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Internet-Draft                  dnsext-wcard           January 9, 2006

DNSEXT Working Group                                          E. Lewis
INTERNET DRAFT                                                 NeuStar
Expiration Date: July 9, 2006                          January 9, 2006
Updates RFC 1034, RFC 2672

                              The Role of Wildcards
                            in the Domain Name System
                      draft-ietf-dnsext-wcard-clarify-10.txt

Status of this Memo

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Copyright Notice

      Copyright (C) The Internet Society (2006).

Abstract

      This is an update to the wildcard definition of RFC 1034.  The
      interaction with wildcards and CNAME is changed, an error
      condition removed, and the words defining some concepts central
      to wildcards are changed.  The overall goal is not to change
      wildcards, but to refine the definition of RFC 1034.




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Table of Contents

1.    Introduction   .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  3
1 1   Motivation                                                     3
1 2   The Original Definition                                        3
1 3   Roadmap to This Document                                       4
1 3 1 New Terms                                                      4
1.3.2 Changed Text                                                   5
1.3.3 Considerations with Special Types                              5
1.4   Standards Terminology                                          5
2.    Wildcard Syntax   .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  6
2.1   Identifying a Wildcard                                         6
2.1.1 Wild Card Domain Name and Asterisk Label                       6
2.1.2 Asterisks and Other Characters                                 6
2.1.3 Non-terminal Wild Card Domain Names                            6
2.2   Existence Rules                                                7
2.2.1 An Example                                                     7
2.2.2 Empty Non-terminals                                            9
2.2.3 Yet Another Definition of Existence                           10
2.3   When is a Wild Card Domain Name Not Special                   10
3.    Impact of a Wild Card Domain Name On a Response .  .  .  .  . 10
3.1   Step 2                                                        10
3.2   Step 3                                                        11
3.3   Part 'c'                                                      11
3.3.1 Closest Encloser and the Source of Synthesis                  12
3.3.2 Closest Encloser and Source of Synthesis Examples             12
3.3.3 Type Matching                                                 13
4.    Considerations with Special Types   .  .  .  .  .  .  .  .  . 13
4.1   SOA RRSet at a Wild Card Domain Name                          13
4.2   NS RRSet at a Wild Card Domain Name                           14
4.2.1 Discarded Notions                                             14
4.3   CNAME RRSet at a Wild Card Domain Name                        15
4.4   DNAME RRSet at a Wild Card Domain Name                        15
4.5   SRV RRSet at a Wild Card Domain Name                          16
4.6   DS RRSet at a Wild Card Domain Name                           16
4.7   NSEC RRSet at a Wild Card Domain Name                         17
4.8   RRSIG at a Wild Card Domain Name                              17
4.9   Empty Non-terminal Wild Card Domain Name                      17
5.    Security Considerations .  .  .  .  .  .  .  .  .  .  .  .  . 17
6.    IANA Considerations     .  .  .  .  .  .  .  .  .  .  .  .  . 17
7.    References              .  .  .  .  .  .  .  .  .  .  .  .  . 17
8.    Editor                  .  .  .  .  .  .  .  .  .  .  .  .  . 18
9.    Others Contributing to the Document    .  .  .  .  .  .  .  . 18
10.   Trailing Boilerplate    .  .  .  .  .  .  .  .  .  .  .  .  . 19








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1. Introduction

      In RFC 1034 [RFC1034], sections 4.3.2 and 4.3.3 describe the
      synthesis of answers from special resource records called
      wildcards.  The definition in RFC 1034 is incomplete and has
      proven to be confusing.  This document describes the wildcard
      synthesis by adding to the discussion and making limited
      modifications.  Modifications are made to close inconsistencies
      that have led to interoperability issues.  This description
      does not expand the service intended by the original definition.

      Staying within the spirit and style of the original documents,
      this document avoids specifying rules for DNS implementations
      regarding wildcards.  The intention is to only describe what is
      needed for interoperability, not restrict implementation choices.
      In addition, consideration is given to minimize any backwards
      compatibility issues with implementations that comply with RFC
      1034's definition.

      This document is focused on the concept of wildcards as defined
      in RFC 1034.  Nothing is implied regarding alternative means of
      synthesizing resource record sets, nor are alternatives discussed.

