Subject: Wildcard Clarify 4

From: "Olaf M. Kolkman" <[email-masked]>
Date: Wed, 3 Nov 2004 16:39:55 +0100

Dear Colleagues,

For some reason wcard-clarify-04 did not make it into the
repository. We think it is important to base discussions next week on
the latest version, so here it is.

(Note that on the agenda we refer to version 3, but it is version
 4 that will be discussed.).

--Olaf
  DNSEXT Co-Chair.

---------

DNSEXT Working Group                                            E. Lewis
INTERNET DRAFT                                                   NeuStar
Expiration Date: April 25, 2005                             October 2004

                 Clarifying the Role of Wild Card Domains
                        in the Domain Name System

                  draft-ietf-dnsext-wcard-clarify-04.txt

Status of this Memo

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Copyright Notice

    Copyright (C) The Internet Society (2004).

Abstract

    The definition of wild cards is recast from the original in RFC 1034,
    in words that are more specific and in line with RFC 2119.  This
    document is meant to supplement the definition in RFC 1034 and not to
    significantly alter the spirit or intent of that definition.

1 Introduction

    In RFC 1034 [RFC1034], sections 4.3.2 and 4.3.3 describe the synthesis
    of answers from special records called wildcards.  The original
    definitions are incomplete.  This document clarifies and describes
    the wildcard synthesis by adding to the discussion and making
    limited modifications.  Modifications are made only where necessary
    to close inconsistencies that have led to interoperability issues.

1.1 Motivation

    Over time many implementations have diverged 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, the impetus for this document lay in the engineering of
    the DNS security extensions [RFC TBD].  With an unclear definition
    of wildcards the design of authenticated denial became entangled.

    Although this document is motivated by DNSSEC and the need to have a
    separate document passed for the sake of DNSSEC, other motivations have
    arisen.  The renewed understanding of wildcards gained is worthy of being
    documented.

1.2 The Original Definition

    This document is intended to make just one change, 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.

    There are a few passages which are changed.  This may seem to
    contradict the goal of not changing the original specification,
    but the changes herein are required because of inconsistencies
    with the wording in RFC 1034.

    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 they are used is
    presented.  The terminology is not consistent, the word "wildcard"
    is clearly defined to be a resource record.  Wildcard has also been
    used to refer to domain names whose first (i.e., left most or least
    significant) label consists of an asterisk.

1.3 The Clarification

    The clarification effort can be divided into three sections:

    o The introduction of new terminology for clarity of the discussion
    o Changes to the wording of passages of RFC 1034 prompted by discoveries of
      conflicting concepts
    o Descriptions of special resource record types in the context of wildcards.

1.3.1 New Terms

    The term "wildcard" has become so overloaded it is virtually useless
    as a description.  A few new terms will be introduced to be more
    descriptive.  The new terms that will be introduced are:

    Asterisk Label - a label consisting of an asterisk ("*") and no
    other characters.

    Wild Card Domain Name - a domain name whose least significant
    label (first when reading left to right) is an asterisk label.
    Other labels might also be asterisk labels.

    Source of Synthesis - a wild card domain name when it is consulted in
    the final paragraph of step 3, part c of RFC 1034's 4.3.2 algorithm.

    Closest Encloser - in RFC 1034's 4.3.2 algorithm, the name at which
    the last match was possible in step 3, part c.  This is the longest
    sequence of exactly matching labels from the root downward in both the
    query name (QNAME) and in the zone being examined.

    Label Match - two labels are equivalent if the label type and label
    length are both the same and if the labels are case-independent
    equivalent strings.  Pattern matching is not involved.

    These terms will be more fully described as needed later.  These
    terms will be used to describe a few changes to the words in RFC
    1034.  A summary of the changes appear next and will be fully
    covered in later sections.

    Note that labels other than the asterisk label which contain
    asterisks have no special significance or terminology in this
    document; thus the fact that a domain names starts with an
    asterisk is also of no special significance (and has no special
    terminology) unless its first label is the asterisk label, e.g.,
    "*foo.example." has no special significance).

1.3.2 Changed Text

    The definition of "existence" is changed, superficially, to exclude
    empty domains that have no subdomains with resource records.  This
    change will not be apparent to implementations; it is needed to
    make descriptions more concise.

    In RFC 1034, there is text that seems to prohibit having two asterisk
    labels in a wild card domain name.  There is no further discussion,
    no prescribed error handling, nor enforcement described.  With this
    document implementations will have to account for such a name's use.

    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.

