3.1.4">3.1.4</a>.  Including DS RRs in a Response . . . . . . . . . <a href="#page-14">14</a>
             <a href="#section-3.1.5">3.1.5</a>.  Responding to Queries for Type AXFR or IXFR  . . <a href="#page-15">15</a>
             3.1.6.  The AD and CD Bits in an Authoritative Response. 16
       <a href="#section-3.2">3.2</a>.  Recursive Name Servers . . . . . . . . . . . . . . . . . <a href="#page-17">17</a>
             <a href="#section-3.2.1">3.2.1</a>.  The DO Bit . . . . . . . . . . . . . . . . . . . <a href="#page-17">17</a>
             <a href="#section-3.2.2">3.2.2</a>.  The CD Bit . . . . . . . . . . . . . . . . . . . <a href="#page-17">17</a>
             <a href="#section-3.2.3">3.2.3</a>.  The AD Bit . . . . . . . . . . . . . . . . . . . <a href="#page-18">18</a>
       <a href="#section-3.3">3.3</a>.  Example DNSSEC Responses . . . . . . . . . . . . . . . . <a href="#page-19">19</a>
   <a href="#section-4">4</a>.  Resolving  . . . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-19">19</a>
       <a href="#section-4.1">4.1</a>.  EDNS Support . . . . . . . . . . . . . . . . . . . . . . <a href="#page-19">19</a>
       <a href="#section-4.2">4.2</a>.  Signature Verification Support . . . . . . . . . . . . . <a href="#page-19">19</a>
       <a href="#section-4.3">4.3</a>.  Determining Security Status of Data  . . . . . . . . . . <a href="#page-20">20</a>
       <a href="#section-4.4">4.4</a>.  Configured Trust Anchors . . . . . . . . . . . . . . . . <a href="#page-21">21</a>
       <a href="#section-4.5">4.5</a>.  Response Caching . . . . . . . . . . . . . . . . . . . . <a href="#page-21">21</a>
       <a href="#section-4.6">4.6</a>.  Handling of the CD and AD Bits . . . . . . . . . . . . . <a href="#page-22">22</a>
       <a href="#section-4.7">4.7</a>.  Caching BAD Data . . . . . . . . . . . . . . . . . . . . <a href="#page-22">22</a>
       <a href="#section-4.8">4.8</a>.  Synthesized CNAMEs . . . . . . . . . . . . . . . . . . . <a href="#page-23">23</a>
       <a href="#section-4.9">4.9</a>.  Stub Resolvers . . . . . . . . . . . . . . . . . . . . . <a href="#page-23">23</a>
             <a href="#section-4.9.1">4.9.1</a>.  Handling of the DO Bit . . . . . . . . . . . . . <a href="#page-24">24</a>
             <a href="#section-4.9.2">4.9.2</a>.  Handling of the CD Bit . . . . . . . . . . . . . <a href="#page-24">24</a>
             <a href="#section-4.9.3">4.9.3</a>.  Handling of the AD Bit . . . . . . . . . . . . . <a href="#page-24">24</a>
   <a href="#section-5">5</a>.  Authenticating DNS Responses . . . . . . . . . . . . . . . . . <a href="#page-25">25</a>
       <a href="#section-5.1">5.1</a>.  Special Considerations for Islands of Security . . . . . <a href="#page-26">26</a>
       <a href="#section-5.2">5.2</a>.  Authenticating Referrals . . . . . . . . . . . . . . . . <a href="#page-26">26</a>
       <a href="#section-5.3">5.3</a>.  Authenticating an RRset with an RRSIG RR . . . . . . . . <a href="#page-28">28</a>
             <a href="#section-5.3.1">5.3.1</a>.  Checking the RRSIG RR Validity . . . . . . . . . <a href="#page-28">28</a>
             <a href="#section-5.3.2">5.3.2</a>.  Reconstructing the Signed Data . . . . . . . . . <a href="#page-29">29</a>
             <a href="#section-5.3.3">5.3.3</a>.  Checking the Signature . . . . . . . . . . . . . <a href="#page-31">31</a>
             5.3.4.  Authenticating a Wildcard Expanded RRset
                     Positive Response. . . . . . . . . . . . . . . . <a href="#page-32">32</a>



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       <a href="#section-5.4">5.4</a>.  Authenticated Denial of Existence  . . . . . . . . . . . <a href="#page-32">32</a>
       <a href="#section-5.5">5.5</a>.  Resolver Behavior When Signatures Do Not Validate  . . . <a href="#page-33">33</a>
       <a href="#section-5.6">5.6</a>.  Authentication Example . . . . . . . . . . . . . . . . . <a href="#page-33">33</a>
   <a href="#section-6">6</a>.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . <a href="#page-33">33</a>
   <a href="#section-7">7</a>.  Security Considerations  . . . . . . . . . . . . . . . . . . . <a href="#page-33">33</a>
   <a href="#section-8">8</a>.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-34">34</a>
   <a href="#section-9">9</a>.  References . . . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-34">34</a>
       <a href="#section-9.1">9.1</a>.  Normative References . . . . . . . . . . . . . . . . . . <a href="#page-34">34</a>
       <a href="#section-9.2">9.2</a>.  Informative References . . . . . . . . . . . . . . . . . <a href="#page-35">35</a>
   <a href="#appendix-A">A</a>.  Signed Zone Example  . . . . . . . . . . . . . . . . . . . . . <a href="#page-36">36</a>
   <a href="#appendix-B">B</a>.  Example Responses  . . . . . . . . . . . . . . . . . . . . . . <a href="#page-41">41</a>
       <a href="#appendix-B.1">B.1</a>.  Answer . . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-41">41</a>
       <a href="#appendix-B.2">B.2</a>.  Name Error . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-43">43</a>
       <a href="#appendix-B.3">B.3</a>.  No Data Error  . . . . . . . . . . . . . . . . . . . . . <a href="#page-44">44</a>
       <a href="#appendix-B.4">B.4</a>.  Referral to Signed Zone  . . . . . . . . . . . . . . . . <a href="#page-44">44</a>
       <a href="#appendix-B.5">B.5</a>.  Referral to Unsigned Zone  . . . . . . . . . . . . . . . <a href="#page-45">45</a>
       <a href="#appendix-B.6">B.6</a>.  Wildcard Expansion . . . . . . . . . . . . . . . . . . . <a href="#page-46">46</a>
       <a href="#appendix-B.7">B.7</a>.  Wildcard No Data Error . . . . . . . . . . . . . . . . . <a href="#page-47">47</a>
       <a href="#appendix-B.8">B.8</a>.  DS Child Zone No Data Error  . . . . . . . . . . . . . . <a href="#page-48">48</a>
   <a href="#appendix-C">C</a>.  Authentication Examples  . . . . . . . . . . . . . . . . . . . <a href="#page-49">49</a>
       <a href="#appendix-C.1">C.1</a>.  Authenticating an Answer . . . . . . . . . . . . . . . . <a href="#page-49">49</a>
             <a href="#appendix-C.1.1">C.1.1</a>.  Authenticating the Example DNSKEY RR . . . . . . <a href="#page-49">49</a>
       <a href="#appendix-C.2">C.2</a>.  Name Error . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-50">50</a>
       <a href="#appendix-C.3">C.3</a>.  No Data Error  . . . . . . . . . . . . . . . . . . . . . <a href="#page-50">50</a>
       <a href="#appendix-C.4">C.4</a>.  Referral to Signed Zone  . . . . . . . . . . . . . . . . <a href="#page-50">50</a>
       <a href="#appendix-C.5">C.5</a>.  Referral to Unsigned Zone  . . . . . . . . . . . . . . . <a href="#page-51">51</a>
       <a href="#appendix-C.6">C.6</a>.  Wildcard Expansion . . . . . . . . . . . . . . . . . . . <a href="#page-51">51</a>
       <a href="#appendix-C.7">C.7</a>.  Wildcard No Data Error . . . . . . . . . . . . . . . . . <a href="#page-51">51</a>
       <a href="#appendix-C.8">C.8</a>.  DS Child Zone No Data Error  . . . . . . . . . . . . . . <a href="#page-51">51</a>
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-52">52</a>
   Full Copyright Statement . . . . . . . . . . . . . . . . . . . . . <a href="#page-53">53</a>

<span class="h2"><a class="selflink" id="section-1" href="#section-1">1</a>.  Introduction</span>

   The DNS Security Extensions (DNSSEC) are a collection of new resource
   records and protocol modifications that add data origin
   authentication and data integrity to the DNS.  This document defines
   the DNSSEC protocol modifications.  <a href="#section-2">Section 2</a> of this document
   defines the concept of a signed zone and lists the requirements for
   zone signing.  <a href="#section-3">Section 3</a> describes the modifications to authoritative
   name server behavior necessary for handling signed zones.  <a href="#section-4">Section 4</a>
   describes the behavior of entities that include security-aware
   resolver functions.  Finally, <a href="#section-5">Section 5</a> defines how to use DNSSEC RRs
   to authenticate a response.







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<span class="h3"><a class="selflink" id="section-1.1" href="#section-1.1">1.1</a>.  Background and Related Documents</span>

   This document is part of a family of documents defining DNSSEC that
   should be read together as a set.

   [<a id="ref-RFC4033">RFC4033</a>] contains an introduction to DNSSEC and definitions of
   common terms; the reader is assumed to be familiar with this
   document.  [<a href="./rfc4033" title="&quot;DNS Security Introduction and Requirements&quot;">RFC4033</a>] also contains a list of other documents updated
   by and obsoleted by this document set.

   [<a id="ref-RFC4034">RFC4034</a>] defines the DNSSEC resource records.

   The reader is also assumed to be familiar with the basic DNS concepts
   described in [<a href="./rfc1034" title="&quot;Domain names - concepts and facilities&quot;">RFC1034</a>], [<a href="./rfc1035" title="&quot;Domain names - implementation and specification&quot;">RFC1035</a>], and the subsequent documents that
   update them; particularly, [<a href="./rfc2181" title="&quot;Clarifications to the DNS Specification&quot;">RFC2181</a>] and [<a href="./rfc2308" title="&quot;Negative Caching of DNS Queries (DNS NCACHE)&quot;">RFC2308</a>].

   This document defines the DNSSEC protocol operations.

<span class="h3"><a class="selflink" id="section-1.2" href="#section-1.2">1.2</a>.  Reserved Words</span>

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [<a href="./rfc2119" title="&quot;Key words for use in RFCs to Indicate Requirement Levels&quot;">RFC2119</a>].

<span class="h2"><a class="selflink" id="section-2" href="#section-2">2</a>.  Zone Signing</span>

   DNSSEC introduces the concept of signed zones.  A signed zone
   includes DNS Public Key (DNSKEY), Resource Record Signature (RRSIG),
   Next Secure (NSEC), and (optionally) Delegation Signer (DS) records
   according to the rules specified in Sections <a href="#section-2.1">2.1</a>, <a href="#section-2.2">2.2</a>, <a href="#section-2.3">2.3</a>, and <a href="#section-2.4">2.4</a>,
   respectively.  A zone that does not include these records according
   to the rules in this section is an unsigned zone.

   DNSSEC requires a change to the definition of the CNAME resource
   record ([<a href="./rfc1035" title="&quot;Domain names - implementation and specification&quot;">RFC1035</a>]).  <a href="#section-2.5">Section 2.5</a> changes the CNAME RR to allow RRSIG
   and NSEC RRs to appear at the same owner name as does a CNAME RR.

   DNSSEC specifies the placement of two new RR types, NSEC and DS,
   which can be placed at the parental side of a zone cut (that is, at a
   delegation point).  This is an exception to the general prohibition
   against putting data in the parent zone at a zone cut.  <a href="#section-2.6">Section 2.6</a>
   describes this change.









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<span class="h3"><a class="selflink" id="section-2.1" href="#section-2.1">2.1</a>.  Including DNSKEY RRs in a Zone</span>

   To sign a zone, the zone's administrator generates one or more
   public/private key pairs and uses the private key(s) to sign
   authoritative RRsets in the zone.  For each private key used to
   create RRSIG RRs in a zone, the zone SHOULD include a zone DNSKEY RR
   containing the corresponding public key.  A zone key DNSKEY RR MUST
   have the Zone Key bit of the flags RDATA field set (see <a href="./rfc4034#section-2.1.1">Section&nbsp;2.1.1
   of [RFC4034]</a>).  Public keys associated with other DNS operations MAY
   be stored in DNSKEY RRs that are not marked as zone keys but MUST NOT
   be used to verify RRSIGs.

   If the zone administrator intends a signed zone to be usable other
   than as an island of security, the zone apex MUST contain at least
   one DNSKEY RR to act as a secure entry point into the zone.  This
   secure entry point could then be used as the target of a secure
   delegation via a corresponding DS RR in the parent zone (see
   [<a href="./rfc4034" title="&quot;Resource Records for DNS Security Extensions&quot;">RFC4034</a>]).

<span class="h3"><a class="selflink" id="section-2.2" href="#section-2.2">2.2</a>.  Including RRSIG RRs in a Zone</span>

   For each authoritative RRset in a signed zone, there MUST be at least
   one RRSIG record that meets the following requirements:

   o  The RRSIG owner name is equal to the RRset owner name.

   o  The RRSIG class is equal to the RRset class.

   o  The RRSIG Type Covered field is equal to the RRset type.

   o  The RRSIG Original TTL field is equal to the TTL of the RRset.

   o  The RRSIG RR's TTL is equal to the TTL of the RRset.

   o  The RRSIG Labels field is equal to the number of labels in the
      RRset owner name, not counting the null root label and not
      counting the leftmost label if it is a wildcard.

   o  The RRSIG Signer's Name field is equal to the name of the zone
      containing the RRset.

   o  The RRSIG Algorithm, Signer's Name, and Key Tag fields identify a
      zone key DNSKEY record at the zone apex.

   The process for constructing the RRSIG RR for a given RRset is
   described in [<a href="./rfc4034" title="&quot;Resource Records for DNS Security Extensions&quot;">RFC4034</a>].  An RRset MAY have multiple RRSIG RRs
   associated with it.  Note that as RRSIG RRs are closely tied to the
   RRsets whose signatures they contain, RRSIG RRs, unlike all other DNS



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   RR types, do not form RRsets.  In particular, the TTL values among
   RRSIG RRs with a common owner name do not follow the RRset rules
   described in [<a href="./rfc2181" title="&quot;Clarifications to the DNS Specification&quot;">RFC2181</a>].

   An RRSIG RR itself MUST NOT be signed, as signing an RRSIG RR would
   add no value and would create an infinite loop in the signing
   process.

   The NS RRset that appears at the zone apex name MUST be signed, but
   the NS RRsets that appear at delegation points (that is, the NS
   RRsets in the parent zone that delegate the name to the child zone's
   name servers) MUST NOT be signed.  Glue address RRsets associated
   with delegations MUST NOT be signed.

   There MUST be an RRSIG for each RRset using at least one DNSKEY of
   each algorithm in the zone apex DNSKEY RRset.  The apex DNSKEY RRset
   itself MUST be signed by each algorithm appearing in the DS RRset
   located at the delegating parent (if any).

<span class="h3"><a class="selflink" id="section-2.3" href="#section-2.3">2.3</a>.  Including NSEC RRs in a Zone</span>

   Each owner name in the zone that has authoritative data or a
   delegation point NS RRset MUST have an NSEC resource record.  The
   format of NSEC RRs and the process for constructing the NSEC RR for a
   given name is described in [<a href="./rfc4034" title="&quot;Resource Records for DNS Security Extensions&quot;">RFC4034</a>].

   The TTL value for any NSEC RR SHOULD be the same as the minimum TTL
   value field in the zone SOA RR.

   An NSEC record (and its associated RRSIG RRset) MUST NOT be the only
   RRset at any particular owner name.  That is, the signing process
   MUST NOT create NSEC or RRSIG RRs for owner name nodes that were not
   the owner name of any RRset before the zone was signed.  The main
   reasons for this are a desire for namespace consistency between
   signed and unsigned versions of the same zone and a desire to reduce
   the risk of response inconsistency in security oblivious recursive
   name servers.

   The type bitmap of every NSEC resource record in a signed zone MUST
   indicate the presence of both the NSEC record itself and its
   corresponding RRSIG record.

   The difference between the set of owner names that require RRSIG
   records and the set of owner names that require NSEC records is
   subtle and worth highlighting.  RRSIG records are present at the
   owner names of all authoritative RRsets.  NSEC records are present at
   the owner names of all names for which the signed zone is
   authoritative and also at the owner names of delegations from the



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   signed zone to its children.  Neither NSEC nor RRSIG records are
   present (in the parent zone) at the owner names of glue address
   RRsets.  Note, however, that this distinction is for the most part
   visible only during the zone signing process, as NSEC RRsets are
   authoritative data and are therefore signed.  Thus, any owner name
   that has an NSEC RRset will have RRSIG RRs as well in the signed
   zone.