1.1 Motivation

      Many DNS implementations diverge, in different ways, from the
      original definition of wildcards.  Although there is clearly a
      need to clarify the original documents in light of this alone,
      the impetus for this document lay in the engineering of the DNS
      security extensions [RFC4033].  With an unclear definition of
      wildcards the design of authenticated denial became entangled.

      This document is intended to limit its changes, documenting only
      those based on implementation experience, and to remain as close
      to the original document as possible.  To reinforce that this
      document is meant to clarify and adjust and not redefine wildcards,
      relevant sections of RFC 1034 are repeated verbatim to facilitate
      comparison of the old and new text.

1.2 The Original Definition

      The definition of the wildcard concept is comprised by the
      documentation of the algorithm by which a name server prepares
      a response (in RFC 1034's section 4.3.2) and the way in which
      a resource record (set) is identified as being a source of
      synthetic data (section 4.3.3).

      This is the definition of the term "wildcard" as it appears in
      RFC 1034, section 4.3.3.



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# In the previous algorithm, special treatment was given to RRs with
# owner names starting with the label "*".  Such RRs are called
# wildcards. Wildcard RRs can be thought of as instructions for
# synthesizing RRs.  When the appropriate conditions are met, the name
# server creates RRs with an owner name equal to the query name and
# contents taken from the wildcard RRs.

      This passage follows the algorithm in which the term wildcard
      is first used.   In this definition, wildcard refers to resource
      records.  In other usage, wildcard has referred to domain names,
      and it has been used to describe the operational practice of
      relying on wildcards to generate answers.  It is clear from this
      that there is a need to define clear and unambiguous terminology
      in the process of discussing wildcards.

      The mention of the use of wildcards in the preparation of a
      response is contained in step 3c of RFC 1034's section 4.3.2
      entitled "Algorithm."  Note that "wildcard" does not appear in
      the algorithm, instead references are made to the "*" label.
      The portion of the algorithm relating to wildcards is
      deconstructed in detail in section 3 of this document, this is
      the beginning of the relevant portion of the "Algorithm."

#    c. If at some label, a match is impossible (i.e., the
#       corresponding label does not exist), look to see if [...]
#       the "*" label exists.

      The scope of this document is the RFC 1034 definition of
      wildcards and the implications of updates to those documents,
      such as DNSSEC.  Alternate schemes for synthesizing answers are
      not considered.  (Note that there is no reference listed.  No
      document is known to describe any alternate schemes, although
      there has been some mention of them in mailing lists.)

1.3 Roadmap to This Document

      This document accomplishes these three items.
      o Defines new terms
      o Makes minor changes to avoid conflicting concepts
      o Describes the actions of certain resource records as wildcards

1.3.1 New Terms

      To help in discussing what resource records are wildcards, two
      terms will be defined - "asterisk label" and "wild card domain
      name".  These are defined in section 2.1.1.

      To assist in clarifying the role of wildcards in the name server
      algorithm in RFC 1034, 4.3.2, "source of synthesis" and "closest
      encloser" are defined.  These definitions are in section 3.3.2.
      "Label match" is defined in section 3.2.

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      The new terms are used to make discussions of wildcards clearer.
      Terminology doesn't directly have an impact on implementations.

1.3.2 Changed Text

      The definition of "existence" is changed superficially.  This
      change will not be apparent to implementations; it is needed to
      make descriptions more precise.  The change appears in section
      2.2.3.

      RFC 1034, section 4.3.3., seems to prohibit having two asterisk
      labels in a wildcard owner name.  With this document the
      restriction is removed entirely.  This change and its implications
      are in section 2.1.3.

      The actions when a source of synthesis owns a CNAME RR are
      changed to mirror the actions if an exact match name owns a
      CNAME RR.  This is an addition to the words in RFC 1034,
      section 4.3.2, step 3, part c.  The discussion of this is in
      section 3.3.3.

      Only the latter change represents an impact to implementations.
      The definition of existence is not a protocol impact.  The change
      to the restriction on names is unlikely to have an impact, as
      RFC 1034 contained no specification on when and how to enforce the
      restriction.