1.3.3 Considerations with Special Types

    This clarification will describe in some detail the semantics of
    wildcard CNAME RRSets, wildcard NS RRSets, wildcard SOA RRSets,
    wildcard DNAME RRSets [RFC 2672], 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.

    By the definition in RFC 1034, there can be no empty non-terminal
    "wildcards" ("RRs are called wildcards").  However, in the algorithm,
    it is possible that an empty non-terminal is sought as the potential
    owner of a "wildcard."  This is one example of why the ordering of the
    discussion in RFC 1034 is confusing.

1.4 Standards Terminology

    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 the document entitled
    "Key words for use in RFCs to Indicate Requirement Levels." [RFC2119]

    Quotations of RFC 1034 (as has already been done once above) are
    denoted by a '#' in the leftmost column.

2 "Wildcard"

    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).

    Tackling the latter first, there are two objectives in defining a
    means to identify a resource record set as a source of synthesis.
    First, to simplify implementations, one objective is to encode synthesis
    rules into the domain tree, i.e., avoiding a special data store for
    synthesis is desirable.  The second objective impacts interoperability,
    that is a master server of one implementation has to be able to
    send the synthesis instructions to the slaves.  Although there are
    alternatives to the use of zone transfers via port 53, a truly
    interoperable record synthesis approach has to be able to insert the
    synthesis instructions into a zone transfer.

    The objectives in describing the synthesis of records in the context
    of the name server algorithm include knowing when to employ the
    process of synthesis and how the synthesis is carried out.

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.

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)

    This is "*" in presentation format.

    The first octet is the normal label type and length for a 1 octet
    long label, the second octet is the ASCII representation [RFC 20] for
    the '*' character.  In RFC 1034, ASCII encoding is assumed to be the
    character encoding.

    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."  This is mentioned to help maintain some
    orientation between this clarification and RFC 1034.  Keep in mind,
    that in "Clarifications to the DNS Specification" [RFC 2181] the name
    of the basic unit of DNS data became the resource record set (RRSet) and
    not the resource record.

2.1.2 Variations on Wild Card Domain Names

    Labels other than the asterisk label which contain the ASCII
    representation of the asterisk (0x2a) have no significance for the
    purposes of this document.

    RFC 1034 and RFC 1035 do not explicitly mention the case in which a
    domain name might be something like "the*.example."  The
    interpretation is that this domain name in a zone would only match
    queries for "the*.example." and not have any other role.  An
    asterisk ('*') occurring other than as the sole character in
    a label is simply a character forming part of the label and has no
    special meaning.   This is not an asterisk label, simply a label
    an asterisk in it.  The same is true for "**.example." and
    "*the.example."

    The interpretation of a wild card domain specification which is not a
    leaf domain is not clearly defined in RFC 1034.  E.g., sub.*.example.,
    is not discussed, not barred.  In wanting to minimize changes from
    the original specification, such names are permitted.  Although
    "sub.*.example." is not a wild card domain name, "*.example." is.

    RRSets used to synthesize records can be owned by a wild card domain
    name that has subdomains.

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 covers names like "*.foo.*.example."  The pre-RFC2119 wording uses
    "should not" which has an ambiguous meaning.  The specification does not
    proscribe actions upon seeing such a name, such as whether or not a
    zone containing the name should fail to be served.  What if a dynamic
    update (RFC2136) requested to add the name to the zone?  The failure
    semantics are not defined.

    The recommendation is that implementations ought to anticipate the
    appearance of such names but generally discourage their use in
    operations.  No standards statement, such as "MUST NOT" nor "SHOULD NOT"
    is made here.

    The interpretation of this is, when seeking a wild card domain name
    for the purposes of record synthesis, an implementation need not to
    check the domain name for subdomains.

    It is possible that a wild card domain name is an empty non-terminal.
    (See the upcoming sections on empty non-terminals.)  In this case,
    the lookup will terminate as would any empty non-terminal match.

2.2 Existence Rules

    The notion that a domain name 'exists' arises numerous times in
    discussions about the wildcard concept.  RFC 1034 raises the issue
    of existence in a number of places, usually in reference to
    non-existence and in reference to processing involving wildcards.
    RFC 1034 contains algorithms that describe how domain names impact
    the preparation of an answer and does define wildcards as a means of
    synthesizing answers.  Because of this a discussion on wildcards
    needs to cover a definition of existence.

