draft-ietf-dnsext-wcard-clarify-02.txt

bind 9.3结合mysql数据库

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Internet Draft   draft-ietf-dnsext-wcard-clarify-02.txt   September 2003


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

2. Defining the Wild Card Domain Name

   A wild card domain name is defined by having the initial label be:

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

   This defines domain names that may play a role in being a wild card,
   that is, being a source for synthesized answers.  Domain names
   conforming to this definition that appear in queries and RDATA
   sections do not have any special role.  These cases will be described
   in more detail in following sections.

   R2.1 A domain name that is to be interpreted as a wild card MUST
        begin with a label of '0000 0001 0010 1010' in binary.

   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.

   In the master file formats used in RFCs, a "*" is a legal
   representation for the wild card label.  Even if the "*" is escaped,
   it is still interpreted as the wild card when it is the only
   character in the label.

   R2.2 A server MUST treat a wild card domain name as the basis of
        synthesized answers regardless of any "escape" sequences in the
        input format.

   RFC 1034 and RFC 1035 ignore the case in which a domain name might be
   "the*.example.com." The interpretation is that this domain name in a
   zone would only match queries for "the*.example.com" and not have any
   other role.

   Note: By virtue of this definition, a wild card domain name may have
   a subdomain.  The subdomain (or sub-subdomain) itself may also be a
   wild card.  E.g., *.*.example. is a wild card, so is *.sub.*.example.
   More discussion on this is given in Appendix A.










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3. Defining Existence

   As described in the Introduction, a precise definition of existence
   is needed.

   R3.1 An authoritative server MUST 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 owns data and/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.

   R3.2 An authoritative server MUST treat a domain name that has
        neither a resource record set nor an existing subdomain as non-
        existent when executing the algorithm in section 4.3.2. of RFC
        1034.

   A note on terminology.  A domain transcends zones, i.e., all DNS data
   is in the root domain but segmented into zones of control.  In this
   document, there are references to a "domain name" in the context of
   existing "in a zone." In this usage, a domain name is the root of a
   domain, not the entire domain.  The domain's root point is said to
   "exist in a zone" if the zone is authoritative for the name.  RR sets
   existing in a domain need not be owned by the domain's root domain
   name, but are owned by other domain names in the domain.

4. Impact of a Wild Card In a Query or in RDATA

   When a wild card domain name appears in a question, e.g., the query
   name is "*.example.", the response in no way differs from any other
   query.  In other words, the wild card label in a QNAME has no special
   meaning, and query processing will proceed using '*' as a literal
   query name.

   R4.1 A wild card domain name acting as a QNAME MUST be treated as any
        other QNAME, there MUST be no special processing accorded it.

   If a wild card domain name appears in the RDATA of a CNAME RR or any
   other RR that has a domain name in it, the same rule applies.  In the
   instance of a CNAME RR, the wild card domain name is used in the same
   manner of as being the original QNAME.  For other RR's, rules vary
   regarding what is done with the domain name(s) appearing in them, in
   no case does the wild card hold special meaning.




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   R4.2 A wild card domain name appearing in any RR's RDATA MUST be
        treated as any other domain name in that situation, there MUST
        be no special processing accorded it.

5. 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., it's 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.

   The context of part 'c' is that the search is progressing label by
   label through the QNAME.  (Note that the data being searched is the
   authoritative data in the server, the cache is searched in step 4.)
   Step 3's part 'a' covers the case that the QNAME has been matched in
   full, regardless of the presence of a CNAME RR.  Step 'b' covers
   crossing a cut point, resulting in a referral.  All that is left is
   to look for the wild card.

   Step 3 of the algorithm also assumes that the search is looking in
   the zone closest to the answer, i.e., in the same class as QCLASS and
   as close to the authority as possible on this server.  If the zone is
   not the authority, then a referral is given, possibly one indicating
   lameness.








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#         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.

   The above paragraph refers to finding the domain name that exists in
   the zone and that most encloses the QNAME.  Such a domain name will
   mark the boundary of candidate wild card domain names that might be
   used to synthesize an answer.  (Remember that at this point, if the
   most enclosing name is the same as the QNAME, part 'a' would have
   recorded an exact match.)  The existence of the enclosing name means
   that no wild card name higher in the tree is a candidate to answer
   the query.