1.3.3 Considerations with Special Types

      This document describes semantics of wildcard RRSets for
      "interesting" types as well as empty non-terminal wildcards.
      Understanding these situations in the context of wildcards has
      been clouded because these types incur special processing if
      they are the result of an exact match.  This discussion is in
      section 4.

      These discussions do not have an implementation impact, they cover
      existing knowledge of the types, but to a greater level of detail.

1.4 Standards Terminology

      This document does not use terms as defined in "Key words for use
      in RFCs to Indicate Requirement Levels." [RFC2119]

      Quotations of RFC 1034 are denoted by a '#' in the leftmost
      column.  References to section "4.3.2" are assumed to refer
      to RFC 1034's section 4.3.2, simply titled "Algorithm."





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2. Wildcard Syntax

      The syntax of a wildcard is the same as any other DNS resource
      record, across all classes and types.  The only significant
      feature is the owner name.

      Because wildcards are encoded as resource records with special
      names, they are included in zone transfers and incremental zone
      transfers[RFC1995] just as non-wildcard resource records are.
      This feature has been under appreciated until discussions on
      alternative approaches to wildcards appeared on mailing lists.

2.1 Identifying a Wildcard

      To provide a more accurate description of wildcards, the
      definition has to start with a discussion of the domain names
      that appear as owners.  Two new terms are needed, "Asterisk
      Label" and "Wild Card Domain Name."

2.1.1 Wild Card Domain Name and Asterisk Label

      A "wild card domain name" is defined by having its initial
      (i.e., left-most or least significant) label be, in binary format:

           0000 0001 0010 1010 (binary) = 0x01 0x2a (hexadecimal)

      The first octet is the normal label type and length for a 1 octet
      long label, the second octet is the ASCII representation [RFC20]
      for the '*' character.

      A descriptive name of a label equaling that value is an "asterisk
      label."

      RFC 1034's definition of wildcard would be "a resource record
      owned by a wild card domain name."

2.1.2 Asterisks and Other Characters

      No label values other than that in section 2.1.1 are asterisk
      labels, hence names beginning with other labels are never wild
      card domain names.  Labels such as 'the*' and '**' are not
      asterisk labels so these labels do not start wild card domain
      names.

2.1.3 Non-terminal Wild Card Domain Names

      In section 4.3.3, the following is stated:

# ..........................  The owner name of the wildcard RRs is of
# the form "*.<anydomain>", where <anydomain> is any domain name.
# <anydomain> should not contain other * labels......................

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      The restriction is now removed.  The original documentation of it
      is incomplete and the restriction does not serve any purpose
      given years of operational experience.

      There are three possible reasons for putting the restriction in
      place, but none of the three has held up over time.  One is
      that the restriction meant that there would never be subdomains
      of wild card domain names, but the restriciton as stated still
      permits "example.*.example." for instance.  Another is that
      wild card domain names are not intended to be empty non-terminals,
      but this situation does not disrupt the algorithm in 4.3.2.
      Finally, "nested" wild card domain names are not ambiguous once
      the concept of the closest encloser had been documented.

      A wild card domain name can have subdomains.  There is no need
      to inspect the subdomains to see if there is another asterisk
      label in any subdomain.

      A wild card domain name can be an empty non-terminal.  (See the
      upcoming sections on empty non-terminals.)  In this case, any
      lookup encountering it will terminate as would any empty
      non-terminal match.

2.2 Existence Rules

      The notion that a domain name 'exists' is mentioned in the
      definition of wildcards.  In section 4.3.3 of RFC 1034:

# Wildcard RRs do not apply:
#
...
#   - When the query name or a name between the wildcard domain and
#     the query name is know[n] to exist.  For example, if a wildcard

      "Existence" is therefore an important concept in the understanding
      of wildcards.  Unfortunately, the definition of what exists, in RFC
      1034, is unclear.  So, in sections 2.2.2. and 2.2.3, another look is
      taken at the definition of existence.