    To help clarify the topic of wild cards, a positive definition of
    existence is needed.  Complicating matters, though, is the
    realization that existence is relative.  To an authoritative server,
    a domain name exists if the domain name plays a role following the
    algorithms of preparing a response.  To a resolver, a domain name
    exists if there is any data available corresponding to the name.  The
    difference between the two is the synthesis of records according to a
    wildcard.

    For the purposes of this document, the point of view of an
    authoritative server is more interesting.  A domain name is said to
    exist if it plays a role in the execution of the algorithms in RFC 1034.

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.
            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
                           |             |
                           |             |
                         _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=_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)

    To the server, all of the domains in the tree exist.  The resolver will
    get answers to some names off the tree, thanks to synthesis.

2.2.2 Empty Non-terminals

    Empty non-terminals are domain names that own no resource records but
    have subdomains that do.  This is defined 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.  According to the definition of
    existence in this document, empty non-terminals do exist at the
    server.

    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 [RFC 1035].  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 clarified by the following paragraph:

         A node is considered to have an impact on the algorithms of
         4.3.2 if it is a leaf node with any resource sets or an interior
         node (with or without a resource set) that has a subdomain that
         is a leaf node with a resource set.  A QNAME and QCLASS matching
         an existing node never results in a response code of
         authoritative name error (RCODE==3).

    The terminology in the above paragraph is chosen to remain as close
    to that in the original document.  The term "with" is a alternate
    form for "owning" in this case, hence "a leaf node owning resources
    sets, or an interior node, owning or not owning any resource set,
    that has a leaf node owning a resource set as a subdomain," is the
    proper interpretation of the middle sentence.  The phrase "resource
    set" appears in the original text of RFC 1034, this would now be
    replaced by "RRSet."

    As an aside, an "authoritative name error", response code (RCODE) 3,
    has been called NXDOMAIN in some RFCs, such as RFC 2136 [RFC 2136].
    NXDOMAIN is the mnemonic assigned to such an error by at least one
    implementation of DNS.

    Summarizing the discussion on existence in non-RFC1034 words:

        An authoritative server is to treat a domain name as existing
        during the execution of the algorithms in RFC 1034 when the
        domain name conforms to the following definition.  A domain name
        is defined to exist if the domain name is on the domain tree and
        either owns data or has a subdomain that exists.

    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 not own a wildcard (record)

    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 On a Response

    The description of how wild cards 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 is directly quoted in lines that begin with a '#' sign.
    Commentary is interleaved.

    There is a documentation issue deserving some explanation.  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.

    Another issue needing explanation is that RFC 1034 is a full
    standard.  There is another RFC, RFC 2672, which makes, or proposes
    an adjustment to RFC 1034's section 4.3.2 for the sake of the DNAME
    RR.  RFC 2672 is a proposed standard.  The dilemma in writing these
    clarifications is knowing which document is the one being clarified.
    Fortunately, the difference between RFC 1034 and RFC 2672 is not
    significant with respect to wild card synthesis, so this document
    will continue to state that it is clarifying RFC 1034.  If RFC 2672
    progresses along the standards track, it will need to refer to
    modifying RFC 1034's algorithm as amended here.

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.

    If an implementation were to attempt to synthesize zones, this would be
    the step to do this.  Note though that each name server listed in the NS
    RRSet for the synthesized zone would have to coherently synthesize the
    zone.

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.)

    The process of label matching  a query name ends in exactly one of three
    choices, the parts 'a', 'b', and 'c'.  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.

    Parts 'a' and 'b' are not an issue for this clarification as they do not
    relate to record synthesis.  Part 'a' generally covers a situation in
    which all of the labels in the query name have a (label) match in the tree.
    Part 'b' generally covers a situation in which any label in the query
    name (label) matches a tree label and the tree label has a NS RRSet.

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 a
#            the "*" label exists.

    To help describe the process of looking 'to see if a [sic] the "*"
    label exists' a term has been coined to describe the last label
    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
    the 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.

    Other terms have been coined on the mailing list in the past.  E.g.,
    it has been said that existing names block the application of
    wildcard records.  This is still an appropriate viewpoint, but
    replacing this notion with the closest encloser and source of
    synthesis terminology depicts the wildcard process is more clearly.

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.

3.3.3 Non-existent Source of Synthesis

    In RFC 1034:

#            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.

    The above passage is clear, evidenced by the lack of discussion and
    mis-implementation of it over the years.  It is included for
    completeness only.  (No attempt is made to re-interpret it lest
    a mistake in editing leads to confusion.)

3.3.4 Type Matching

     RFC 1034 concludes part 'c' with this:

#            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.

    This 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 a change has been made.