   The bitmap for the NSEC RR at a delegation point requires special
   attention.  Bits corresponding to the delegation NS RRset and any
   RRsets for which the parent zone has authoritative data MUST be set;
   bits corresponding to any non-NS RRset for which the parent is not
   authoritative MUST be clear.

<span class="h3"><a class="selflink" id="section-2.4" href="#section-2.4">2.4</a>.  Including DS RRs in a Zone</span>

   The DS resource record establishes authentication chains between DNS
   zones.  A DS RRset SHOULD be present at a delegation point when the
   child zone is signed.  The DS RRset MAY contain multiple records,
   each referencing a public key in the child zone used to verify the
   RRSIGs in that zone.  All DS RRsets in a zone MUST be signed, and DS
   RRsets MUST NOT appear at a zone's apex.

   A DS RR SHOULD point to a DNSKEY RR that is present in the child's
   apex DNSKEY RRset, and the child's apex DNSKEY RRset SHOULD be signed
   by the corresponding private key.  DS RRs that fail to meet these
   conditions are not useful for validation, but because the DS RR and
   its corresponding DNSKEY RR are in different zones, and because the
   DNS is only loosely consistent, temporary mismatches can occur.

   The TTL of a DS RRset SHOULD match the TTL of the delegating NS RRset
   (that is, the NS RRset from the same zone containing the DS RRset).

   Construction of a DS RR requires knowledge of the corresponding
   DNSKEY RR in the child zone, which implies communication between the
   child and parent zones.  This communication is an operational matter
   not covered by this document.

<span class="h3"><a class="selflink" id="section-2.5" href="#section-2.5">2.5</a>.  Changes to the CNAME Resource Record</span>

   If a CNAME RRset is present at a name in a signed zone, appropriate
   RRSIG and NSEC RRsets are REQUIRED at that name.  A KEY RRset at that
   name for secure dynamic update purposes is also allowed ([<a href="./rfc3007" title="&quot;Secure Domain Name System (DNS) Dynamic Update&quot;">RFC3007</a>]).
   Other types MUST NOT be present at that name.

   This is a modification to the original CNAME definition given in
   [<a href="./rfc1034" title="&quot;Domain names - concepts and facilities&quot;">RFC1034</a>].  The original definition of the CNAME RR did not allow any
   other types to coexist with a CNAME record, but a signed zone



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   requires NSEC and RRSIG RRs for every authoritative name.  To resolve
   this conflict, this specification modifies the definition of the
   CNAME resource record to allow it to coexist with NSEC and RRSIG RRs.

<span class="h3"><a class="selflink" id="section-2.6" href="#section-2.6">2.6</a>.  DNSSEC RR Types Appearing at Zone Cuts</span>

   DNSSEC introduced two new RR types that are unusual in that they can
   appear at the parental side of a zone cut.  At the parental side of a
   zone cut (that is, at a delegation point), NSEC RRs are REQUIRED at
   the owner name.  A DS RR could also be present if the zone being
   delegated is signed and seeks to have a chain of authentication to
   the parent zone.  This is an exception to the original DNS
   specification ([<a href="./rfc1034" title="&quot;Domain names - concepts and facilities&quot;">RFC1034</a>]), which states that only NS RRsets could
   appear at the parental side of a zone cut.

   This specification updates the original DNS specification to allow
   NSEC and DS RR types at the parent side of a zone cut.  These RRsets
   are authoritative for the parent when they appear at the parent side
   of a zone cut.

<span class="h3"><a class="selflink" id="section-2.7" href="#section-2.7">2.7</a>.  Example of a Secure Zone</span>

   <a href="#appendix-A">Appendix A</a> shows a complete example of a small signed zone.

<span class="h2"><a class="selflink" id="section-3" href="#section-3">3</a>.  Serving</span>

   This section describes the behavior of entities that include
   security-aware name server functions.  In many cases such functions
   will be part of a security-aware recursive name server, but a
   security-aware authoritative name server has some of the same
   requirements.  Functions specific to security-aware recursive name
   servers are described in <a href="#section-3.2">Section 3.2</a>; functions specific to
   authoritative servers are described in <a href="#section-3.1">Section 3.1</a>.

   In the following discussion, the terms "SNAME", "SCLASS", and "STYPE"
   are as used in [<a href="./rfc1034" title="&quot;Domain names - concepts and facilities&quot;">RFC1034</a>].

   A security-aware name server MUST support the EDNS0 ([<a href="./rfc2671" title="&quot;Extension Mechanisms for DNS (EDNS0)&quot;">RFC2671</a>])
   message size extension, MUST support a message size of at least 1220
   octets, and SHOULD support a message size of 4000 octets.  As IPv6
   packets can only be fragmented by the source host, a security aware
   name server SHOULD take steps to ensure that UDP datagrams it
   transmits over IPv6 are fragmented, if necessary, at the minimum IPv6
   MTU, unless the path MTU is known.  Please see [<a href="./rfc1122" title="&quot;Requirements for Internet Hosts - Communication Layers&quot;">RFC1122</a>], [<a href="./rfc2460" title="&quot;Internet Protocol, Version 6 (IPv6) Specification&quot;">RFC2460</a>],
   and [<a href="./rfc3226" title="&quot;DNSSEC and IPv6 A6 aware server/resolver message size requirements&quot;">RFC3226</a>] for further discussion of packet size and fragmentation
   issues.





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   A security-aware name server that receives a DNS query that does not
   include the EDNS OPT pseudo-RR or that has the DO bit clear MUST
   treat the RRSIG, DNSKEY, and NSEC RRs as it would any other RRset and
   MUST NOT perform any of the additional processing described below.
   Because the DS RR type has the peculiar property of only existing in
   the parent zone at delegation points, DS RRs always require some
   special processing, as described in <a href="#section-3.1.4.1">Section 3.1.4.1</a>.

   Security aware name servers that receive explicit queries for
   security RR types that match the content of more than one zone that
   it serves (for example, NSEC and RRSIG RRs above and below a
   delegation point where the server is authoritative for both zones)
   should behave self-consistently.  As long as the response is always
   consistent for each query to the name server, the name server MAY
   return one of the following:

   o  The above-delegation RRsets.
   o  The below-delegation RRsets.
   o  Both above and below-delegation RRsets.
   o  Empty answer section (no records).
   o  Some other response.
   o  An error.

   DNSSEC allocates two new bits in the DNS message header: the CD
   (Checking Disabled) bit and the AD (Authentic Data) bit.  The CD bit
   is controlled by resolvers; a security-aware name server MUST copy
   the CD bit from a query into the corresponding response.  The AD bit
   is controlled by name servers; a security-aware name server MUST
   ignore the setting of the AD bit in queries.  See Sections <a href="#section-3.1.6">3.1.6</a>,
   3.2.2, 3.2.3, 4, and 4.9 for details on the behavior of these bits.

   A security aware name server that synthesizes CNAME RRs from DNAME
   RRs as described in [<a href="./rfc2672" title="&quot;Non-Terminal DNS Name Redirection&quot;">RFC2672</a>] SHOULD NOT generate signatures for the
   synthesized CNAME RRs.

<span class="h3"><a class="selflink" id="section-3.1" href="#section-3.1">3.1</a>.  Authoritative Name Servers</span>

   Upon receiving a relevant query that has the EDNS ([<a href="./rfc2671" title="&quot;Extension Mechanisms for DNS (EDNS0)&quot;">RFC2671</a>]) OPT
   pseudo-RR DO bit ([<a href="./rfc3225" title="&quot;Indicating Resolver Support of DNSSEC&quot;">RFC3225</a>]) set, a security-aware authoritative name
   server for a signed zone MUST include additional RRSIG, NSEC, and DS
   RRs, according to the following rules:

   o  RRSIG RRs that can be used to authenticate a response MUST be
      included in the response according to the rules in <a href="#section-3.1.1">Section 3.1.1</a>.







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   o  NSEC RRs that can be used to provide authenticated denial of
      existence MUST be included in the response automatically according
      to the rules in <a href="#section-3.1.3">Section 3.1.3</a>.

   o  Either a DS RRset or an NSEC RR proving that no DS RRs exist MUST
      be included in referrals automatically according to the rules in
      <a href="#section-3.1.4">Section 3.1.4</a>.

   These rules only apply to responses where the semantics convey
   information about the presence or absence of resource records.  That
   is, these rules are not intended to rule out responses such as RCODE
   4 ("Not Implemented") or RCODE 5 ("Refused").

   DNSSEC does not change the DNS zone transfer protocol.  <a href="#section-3.1.5">Section 3.1.5</a>
   discusses zone transfer requirements.

<span class="h4"><a class="selflink" id="section-3.1.1" href="#section-3.1.1">3.1.1</a>.  Including RRSIG RRs in a Response</span>

   When responding to a query that has the DO bit set, a security-aware
   authoritative name server SHOULD attempt to send RRSIG RRs that a
   security-aware resolver can use to authenticate the RRsets in the
   response.  A name server SHOULD make every attempt to keep the RRset
   and its associated RRSIG(s) together in a response.  Inclusion of
   RRSIG RRs in a response is subject to the following rules:

   o  When placing a signed RRset in the Answer section, the name server
      MUST also place its RRSIG RRs in the Answer section.  The RRSIG
      RRs have a higher priority for inclusion than any other RRsets
      that may have to be included.  If space does not permit inclusion
      of these RRSIG RRs, the name server MUST set the TC bit.

   o  When placing a signed RRset in the Authority section, the name
      server MUST also place its RRSIG RRs in the Authority section.
      The RRSIG RRs have a higher priority for inclusion than any other
      RRsets that may have to be included.  If space does not permit
      inclusion of these RRSIG RRs, the name server MUST set the TC bit.

   o  When placing a signed RRset in the Additional section, the name
      server MUST also place its RRSIG RRs in the Additional section.
      If space does not permit inclusion of both the RRset and its
      associated RRSIG RRs, the name server MAY retain the RRset while
      dropping the RRSIG RRs.  If this happens, the name server MUST NOT
      set the TC bit solely because these RRSIG RRs didn't fit.








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<span class="h4"><a class="selflink" id="section-3.1.2" href="#section-3.1.2">3.1.2</a>.  Including DNSKEY RRs in a Response</span>

   When responding to a query that has the DO bit set and that requests
   the SOA or NS RRs at the apex of a signed zone, a security-aware
   authoritative name server for that zone MAY return the zone apex
   DNSKEY RRset in the Additional section.  In this situation, the
   DNSKEY RRset and associated RRSIG RRs have lower priority than does
   any other information that would be placed in the additional section.
   The name server SHOULD NOT include the DNSKEY RRset unless there is
   enough space in the response message for both the DNSKEY RRset and
   its associated RRSIG RR(s).  If there is not enough space to include
   these DNSKEY and RRSIG RRs, the name server MUST omit them and MUST
   NOT set the TC bit solely because these RRs didn't fit (see <a href="#section-3.1.1">Section</a>
   <a href="#section-3.1.1">3.1.1</a>).

<span class="h4"><a class="selflink" id="section-3.1.3" href="#section-3.1.3">3.1.3</a>.  Including NSEC RRs in a Response</span>

   When responding to a query that has the DO bit set, a security-aware
   authoritative name server for a signed zone MUST include NSEC RRs in
   each of the following cases:

   No Data: The zone contains RRsets that exactly match &lt;SNAME, SCLASS&gt;
      but does not contain any RRsets that exactly match &lt;SNAME, SCLASS,
      STYPE&gt;.

   Name Error: The zone does not contain any RRsets that match &lt;SNAME,
      SCLASS&gt; either exactly or via wildcard name expansion.

   Wildcard Answer: The zone does not contain any RRsets that exactly
      match &lt;SNAME, SCLASS&gt; but does contain an RRset that matches
      &lt;SNAME, SCLASS, STYPE&gt; via wildcard name expansion.

   Wildcard No Data: The zone does not contain any RRsets that exactly
      match &lt;SNAME, SCLASS&gt; and does contain one or more RRsets that
      match &lt;SNAME, SCLASS&gt; via wildcard name expansion, but does not
      contain any RRsets that match &lt;SNAME, SCLASS, STYPE&gt; via wildcard
      name expansion.

   In each of these cases, the name server includes NSEC RRs in the
   response to prove that an exact match for &lt;SNAME, SCLASS, STYPE&gt; was
   not present in the zone and that the response that the name server is
   returning is correct given the data in the zone.









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<span class="h5"><a class="selflink" id="section-3.1.3.1" href="#section-3.1.3.1">3.1.3.1</a>.  Including NSEC RRs: No Data Response</span>

   If the zone contains RRsets matching &lt;SNAME, SCLASS&gt; but contains no
   RRset matching &lt;SNAME, SCLASS, STYPE&gt;, then the name server MUST
   include the NSEC RR for &lt;SNAME, SCLASS&gt; along with its associated
   RRSIG RR(s) in the Authority section of the response (see <a href="#section-3.1.1">Section</a>
   <a href="#section-3.1.1">3.1.1</a>).  If space does not permit inclusion of the NSEC RR or its
   associated RRSIG RR(s), the name server MUST set the TC bit (see
   <a href="#section-3.1.1">Section 3.1.1</a>).

   Since the search name exists, wildcard name expansion does not apply
   to this query, and a single signed NSEC RR suffices to prove that the
   requested RR type does not exist.

<span class="h5"><a class="selflink" id="section-3.1.3.2" href="#section-3.1.3.2">3.1.3.2</a>.  Including NSEC RRs: Name Error Response</span>

   If the zone does not contain any RRsets matching &lt;SNAME, SCLASS&gt;
   either exactly or via wildcard name expansion, then the name server
   MUST include the following NSEC RRs in the Authority section, along
   with their associated RRSIG RRs:

   o  An NSEC RR proving that there is no exact match for &lt;SNAME,
      SCLASS&gt;.

   o  An NSEC RR proving that the zone contains no RRsets that would
      match &lt;SNAME, SCLASS&gt; via wildcard name expansion.

   In some cases, a single NSEC RR may prove both of these points.  If
   it does, the name server SHOULD only include the NSEC RR and its
   RRSIG RR(s) once in the Authority section.

   If space does not permit inclusion of these NSEC and RRSIG RRs, the
   name server MUST set the TC bit (see <a href="#section-3.1.1">Section 3.1.1</a>).

   The owner names of these NSEC and RRSIG RRs are not subject to
   wildcard name expansion when these RRs are included in the Authority
   section of the response.

   Note that this form of response includes cases in which SNAME
   corresponds to an empty non-terminal name within the zone (a name
   that is not the owner name for any RRset but that is the parent name
   of one or more RRsets).

<span class="h5"><a class="selflink" id="section-3.1.3.3" href="#section-3.1.3.3">3.1.3.3</a>.  Including NSEC RRs: Wildcard Answer Response</span>

   If the zone does not contain any RRsets that exactly match &lt;SNAME,
   SCLASS&gt; but does contain an RRset that matches &lt;SNAME, SCLASS, STYPE&gt;
   via wildcard name expansion, the name server MUST include the



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   wildcard-expanded answer and the corresponding wildcard-expanded
   RRSIG RRs in the Answer section and MUST include in the Authority
   section an NSEC RR and associated RRSIG RR(s) proving that the zone
   does not contain a closer match for &lt;SNAME, SCLASS&gt;.  If space does
   not permit inclusion of the answer, NSEC and RRSIG RRs, the name
   server MUST set the TC bit (see <a href="#section-3.1.1">Section 3.1.1</a>).

<span class="h5"><a class="selflink" id="section-3.1.3.4" href="#section-3.1.3.4">3.1.3.4</a>.  Including NSEC RRs: Wildcard No Data Response</span>

   This case is a combination of the previous cases.  The zone does not
   contain an exact match for &lt;SNAME, SCLASS&gt;, and although the zone
   does contain RRsets that match &lt;SNAME, SCLASS&gt; via wildcard
   expansion, none of those RRsets matches STYPE.  The name server MUST
   include the following NSEC RRs in the Authority section, along with
   their associated RRSIG RRs:

   o  An NSEC RR proving that there are no RRsets matching STYPE at the
      wildcard owner name that matched &lt;SNAME, SCLASS&gt; via wildcard
      expansion.

   o  An NSEC RR proving that there are no RRsets in the zone that would
      have been a closer match for &lt;SNAME, SCLASS&gt;.

   In some cases, a single NSEC RR may prove both of these points.  If
   it does, the name server SHOULD only include the NSEC RR and its
   RRSIG RR(s) once in the Authority section.

   The owner names of these NSEC and RRSIG RRs are not subject to
   wildcard name expansion when these RRs are included in the Authority
   section of the response.

   If space does not permit inclusion of these NSEC and RRSIG RRs, the
   name server MUST set the TC bit (see <a href="#section-3.1.1">Section 3.1.1</a>).

<span class="h5"><a class="selflink" id="section-3.1.3.5" href="#section-3.1.3.5">3.1.3.5</a>.  Finding the Right NSEC RRs</span>

   As explained above, there are several situations in which a
   security-aware authoritative name server has to locate an NSEC RR
   that proves that no RRsets matching a particular SNAME exist.
   Locating such an NSEC RR within an authoritative zone is relatively
   simple, at least in concept.  The following discussion assumes that
   the name server is authoritative for the zone that would have held
   the non-existent RRsets matching SNAME.  The algorithm below is
   written for clarity, not for efficiency.