2.2.1 An Example

      To illustrate what is meant by existence consider this complete
      zone:









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        $ORIGIN example.
        example.                 3600 IN  SOA   <SOA RDATA>
        example.                 3600     NS    ns.example.com.
        example.                 3600     NS    ns.example.net.
        *.example.               3600     TXT   "this is a wild card"
        *.example.               3600     MX    10 host1.example.
        sub.*.example.           3600     TXT   "this is not a wild card"
        host1.example.           3600     A     192.0.4.1
        _ssh._tcp.host1.example. 3600     SRV  <SRV RDATA>
        _ssh._tcp.host2.example. 3600     SRV  <SRV RDATA>
        subdel.example.          3600     NS   ns.example.com.
        subdel.example.          3600     NS   ns.example.net.

      A look at the domain names in a tree structure is helpful:

                                    |
                    -------------example------------
                   /           /         \          \
                  /           /           \          \
                 /           /             \          \
                *          host1          host2      subdel
                |            |             |
                |            |             |
               sub         _tcp          _tcp
                             |             |
                             |             |
                           _ssh          _ssh

      The following responses would be synthesized from one of the
      wildcards in the zone:

          QNAME=host3.example. QTYPE=MX, QCLASS=IN
               the answer will be a "host3.example. IN MX ..."

          QNAME=host3.example. QTYPE=A, QCLASS=IN
               the answer will reflect "no error, but no data"
               because there is no A RR set at '*.example.'

          QNAME=foo.bar.example. QTYPE=TXT, QCLASS=IN
               the answer will be "foo.bar.example. IN TXT ..."
               because bar.example. does not exist, but the wildcard
               does.

      The following responses would not be synthesized from any of the
      wildcards in the zone:

          QNAME=host1.example., QTYPE=MX, QCLASS=IN
               because host1.example. exists

          QNAME=sub.*.example., QTYPE=MX, QCLASS=IN
               because sub.*.example. exists

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          QNAME=_telnet._tcp.host1.example., QTYPE=SRV, QCLASS=IN
               because _tcp.host1.example. exists (without data)

          QNAME=host.subdel.example., QTYPE=A, QCLASS=IN
               because subdel.example. exists (and is a zone cut)

          QNAME=ghost.*.example., QTYPE=MX, QCLASS=IN
               because *.example. exists

      The final example highlights one common misconception about
      wildcards.  A wildcard "blocks itself" in the sense that a
      wildcard does not match its own subdomains.  I.e. "*.example."
      does not match all names in the "example." zone, it fails to
      match the names below "*.example." To cover names under
      "*.example.", another wild card domain name is needed -
      "*.*.example." - which covers all but it's own subdomains.

2.2.2 Empty Non-terminals

      Empty non-terminals [RFC2136, Section 7.16] are domain names
      that own no resource records but have subdomains that do.  In
      section 2.2.1, "_tcp.host1.example." is an example of a empty
      non-terminal name.  Empty non-terminals are introduced by this
      text in section 3.1 of RFC 1034:

# The domain name space is a tree structure.  Each node and leaf on
# the tree corresponds to a resource set (which may be empty).  The
# domain system makes no distinctions between the uses of the
# interior nodes and leaves, and this memo uses the term "node" to
# refer to both.

      The parenthesized "which may be empty" specifies that empty non-
      terminals are explicitly recognized, and that empty non-terminals
      "exist."

      Pedantically reading the above paragraph can lead to an
      interpretation that all possible domains exist - up to the
      suggested limit of 255 octets for a domain name [RFC1035].
      For example, www.example. may have an A RR, and as far as is
      practically concerned, is a leaf of the domain tree.  But the
      definition can be taken to mean that sub.www.example. also
      exists, albeit with no data.  By extension, all possible domains
      exist, from the root on down.

      As RFC 1034 also defines "an authoritative name error indicating
      that the name does not exist" in section 4.3.1, so this apparently
      is not the intent of the original definition, justifying the
      need for an updated definition in the next section.




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2.2.3 Yet Another Definition of Existence

      RFC1034's wording is fixed by the following paragraph:

      The domain name space is a tree structure.  Nodes in the tree
      either own at least one RRSet and/or have descendants that
      collectively own at least one RRSet.  A node may exist with no
      RRSets only if it has descendents that do, this node is an empty
      non-terminal.

      A node with no descendants is a leaf node.  Empty leaf nodes do
      not exist.

