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DNSEXT Working Group                                          E. Lewis
INTERNET DRAFT                                                 NeuStar
Expiration Date: November 16, 2005                        May 16, 2005

                            The Role of Wildcards
                          in the Domain Name System
                    draft-ietf-dnsext-wcard-clarify-07.txt

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Copyright Notice

    Copyright (C) The Internet Society (2005).

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.

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 has been given to minimize any
    backwards compatibility with implementations that have complied
    with RFC 1034's definition.

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

1.1 Motivation

    Many DNS implementations have diverged with respect to wildcards
    in different ways from the original definition, or at from least
    what had been intended.  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 changes,  only those based on
    implementation experience, and to remain as close to the original
    document as possible.  To reinforce this, relevant sections of RFC
    1034 are repeated verbatim to help compare the old and new text.

1.2 The Original Definition

    The context of the wildcard concept involves 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).

    The beginning of the discussion ought to start with the definition
    of the term "wildcard" as it appears in RFC 1034, section 4.3.3.

# 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 appears after 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 passage.

#    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 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.

    The introduction of new terms ought not have an impact on any
    existing implementations.  The new terms are used only to make
    discussions of wildcards clearer.

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
    there was no discussion of how to enforce the restriction.

1.3.3 Considerations with Special Types

    This document describes semantics of wildcard CNAME RRSets
    [RFC2181], wildcard NS RRSets, wildcard SOA RRSets, wildcard
    DNAME RRSets [RFC2672], wildcard DS RRSets [RFC TBD], and empty
    non-terminal wildcards.  Understanding these types 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.

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].  This feature has been underappreciated 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, they 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......................

    This restriction is lifted because the original documentation of it
    is incomplete and the restriction does not serve any purpose given
    years of operational experience.

    Indirectly, the above passage raises questions about wild card
    domain names having subdomains and possibly being an empty
    non-terminal.  By thinking of domain names such as
    "*.example.*.example." and "*.*.example." and focusing on the
    right-most asterisk label in each, the issues become apparent.

    Although those example names have been restricted per RFC 1034,
    a name such as "example.*.example." illustrates the same problems.
    The sticky issue of subdomains and empty non-terminals is not
    removed by the restriction.  With that conclusion, the restriction
    appears to be meaningless, worse yet, it implies that an
    implementation would have to perform checks that do little more
    than waste CPU cycles.

    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

    RFC 1034 also refers to non-existence in the process of generating
    a response that results in a return code of "name error."
    NXDOMAIN is introduced in RFC 2308, section 2.1 says "In this
    case the domain ... does not exist." The overloading of the term
    "existence" is confusing.

    For the purposes of this document, a domain name is said to
    exist if it plays a role in the execution of the algorithms in
    RFC 1034.  This document avoids discussion determining when an
    authoritative name error has occurred.

2.2.1 An Example

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

      $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 queries would be synthesized from one of the
    wildcards:

        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 queries would not be synthesized from any of the
    wildcards:

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

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

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

        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)

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, this is not the intent of the original document.

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 on RRSet.  A node may have no RRSets
    if it has descendents that do, this node is a empty non-terminal.
    A node may have its own RRSets and have descendants with RRSets
    too.

    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.  At the delegating server, 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 does a Wild Card Domain Name is 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 (label) matches an 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

    The description of how wildcards impact response generation is in
    RFC 1034, 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 wild card.

    The algorithm in RFC 1034, 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 suggestion.  As such, in
    step 3, parts a, b, and c, do not have to be implemented in
    that order.

3.1 Step 2

    Step 2 of the RFC 1034's 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.

    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.  It is
    possible, from the description given, that a query might fit
    into both part a and part b, this is not within the scope of
    this document.

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."

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

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':

             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.

    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 reason is that the asterisk
    label only becomes significant when RFC 1034's 4.3.2, step 3
    part 'c' in 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 RR 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) become unclear.

    After some lengthy discussions, there has been no clear "best
    answer" on how to document the semantics of such a situation.
    Barring such records from the DNS would require definition of
    rules for that, as well as introducing a restriction on records
    that were once legal.  Allowing such records and amending the
    process of signature management would entail complicating the
    DNSSEC definition.

    Combining these observations with thought that a wild card
    domain name owning an NS record is an operationally uninteresting
    scenario, i.e., it won't happen in the normal course of events,
    accomodating this situation in the specification would also be
    categorized as "needless complication." Further, expending more
    effort on this topic has proven to be an exercise in diminishing
    returns.

    In summary, 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.

4.3 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 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.tld." and another
    cache obtains "b.example. DNAME foo.bar.tld.", both generated
    from the record "*.example. DNAME foo.bar.tld." by an
    authoritative server.

    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 a domain 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 it 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.

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.

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

    [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

    [RFC2181] Clarifications to the DNS Specification, R. Elz and
              R. Bush, July 1997

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

    [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

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

    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.

10. Trailing Boilerplate

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