   To find the NSEC that proves that no RRsets matching name N exist in
   the zone Z that would have held them, construct a sequence, S,
   consisting of the owner names of every RRset in Z, sorted into



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   canonical order ([<a href="./rfc4034" title="&quot;Resource Records for DNS Security Extensions&quot;">RFC4034</a>]), with no duplicate names.  Find the name
   M that would have immediately preceded N in S if any RRsets with
   owner name N had existed.  M is the owner name of the NSEC RR that
   proves that no RRsets exist with owner name N.

   The algorithm for finding the NSEC RR that proves that a given name
   is not covered by any applicable wildcard is similar but requires an
   extra step.  More precisely, the algorithm for finding the NSEC
   proving that no RRsets exist with the applicable wildcard name is
   precisely the same as the algorithm for finding the NSEC RR that
   proves that RRsets with any other owner name do not exist.  The part
   that's missing is a method of determining the name of the non-
   existent applicable wildcard.  In practice, this is easy, because the
   authoritative name server has already checked for the presence of
   precisely this wildcard name as part of step (1)(c) of the normal
   lookup algorithm described in <a href="./rfc1034#section-4.3.2">Section&nbsp;4.3.2 of [RFC1034]</a>.

<span class="h4"><a class="selflink" id="section-3.1.4" href="#section-3.1.4">3.1.4</a>.  Including DS RRs in a Response</span>

   When responding to a query that has the DO bit set, a security-aware
   authoritative name server returning a referral includes DNSSEC data
   along with the NS RRset.

   If a DS RRset is present at the delegation point, the name server
   MUST return both the DS RRset and its associated RRSIG RR(s) in the
   Authority section along with the NS RRset.

   If no DS RRset is present at the delegation point, the name server
   MUST return both the NSEC RR that proves that the DS RRset is not
   present and the NSEC RR's associated RRSIG RR(s) along with the NS
   RRset.  The name server MUST place the NS RRset before the NSEC RRset
   and its associated RRSIG RR(s).

   Including these DS, NSEC, and RRSIG RRs increases the size of
   referral messages and may cause some or all glue RRs to be omitted.
   If space does not permit inclusion of the DS or NSEC RRset and
   associated RRSIG RRs, the name server MUST set the TC bit (see
   <a href="#section-3.1.1">Section 3.1.1</a>).

<span class="h5"><a class="selflink" id="section-3.1.4.1" href="#section-3.1.4.1">3.1.4.1</a>.  Responding to Queries for DS RRs</span>

   The DS resource record type is unusual in that it appears only on the
   parent zone's side of a zone cut.  For example, the DS RRset for the
   delegation of "foo.example" is stored in the "example" zone rather
   than in the "foo.example" zone.  This requires special processing
   rules for both name servers and resolvers, as the name server for the
   child zone is authoritative for the name at the zone cut by the
   normal DNS rules but the child zone does not contain the DS RRset.



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   A security-aware resolver sends queries to the parent zone when
   looking for a needed DS RR at a delegation point (see <a href="#section-4.2">Section 4.2</a>).
   However, special rules are necessary to avoid confusing
   security-oblivious resolvers which might become involved in
   processing such a query (for example, in a network configuration that
   forces a security-aware resolver to channel its queries through a
   security-oblivious recursive name server).  The rest of this section
   describes how a security-aware name server processes DS queries in
   order to avoid this problem.

   The need for special processing by a security-aware name server only
   arises when all the following conditions are met:

   o  The name server has received a query for the DS RRset at a zone
      cut.

   o  The name server is authoritative for the child zone.

   o  The name server is not authoritative for the parent zone.

   o  The name server does not offer recursion.

   In all other cases, the name server either has some way of obtaining
   the DS RRset or could not have been expected to have the DS RRset
   even by the pre-DNSSEC processing rules, so the name server can
   return either the DS RRset or an error response according to the
   normal processing rules.

   If all the above conditions are met, however, the name server is
   authoritative for SNAME but cannot supply the requested RRset.  In
   this case, the name server MUST return an authoritative "no data"
   response showing that the DS RRset does not exist in the child zone's
   apex.  See <a href="#appendix-B.8">Appendix B.8</a> for an example of such a response.

<span class="h4"><a class="selflink" id="section-3.1.5" href="#section-3.1.5">3.1.5</a>.  Responding to Queries for Type AXFR or IXFR</span>

   DNSSEC does not change the DNS zone transfer process.  A signed zone
   will contain RRSIG, DNSKEY, NSEC, and DS resource records, but these
   records have no special meaning with respect to a zone transfer
   operation.

   An authoritative name server is not required to verify that a zone is
   properly signed before sending or accepting a zone transfer.
   However, an authoritative name server MAY choose to reject the entire
   zone transfer if the zone fails to meet any of the signing
   requirements described in <a href="#section-2">Section 2</a>.  The primary objective of a zone
   transfer is to ensure that all authoritative name servers have
   identical copies of the zone.  An authoritative name server that



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   chooses to perform its own zone validation MUST NOT selectively
   reject some RRs and accept others.

   DS RRsets appear only on the parental side of a zone cut and are
   authoritative data in the parent zone.  As with any other
   authoritative RRset, the DS RRset MUST be included in zone transfers
   of the zone in which the RRset is authoritative data.  In the case of
   the DS RRset, this is the parent zone.

   NSEC RRs appear in both the parent and child zones at a zone cut and
   are authoritative data in both the parent and child zones.  The
   parental and child NSEC RRs at a zone cut are never identical to each
   other, as the NSEC RR in the child zone's apex will always indicate
   the presence of the child zone's SOA RR whereas the parental NSEC RR
   at the zone cut will never indicate the presence of an SOA RR.  As
   with any other authoritative RRs, NSEC RRs MUST be included in zone
   transfers of the zone in which they are authoritative data.  The
   parental NSEC RR at a zone cut MUST be included in zone transfers of
   the parent zone, and the NSEC at the zone apex of the child zone MUST
   be included in zone transfers of the child zone.

   RRSIG RRs appear in both the parent and child zones at a zone cut and
   are authoritative in whichever zone contains the authoritative RRset
   for which the RRSIG RR provides the signature.  That is, the RRSIG RR
   for a DS RRset or a parental NSEC RR at a zone cut will be
   authoritative in the parent zone, and the RRSIG for any RRset in the
   child zone's apex will be authoritative in the child zone.  Parental
   and child RRSIG RRs at a zone cut will never be identical to each
   other, as the Signer's Name field of an RRSIG RR in the child zone's
   apex will indicate a DNSKEY RR in the child zone's apex whereas the
   same field of a parental RRSIG RR at the zone cut will indicate a
   DNSKEY RR in the parent zone's apex.  As with any other authoritative
   RRs, RRSIG RRs MUST be included in zone transfers of the zone in
   which they are authoritative data.

<span class="h4"><a class="selflink" id="section-3.1.6" href="#section-3.1.6">3.1.6</a>.  The AD and CD Bits in an Authoritative Response</span>

   The CD and AD bits are designed for use in communication between
   security-aware resolvers and security-aware recursive name servers.
   These bits are for the most part not relevant to query processing by
   security-aware authoritative name servers.

   A security-aware name server does not perform signature validation
   for authoritative data during query processing, even when the CD bit
   is clear.  A security-aware name server SHOULD clear the CD bit when
   composing an authoritative response.





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   A security-aware name server MUST NOT set the AD bit in a response
   unless the name server considers all RRsets in the Answer and
   Authority sections of the response to be authentic.  A security-aware
   name server's local policy MAY consider data from an authoritative
   zone to be authentic without further validation.  However, the name
   server MUST NOT do so unless the name server obtained the
   authoritative zone via secure means (such as a secure zone transfer
   mechanism) and MUST NOT do so unless this behavior has been
   configured explicitly.

   A security-aware name server that supports recursion MUST follow the
   rules for the CD and AD bits given in <a href="#section-3.2">Section 3.2</a> when generating a
   response that involves data obtained via recursion.

<span class="h3"><a class="selflink" id="section-3.2" href="#section-3.2">3.2</a>.  Recursive Name Servers</span>

   As explained in [<a href="./rfc4033" title="&quot;DNS Security Introduction and Requirements&quot;">RFC4033</a>], a security-aware recursive name server is
   an entity that acts in both the security-aware name server and
   security-aware resolver roles.  This section uses the terms "name
   server side" and "resolver side" to refer to the code within a
   security-aware recursive name server that implements the
   security-aware name server role and the code that implements the
   security-aware resolver role, respectively.

   The resolver side follows the usual rules for caching and negative
   caching that would apply to any security-aware resolver.

<span class="h4"><a class="selflink" id="section-3.2.1" href="#section-3.2.1">3.2.1</a>.  The DO Bit</span>

   The resolver side of a security-aware recursive name server MUST set
   the DO bit when sending requests, regardless of the state of the DO
   bit in the initiating request received by the name server side.  If
   the DO bit in an initiating query is not set, the name server side
   MUST strip any authenticating DNSSEC RRs from the response but MUST
   NOT strip any DNSSEC RR types that the initiating query explicitly
   requested.

<span class="h4"><a class="selflink" id="section-3.2.2" href="#section-3.2.2">3.2.2</a>.  The CD Bit</span>

   The CD bit exists in order to allow a security-aware resolver to
   disable signature validation in a security-aware name server's
   processing of a particular query.

   The name server side MUST copy the setting of the CD bit from a query
   to the corresponding response.

   The name server side of a security-aware recursive name server MUST
   pass the state of the CD bit to the resolver side along with the rest



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   of an initiating query, so that the resolver side will know whether
   it is required to verify the response data it returns to the name
   server side.  If the CD bit is set, it indicates that the originating
   resolver is willing to perform whatever authentication its local
   policy requires.  Thus, the resolver side of the recursive name
   server need not perform authentication on the RRsets in the response.
   When the CD bit is set, the recursive name server SHOULD, if
   possible, return the requested data to the originating resolver, even
   if the recursive name server's local authentication policy would
   reject the records in question.  That is, by setting the CD bit, the
   originating resolver has indicated that it takes responsibility for
   performing its own authentication, and the recursive name server
   should not interfere.

   If the resolver side implements a BAD cache (see <a href="#section-4.7">Section 4.7</a>) and the
   name server side receives a query that matches an entry in the
   resolver side's BAD cache, the name server side's response depends on
   the state of the CD bit in the original query.  If the CD bit is set,
   the name server side SHOULD return the data from the BAD cache; if
   the CD bit is not set, the name server side MUST return RCODE 2
   (server failure).

   The intent of the above rule is to provide the raw data to clients
   that are capable of performing their own signature verification
   checks while protecting clients that depend on the resolver side of a
   security-aware recursive name server to perform such checks.  Several
   of the possible reasons why signature validation might fail involve
   conditions that may not apply equally to the recursive name server
   and the client that invoked it.  For example, the recursive name
   server's clock may be set incorrectly, or the client may have
   knowledge of a relevant island of security that the recursive name
   server does not share.  In such cases, "protecting" a client that is
   capable of performing its own signature validation from ever seeing
   the "bad" data does not help the client.

<span class="h4"><a class="selflink" id="section-3.2.3" href="#section-3.2.3">3.2.3</a>.  The AD Bit</span>

   The name server side of a security-aware recursive name server MUST
   NOT set the AD bit in a response unless the name server considers all
   RRsets in the Answer and Authority sections of the response to be
   authentic.  The name server side SHOULD set the AD bit if and only if
   the resolver side considers all RRsets in the Answer section and any
   relevant negative response RRs in the Authority section to be
   authentic.  The resolver side MUST follow the procedure described in
   <a href="#section-5">Section 5</a> to determine whether the RRs in question are authentic.
   However, for backward compatibility, a recursive name server MAY set
   the AD bit when a response includes unsigned CNAME RRs if those CNAME




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   RRs demonstrably could have been synthesized from an authentic DNAME
   RR that is also included in the response according to the synthesis
   rules described in [<a href="./rfc2672" title="&quot;Non-Terminal DNS Name Redirection&quot;">RFC2672</a>].

<span class="h3"><a class="selflink" id="section-3.3" href="#section-3.3">3.3</a>.  Example DNSSEC Responses</span>

   See <a href="#appendix-B">Appendix B</a> for example response packets.

<span class="h2"><a class="selflink" id="section-4" href="#section-4">4</a>.  Resolving</span>

   This section describes the behavior of entities that include
   security-aware resolver functions.  In many cases such functions will
   be part of a security-aware recursive name server, but a stand-alone
   security-aware resolver has many of the same requirements.  Functions
   specific to security-aware recursive name servers are described in
   <a href="#section-3.2">Section 3.2</a>.

<span class="h3"><a class="selflink" id="section-4.1" href="#section-4.1">4.1</a>.  EDNS Support</span>

   A security-aware resolver MUST include an EDNS ([<a href="./rfc2671" title="&quot;Extension Mechanisms for DNS (EDNS0)&quot;">RFC2671</a>]) OPT
   pseudo-RR with the DO ([<a href="./rfc3225" title="&quot;Indicating Resolver Support of DNSSEC&quot;">RFC3225</a>]) bit set when sending queries.

   A security-aware resolver MUST support a message size of at least
   1220 octets, SHOULD support a message size of 4000 octets, and MUST
   use the "sender's UDP payload size" field in the EDNS OPT pseudo-RR
   to advertise the message size that it is willing to accept.  A
   security-aware resolver's IP layer MUST handle fragmented UDP packets
   correctly regardless of whether any such fragmented packets were
   received via IPv4 or IPv6.  Please see [<a href="./rfc1122" title="&quot;Requirements for Internet Hosts - Communication Layers&quot;">RFC1122</a>], [<a href="./rfc2460" title="&quot;Internet Protocol, Version 6 (IPv6) Specification&quot;">RFC2460</a>], and
   [<a href="./rfc3226" title="&quot;DNSSEC and IPv6 A6 aware server/resolver message size requirements&quot;">RFC3226</a>] for discussion of these requirements.

<span class="h3"><a class="selflink" id="section-4.2" href="#section-4.2">4.2</a>.  Signature Verification Support</span>

   A security-aware resolver MUST support the signature verification
   mechanisms described in <a href="#section-5">Section 5</a> and SHOULD apply them to every
   received response, except when:

   o  the security-aware resolver is part of a security-aware recursive
      name server, and the response is the result of recursion on behalf
      of a query received with the CD bit set;

   o  the response is the result of a query generated directly via some
      form of application interface that instructed the security-aware
      resolver not to perform validation for this query; or

   o  validation for this query has been disabled by local policy.





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   A security-aware resolver's support for signature verification MUST
   include support for verification of wildcard owner names.

   Security-aware resolvers MAY query for missing security RRs in an
   attempt to perform validation; implementations that choose to do so
   must be aware that the answers received may not be sufficient to
   validate the original response.  For example, a zone update may have
   changed (or deleted) the desired information between the original and
   follow-up queries.

   When attempting to retrieve missing NSEC RRs that reside on the
   parental side at a zone cut, a security-aware iterative-mode resolver
   MUST query the name servers for the parent zone, not the child zone.

   When attempting to retrieve a missing DS, a security-aware
   iterative-mode resolver MUST query the name servers for the parent
   zone, not the child zone.  As explained in <a href="#section-3.1.4.1">Section 3.1.4.1</a>,
   security-aware name servers need to apply special processing rules to
   handle the DS RR, and in some situations the resolver may also need
   to apply special rules to locate the name servers for the parent zone
   if the resolver does not already have the parent's NS RRset.  To
   locate the parent NS RRset, the resolver can start with the
   delegation name, strip off the leftmost label, and query for an NS
   RRset by that name.  If no NS RRset is present at that name, the
   resolver then strips off the leftmost remaining label and retries the
   query for that name, repeating this process of walking up the tree
   until it either finds the NS RRset or runs out of labels.

<span class="h3"><a class="selflink" id="section-4.3" href="#section-4.3">4.3</a>.  Determining Security Status of Data</span>

   A security-aware resolver MUST be able to determine whether it should
   expect a particular RRset to be signed.  More precisely, a
   security-aware resolver must be able to distinguish between four
   cases:

   Secure: An RRset for which the resolver is able to build a chain of
      signed DNSKEY and DS RRs from a trusted security anchor to the
      RRset.  In this case, the RRset should be signed and is subject to
      signature validation, as described above.

   Insecure: An RRset for which the resolver knows that it has no chain
      of signed DNSKEY and DS RRs from any trusted starting point to the
      RRset.  This can occur when the target RRset lies in an unsigned
      zone or in a descendent of an unsigned zone.  In this case, the
      RRset may or may not be signed, but the resolver will not be able
      to verify the signature.