      Note that at a zone boundary, the domain name owns data,
      including the NS RR set.  In the delegating zone, the NS RR
      set is not authoritative, but that is of no consequence here.
      The domain name owns data, therefore, it exists.

2.3 When is a Wild Card Domain Name Not Special

      When a wild card domain name appears in a message's query section,
      no special processing occurs.  An asterisk label in a query name
      only matches a single, corresponding asterisk label in the
      existing zone tree when the 4.3.2 algorithm is being followed.

      When a wild card domain name appears in the resource data of a
      record, no special processing occurs.  An asterisk label in that
      context literally means just an asterisk.

3. Impact of a Wild Card Domain Name On a Response

      RFC 1034's description of how wildcards impact response
      generation is in its section 4.3.2.  That passage contains the
      algorithm followed by a server in constructing a response.
      Within that algorithm, step 3, part 'c' defines the behavior of
      the wildcard.

      The algorithm in section 4.3.2. is not intended to be pseudo-code,
      i.e., its steps are not intended to be followed in strict order.
      The "algorithm" is a suggested means of implementing the
      requirements.  As such, in step 3, parts a, b, and c, do not have
      to be implemented in that order, provided that the result of the
      implemented code is compliant with the protocol's specification.

3.1 Step 2

      Step 2 of section 4.3.2 reads:

#   2. Search the available zones for the zone which is the nearest
#      ancestor to QNAME.  If such a zone is found, go to step 3,
#      otherwise step 4.

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      In this step, the most appropriate zone for the response is
      chosen.  The significance of this step is that it means all of
      step 3 is being performed within one zone.  This has significance
      when considering whether or not an SOA RR can be ever be used for
      synthesis.

3.2 Step 3

      Step 3 is dominated by three parts, labelled 'a', 'b', and 'c'.
      But the beginning of the step is important and needs explanation.

#   3. Start matching down, label by label, in the zone.  The
#      matching process can terminate several ways:

      The word 'matching' refers to label matching.  The concept
      is based in the view of the zone as the tree of existing names.
      The query name is considered to be an ordered sequence of
      labels - as if the name were a path from the root to the owner
      of the desired data.  (Which it is - 3rd paragraph of RFC 1034,
      section 3.1.)

      The process of label matching a query name ends in exactly one of
      three choices, the parts 'a', 'b', and 'c'.  Either the name is
      found, the name is below a cut point, or the name is not found.

      Once one of the parts is chosen, the other parts are not
      considered.  (E.g., do not execute part 'c' and then change
      the execution path to finish in part 'b'.)  The process of label
      matching is also done independent of the query type (QTYPE).

      Parts 'a' and 'b' are not an issue for this clarification as they
      do not relate to record synthesis.  Part 'a' is an exact match
      that results in an answer, part 'b' is a referral.

3.3 Part 'c'

      The context of part 'c' is that the process of label matching the
      labels of the query name has resulted in a situation in which
      there is no corresponding label in the tree.  It is as if the
      lookup has "fallen off the tree."

#     c. If at some label, a match is impossible (i.e., the
#        corresponding label does not exist), look to see if [...]
#        the "*" label exists.

      To help describe the process of looking 'to see if [...] the "*"
      label exists' a term has been coined to describe the last domain
      (node) matched.  The term is "closest encloser."




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3.3.1 Closest Encloser and the Source of Synthesis

      The closest encloser is the node in the zone's tree of existing
      domain names that has the most labels matching the query name
      (consecutively, counting from the root label downward). Each match
      is a "label match" and the order of the labels is the same.

      The closest encloser is, by definition, an existing name in the
      zone.  The closest encloser might be an empty non-terminal or even
      be a wild card domain name itself.  In no circumstances is the
      closest encloser to be used to synthesize records for the current
      query.

      The source of synthesis is defined in the context of a query
      process as that wild card domain name immediately descending
      from the closest encloser, provided that this wild card domain
      name exists.  "Immediately descending" means that the source
      of synthesis has a name of the form:
            <asterisk label>.<closest encloser>.
      A source of synthesis does not guarantee having a RRSet to use
      for synthesis.  The source of synthesis could be an empty
      non-terminal.

      If the source of synthesis does not exist (not on the domain
      tree), there will be no wildcard synthesis.  There is no search
      for an alternate.