    The change is to add the following text:

             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

    Five types of RRSets owned by a wild card domain name have caused
    confusion.  Four explicit types causing confusion are SOA, NS, CNAME,
    DNAME, and the fifth type - "none."

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., if *.example. has an SOA record, then only a query like
    QNAME=*.example., QTYPE=A, QCLASS=IN would see it.  A query like
    QNAME=foo.example., QTYPE=A, QCLASS=IN would not see it - a different
    zone would have been picked in Step 2. A QNAME of www.*.example.
    would result in a query referencing the *.example zone.

4.2. NS RRSet at a Wild Card Domain Name

    The semantics of a wild card domain name's ownership of a NS RRSet
    has been unclear.  Looking through RFC 1034, the recommendation
    is to have the NS RRSet act the same a any non-special type, e.g.,
    like an A RRSet.

    If the NS RRSet in question is at the top of the zone, i.e., the
    name also owns an SOA RRSet, the QNAME equals the zone name.  This
    would trigger part 'a' of Step 3.

    In any other case, the wild card domain name owned NS RRSet would
    be the only RRSet (prior to changes instituted by DNSSEC) at the
    node by DNS rules.  If the QNAME equals the wild card domain name
    or is a subdomain of it, then the node would be considered in part
    'b' of Step 3.  [should dnssec be left out of this?]

    Note that there is no synthesis of records in the authority section
    because part 'b' does not specify synthesis.  The referral returned
    would have the wild card domain name in the authority section unchanged.

    If the QNAME is not the same as the wild card domain name nor a
    subdomain of it, then part 'c' of Step 3 has been triggered.  Once
    part 'c' is entered, there is no reverting to part 'b' - i.e.,
    once an NS RRSet is synthesized it does not mean that the server has
    to consider the name delegated away.  I.e., the server is not
    synthesizing a record (the NS RRSet) that means the server does not
    have the right to synthesize.  (Only an authoritative server can
    perform synthesis.  By synthesizing an NS RRSet, it appears that the
    authority for the name has been delegated to another authority.)

    In summation, an NS RRSet at a wild card domain name will not result in
    the generation of referral messages for non-existent domains.

4.3. CNAME RRSet at a Wild Card Domain Name

    The issue of a CNAME RRSet owned by wild card domain names 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 3.3.4 of this document.

4.4. DNAME RRSet at a Wild Card Domain Name

    The specification of the DNAME RR, which is at the proposed level of
    standardization, is not as mature as the full standard in RFC 1034.
    Because of this, or the reason for this is, there appears to be a
    a number of issues with that definition and it's rewrite of the algorithm
    in 4.3.2.  For the time being, when it comes to wild card processing
    issues, a DNAME can be considered to be a CNAME synthesizer.  A DNAME
    at a wild card domain name is effectively the same as a CNAME at a
    wild card domain name.

4.5 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. References

    Normative References

    [RFC 20] ASCII Format for Network Interchange, V.G. Cerf, Oct-16-1969

    [RFC 1034] Domain Names - Concepts and Facilities, P.V. Mockapetris,
               Nov-01-1987

    [RFC 1035] Domain Names - Implementation and Specification, P.V
               Mockapetris, Nov-01-1987

    [RFC 2119] Key Words for Use in RFCs to Indicate Requirement Levels, S
               Bradner, March 1997

    [RFC 2181] Clarifications to the DNS Specification, R. Elz and R. Bush,
               July 1997.

    Informative References

    [RFC 2136] Dynamic Updates in the Domain Name System (DNS UPDATE), P.
               Vixie, Ed., S. Thomson, Y. Rekhter, J. Bound, April 1997

    [RFC 2535] Domain Name System Security Extensions, D. Eastlake, March 1999

    [RFC 2672] Non-Terminal DNS Name Redirection, M. Crawford, August 1999

7. Others Contributing to This Document

    Others who have been editors of this document: Bob Halley.
    Others who have directly caused text to appear in the document: Alex
    Bligh, Robert Elz, Paul Vixie and Olaf Kolkman.
    Many others have indirect influences on the content.

8. Editor

         Name:         Edward Lewis
         Affiliation:  NeuStar
         Address:      46000 Center Oak Plaza, Sterling, VA, 20166, US
         Phone:        +1-571-434-5468
         Email:        [email-masked]

    Comments on this document can be sent to the editor or the mailing
    list for the DNSEXT WG, [email-masked].

9. Trailing Boilerplate

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    to the rights, licenses and restrictions contained in BCP 78 and
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Expiration

    This document expires on or about 25 April 2005.

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