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   Bogus: An RRset for which the resolver believes that it ought to be
      able to establish a chain of trust but for which it is unable to
      do so, either due to signatures that for some reason fail to
      validate or due to missing data that the relevant DNSSEC RRs
      indicate should be present.  This case may indicate an attack but
      may also indicate a configuration error or some form of data
      corruption.

   Indeterminate: An RRset for which the resolver is not able to
      determine whether the RRset should be signed, as the resolver is
      not able to obtain the necessary DNSSEC RRs.  This can occur when
      the security-aware resolver is not able to contact security-aware
      name servers for the relevant zones.

<span class="h3"><a class="selflink" id="section-4.4" href="#section-4.4">4.4</a>.  Configured Trust Anchors</span>

   A security-aware resolver MUST be capable of being configured with at
   least one trusted public key or DS RR and SHOULD be capable of being
   configured with multiple trusted public keys or DS RRs.  Since a
   security-aware resolver will not be able to validate signatures
   without such a configured trust anchor, the resolver SHOULD have some
   reasonably robust mechanism for obtaining such keys when it boots;
   examples of such a mechanism would be some form of non-volatile
   storage (such as a disk drive) or some form of trusted local network
   configuration mechanism.

   Note that trust anchors also cover key material that is updated in a
   secure manner.  This secure manner could be through physical media, a
   key exchange protocol, or some other out-of-band means.

<span class="h3"><a class="selflink" id="section-4.5" href="#section-4.5">4.5</a>.  Response Caching</span>

   A security-aware resolver SHOULD cache each response as a single
   atomic entry containing the entire answer, including the named RRset
   and any associated DNSSEC RRs.  The resolver SHOULD discard the
   entire atomic entry when any of the RRs contained in it expire.  In
   most cases the appropriate cache index for the atomic entry will be
   the triple &lt;QNAME, QTYPE, QCLASS&gt;, but in cases such as the response
   form described in <a href="#section-3.1.3.2">Section 3.1.3.2</a> the appropriate cache index will be
   the double &lt;QNAME,QCLASS&gt;.

   The reason for these recommendations is that, between the initial
   query and the expiration of the data from the cache, the
   authoritative data might have been changed (for example, via dynamic
   update).






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   There are two situations for which this is relevant:

   1.  By using the RRSIG record, it is possible to deduce that an
       answer was synthesized from a wildcard.  A security-aware
       recursive name server could store this wildcard data and use it
       to generate positive responses to queries other than the name for
       which the original answer was first received.

   2.  NSEC RRs received to prove the non-existence of a name could be
       reused by a security-aware resolver to prove the non-existence of
       any name in the name range it spans.

   In theory, a resolver could use wildcards or NSEC RRs to generate
   positive and negative responses (respectively) until the TTL or
   signatures on the records in question expire.  However, it seems
   prudent for resolvers to avoid blocking new authoritative data or
   synthesizing new data on their own.  Resolvers that follow this
   recommendation will have a more consistent view of the namespace.

<span class="h3"><a class="selflink" id="section-4.6" href="#section-4.6">4.6</a>.  Handling of the CD and AD Bits</span>

   A security-aware resolver MAY set a query's CD bit in order to
   indicate that the resolver takes responsibility for performing
   whatever authentication its local policy requires on the RRsets in
   the response.  See <a href="#section-3.2">Section 3.2</a> for the effect this bit has on the
   behavior of security-aware recursive name servers.

   A security-aware resolver MUST clear the AD bit when composing query
   messages to protect against buggy name servers that blindly copy
   header bits that they do not understand from the query message to the
   response message.

   A resolver MUST disregard the meaning of the CD and AD bits in a
   response unless the response was obtained by using a secure channel
   or the resolver was specifically configured to regard the message
   header bits without using a secure channel.

<span class="h3"><a class="selflink" id="section-4.7" href="#section-4.7">4.7</a>.  Caching BAD Data</span>

   While many validation errors will be transient, some are likely to be
   more persistent, such as those caused by administrative error
   (failure to re-sign a zone, clock skew, and so forth).  Since
   requerying will not help in these cases, validating resolvers might
   generate a significant amount of unnecessary DNS traffic as a result
   of repeated queries for RRsets with persistent validation failures.

   To prevent such unnecessary DNS traffic, security-aware resolvers MAY
   cache data with invalid signatures, with some restrictions.



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   Conceptually, caching such data is similar to negative caching
   ([<a href="./rfc2308" title="&quot;Negative Caching of DNS Queries (DNS NCACHE)&quot;">RFC2308</a>]), except that instead of caching a valid negative
   response, the resolver is caching the fact that a particular answer
   failed to validate.  This document refers to a cache of data with
   invalid signatures as a "BAD cache".

   Resolvers that implement a BAD cache MUST take steps to prevent the
   cache from being useful as a denial-of-service attack amplifier,
   particularly the following:

   o  Since RRsets that fail to validate do not have trustworthy TTLs,
      the implementation MUST assign a TTL.  This TTL SHOULD be small,
      in order to mitigate the effect of caching the results of an
      attack.

   o  In order to prevent caching of a transient validation failure
      (which might be the result of an attack), resolvers SHOULD track
      queries that result in validation failures and SHOULD only answer
      from the BAD cache after the number of times that responses to
      queries for that particular &lt;QNAME, QTYPE, QCLASS&gt; have failed to
      validate exceeds a threshold value.

   Resolvers MUST NOT return RRsets from the BAD cache unless the
   resolver is not required to validate the signatures of the RRsets in
   question under the rules given in <a href="#section-4.2">Section 4.2</a> of this document.  See
   <a href="#section-3.2.2">Section 3.2.2</a> for discussion of how the responses returned by a
   security-aware recursive name server interact with a BAD cache.

<span class="h3"><a class="selflink" id="section-4.8" href="#section-4.8">4.8</a>.  Synthesized CNAMEs</span>

   A validating security-aware resolver MUST treat the signature of a
   valid signed DNAME RR as also covering unsigned CNAME RRs that could
   have been synthesized from the DNAME RR, as described in [<a href="./rfc2672" title="&quot;Non-Terminal DNS Name Redirection&quot;">RFC2672</a>],
   at least to the extent of not rejecting a response message solely
   because it contains such CNAME RRs.  The resolver MAY retain such
   CNAME RRs in its cache or in the answers it hands back, but is not
   required to do so.

<span class="h3"><a class="selflink" id="section-4.9" href="#section-4.9">4.9</a>.  Stub Resolvers</span>

   A security-aware stub resolver MUST support the DNSSEC RR types, at
   least to the extent of not mishandling responses just because they
   contain DNSSEC RRs.








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<span class="h4"><a class="selflink" id="section-4.9.1" href="#section-4.9.1">4.9.1</a>.  Handling of the DO Bit</span>

   A non-validating security-aware stub resolver MAY include the DNSSEC
   RRs returned by a security-aware recursive name server as part of the
   data that the stub resolver hands back to the application that
   invoked it, but is not required to do so.  A non-validating stub
   resolver that seeks to do this will need to set the DO bit in order
   to receive DNSSEC RRs from the recursive name server.

   A validating security-aware stub resolver MUST set the DO bit,
   because otherwise it will not receive the DNSSEC RRs it needs to
   perform signature validation.

<span class="h4"><a class="selflink" id="section-4.9.2" href="#section-4.9.2">4.9.2</a>.  Handling of the CD Bit</span>

   A non-validating security-aware stub resolver SHOULD NOT set the CD
   bit when sending queries unless it is requested by the application
   layer, as by definition, a non-validating stub resolver depends on
   the security-aware recursive name server to perform validation on its
   behalf.

   A validating security-aware stub resolver SHOULD set the CD bit,
   because otherwise the security-aware recursive name server will
   answer the query using the name server's local policy, which may
   prevent the stub resolver from receiving data that would be
   acceptable to the stub resolver's local policy.

<span class="h4"><a class="selflink" id="section-4.9.3" href="#section-4.9.3">4.9.3</a>.  Handling of the AD Bit</span>

   A non-validating security-aware stub resolver MAY chose to examine
   the setting of the AD bit in response messages that it receives in
   order to determine whether the security-aware recursive name server
   that sent the response claims to have cryptographically verified the
   data in the Answer and Authority sections of the response message.
   Note, however, that the responses received by a security-aware stub
   resolver are heavily dependent on the local policy of the
   security-aware recursive name server.  Therefore, there may be little
   practical value in checking the status of the AD bit, except perhaps
   as a debugging aid.  In any case, a security-aware stub resolver MUST
   NOT place any reliance on signature validation allegedly performed on
   its behalf, except when the security-aware stub resolver obtained the
   data in question from a trusted security-aware recursive name server
   via a secure channel.

   A validating security-aware stub resolver SHOULD NOT examine the
   setting of the AD bit in response messages, as, by definition, the
   stub resolver performs its own signature validation regardless of the
   setting of the AD bit.



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<span class="h2"><a class="selflink" id="section-5" href="#section-5">5</a>.  Authenticating DNS Responses</span>

   To use DNSSEC RRs for authentication, a security-aware resolver
   requires configured knowledge of at least one authenticated DNSKEY or
   DS RR.  The process for obtaining and authenticating this initial
   trust anchor is achieved via some external mechanism.  For example, a
   resolver could use some off-line authenticated exchange to obtain a
   zone's DNSKEY RR or to obtain a DS RR that identifies and
   authenticates a zone's DNSKEY RR.  The remainder of this section
   assumes that the resolver has somehow obtained an initial set of
   trust anchors.

   An initial DNSKEY RR can be used to authenticate a zone's apex DNSKEY
   RRset.  To authenticate an apex DNSKEY RRset by using an initial key,
   the resolver MUST:

   1.  verify that the initial DNSKEY RR appears in the apex DNSKEY
       RRset, and that the DNSKEY RR has the Zone Key Flag (DNSKEY RDATA
       bit 7) set; and

   2.  verify that there is some RRSIG RR that covers the apex DNSKEY
       RRset, and that the combination of the RRSIG RR and the initial
       DNSKEY RR authenticates the DNSKEY RRset.  The process for using
       an RRSIG RR to authenticate an RRset is described in <a href="#section-5.3">Section 5.3</a>.

   Once the resolver has authenticated the apex DNSKEY RRset by using an
   initial DNSKEY RR, delegations from that zone can be authenticated by
   using DS RRs.  This allows a resolver to start from an initial key
   and use DS RRsets to proceed recursively down the DNS tree, obtaining
   other apex DNSKEY RRsets.  If the resolver were configured with a
   root DNSKEY RR, and if every delegation had a DS RR associated with
   it, then the resolver could obtain and validate any apex DNSKEY
   RRset.  The process of using DS RRs to authenticate referrals is
   described in <a href="#section-5.2">Section 5.2</a>.

   <a href="#section-5.3">Section 5.3</a> shows how the resolver can use DNSKEY RRs in the apex
   DNSKEY RRset and RRSIG RRs from the zone to authenticate any other
   RRsets in the zone once the resolver has authenticated a zone's apex
   DNSKEY RRset.  <a href="#section-5.4">Section 5.4</a> shows how the resolver can use
   authenticated NSEC RRsets from the zone to prove that an RRset is not
   present in the zone.

   When a resolver indicates support for DNSSEC (by setting the DO bit),
   a security-aware name server should attempt to provide the necessary
   DNSKEY, RRSIG, NSEC, and DS RRsets in a response (see <a href="#section-3">Section 3</a>).
   However, a security-aware resolver may still receive a response that
   lacks the appropriate DNSSEC RRs, whether due to configuration issues
   such as an upstream security-oblivious recursive name server that



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   accidentally interferes with DNSSEC RRs or due to a deliberate attack
   in which an adversary forges a response, strips DNSSEC RRs from a
   response, or modifies a query so that DNSSEC RRs appear not to be
   requested.  The absence of DNSSEC data in a response MUST NOT by
   itself be taken as an indication that no authentication information
   exists.

   A resolver SHOULD expect authentication information from signed
   zones.  A resolver SHOULD believe that a zone is signed if the
   resolver has been configured with public key information for the
   zone, or if the zone's parent is signed and the delegation from the
   parent contains a DS RRset.

<span class="h3"><a class="selflink" id="section-5.1" href="#section-5.1">5.1</a>.  Special Considerations for Islands of Security</span>

   Islands of security (see [<a href="./rfc4033" title="&quot;DNS Security Introduction and Requirements&quot;">RFC4033</a>]) are signed zones for which it is
   not possible to construct an authentication chain to the zone from
   its parent.  Validating signatures within an island of security
   requires that the validator have some other means of obtaining an
   initial authenticated zone key for the island.  If a validator cannot
   obtain such a key, it SHOULD switch to operating as if the zones in
   the island of security are unsigned.

   All the normal processes for validating responses apply to islands of
   security.  The only difference between normal validation and
   validation within an island of security is in how the validator
   obtains a trust anchor for the authentication chain.

<span class="h3"><a class="selflink" id="section-5.2" href="#section-5.2">5.2</a>.  Authenticating Referrals</span>

   Once the apex DNSKEY RRset for a signed parent zone has been
   authenticated, DS RRsets can be used to authenticate the delegation
   to a signed child zone.  A DS RR identifies a DNSKEY RR in the child
   zone's apex DNSKEY RRset and contains a cryptographic digest of the
   child zone's DNSKEY RR.  Use of a strong cryptographic digest
   algorithm ensures that it is computationally infeasible for an
   adversary to generate a DNSKEY RR that matches the digest.  Thus,
   authenticating the digest allows a resolver to authenticate the
   matching DNSKEY RR.  The resolver can then use this child DNSKEY RR
   to authenticate the entire child apex DNSKEY RRset.

   Given a DS RR for a delegation, the child zone's apex DNSKEY RRset
   can be authenticated if all of the following hold:

   o  The DS RR has been authenticated using some DNSKEY RR in the
      parent's apex DNSKEY RRset (see <a href="#section-5.3">Section 5.3</a>).





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   o  The Algorithm and Key Tag in the DS RR match the Algorithm field
      and the key tag of a DNSKEY RR in the child zone's apex DNSKEY
      RRset, and, when the DNSKEY RR's owner name and RDATA are hashed
      using the digest algorithm specified in the DS RR's Digest Type
      field, the resulting digest value matches the Digest field of the
      DS RR.

   o  The matching DNSKEY RR in the child zone has the Zone Flag bit
      set, the corresponding private key has signed the child zone's
      apex DNSKEY RRset, and the resulting RRSIG RR authenticates the
      child zone's apex DNSKEY RRset.

   If the referral from the parent zone did not contain a DS RRset, the
   response should have included a signed NSEC RRset proving that no DS
   RRset exists for the delegated name (see <a href="#section-3.1.4">Section 3.1.4</a>).  A
   security-aware resolver MUST query the name servers for the parent
   zone for the DS RRset if the referral includes neither a DS RRset nor
   a NSEC RRset proving that the DS RRset does not exist (see <a href="#section-4">Section</a>
   <a href="#section-4">4</a>).

   If the validator authenticates an NSEC RRset that proves that no DS
   RRset is present for this zone, then there is no authentication path
   leading from the parent to the child.  If the resolver has an initial
   DNSKEY or DS RR that belongs to the child zone or to any delegation
   below the child zone, this initial DNSKEY or DS RR MAY be used to
   re-establish an authentication path.  If no such initial DNSKEY or DS
   RR exists, the validator cannot authenticate RRsets in or below the
   child zone.

   If the validator does not support any of the algorithms listed in an
   authenticated DS RRset, then the resolver has no supported
   authentication path leading from the parent to the child.  The
   resolver should treat this case as it would the case of an
   authenticated NSEC RRset proving that no DS RRset exists, as
   described above.

   Note that, for a signed delegation, there are two NSEC RRs associated
   with the delegated name.  One NSEC RR resides in the parent zone and
   can be used to prove whether a DS RRset exists for the delegated
   name.  The second NSEC RR resides in the child zone and identifies
   which RRsets are present at the apex of the child zone.  The parent
   NSEC RR and child NSEC RR can always be distinguished because the SOA
   bit will be set in the child NSEC RR and clear in the parent NSEC RR.
   A security-aware resolver MUST use the parent NSEC RR when attempting
   to prove that a DS RRset does not exist.






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   If the resolver does not support any of the algorithms listed in an
   authenticated DS RRset, then the resolver will not be able to verify
   the authentication path to the child zone.  In this case, the
   resolver SHOULD treat the child zone as if it were unsigned.

<span class="h3"><a class="selflink" id="section-5.3" href="#section-5.3">5.3</a>.  Authenticating an RRset with an RRSIG RR</span>

   A validator can use an RRSIG RR and its corresponding DNSKEY RR to
   attempt to authenticate RRsets.  The validator first checks the RRSIG
   RR to verify that it covers the RRset, has a valid time interval, and
   identifies a valid DNSKEY RR.  The validator then constructs the
   canonical form of the signed data by appending the RRSIG RDATA
   (excluding the Signature Field) with the canonical form of the
   covered RRset.  Finally, the validator uses the public key and
   signature to authenticate the signed data.  Sections <a href="#section-5.3.1">5.3.1</a>, <a href="#section-5.3.2">5.3.2</a>,
   and 5.3.3 describe each step in detail.