      The important concept is that for any given lookup process, there
      is at most one place at which wildcard synthetic records can be
      obtained.  If the source of synthesis does not exist, the lookup
      terminates, the lookup does not look for other wildcard records.

3.3.2 Closest Encloser and Source of Synthesis Examples

      To illustrate, using the example zone in section 2.2.1 of this
      document, the following chart shows QNAMEs and the closest
      enclosers.

      QNAME                       Closest Encloser    Source of Synthesis
      host3.example.              example.            *.example.
      _telnet._tcp.host1.example. _tcp.host1.example. no source
      _telnet._tcp.host2.example. host2.example.      no source
      _telnet._tcp.host3.example. example.            *.example.
      _chat._udp.host3.example.   example.            *.example.
      foobar.*.example.           *.example.          no source







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3.3.3 Type Matching

       RFC 1034 concludes part 'c' with this:

#            If the "*" label does not exist, check whether the name
#            we are looking for is the original QNAME in the query
#            or a name we have followed due to a CNAME.  If the name
#            is original, set an authoritative name error in the
#            response and exit.  Otherwise just exit.
#
#            If the "*" label does exist, match RRs at that node
#            against QTYPE.  If any match, copy them into the answer
#            section, but set the owner of the RR to be QNAME, and
#            not the node with the "*" label.  Go to step 6.

      The final paragraph covers the role of the QTYPE in the lookup
      process.

      Based on implementation feedback and similarities between step
      'a' and step 'c' a change to this passage has been made.

      The change is to add the following text to step 'c' prior to the
      instructions to "go to step 6":

               If the data at the source of synthesis is a CNAME, and
               QTYPE doesn't match CNAME, copy the CNAME RR into the
               answer section of the response changing the owner name
               to the QNAME, change QNAME to the canonical name in the
               CNAME RR, and go back to step 1.

      This is essentially the same text in step a covering the
      processing of CNAME RRSets.

4. Considerations with Special Types

      Sections 2 and 3 of this document discuss wildcard synthesis
      with respect to names in the domain tree and ignore the impact
      of types.  In this section, the implication of wildcards of
      specific types are discussed.  The types covered are those
      that have proven to be the most difficult to understand.  The
      types are SOA, NS, CNAME, DNAME, SRV, DS, NSEC, RRSIG and
      "none," i.e., empty non-terminal wild card domain names.

4.1 SOA RRSet at a Wild Card Domain Name

      A wild card domain name owning an SOA RRSet means that the
      domain is at the root of the zone (apex).  The domain can not
      be a source of synthesis because that is, by definition, a
      descendent node (of the closest encloser) and a zone apex is
      at the top of the zone.


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      Although a wild card domain name owning an SOA RRSet can never
      be a source of synthesis, there is no reason to forbid the
      ownership of an SOA RRSet.

      E.g., given this zone:
             $ORIGIN *.example.
             @                 3600 IN  SOA   <SOA RDATA>
                               3600     NS    ns1.example.com.
                               3600     NS    ns1.example.net.
             www               3600     TXT   "the www txt record"

      A query for www.*.example.'s TXT record would still find the
      "the www txt record" answer.  The asterisk label only becomes
      significant when section 4.3.2, step 3 part 'c' is in effect.

      Of course, there would need to be a delegation in the parent
      zone, "example." for this to work too.  This is covered in the
      next section.

4.2 NS RRSet at a Wild Card Domain Name

      With the definition of DNSSEC [RFC4033, RFC4034, RFC4035] now
      in place, the semantics of a wild card domain name owning an
      NS RRSet has come to be poorly defined.  The dilemma relates to
      a conflict between the rules for synthesis in part 'c' and the
      fact that the resulting synthesis generates a record for which
      the zone is not authoritative.  In a DNSSEC signed zone, the
      mechanics of signature management (generation and inclusion
      in a message) have become unclear.

      Salient points of the working group discussion on this topic is
      summarized in section 4.2.1.

      As a result of these discussion, there is no definition given for
      wild card domain names owning an NS RRSet.  The semantics are
      left undefined until there is a clear need to have a set defined,
      and until there is a clear direction to proceed.  Operationally,
      inclusion of wild card NS RRSets in a zone is discouraged, but
      not barred.

4.2.1 Discarded Notions

      Prior to DNSSEC, a wild card domain name owning a NS RRSet
      appeared to be workable, and there are some instances in which
      it is found in deployments using implementations that support
      this.  Continuing to allow this in the specification is not
      tenable with DNSSEC.  The reason is that the synthesis of the
      NS RRSet is being done in a zone that has delegated away the
      responsibility for the name.  This "unauthorized" synthesis is
      not a problem for the base DNS protocol, but DNSSEC, in affirming
      the authorization model for DNS exposes the problem.

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      Outright banning of wildcards of type NS is also untenable as
      the DNS protocol does not define how to handle "illegal" data.
      Implementations may choose not to load a zone, but there is no
      protocol definition.  The lack of the definition is complicated
      by having to cover dynamic update [RFC 2136], zone transfers,
      as well as loading at the master server.  The case of a client
      (resolver, caching server) getting a wildcard of type NS in
      a reply would also have to be considered.

      Given the daunting challenge of a complete definition of how to
      ban such records, dealing with existing implementations that
      permit the records today is a further complication.  There are
      uses of wild card domain name owning NS RRSets.

      One compromise proposed would have redefined wildcards of type
      NS to not be used in synthesis, this compromise fell apart
      because it would have required significant edits to the DNSSEC
      signing and validation work.  (Again, DNSSEC catches
      unauthorized data.)

      With no clear consensus forming on the solution to this dilemma,
      and the realization that wildcards of type NS are a rarity in
      operations, the best course of action is to leave this open-ended
      until "it matters."

4.3 CNAME RRSet at a Wild Card Domain Name

      The issue of a CNAME RRSet owned by a wild card domain name has
      prompted a suggested change to the last paragraph of step 3c of
      the algorithm in 4.3.2.  The changed text appears in section
      3.3.3 of this document.

4.4 DNAME RRSet at a Wild Card Domain Name

      Ownership of a DNAME [RFC2672] RRSet by a wild card domain name
      represents a threat to the coherency of the DNS and is to be
      avoided or outright rejected.  Such a DNAME RRSet represents
      non-deterministic synthesis of rules fed to different caches.
      As caches are fed the different rules (in an unpredictable
      manner) the caches will cease to be coherent.  ("As caches
      are fed" refers to the storage in a cache of records obtained
      in responses by recursive or iterative servers.)

      For example, assume one cache, responding to a recursive
      request, obtains the record:
         "a.b.example. DNAME foo.bar.example.net."
      and another cache obtains:
         "b.example.  DNAME foo.bar.example.net."
      both generated from the record:
         "*.example. DNAME foo.bar.example.net."
      by an authoritative server.

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      The DNAME specification is not clear on whether DNAME records
      in a cache are used to rewrite queries.  In some interpretations,
      the rewrite occurs, in some, it is not.  Allowing for the
      occurrence of rewriting, queries for "sub.a.b.example. A" may
      be rewritten as "sub.foo.bar.tld. A" by the former caching
      server and may be rewritten as "sub.a.foo.bar.tld. A" by the
      latter.  Coherency is lost, an operational nightmare ensues.

      Another justification for banning or avoiding wildcard DNAME
      records is the observation that such a record could synthesize
      a DNAME owned by "sub.foo.bar.example." and "foo.bar.example."
      There is a restriction in the DNAME definition that no domain
      exist below a DNAME-owning domain, hence, the wildcard DNAME
      is not to be permitted.

4.5 SRV RRSet at a Wild Card Domain Name

      The definition of the SRV RRset is RFC 2782 [RFC2782].  In the
      definition of the record, there is some confusion over the term
      "Name."  The definition reads as follows:

# The format of the SRV RR
...
#    _Service._Proto.Name TTL Class SRV Priority Weight Port Target
...
#  Name
#   The domain this RR refers to.  The SRV RR is unique in that the
#   name one searches for is not this name; the example near the end
#   shows this clearly.

      Do not confuse the definition "Name" with the owner name.  I.e.,
      once removing the _Service and _Proto labels from the owner name
      of the SRV RRSet, what remains could be a wild card domain name
      but this is immaterial to the SRV RRSet.