<span class="h4"><a class="selflink" id="section-5.3.1" href="#section-5.3.1">5.3.1</a>.  Checking the RRSIG RR Validity</span>

   A security-aware resolver can use an RRSIG RR to authenticate an
   RRset if all of the following conditions hold:

   o  The RRSIG RR and the RRset MUST have the same owner name and the
      same class.

   o  The RRSIG RR's Signer's Name field MUST be the name of the zone
      that contains the RRset.

   o  The RRSIG RR's Type Covered field MUST equal the RRset's type.

   o  The number of labels in the RRset owner name MUST be greater than
      or equal to the value in the RRSIG RR's Labels field.

   o  The validator's notion of the current time MUST be less than or
      equal to the time listed in the RRSIG RR's Expiration field.

   o  The validator's notion of the current time MUST be greater than or
      equal to the time listed in the RRSIG RR's Inception field.

   o  The RRSIG RR's Signer's Name, Algorithm, and Key Tag fields MUST
      match the owner name, algorithm, and key tag for some DNSKEY RR in
      the zone's apex DNSKEY RRset.

   o  The matching DNSKEY RR MUST be present in the zone's apex DNSKEY
      RRset, and MUST have the Zone Flag bit (DNSKEY RDATA Flag bit 7)
      set.





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   It is possible for more than one DNSKEY RR to match the conditions
   above.  In this case, the validator cannot predetermine which DNSKEY
   RR to use to authenticate the signature, and it MUST try each
   matching DNSKEY RR until either the signature is validated or the
   validator has run out of matching public keys to try.

   Note that this authentication process is only meaningful if the
   validator authenticates the DNSKEY RR before using it to validate
   signatures.  The matching DNSKEY RR is considered to be authentic if:

   o  the apex DNSKEY RRset containing the DNSKEY RR is considered
      authentic; or

   o  the RRset covered by the RRSIG RR is the apex DNSKEY RRset itself,
      and the DNSKEY RR either matches an authenticated DS RR from the
      parent zone or matches a trust anchor.

<span class="h4"><a class="selflink" id="section-5.3.2" href="#section-5.3.2">5.3.2</a>.  Reconstructing the Signed Data</span>

   Once the RRSIG RR has met the validity requirements described in
   <a href="#section-5.3.1">Section 5.3.1</a>, the validator has to reconstruct the original signed
   data.  The original signed data includes RRSIG RDATA (excluding the
   Signature field) and the canonical form of the RRset.  Aside from
   being ordered, the canonical form of the RRset might also differ from
   the received RRset due to DNS name compression, decremented TTLs, or
   wildcard expansion.  The validator should use the following to
   reconstruct the original signed data:

         signed_data = RRSIG_RDATA | RR(1) | RR(2)...  where

            "|" denotes concatenation

            RRSIG_RDATA is the wire format of the RRSIG RDATA fields
               with the Signature field excluded and the Signer's Name
               in canonical form.

            RR(i) = name | type | class | OrigTTL | RDATA length | RDATA

               name is calculated according to the function below

               class is the RRset's class

               type is the RRset type and all RRs in the class

               OrigTTL is the value from the RRSIG Original TTL field

               All names in the RDATA field are in canonical form




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               The set of all RR(i) is sorted into canonical order.

            To calculate the name:
               let rrsig_labels = the value of the RRSIG Labels field

               let fqdn = RRset's fully qualified domain name in
                               canonical form

               let fqdn_labels = Label count of the fqdn above.

               if rrsig_labels = fqdn_labels,
                   name = fqdn

               if rrsig_labels &lt; fqdn_labels,
                  name = "*." | the rightmost rrsig_label labels of the
                                fqdn

               if rrsig_labels &gt; fqdn_labels
                  the RRSIG RR did not pass the necessary validation
                  checks and MUST NOT be used to authenticate this
                  RRset.

   The canonical forms for names and RRsets are defined in [<a href="./rfc4034" title="&quot;Resource Records for DNS Security Extensions&quot;">RFC4034</a>].

   NSEC RRsets at a delegation boundary require special processing.
   There are two distinct NSEC RRsets associated with a signed delegated
   name.  One NSEC RRset resides in the parent zone, and specifies which
   RRsets are present at the parent zone.  The second NSEC RRset resides
   at the child zone and identifies which RRsets are present at the apex
   in the child zone.  The parent NSEC RRset and child NSEC RRset can
   always be distinguished as only a child NSEC RR will indicate that an
   SOA RRset exists at the name.  When reconstructing the original NSEC
   RRset for the delegation from the parent zone, the NSEC RRs MUST NOT
   be combined with NSEC RRs from the child zone.  When reconstructing
   the original NSEC RRset for the apex of the child zone, the NSEC RRs
   MUST NOT be combined with NSEC RRs from the parent zone.

   Note that each of the two NSEC RRsets at a delegation point has a
   corresponding RRSIG RR with an owner name matching the delegated
   name, and each of these RRSIG RRs is authoritative data associated
   with the same zone that contains the corresponding NSEC RRset.  If
   necessary, a resolver can tell these RRSIG RRs apart by checking the
   Signer's Name field.








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<span class="h4"><a class="selflink" id="section-5.3.3" href="#section-5.3.3">5.3.3</a>.  Checking the Signature</span>

   Once the resolver has validated the RRSIG RR as described in <a href="#section-5.3.1">Section</a>
   <a href="#section-5.3.1">5.3.1</a> and reconstructed the original signed data as described in
   <a href="#section-5.3.2">Section 5.3.2</a>, the validator can attempt to use the cryptographic
   signature to authenticate the signed data, and thus (finally!)
   authenticate the RRset.

   The Algorithm field in the RRSIG RR identifies the cryptographic
   algorithm used to generate the signature.  The signature itself is
   contained in the Signature field of the RRSIG RDATA, and the public
   key used to verify the signature is contained in the Public Key field
   of the matching DNSKEY RR(s) (found in <a href="#section-5.3.1">Section 5.3.1</a>).  [<a href="./rfc4034" title="&quot;Resource Records for DNS Security Extensions&quot;">RFC4034</a>]
   provides a list of algorithm types and provides pointers to the
   documents that define each algorithm's use.

   Note that it is possible for more than one DNSKEY RR to match the
   conditions in <a href="#section-5.3.1">Section 5.3.1</a>.  In this case, the validator can only
   determine which DNSKEY RR is correct by trying each matching public
   key until the validator either succeeds in validating the signature
   or runs out of keys to try.

   If the Labels field of the RRSIG RR is not equal to the number of
   labels in the RRset's fully qualified owner name, then the RRset is
   either invalid or the result of wildcard expansion.  The resolver
   MUST verify that wildcard expansion was applied properly before
   considering the RRset to be authentic.  <a href="#section-5.3.4">Section 5.3.4</a> describes how
   to determine whether a wildcard was applied properly.

   If other RRSIG RRs also cover this RRset, the local resolver security
   policy determines whether the resolver also has to test these RRSIG
   RRs and how to resolve conflicts if these RRSIG RRs lead to differing
   results.

   If the resolver accepts the RRset as authentic, the validator MUST
   set the TTL of the RRSIG RR and each RR in the authenticated RRset to
   a value no greater than the minimum of:

   o  the RRset's TTL as received in the response;

   o  the RRSIG RR's TTL as received in the response;

   o  the value in the RRSIG RR's Original TTL field; and

   o  the difference of the RRSIG RR's Signature Expiration time and the
      current time.





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<span class="h4"><a class="selflink" id="section-5.3.4" href="#section-5.3.4">5.3.4</a>.  Authenticating a Wildcard Expanded RRset Positive Response</span>

   If the number of labels in an RRset's owner name is greater than the
   Labels field of the covering RRSIG RR, then the RRset and its
   covering RRSIG RR were created as a result of wildcard expansion.
   Once the validator has verified the signature, as described in
   <a href="#section-5.3">Section 5.3</a>, it must take additional steps to verify the non-
   existence of an exact match or closer wildcard match for the query.
   <a href="#section-5.4">Section 5.4</a> discusses these steps.

   Note that the response received by the resolver should include all
   NSEC RRs needed to authenticate the response (see <a href="#section-3.1.3">Section 3.1.3</a>).

<span class="h3"><a class="selflink" id="section-5.4" href="#section-5.4">5.4</a>.  Authenticated Denial of Existence</span>

   A resolver can use authenticated NSEC RRs to prove that an RRset is
   not present in a signed zone.  Security-aware name servers should
   automatically include any necessary NSEC RRs for signed zones in
   their responses to security-aware resolvers.

   Denial of existence is determined by the following rules:

   o  If the requested RR name matches the owner name of an
      authenticated NSEC RR, then the NSEC RR's type bit map field lists
      all RR types present at that owner name, and a resolver can prove
      that the requested RR type does not exist by checking for the RR
      type in the bit map.  If the number of labels in an authenticated
      NSEC RR's owner name equals the Labels field of the covering RRSIG
      RR, then the existence of the NSEC RR proves that wildcard
      expansion could not have been used to match the request.

   o  If the requested RR name would appear after an authenticated NSEC
      RR's owner name and before the name listed in that NSEC RR's Next
      Domain Name field according to the canonical DNS name order
      defined in [<a href="./rfc4034" title="&quot;Resource Records for DNS Security Extensions&quot;">RFC4034</a>], then no RRsets with the requested name exist
      in the zone.  However, it is possible that a wildcard could be
      used to match the requested RR owner name and type, so proving
      that the requested RRset does not exist also requires proving that
      no possible wildcard RRset exists that could have been used to
      generate a positive response.

   In addition, security-aware resolvers MUST authenticate the NSEC
   RRsets that comprise the non-existence proof as described in <a href="#section-5.3">Section</a>
   <a href="#section-5.3">5.3</a>.

   To prove the non-existence of an RRset, the resolver must be able to
   verify both that the queried RRset does not exist and that no
   relevant wildcard RRset exists.  Proving this may require more than



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   one NSEC RRset from the zone.  If the complete set of necessary NSEC
   RRsets is not present in a response (perhaps due to message
   truncation), then a security-aware resolver MUST resend the query in
   order to attempt to obtain the full collection of NSEC RRs necessary
   to verify the non-existence of the requested RRset.  As with all DNS
   operations, however, the resolver MUST bound the work it puts into
   answering any particular query.

   Since a validated NSEC RR proves the existence of both itself and its
   corresponding RRSIG RR, a validator MUST ignore the settings of the
   NSEC and RRSIG bits in an NSEC RR.

<span class="h3"><a class="selflink" id="section-5.5" href="#section-5.5">5.5</a>.  Resolver Behavior When Signatures Do Not Validate</span>

   If for whatever reason none of the RRSIGs can be validated, the
   response SHOULD be considered BAD.  If the validation was being done
   to service a recursive query, the name server MUST return RCODE 2 to
   the originating client.  However, it MUST return the full response if
   and only if the original query had the CD bit set.  Also see <a href="#section-4.7">Section</a>
   <a href="#section-4.7">4.7</a> on caching responses that do not validate.

<span class="h3"><a class="selflink" id="section-5.6" href="#section-5.6">5.6</a>.  Authentication Example</span>

   <a href="#appendix-C">Appendix C</a> shows an example of the authentication process.

<span class="h2"><a class="selflink" id="section-6" href="#section-6">6</a>.  IANA Considerations</span>

   [<a id="ref-RFC4034">RFC4034</a>] contains a review of the IANA considerations introduced by
   DNSSEC.  The following are additional IANA considerations discussed
   in this document:

   [<a id="ref-RFC2535">RFC2535</a>] reserved the CD and AD bits in the message header.  The
   meaning of the AD bit was redefined in [<a href="./rfc3655" title="&quot;Redefinition of DNS Authenticated Data (AD) bit&quot;">RFC3655</a>], and the meaning of
   both the CD and AD bit are restated in this document.  No new bits in
   the DNS message header are defined in this document.

   [<a id="ref-RFC2671">RFC2671</a>] introduced EDNS, and [<a href="./rfc3225" title="&quot;Indicating Resolver Support of DNSSEC&quot;">RFC3225</a>] reserved the DNSSEC OK bit
   and defined its use.  The use is restated but not altered in this
   document.

<span class="h2"><a class="selflink" id="section-7" href="#section-7">7</a>.  Security Considerations</span>

   This document describes how the DNS security extensions use public
   key cryptography to sign and authenticate DNS resource record sets.
   Please see [<a href="./rfc4033" title="&quot;DNS Security Introduction and Requirements&quot;">RFC4033</a>] for terminology and general security
   considerations related to DNSSEC; see [<a href="./rfc4034" title="&quot;Resource Records for DNS Security Extensions&quot;">RFC4034</a>] for considerations
   specific to the DNSSEC resource record types.




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   An active attacker who can set the CD bit in a DNS query message or
   the AD bit in a DNS response message can use these bits to defeat the
   protection that DNSSEC attempts to provide to security-oblivious
   recursive-mode resolvers.  For this reason, use of these control bits
   by a security-aware recursive-mode resolver requires a secure
   channel.  See Sections <a href="#section-3.2.2">3.2.2</a> and <a href="#section-4.9">4.9</a> for further discussion.

   The protocol described in this document attempts to extend the
   benefits of DNSSEC to security-oblivious stub resolvers.  However, as
   recovery from validation failures is likely to be specific to
   particular applications, the facilities that DNSSEC provides for stub
   resolvers may prove inadequate.  Operators of security-aware
   recursive name servers will have to pay close attention to the
   behavior of the applications that use their services when choosing a
   local validation policy; failure to do so could easily result in the
   recursive name server accidentally denying service to the clients it
   is intended to support.

<span class="h2"><a class="selflink" id="section-8" href="#section-8">8</a>.  Acknowledgements</span>

   This document was created from the input and ideas of the members of
   the DNS Extensions Working Group and working group mailing list.  The
   editors would like to express their thanks for the comments and
   suggestions received during the revision of these security extension
   specifications.  Although explicitly listing everyone who has
   contributed during the decade in which DNSSEC has been under
   development would be impossible, [<a href="./rfc4033" title="&quot;DNS Security Introduction and Requirements&quot;">RFC4033</a>] includes a list of some of
   the participants who were kind enough to comment on these documents.

<span class="h2"><a class="selflink" id="section-9" href="#section-9">9</a>.  References</span>

<span class="h3"><a class="selflink" id="section-9.1" href="#section-9.1">9.1</a>.  Normative References</span>

   [<a id="ref-RFC1034">RFC1034</a>]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, <a href="./rfc1034">RFC 1034</a>, November 1987.

   [<a id="ref-RFC1035">RFC1035</a>]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, <a href="./rfc1035">RFC 1035</a>, November 1987.

   [<a id="ref-RFC1122">RFC1122</a>]  Braden, R., "Requirements for Internet Hosts -
              Communication Layers", STD 3, <a href="./rfc1122">RFC 1122</a>, October 1989.

   [<a id="ref-RFC2119">RFC2119</a>]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", <a href="https://www.rfc-editor.org/bcp/bcp14">BCP 14</a>, <a href="./rfc2119">RFC 2119</a>, March 1997.

   [<a id="ref-RFC2181">RFC2181</a>]  Elz, R. and R. Bush, "Clarifications to the DNS
              Specification", <a href="./rfc2181">RFC 2181</a>, July 1997.




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   [<a id="ref-RFC2460">RFC2460</a>]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", <a href="./rfc2460">RFC 2460</a>, December 1998.

   [<a id="ref-RFC2671">RFC2671</a>]  Vixie, P., "Extension Mechanisms for DNS (EDNS0)", <a href="./rfc2671">RFC</a>
              <a href="./rfc2671">2671</a>, August 1999.

   [<a id="ref-RFC2672">RFC2672</a>]  Crawford, M., "Non-Terminal DNS Name Redirection", <a href="./rfc2672">RFC</a>
              <a href="./rfc2672">2672</a>, August 1999.

   [<a id="ref-RFC3225">RFC3225</a>]  Conrad, D., "Indicating Resolver Support of DNSSEC", <a href="./rfc3225">RFC</a>
              <a href="./rfc3225">3225</a>, December 2001.

   [<a id="ref-RFC3226">RFC3226</a>]  Gudmundsson, O., "DNSSEC and IPv6 A6 aware server/resolver
              message size requirements", <a href="./rfc3226">RFC 3226</a>, December 2001.

   [<a id="ref-RFC4033">RFC4033</a>]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements", <a href="./rfc4033">RFC</a>
              <a href="./rfc4033">4033</a>, March 2005.

   [<a id="ref-RFC4034">RFC4034</a>]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Resource Records for DNS Security Extensions", <a href="./rfc4034">RFC</a>
              <a href="./rfc4034">4034</a>, March 2005.

<span class="h3"><a class="selflink" id="section-9.2" href="#section-9.2">9.2</a>.  Informative References</span>

   [<a id="ref-RFC2308">RFC2308</a>]  Andrews, M., "Negative Caching of DNS Queries (DNS
              NCACHE)", <a href="./rfc2308">RFC 2308</a>, March 1998.