      E.g.,  If an SRV record is:
         _foo._udp.*.example. 10800 IN SRV 0 1 9 old-slow-box.example.

      *.example is a wild card domain name and although it is the Name
      of the SRV RR, it is not the owner (domain name).  The owner
      domain name is "_foo._udp.*.example." which is not a wild card
      domain name.

      The confusion is likely based on the mixture of the specification
      of the SRV RR and the description of a "use case."

4.6 DS RRSet at a Wild Card Domain Name

      A DS RRSet owned by a wild card domain name is meaningless and
      harmless.  This statement is made in the context that an NS RRSet
      at a wild card domain name is undefined.  At a non-delegation

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      point, a DS RRSet has no value (no corresponding DNSKEY RRSet
      will be used in DNSSEC validation).  If there is a synthesized
      DS RRSet, it alone will not be very useful as it exists in the
      context of a delegation point.

4.7 NSEC RRSet at a Wild Card Domain Name

      Wild card domain names in DNSSEC signed zones will have an NSEC
      RRSet.  Synthesis of these records will only occur when the
      query exactly matches the record.  Synthesized NSEC RR's will not
      be harmful as they will never be used in negative caching or to
      generate a negative response.  [RFC2308]

4.8 RRSIG at a Wild Card Domain Name

      RRSIG records will be present at a wild card domain name in a
      signed zone, and will be synthesized along with data sought in a
      query.  The fact that the owner name is synthesized is not a
      problem as the label count in the RRSIG will instruct the
      verifying code to ignore it.

4.9 Empty Non-terminal Wild Card Domain Name

      If a source of synthesis is an empty non-terminal, then the
      response will be one of no error in the return code and no RRSet
      in the answer section.

5. Security Considerations

      This document is refining the specifications to make it more
      likely that security can be added to DNS.  No functional
      additions are being made, just refining what is considered
      proper to allow the DNS, security of the DNS, and extending
      the DNS to be more predictable.

6. IANA Considerations

       None.

7. References

      Normative References

      [RFC20]   ASCII Format for Network Interchange, V.G. Cerf,
                Oct-16-1969

      [RFC1034] Domain Names - Concepts and Facilities,
                P.V. Mockapetris, Nov-01-1987

      [RFC1035] Domain Names - Implementation and Specification, P.V
                Mockapetris, Nov-01-1987

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      [RFC1995] Incremental Zone Transfer in DNS, M. Ohta, August 1996

      [RFC2119] Key Words for Use in RFCs to Indicate Requirement
                Levels, S Bradner, March 1997

      [RFC2308] Negative Caching of DNS Queries (DNS NCACHE),
                M. Andrews, March 1998

      [RFC2672] Non-Terminal DNS Name Redirection, M. Crawford,
                August 1999.

      [RFC2782] A DNS RR for specifying the location of services (DNS
                SRV), A. Gulbrandsen, et.al., February 2000

      [RFC4033] DNS Security Introduction and Requirements, R. Arends,
                et.al., March 2005

      [RFC4034] Resource Records for the DNS Security Extensions,
                R. Arends, et.al., March 2005

      [RFC4035] Protocol Modifications for the DNS Security Extensions,
                R. Arends, et.al., March 2005

      Informative References

      [RFC2136] Dynamic Updates in the Domain Name System (DNS UPDATE),
                P. Vixie, Ed., S. Thomson, Y. Rekhter, J. Bound,
                April 1997

8. Editor

           Name:         Edward Lewis
           Affiliation:  NeuStar
           Address:      46000 Center Oak Plaza, Sterling, VA, 20166, US
           Phone:        +1-571-434-5468
           Email:        ed.lewis@neustar.biz

      Comments on this document can be sent to the editor or the mailing
      list for the DNSEXT WG, namedroppers@ops.ietf.org.

9. Others Contributing to the Document

      This document represents the work of a large working group.  The
      editor merely recorded the collective wisdom of the working group.









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10. Trailing Boilerplate

      Copyright (C) The Internet Society (2006).

      This document is subject to the rights, licenses and restrictions
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      This document and the information contained herein are provided
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Acknowledgement

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Expiration

      This document expires on or about July 9, 2006.



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