   [<a id="ref-RFC2535">RFC2535</a>]  Eastlake 3rd, D., "Domain Name System Security
              Extensions", <a href="./rfc2535">RFC 2535</a>, March 1999.

   [<a id="ref-RFC3007">RFC3007</a>]  Wellington, B., "Secure Domain Name System (DNS) Dynamic
              Update", <a href="./rfc3007">RFC 3007</a>, November 2000.

   [<a id="ref-RFC3655">RFC3655</a>]  Wellington, B. and O. Gudmundsson, "Redefinition of DNS
              Authenticated Data (AD) bit", <a href="./rfc3655">RFC 3655</a>, November 2003.















<span class="grey">Arends, et al.              Standards Track                    [Page 35]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-36" ></span>
<span class="grey"><a href="./rfc4035">RFC 4035</a>             DNSSEC Protocol Modifications            March 2005</span>


<span class="h2"><a class="selflink" id="appendix-A" href="#appendix-A">Appendix A</a>.  Signed Zone Example</span>

   The following example shows a (small) complete signed zone.

   example.       3600 IN SOA ns1.example. bugs.x.w.example. (
                              1081539377
                              3600
                              300
                              3600000
                              3600
                              )
                  3600 RRSIG  SOA 5 1 3600 20040509183619 (
                              20040409183619 38519 example.
                              ONx0k36rcjaxYtcNgq6iQnpNV5+drqYAsC9h
                              7TSJaHCqbhE67Sr6aH2xDUGcqQWu/n0UVzrF
                              vkgO9ebarZ0GWDKcuwlM6eNB5SiX2K74l5LW
                              DA7S/Un/IbtDq4Ay8NMNLQI7Dw7n4p8/rjkB
                              jV7j86HyQgM5e7+miRAz8V01b0I= )
                  3600 NS     ns1.example.
                  3600 NS     ns2.example.
                  3600 RRSIG  NS 5 1 3600 20040509183619 (
                              20040409183619 38519 example.
                              gl13F00f2U0R+SWiXXLHwsMY+qStYy5k6zfd
                              EuivWc+wd1fmbNCyql0Tk7lHTX6UOxc8AgNf
                              4ISFve8XqF4q+o9qlnqIzmppU3LiNeKT4FZ8
                              RO5urFOvoMRTbQxW3U0hXWuggE4g3ZpsHv48
                              0HjMeRaZB/FRPGfJPajngcq6Kwg= )
                  3600 MX     1 xx.example.
                  3600 RRSIG  MX 5 1 3600 20040509183619 (
                              20040409183619 38519 example.
                              HyDHYVT5KHSZ7HtO/vypumPmSZQrcOP3tzWB
                              2qaKkHVPfau/DgLgS/IKENkYOGL95G4N+NzE
                              VyNU8dcTOckT+ChPcGeVjguQ7a3Ao9Z/ZkUO
                              6gmmUW4b89rz1PUxW4jzUxj66PTwoVtUU/iM
                              W6OISukd1EQt7a0kygkg+PEDxdI= )
                  3600 NSEC   a.example. NS SOA MX RRSIG NSEC DNSKEY
                  3600 RRSIG  NSEC 5 1 3600 20040509183619 (
                              20040409183619 38519 example.
                              O0k558jHhyrC97ISHnislm4kLMW48C7U7cBm
                              FTfhke5iVqNRVTB1STLMpgpbDIC9hcryoO0V
                              Z9ME5xPzUEhbvGnHd5sfzgFVeGxr5Nyyq4tW
                              SDBgIBiLQUv1ivy29vhXy7WgR62dPrZ0PWvm
                              jfFJ5arXf4nPxp/kEowGgBRzY/U= )
                  3600 DNSKEY 256 3 5 (
                              AQOy1bZVvpPqhg4j7EJoM9rI3ZmyEx2OzDBV
                              rZy/lvI5CQePxXHZS4i8dANH4DX3tbHol61e
                              k8EFMcsGXxKciJFHyhl94C+NwILQdzsUlSFo
                              vBZsyl/NX6yEbtw/xN9ZNcrbYvgjjZ/UVPZI



<span class="grey">Arends, et al.              Standards Track                    [Page 36]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-37" ></span>
<span class="grey"><a href="./rfc4035">RFC 4035</a>             DNSSEC Protocol Modifications            March 2005</span>


                              ySFNsgEYvh0z2542lzMKR4Dh8uZffQ==
                              )
                  3600 DNSKEY 257 3 5 (
                              AQOeX7+baTmvpVHb2CcLnL1dMRWbuscRvHXl
                              LnXwDzvqp4tZVKp1sZMepFb8MvxhhW3y/0QZ
                              syCjczGJ1qk8vJe52iOhInKROVLRwxGpMfzP
                              RLMlGybr51bOV/1se0ODacj3DomyB4QB5gKT
                              Yot/K9alk5/j8vfd4jWCWD+E1Sze0Q==
                              )
                  3600 RRSIG  DNSKEY 5 1 3600 20040509183619 (
                              20040409183619 9465 example.
                              ZxgauAuIj+k1YoVEOSlZfx41fcmKzTFHoweZ
                              xYnz99JVQZJ33wFS0Q0jcP7VXKkaElXk9nYJ
                              XevO/7nAbo88iWsMkSpSR6jWzYYKwfrBI/L9
                              hjYmyVO9m6FjQ7uwM4dCP/bIuV/DKqOAK9NY
                              NC3AHfvCV1Tp4VKDqxqG7R5tTVM= )
                  3600 RRSIG  DNSKEY 5 1 3600 20040509183619 (
                              20040409183619 38519 example.
                              eGL0s90glUqcOmloo/2y+bSzyEfKVOQViD9Z
                              DNhLz/Yn9CQZlDVRJffACQDAUhXpU/oP34ri
                              bKBpysRXosczFrKqS5Oa0bzMOfXCXup9qHAp
                              eFIku28Vqfr8Nt7cigZLxjK+u0Ws/4lIRjKk
                              7z5OXogYVaFzHKillDt3HRxHIZM= )
   a.example.     3600 IN NS  ns1.a.example.
                  3600 IN NS  ns2.a.example.
                  3600 DS     57855 5 1 (
                              B6DCD485719ADCA18E5F3D48A2331627FDD3
                              636B )
                  3600 RRSIG  DS 5 2 3600 20040509183619 (
                              20040409183619 38519 example.
                              oXIKit/QtdG64J/CB+Gi8dOvnwRvqrto1AdQ
                              oRkAN15FP3iZ7suB7gvTBmXzCjL7XUgQVcoH
                              kdhyCuzp8W9qJHgRUSwKKkczSyuL64nhgjuD
                              EML8l9wlWVsl7PR2VnZduM9bLyBhaaPmRKX/
                              Fm+v6ccF2EGNLRiY08kdkz+XHHo= )
                  3600 NSEC   ai.example. NS DS RRSIG NSEC
                  3600 RRSIG  NSEC 5 2 3600 20040509183619 (
                              20040409183619 38519 example.
                              cOlYgqJLqlRqmBQ3iap2SyIsK4O5aqpKSoba
                              U9fQ5SMApZmHfq3AgLflkrkXRXvgxTQSKkG2
                              039/cRUs6Jk/25+fi7Xr5nOVJsb0lq4zsB3I
                              BBdjyGDAHE0F5ROJj87996vJupdm1fbH481g
                              sdkOW6Zyqtz3Zos8N0BBkEx+2G4= )
   ns1.a.example. 3600 IN A   192.0.2.5
   ns2.a.example. 3600 IN A   192.0.2.6
   ai.example.    3600 IN A   192.0.2.9
                  3600 RRSIG  A 5 2 3600 20040509183619 (
                              20040409183619 38519 example.



<span class="grey">Arends, et al.              Standards Track                    [Page 37]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-38" ></span>
<span class="grey"><a href="./rfc4035">RFC 4035</a>             DNSSEC Protocol Modifications            March 2005</span>


                              pAOtzLP2MU0tDJUwHOKE5FPIIHmdYsCgTb5B
                              ERGgpnJluA9ixOyf6xxVCgrEJW0WNZSsJicd
                              hBHXfDmAGKUajUUlYSAH8tS4ZnrhyymIvk3u
                              ArDu2wfT130e9UHnumaHHMpUTosKe22PblOy
                              6zrTpg9FkS0XGVmYRvOTNYx2HvQ= )
                  3600 HINFO  "KLH-10" "ITS"
                  3600 RRSIG  HINFO 5 2 3600 20040509183619 (
                              20040409183619 38519 example.
                              Iq/RGCbBdKzcYzlGE4ovbr5YcB+ezxbZ9W0l
                              e/7WqyvhOO9J16HxhhL7VY/IKmTUY0GGdcfh
                              ZEOCkf4lEykZF9NPok1/R/fWrtzNp8jobuY7
                              AZEcZadp1WdDF3jc2/ndCa5XZhLKD3JzOsBw
                              FvL8sqlS5QS6FY/ijFEDnI4RkZA= )
                  3600 AAAA   2001:db8::f00:baa9
                  3600 RRSIG  AAAA 5 2 3600 20040509183619 (
                              20040409183619 38519 example.
                              nLcpFuXdT35AcE+EoafOUkl69KB+/e56XmFK
                              kewXG2IadYLKAOBIoR5+VoQV3XgTcofTJNsh
                              1rnF6Eav2zpZB3byI6yo2bwY8MNkr4A7cL9T
                              cMmDwV/hWFKsbGBsj8xSCN/caEL2CWY/5XP2
                              sZM6QjBBLmukH30+w1z3h8PUP2o= )
                  3600 NSEC   b.example. A HINFO AAAA RRSIG NSEC
                  3600 RRSIG  NSEC 5 2 3600 20040509183619 (
                              20040409183619 38519 example.
                              QoshyPevLcJ/xcRpEtMft1uoIrcrieVcc9pG
                              CScIn5Glnib40T6ayVOimXwdSTZ/8ISXGj4p
                              P8Sh0PlA6olZQ84L453/BUqB8BpdOGky4hsN
                              3AGcLEv1Gr0QMvirQaFcjzOECfnGyBm+wpFL
                              AhS+JOVfDI/79QtyTI0SaDWcg8U= )
   b.example.     3600 IN NS  ns1.b.example.
                  3600 IN NS  ns2.b.example.
                  3600 NSEC   ns1.example. NS RRSIG NSEC
                  3600 RRSIG  NSEC 5 2 3600 20040509183619 (
                              20040409183619 38519 example.
                              GNuxHn844wfmUhPzGWKJCPY5ttEX/RfjDoOx
                              9ueK1PtYkOWKOOdiJ/PJKCYB3hYX+858dDWS
                              xb2qnV/LSTCNVBnkm6owOpysY97MVj5VQEWs
                              0lm9tFoqjcptQkmQKYPrwUnCSNwvvclSF1xZ
                              vhRXgWT7OuFXldoCG6TfVFMs9xE= )
   ns1.b.example. 3600 IN A   192.0.2.7
   ns2.b.example. 3600 IN A   192.0.2.8
   ns1.example.   3600 IN A   192.0.2.1
                  3600 RRSIG  A 5 2 3600 20040509183619 (
                              20040409183619 38519 example.
                              F1C9HVhIcs10cZU09G5yIVfKJy5yRQQ3qVet
                              5pGhp82pzhAOMZ3K22JnmK4c+IjUeFp/to06
                              im5FVpHtbFisdjyPq84bhTv8vrXt5AB1wNB+
                              +iAqvIfdgW4sFNC6oADb1hK8QNauw9VePJhK



<span class="grey">Arends, et al.              Standards Track                    [Page 38]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-39" ></span>
<span class="grey"><a href="./rfc4035">RFC 4035</a>             DNSSEC Protocol Modifications            March 2005</span>


                              v/iVXSYC0b7mPSU+EOlknFpVECs= )
                  3600 NSEC   ns2.example. A RRSIG NSEC
                  3600 RRSIG  NSEC 5 2 3600 20040509183619 (
                              20040409183619 38519 example.
                              I4hj+Kt6+8rCcHcUdolks2S+Wzri9h3fHas8
                              1rGN/eILdJHN7JpV6lLGPIh/8fIBkfvdyWnB
                              jjf1q3O7JgYO1UdI7FvBNWqaaEPJK3UkddBq
                              ZIaLi8Qr2XHkjq38BeQsbp8X0+6h4ETWSGT8
                              IZaIGBLryQWGLw6Y6X8dqhlnxJM= )
   ns2.example.   3600 IN A   192.0.2.2
                  3600 RRSIG  A 5 2 3600 20040509183619 (
                              20040409183619 38519 example.
                              V7cQRw1TR+knlaL1z/psxlS1PcD37JJDaCMq
                              Qo6/u1qFQu6x+wuDHRH22Ap9ulJPQjFwMKOu
                              yfPGQPC8KzGdE3vt5snFEAoE1Vn3mQqtu7SO
                              6amIjk13Kj/jyJ4nGmdRIc/3cM3ipXFhNTKq
                              rdhx8SZ0yy4ObIRzIzvBFLiSS8o= )
                  3600 NSEC   *.w.example. A RRSIG NSEC
                  3600 RRSIG  NSEC 5 2 3600 20040509183619 (
                              20040409183619 38519 example.
                              N0QzHvaJf5NRw1rE9uxS1Ltb2LZ73Qb9bKGE
                              VyaISkqzGpP3jYJXZJPVTq4UVEsgT3CgeHvb
                              3QbeJ5Dfb2V9NGCHj/OvF/LBxFFWwhLwzngH
                              l+bQAgAcMsLu/nL3nDi1y/JSQjAcdZNDl4bw
                              Ymx28EtgIpo9A0qmP08rMBqs1Jw= )
   *.w.example.   3600 IN MX  1 ai.example.
                  3600 RRSIG  MX 5 2 3600 20040509183619 (
                              20040409183619 38519 example.
                              OMK8rAZlepfzLWW75Dxd63jy2wswESzxDKG2
                              f9AMN1CytCd10cYISAxfAdvXSZ7xujKAtPbc
                              tvOQ2ofO7AZJ+d01EeeQTVBPq4/6KCWhqe2X
                              TjnkVLNvvhnc0u28aoSsG0+4InvkkOHknKxw
                              4kX18MMR34i8lC36SR5xBni8vHI= )
                  3600 NSEC   x.w.example. MX RRSIG NSEC
                  3600 RRSIG  NSEC 5 2 3600 20040509183619 (
                              20040409183619 38519 example.
                              r/mZnRC3I/VIcrelgIcteSxDhtsdlTDt8ng9
                              HSBlABOlzLxQtfgTnn8f+aOwJIAFe1Ee5RvU
                              5cVhQJNP5XpXMJHfyps8tVvfxSAXfahpYqtx
                              91gsmcV/1V9/bZAG55CefP9cM4Z9Y9NT9XQ8
                              s1InQ2UoIv6tJEaaKkP701j8OLA= )
   x.w.example.   3600 IN MX  1 xx.example.
                  3600 RRSIG  MX 5 3 3600 20040509183619 (
                              20040409183619 38519 example.
                              Il2WTZ+Bkv+OytBx4LItNW5mjB4RCwhOO8y1
                              XzPHZmZUTVYL7LaA63f6T9ysVBzJRI3KRjAP
                              H3U1qaYnDoN1DrWqmi9RJe4FoObkbcdm7P3I
                              kx70ePCoFgRz1Yq+bVVXCvGuAU4xALv3W/Y1



<span class="grey">Arends, et al.              Standards Track                    [Page 39]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-40" ></span>
<span class="grey"><a href="./rfc4035">RFC 4035</a>             DNSSEC Protocol Modifications            March 2005</span>


                              jNSlwZ2mSWKHfxFQxPtLj8s32+k= )
                  3600 NSEC   x.y.w.example. MX RRSIG NSEC
                  3600 RRSIG  NSEC 5 3 3600 20040509183619 (
                              20040409183619 38519 example.
                              aRbpHftxggzgMXdDlym9SsADqMZovZZl2QWK
                              vw8J0tZEUNQByH5Qfnf5N1FqH/pS46UA7A4E
                              mcWBN9PUA1pdPY6RVeaRlZlCr1IkVctvbtaI
                              NJuBba/VHm+pebTbKcAPIvL9tBOoh+to1h6e
                              IjgiM8PXkBQtxPq37wDKALkyn7Q= )
   x.y.w.example. 3600 IN MX  1 xx.example.
                  3600 RRSIG  MX 5 4 3600 20040509183619 (
                              20040409183619 38519 example.
                              k2bJHbwP5LH5qN4is39UiPzjAWYmJA38Hhia
                              t7i9t7nbX/e0FPnvDSQXzcK7UL+zrVA+3MDj
                              q1ub4q3SZgcbLMgexxIW3Va//LVrxkP6Xupq
                              GtOB9prkK54QTl/qZTXfMQpW480YOvVknhvb
                              +gLcMZBnHJ326nb/TOOmrqNmQQE= )
                  3600 NSEC   xx.example. MX RRSIG NSEC
                  3600 RRSIG  NSEC 5 4 3600 20040509183619 (
                              20040409183619 38519 example.
                              OvE6WUzN2ziieJcvKPWbCAyXyP6ef8cr6Csp
                              ArVSTzKSquNwbezZmkU7E34o5lmb6CWSSSpg
                              xw098kNUFnHcQf/LzY2zqRomubrNQhJTiDTX
                              a0ArunJQCzPjOYq5t0SLjm6qp6McJI1AP5Vr
                              QoKqJDCLnoAlcPOPKAm/jJkn3jk= )
   xx.example.    3600 IN A   192.0.2.10
                  3600 RRSIG  A 5 2 3600 20040509183619 (
                              20040409183619 38519 example.
                              kBF4YxMGWF0D8r0cztL+2fWWOvN1U/GYSpYP
                              7SoKoNQ4fZKyk+weWGlKLIUM+uE1zjVTPXoa
                              0Z6WG0oZp46rkl1EzMcdMgoaeUzzAJ2BMq+Y
                              VdxG9IK1yZkYGY9AgbTOGPoAgbJyO9EPULsx
                              kbIDV6GPPSZVusnZU6OMgdgzHV4= )
                  3600 HINFO  "KLH-10" "TOPS-20"
                  3600 RRSIG  HINFO 5 2 3600 20040509183619 (
                              20040409183619 38519 example.
                              GY2PLSXmMHkWHfLdggiox8+chWpeMNJLkML0
                              t+U/SXSUsoUdR91KNdNUkTDWamwcF8oFRjhq
                              BcPZ6EqrF+vl5v5oGuvSF7U52epfVTC+wWF8
                              3yCUeUw8YklhLWlvk8gQ15YKth0ITQy8/wI+
                              RgNvuwbioFSEuv2pNlkq0goYxNY= )
                  3600 AAAA   2001:db8::f00:baaa
                  3600 RRSIG  AAAA 5 2 3600 20040509183619 (
                              20040409183619 38519 example.
                              Zzj0yodDxcBLnnOIwDsuKo5WqiaK24DlKg9C
                              aGaxDFiKgKobUj2jilYQHpGFn2poFRetZd4z
                              ulyQkssz2QHrVrPuTMS22knudCiwP4LWpVTr
                              U4zfeA+rDz9stmSBP/4PekH/x2IoAYnwctd/



<span class="grey">Arends, et al.              Standards Track                    [Page 40]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-41" ></span>
<span class="grey"><a href="./rfc4035">RFC 4035</a>             DNSSEC Protocol Modifications            March 2005</span>


                              xS9cL2QgW7FChw16mzlkH6/vsfs= )
                  3600 NSEC   example. A HINFO AAAA RRSIG NSEC
                  3600 RRSIG  NSEC 5 2 3600 20040509183619 (
                              20040409183619 38519 example.
                              ZFWUln6Avc8bmGl5GFjD3BwT530DUZKHNuoY
                              9A8lgXYyrxu+pqgFiRVbyZRQvVB5pccEOT3k
                              mvHgEa/HzbDB4PIYY79W+VHrgOxzdQGGCZzi
                              asXrpSGOWwSOElghPnMIi8xdF7qtCntr382W
                              GghLahumFIpg4MO3LS/prgzVVWo= )

   The apex DNSKEY set includes two DNSKEY RRs, and the DNSKEY RDATA
   Flags indicate that each of these DNSKEY RRs is a zone key.  One of
   these DNSKEY RRs also has the SEP flag set and has been used to sign
   the apex DNSKEY RRset; this is the key that should be hashed to
   generate a DS record to be inserted into the parent zone.  The other
   DNSKEY is used to sign all the other RRsets in the zone.

   The zone includes a wildcard entry, "*.w.example".  Note that the
   name "*.w.example" is used in constructing NSEC chains, and that the
   RRSIG covering the "*.w.example" MX RRset has a label count of 2.

   The zone also includes two delegations.  The delegation to
   "b.example" includes an NS RRset, glue address records, and an NSEC
   RR; note that only the NSEC RRset is signed.  The delegation to
   "a.example" provides a DS RR; note that only the NSEC and DS RRsets
   are signed.

<span class="h2"><a class="selflink" id="appendix-B" href="#appendix-B">Appendix B</a>.  Example Responses</span>

   The examples in this section show response messages using the signed
   zone example in <a href="#appendix-A">Appendix A</a>.

<span class="h3"><a class="selflink" id="appendix-B.1" href="#appendix-B.1">B.1</a>.  Answer</span>

   A successful query to an authoritative server.

   ;; Header: QR AA DO RCODE=0
   ;;
   ;; Question
   x.w.example.        IN MX

   ;; Answer
   x.w.example.   3600 IN MX  1 xx.example.
   x.w.example.   3600 RRSIG  MX 5 3 3600 20040509183619 (
                              20040409183619 38519 example.
                              Il2WTZ+Bkv+OytBx4LItNW5mjB4RCwhOO8y1
                              XzPHZmZUTVYL7LaA63f6T9ysVBzJRI3KRjAP
                              H3U1qaYnDoN1DrWqmi9RJe4FoObkbcdm7P3I



<span class="grey">Arends, et al.              Standards Track                    [Page 41]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-42" ></span>
<span class="grey"><a href="./rfc4035">RFC 4035</a>             DNSSEC Protocol Modifications            March 2005</span>


                              kx70ePCoFgRz1Yq+bVVXCvGuAU4xALv3W/Y1
                              jNSlwZ2mSWKHfxFQxPtLj8s32+k= )

   ;; Authority
   example.       3600 NS     ns1.example.
   example.       3600 NS     ns2.example.
   example.       3600 RRSIG  NS 5 1 3600 20040509183619 (
                              20040409183619 38519 example.
                              gl13F00f2U0R+SWiXXLHwsMY+qStYy5k6zfd
                              EuivWc+wd1fmbNCyql0Tk7lHTX6UOxc8AgNf
                              4ISFve8XqF4q+o9qlnqIzmppU3LiNeKT4FZ8
                              RO5urFOvoMRTbQxW3U0hXWuggE4g3ZpsHv48
                              0HjMeRaZB/FRPGfJPajngcq6Kwg= )

   ;; Additional
   xx.example.    3600 IN A   192.0.2.10
   xx.example.    3600 RRSIG  A 5 2 3600 20040509183619 (
                              20040409183619 38519 example.
                              kBF4YxMGWF0D8r0cztL+2fWWOvN1U/GYSpYP
                              7SoKoNQ4fZKyk+weWGlKLIUM+uE1zjVTPXoa
                              0Z6WG0oZp46rkl1EzMcdMgoaeUzzAJ2BMq+Y
                              VdxG9IK1yZkYGY9AgbTOGPoAgbJyO9EPULsx
                              kbIDV6GPPSZVusnZU6OMgdgzHV4= )
   xx.example.    3600 AAAA   2001:db8::f00:baaa
   xx.example.    3600 RRSIG  AAAA 5 2 3600 20040509183619 (
                              20040409183619 38519 example.
                              Zzj0yodDxcBLnnOIwDsuKo5WqiaK24DlKg9C
                              aGaxDFiKgKobUj2jilYQHpGFn2poFRetZd4z
                              ulyQkssz2QHrVrPuTMS22knudCiwP4LWpVTr
                              U4zfeA+rDz9stmSBP/4PekH/x2IoAYnwctd/
                              xS9cL2QgW7FChw16mzlkH6/vsfs= )
   ns1.example.   3600 IN A   192.0.2.1
   ns1.example.   3600 RRSIG  A 5 2 3600 20040509183619 (
                              20040409183619 38519 example.
                              F1C9HVhIcs10cZU09G5yIVfKJy5yRQQ3qVet
                              5pGhp82pzhAOMZ3K22JnmK4c+IjUeFp/to06
                              im5FVpHtbFisdjyPq84bhTv8vrXt5AB1wNB+
                              +iAqvIfdgW4sFNC6oADb1hK8QNauw9VePJhK
                              v/iVXSYC0b7mPSU+EOlknFpVECs= )
   ns2.example.   3600 IN A   192.0.2.2
   ns2.example.   3600 RRSIG  A 5 2 3600 20040509183619 (
                              20040409183619 38519 example.
                              V7cQRw1TR+knlaL1z/psxlS1PcD37JJDaCMq
                              Qo6/u1qFQu6x+wuDHRH22Ap9ulJPQjFwMKOu
                              yfPGQPC8KzGdE3vt5snFEAoE1Vn3mQqtu7SO
                              6amIjk13Kj/jyJ4nGmdRIc/3cM3ipXFhNTKq
                              rdhx8SZ0yy4ObIRzIzvBFLiSS8o= )




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<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-43" ></span>
<span class="grey"><a href="./rfc4035">RFC 4035</a>             DNSSEC Protocol Modifications            March 2005</span>


<span class="h3"><a class="selflink" id="appendix-B.2" href="#appendix-B.2">B.2</a>.  Name Error</span>

   An authoritative name error.  The NSEC RRs prove that the name does
   not exist and that no covering wildcard exists.

   ;; Header: QR AA DO RCODE=3
   ;;
   ;; Question
   ml.example.         IN A

   ;; Answer
   ;; (empty)

   ;; Authority
   example.       3600 IN SOA ns1.example. bugs.x.w.example. (
                              1081539377
                              3600
                              300
                              3600000
                              3600
                              )
   example.       3600 RRSIG  SOA 5 1 3600 20040509183619 (
                              20040409183619 38519 example.
                              ONx0k36rcjaxYtcNgq6iQnpNV5+drqYAsC9h
                              7TSJaHCqbhE67Sr6aH2xDUGcqQWu/n0UVzrF
                              vkgO9ebarZ0GWDKcuwlM6eNB5SiX2K74l5LW
                              DA7S/Un/IbtDq4Ay8NMNLQI7Dw7n4p8/rjkB
                              jV7j86HyQgM5e7+miRAz8V01b0I= )
   b.example.     3600 NSEC   ns1.example. NS RRSIG NSEC
   b.example.     3600 RRSIG  NSEC 5 2 3600 20040509183619 (
                              20040409183619 38519 example.
                              GNuxHn844wfmUhPzGWKJCPY5ttEX/RfjDoOx
                              9ueK1PtYkOWKOOdiJ/PJKCYB3hYX+858dDWS
                              xb2qnV/LSTCNVBnkm6owOpysY97MVj5VQEWs
                              0lm9tFoqjcptQkmQKYPrwUnCSNwvvclSF1xZ
                              vhRXgWT7OuFXldoCG6TfVFMs9xE= )
   example.       3600 NSEC   a.example. NS SOA MX RRSIG NSEC DNSKEY
   example.       3600 RRSIG  NSEC 5 1 3600 20040509183619 (
                              20040409183619 38519 example.
                              O0k558jHhyrC97ISHnislm4kLMW48C7U7cBm
                              FTfhke5iVqNRVTB1STLMpgpbDIC9hcryoO0V
                              Z9ME5xPzUEhbvGnHd5sfzgFVeGxr5Nyyq4tW
                              SDBgIBiLQUv1ivy29vhXy7WgR62dPrZ0PWvm
                              jfFJ5arXf4nPxp/kEowGgBRzY/U= )

   ;; Additional
   ;; (empty)




<span class="grey">Arends, et al.              Standards Track                    [Page 43]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-44" ></span>
<span class="grey"><a href="./rfc4035">RFC 4035</a>             DNSSEC Protocol Modifications            March 2005</span>


<span class="h3"><a class="selflink" id="appendix-B.3" href="#appendix-B.3">B.3</a>.  No Data Error</span>

   A "no data" response.  The NSEC RR proves that the name exists and
   that the requested RR type does not.

   ;; Header: QR AA DO RCODE=0
   ;;
   ;; Question
   ns1.example.        IN MX

   ;; Answer
   ;; (empty)

   ;; Authority
   example.       3600 IN SOA ns1.example. bugs.x.w.example. (
                              1081539377
                              3600
                              300
                              3600000
                              3600
                              )
   example.       3600 RRSIG  SOA 5 1 3600 20040509183619 (
                              20040409183619 38519 example.
                              ONx0k36rcjaxYtcNgq6iQnpNV5+drqYAsC9h
                              7TSJaHCqbhE67Sr6aH2xDUGcqQWu/n0UVzrF
                              vkgO9ebarZ0GWDKcuwlM6eNB5SiX2K74l5LW
                              DA7S/Un/IbtDq4Ay8NMNLQI7Dw7n4p8/rjkB
                              jV7j86HyQgM5e7+miRAz8V01b0I= )
   ns1.example.   3600 NSEC   ns2.example. A RRSIG NSEC
   ns1.example.   3600 RRSIG  NSEC 5 2 3600 20040509183619 (
                              20040409183619 38519 example.
                              I4hj+Kt6+8rCcHcUdolks2S+Wzri9h3fHas8
                              1rGN/eILdJHN7JpV6lLGPIh/8fIBkfvdyWnB
                              jjf1q3O7JgYO1UdI7FvBNWqaaEPJK3UkddBq
                              ZIaLi8Qr2XHkjq38BeQsbp8X0+6h4ETWSGT8
                              IZaIGBLryQWGLw6Y6X8dqhlnxJM= )

   ;; Additional
   ;; (empty)

<span class="h3"><a class="selflink" id="appendix-B.4" href="#appendix-B.4">B.4</a>.  Referral to Signed Zone</span>

   Referral to a signed zone.  The DS RR contains the data which the
   resolver will need to validate the corresponding DNSKEY RR in the
   child zone's apex.

   ;; Header: QR DO RCODE=0
   ;;



<span class="grey">Arends, et al.              Standards Track                    [Page 44]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-45" ></span>
<span class="grey"><a href="./rfc4035">RFC 4035</a>             DNSSEC Protocol Modifications            March 2005</span>


   ;; Question
   mc.a.example.       IN MX

   ;; Answer
   ;; (empty)

   ;; Authority
   a.example.     3600 IN NS  ns1.a.example.
   a.example.     3600 IN NS  ns2.a.example.
   a.example.     3600 DS     57855 5 1 (
                              B6DCD485719ADCA18E5F3D48A2331627FDD3
                              636B )
   a.example.     3600 RRSIG  DS 5 2 3600 20040509183619 (
                              20040409183619 38519 example.
                              oXIKit/QtdG64J/CB+Gi8dOvnwRvqrto1AdQ
                              oRkAN15FP3iZ7suB7gvTBmXzCjL7XUgQVcoH
                              kdhyCuzp8W9qJHgRUSwKKkczSyuL64nhgjuD
                              EML8l9wlWVsl7PR2VnZduM9bLyBhaaPmRKX/
                              Fm+v6ccF2EGNLRiY08kdkz+XHHo= )

   ;; Additional
   ns1.a.example. 3600 IN A   192.0.2.5
   ns2.a.example. 3600 IN A   192.0.2.6

<span class="h3"><a class="selflink" id="appendix-B.5" href="#appendix-B.5">B.5</a>.  Referral to Unsigned Zone</span>

   Referral to an unsigned zone.  The NSEC RR proves that no DS RR for
   this delegation exists in the parent zone.

   ;; Header: QR DO RCODE=0
   ;;
   ;; Question
   mc.b.example.       IN MX

   ;; Answer
   ;; (empty)

   ;; Authority
   b.example.     3600 IN NS  ns1.b.example.
   b.example.     3600 IN NS  ns2.b.example.
   b.example.     3600 NSEC   ns1.example. NS RRSIG NSEC
   b.example.     3600 RRSIG  NSEC 5 2 3600 20040509183619 (
                              20040409183619 38519 example.
                              GNuxHn844wfmUhPzGWKJCPY5ttEX/RfjDoOx
                              9ueK1PtYkOWKOOdiJ/PJKCYB3hYX+858dDWS
                              xb2qnV/LSTCNVBnkm6owOpysY97MVj5VQEWs
                              0lm9tFoqjcptQkmQKYPrwUnCSNwvvclSF1xZ
                              vhRXgWT7OuFXldoCG6TfVFMs9xE= )



<span class="grey">Arends, et al.              Standards Track                    [Page 45]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-46" ></span>
<span class="grey"><a href="./rfc4035">RFC 4035</a>             DNSSEC Protocol Modifications            March 2005</span>


   ;; Additional
   ns1.b.example. 3600 IN A   192.0.2.7
   ns2.b.example. 3600 IN A   192.0.2.8

<span class="h3"><a class="selflink" id="appendix-B.6" href="#appendix-B.6">B.6</a>.  Wildcard Expansion</span>

   A successful query that was answered via wildcard expansion.  The
   label count in the answer's RRSIG RR indicates that a wildcard RRset
   was expanded to produce this response, and the NSEC RR proves that no
   closer match exists in the zone.

   ;; Header: QR AA DO RCODE=0
   ;;
   ;; Question
   a.z.w.example.      IN MX

   ;; Answer
   a.z.w.example. 3600 IN MX  1 ai.example.
   a.z.w.example. 3600 RRSIG  MX 5 2 3600 20040509183619 (
                              20040409183619 38519 example.
                              OMK8rAZlepfzLWW75Dxd63jy2wswESzxDKG2
                              f9AMN1CytCd10cYISAxfAdvXSZ7xujKAtPbc
                              tvOQ2ofO7AZJ+d01EeeQTVBPq4/6KCWhqe2X
                              TjnkVLNvvhnc0u28aoSsG0+4InvkkOHknKxw
                              4kX18MMR34i8lC36SR5xBni8vHI= )

   ;; Authority
   example.       3600 NS     ns1.example.
   example.       3600 NS     ns2.example.
   example.       3600 RRSIG  NS 5 1 3600 20040509183619 (
                              20040409183619 38519 example.
                              gl13F00f2U0R+SWiXXLHwsMY+qStYy5k6zfd
                              EuivWc+wd1fmbNCyql0Tk7lHTX6UOxc8AgNf
                              4ISFve8XqF4q+o9qlnqIzmppU3LiNeKT4FZ8
                              RO5urFOvoMRTbQxW3U0hXWuggE4g3ZpsHv48
                              0HjMeRaZB/FRPGfJPajngcq6Kwg= )
   x.y.w.example. 3600 NSEC   xx.example. MX RRSIG NSEC
   x.y.w.example. 3600 RRSIG  NSEC 5 4 3600 20040509183619 (
                              20040409183619 38519 example.
                              OvE6WUzN2ziieJcvKPWbCAyXyP6ef8cr6Csp
                              ArVSTzKSquNwbezZmkU7E34o5lmb6CWSSSpg
                              xw098kNUFnHcQf/LzY2zqRomubrNQhJTiDTX
                              a0ArunJQCzPjOYq5t0SLjm6qp6McJI1AP5Vr
                              QoKqJDCLnoAlcPOPKAm/jJkn3jk= )

   ;; Additional
   ai.example.    3600 IN A   192.0.2.9
   ai.example.    3600 RRSIG  A 5 2 3600 20040509183619 (



<span class="grey">Arends, et al.              Standards Track                    [Page 46]</span></pre>
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<span class="grey"><a href="./rfc4035">RFC 4035</a>             DNSSEC Protocol Modifications            March 2005</span>


                              20040409183619 38519 example.
                              pAOtzLP2MU0tDJUwHOKE5FPIIHmdYsCgTb5B
                              ERGgpnJluA9ixOyf6xxVCgrEJW0WNZSsJicd
                              hBHXfDmAGKUajUUlYSAH8tS4ZnrhyymIvk3u
                              ArDu2wfT130e9UHnumaHHMpUTosKe22PblOy
                              6zrTpg9FkS0XGVmYRvOTNYx2HvQ= )
   ai.example.    3600 AAAA   2001:db8::f00:baa9
   ai.example.    3600 RRSIG  AAAA 5 2 3600 20040509183619 (
                              20040409183619 38519 example.
                              nLcpFuXdT35AcE+EoafOUkl69KB+/e56XmFK
                              kewXG2IadYLKAOBIoR5+VoQV3XgTcofTJNsh
                              1rnF6Eav2zpZB3byI6yo2bwY8MNkr4A7cL9T
                              cMmDwV/hWFKsbGBsj8xSCN/caEL2CWY/5XP2
                              sZM6QjBBLmukH30+w1z3h8PUP2o= )

<span class="h3"><a class="selflink" id="appendix-B.7" href="#appendix-B.7">B.7</a>.  Wildcard No Data Error</span>

   A "no data" response for a name covered by a wildcard.  The NSEC RRs
   prove that the matching wildcard name does not have any RRs of the
   requested type and that no closer match exists in the zone.

   ;; Header: QR AA DO RCODE=0
   ;;
   ;; Question
   a.z.w.example.      IN AAAA

   ;; Answer
   ;; (empty)

   ;; Authority
   example.       3600 IN SOA ns1.example. bugs.x.w.example. (
                              1081539377
                              3600
                              300
                              3600000
                              3600
                              )
   example.       3600 RRSIG  SOA 5 1 3600 20040509183619 (
                              20040409183619 38519 example.
                              ONx0k36rcjaxYtcNgq6iQnpNV5+drqYAsC9h
                              7TSJaHCqbhE67Sr6aH2xDUGcqQWu/n0UVzrF
                              vkgO9ebarZ0GWDKcuwlM6eNB5SiX2K74l5LW
                              DA7S/Un/IbtDq4Ay8NMNLQI7Dw7n4p8/rjkB
                              jV7j86HyQgM5e7+miRAz8V01b0I= )
   x.y.w.example. 3600 NSEC   xx.example. MX RRSIG NSEC
   x.y.w.example. 3600 RRSIG  NSEC 5 4 3600 20040509183619 (
                              20040409183619 38519 example.
                              OvE6WUzN2ziieJcvKPWbCAyXyP6ef8cr6Csp



<span class="grey">Arends, et al.              Standards Track                    [Page 47]</span></pre>
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<span class="grey"><a href="./rfc4035">RFC 4035</a>             DNSSEC Protocol Modifications            March 2005</span>


                              ArVSTzKSquNwbezZmkU7E34o5lmb6CWSSSpg
                              xw098kNUFnHcQf/LzY2zqRomubrNQhJTiDTX
                              a0ArunJQCzPjOYq5t0SLjm6qp6McJI1AP5Vr
                              QoKqJDCLnoAlcPOPKAm/jJkn3jk= )
   *.w.example.   3600 NSEC   x.w.example. MX RRSIG NSEC
   *.w.example.   3600 RRSIG  NSEC 5 2 3600 20040509183619 (
                              20040409183619 38519 example.
                              r/mZnRC3I/VIcrelgIcteSxDhtsdlTDt8ng9
                              HSBlABOlzLxQtfgTnn8f+aOwJIAFe1Ee5RvU
                              5cVhQJNP5XpXMJHfyps8tVvfxSAXfahpYqtx
                              91gsmcV/1V9/bZAG55CefP9cM4Z9Y9NT9XQ8
                              s1InQ2UoIv6tJEaaKkP701j8OLA= )

   ;; Additional
   ;; (empty)

<span class="h3"><a class="selflink" id="appendix-B.8" href="#appendix-B.8">B.8</a>.  DS Child Zone No Data Error</span>

   A "no data" response for a QTYPE=DS query that was mistakenly sent to
   a name server for the child zone.

   ;; Header: QR AA DO RCODE=0
   ;;
   ;; Question
   example.            IN DS

   ;; Answer
   ;; (empty)

   ;; Authority
   example.       3600 IN SOA ns1.example. bugs.x.w.example. (
                              1081539377
                              3600
                              300
                              3600000
                              3600
                              )
   example.       3600 RRSIG  SOA 5 1 3600 20040509183619 (
                              20040409183619 38519 example.
                              ONx0k36rcjaxYtcNgq6iQnpNV5+drqYAsC9h
                              7TSJaHCqbhE67Sr6aH2xDUGcqQWu/n0UVzrF
                              vkgO9ebarZ0GWDKcuwlM6eNB5SiX2K74l5LW
                              DA7S/Un/IbtDq4Ay8NMNLQI7Dw7n4p8/rjkB
                              jV7j86HyQgM5e7+miRAz8V01b0I= )
   example.       3600 NSEC   a.example. NS SOA MX RRSIG NSEC DNSKEY
   example.       3600 RRSIG  NSEC 5 1 3600 20040509183619 (
                              20040409183619 38519 example.
                              O0k558jHhyrC97ISHnislm4kLMW48C7U7cBm



<span class="grey">Arends, et al.              Standards Track                    [Page 48]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-49" ></span>
<span class="grey"><a href="./rfc4035">RFC 4035</a>             DNSSEC Protocol Modifications            March 2005</span>


                              FTfhke5iVqNRVTB1STLMpgpbDIC9hcryoO0V
                              Z9ME5xPzUEhbvGnHd5sfzgFVeGxr5Nyyq4tW
                              SDBgIBiLQUv1ivy29vhXy7WgR62dPrZ0PWvm
                              jfFJ5arXf4nPxp/kEowGgBRzY/U= )

   ;; Additional
   ;; (empty)

<span class="h2"><a class="selflink" id="appendix-C" href="#appendix-C">Appendix C</a>.  Authentication Examples</span>

   The examples in this section show how the response messages in
   <a href="#appendix-B">Appendix B</a> are authenticated.

<span class="h3"><a class="selflink" id="appendix-C.1" href="#appendix-C.1">C.1</a>.  Authenticating an Answer</span>

   The query in <a href="#appendix-B.1">Appendix B.1</a> returned an MX RRset for "x.w.example.com".
   The corresponding RRSIG indicates that the MX RRset was signed by an
   "example" DNSKEY with algorithm 5 and key tag 38519.  The resolver
   needs the corresponding DNSKEY RR in order to authenticate this
   answer.  The discussion below describes how a resolver might obtain
   this DNSKEY RR.

   The RRSIG indicates the original TTL of the MX RRset was 3600, and,
   for the purpose of authentication, the current TTL is replaced by
   3600.  The RRSIG labels field value of 3 indicates that the answer
   was not the result of wildcard expansion.  The "x.w.example.com" MX
   RRset is placed in canonical form, and, assuming the current time
   falls between the signature inception and expiration dates, the
   signature is authenticated.

<span class="h4"><a class="selflink" id="appendix-C.1.1" href="#appendix-C.1.1">C.1.1</a>.  Authenticating the Example DNSKEY RR</span>

   This example shows the logical authentication process that starts
   from the a configured root DNSKEY (or DS RR) and moves down the tree
   to authenticate the desired "example" DNSKEY RR.  Note that the
   logical order is presented for clarity.  An implementation may choose
   to construct the authentication as referrals are received or to
   construct the authentication chain only after all RRsets have been
   obtained, or in any other combination it sees fit.  The example here
   demonstrates only the logical process and does not dictate any
   implementation rules.

   We assume the resolver starts with a configured DNSKEY RR for the
   root zone (or a configured DS RR for the root zone).  The resolver
   checks whether this configured DNSKEY RR is present in the root
   DNSKEY RRset (or whether the DS RR matches some DNSKEY in the root
   DNSKEY RRset), whether this DNSKEY RR has signed the root DNSKEY
   RRset, and whether the signature lifetime is valid.  If all these



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<span class="grey"><a href="./rfc4035">RFC 4035</a>             DNSSEC Protocol Modifications            March 2005</span>


   conditions are met, all keys in the DNSKEY RRset are considered
   authenticated.  The resolver then uses one (or more) of the root
   DNSKEY RRs to authenticate the "example" DS RRset.  Note that the
   resolver may have to query the root zone to obtain the root DNSKEY
   RRset or "example" DS RRset.

   Once the DS RRset has been authenticated using the root DNSKEY, the
   resolver checks the "example" DNSKEY RRset for some "example" DNSKEY
   RR that matches one of the authenticated "example" DS RRs.  If such a
   matching "example" DNSKEY is found, the resolver checks whether this
   DNSKEY RR has signed the "example" DNSKEY RRset and the signature
   lifetime is valid.  If these conditions are met, all keys in the
   "example" DNSKEY RRset are considered authenticated.

   Finally, the resolver checks that some DNSKEY RR in the "example"
   DNSKEY RRset uses algorithm 5 and has a key tag of 38519.  This
   DNSKEY is used to authenticate the RRSIG included in the response.
   If multiple "example" DNSKEY RRs match this algorithm and key tag,
   then each DNSKEY RR is tried, and the answer is authenticated if any
   of the matching DNSKEY RRs validate the signature as described above.

<span class="h3"><a class="selflink" id="appendix-C.2" href="#appendix-C.2">C.2</a>.  Name Error</span>

   The query in <a href="#appendix-B.2">Appendix B.2</a> returned NSEC RRs that prove that the
   requested data does not exist and no wildcard applies.  The negative
   reply is authenticated by verifying both NSEC RRs.  The NSEC RRs are
   authenticated in a manner identical to that of the MX RRset discussed
   above.

<span class="h3"><a class="selflink" id="appendix-C.3" href="#appendix-C.3">C.3</a>.  No Data Error</span>

   The query in <a href="#appendix-B.3">Appendix B.3</a> returned an NSEC RR that proves that the
   requested name exists, but the requested RR type does not exist.  The
   negative reply is authenticated by verifying the NSEC RR.  The NSEC
   RR is authenticated in a manner identical to that of the MX RRset
   discussed above.

<span class="h3"><a class="selflink" id="appendix-C.4" href="#appendix-C.4">C.4</a>.  Referral to Signed Zone</span>

   The query in <a href="#appendix-B.4">Appendix B.4</a> returned a referral to the signed
   "a.example." zone.  The DS RR is authenticated in a manner identical
   to that of the MX RRset discussed above.  This DS RR is used to
   authenticate the "a.example" DNSKEY RRset.

   Once the "a.example" DS RRset has been authenticated using the
   "example" DNSKEY, the resolver checks the "a.example" DNSKEY RRset
   for some "a.example" DNSKEY RR that matches the DS RR.  If such a
   matching "a.example" DNSKEY is found, the resolver checks whether



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<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-51" ></span>
<span class="grey"><a href="./rfc4035">RFC 4035</a>             DNSSEC Protocol Modifications            March 2005</span>


   this DNSKEY RR has signed the "a.example" DNSKEY RRset and whether
   the signature lifetime is valid.  If all these conditions are met,
   all keys in the "a.example" DNSKEY RRset are considered
   authenticated.

<span class="h3"><a class="selflink" id="appendix-C.5" href="#appendix-C.5">C.5</a>.  Referral to Unsigned Zone</span>

   The query in <a href="#appendix-B.5">Appendix B.5</a> returned a referral to an unsigned
   "b.example." zone.  The NSEC proves that no authentication leads from
   "example" to "b.example", and the NSEC RR is authenticated in a
   manner identical to that of the MX RRset discussed above.

<span class="h3"><a class="selflink" id="appendix-C.6" href="#appendix-C.6">C.6</a>.  Wildcard Expansion</span>

   The query in <a href="#appendix-B.6">Appendix B.6</a> returned an answer that was produced as a
   result of wildcard expansion.  The answer section contains a wildcard
   RRset expanded as it would be in a traditional DNS response, and the
   corresponding RRSIG indicates that the expanded wildcard MX RRset was
   signed by an "example" DNSKEY with algorithm 5 and key tag 38519.
   The RRSIG indicates that the original TTL of the MX RRset was 3600,
   and, for the purpose of authentication, the current TTL is replaced
   by 3600.  The RRSIG labels field value of 2 indicates that the answer
   is the result of wildcard expansion, as the "a.z.w.example" name
   contains 4 labels.  The name "a.z.w.w.example" is replaced by
   "*.w.example", the MX RRset is placed in canonical form, and,
   assuming that the current time falls between the signature inception
   and expiration dates, the signature is authenticated.

   The NSEC proves that no closer match (exact or closer wildcard) could
   have been used to answer this query, and the NSEC RR must also be
   authenticated before the answer is considered valid.

<span class="h3"><a class="selflink" id="appendix-C.7" href="#appendix-C.7">C.7</a>.  Wildcard No Data Error</span>

   The query in <a href="#appendix-B.7">Appendix B.7</a> returned NSEC RRs that prove that the
   requested data does not exist and no wildcard applies.  The negative
   reply is authenticated by verifying both NSEC RRs.

<span class="h3"><a class="selflink" id="appendix-C.8" href="#appendix-C.8">C.8</a>.  DS Child Zone No Data Error</span>

   The query in <a href="#appendix-B.8">Appendix B.8</a> returned NSEC RRs that shows the requested
   was answered by a child server ("example" server).  The NSEC RR
   indicates the presence of an SOA RR, showing that the answer is from
   the child .  Queries for the "example" DS RRset should be sent to the
   parent servers ("root" servers).






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<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-52" ></span>
<span class="grey"><a href="./rfc4035">RFC 4035</a>             DNSSEC Protocol Modifications            March 2005</span>


Authors' Addresses

   Roy Arends
   Telematica Instituut
   Brouwerijstraat 1
   7523 XC  Enschede
   NL

   EMail: roy.arends@telin.nl


   Rob Austein
   Internet Systems Consortium
   950 Charter Street
   Redwood City, CA  94063
   USA

   EMail: sra@isc.org


   Matt Larson
   VeriSign, Inc.
   21345 Ridgetop Circle
   Dulles, VA  20166-6503
   USA

   EMail: mlarson@verisign.com


   Dan Massey
   Colorado State University
   Department of Computer Science
   Fort Collins, CO 80523-1873

   EMail: massey@cs.colostate.edu


   Scott Rose
   National Institute for Standards and Technology
   100 Bureau Drive
   Gaithersburg, MD  20899-8920
   USA

   EMail: scott.rose@nist.gov







<span class="grey">Arends, et al.              Standards Track                    [Page 52]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-53" ></span>
<span class="grey"><a href="./rfc4035">RFC 4035</a>             DNSSEC Protocol Modifications            March 2005</span>


Full Copyright Statement

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