   Once the closest enclosing node is identified, there's the matter of
   what exists below it.  It may have subdomains, but none will be
   closer to the QNAME.  One of the subdomains just might be a wild
   card.  If it exists, this is the only wild card eligible to be used
   to synthesize an answer for the query.  Even if the closest enclosing
   node conforms to the syntax rule in section 2 for being a wild card
   domain name, the closest enclosing node is not eligible to be a
   source of a synthesized answer.

   The only wild card domain name that is a candidate to synthesize an
   answer will be the "*" subdomain of the closest enclosing domain
   name.  Three possibilities can happen.  The "*" subdomain does not
   exist, the "*" subdomain does but does not have an RR set of the same
   type as the QTYPE, or it exists and has the desired RR set.

   For the sake of brevity, the closest enclosing node can be referred
   to as the "closest encloser." The closest encloser is the most
   important concept in this clarification.  Describing the closest
   encloser is a bit tricky, but it is an easy concept.

   To find the closest encloser, you have to first locate the zone that
   is the authority for the query name.  This eliminates the need to be
   concerned that the closest encloser is a cut point.  In addition, we
   can assume too that the query name does not exist, hence the closest
   encloser is not equal to the query name.  We can assume away these
   two cases because they are handled in steps 2, 3a and 3b of section
   4.3.2.'s algorithm.

   What is left is to identify the existing domain name that would have
   been up the tree (closer to the root) from the query name.  Knowing
   that an exact match is impossible, if there is a "*" label descending
   from the unique closest encloser, this is the one and only wild card
   from which an answer can be synthesized for the query.





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   To illustrate, using the example in section 1.2 of this document, the
   following chart shows QNAMEs and the closest enclosers.  In
   Appendix A there is another chart showing unusual cases.

        QNAME                        Closest Encloser     Wild Card Source
        host3.example.               example.             *.example.
        _telnet._tcp.host1.example.  _tcp.host1.example.  no wild card
        _telnet._tcp.host2.example.  host2.example.       no wild card
        _telnet._tcp.host3.example.  example.             *.example.
        _chat._udp.host3.example.    example.             *.example.

   Note that host1.subdel.example. is in a subzone, so the search for it
   ends in a referral in part 'b', thus does not enter into finding a
   closest encloser.

   The fact that a closest encloser will be the only superdomain that
   can have a candidate wild card will have an impact when it comes to
   designing authenticated denial of existence proofs.

#            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 says that if there is not even a wild card domain
   name to match at this point (failing to find an explicit answer
   elsewhere), we are to return an authoritative name error at this
   point.  If we were following a CNAME, the specification is unclear,
   but seems to imply that a no error return code is appropriate, with
   just the CNAME RR (or sequence of CNAME RRs) in the answer section.

#            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 process.
   Note that if no resource record set matches the QTYPE the result is
   that no data is copied, but the search still ceases ("Go to step
   6.").  In the following section, a suggested change is made to this,
   under the heading "CNAME RRs at a Wild Card Domain Name."









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6. Considerations with Special Types

   For the purposes of this section, "special" means that a record
   induces processing at the server beyond simple lookup.  The special
   types in this section are SOA, NS, CNAME, and DNAME.  SOA is special
   because it is used as a zone marker and has an impact on step 2 of
   the algorithm in 4.3.2.  NS denotes a cut point and has an impact on
   step 3b.  CNAME redirects the query and is mentioned in steps 3a and
   3b.  DNAME is a "CNAME generator."

6.1. SOA RR's at a Wild Card Domain Name

   If the owner of an SOA record conforms to the basic rules of owning
   an SOA RR (meaning it is the apex of a zone) the impact on the search
   algorithm is not in section 3c (where records are synthesized) as
   would be expected.  The impact is really in step 2 of the algorithm,
   the choice of zone.

   We are no longer talking about whether or not an SOA RR can be
   synthesized in a response because we are shifting attention to step
   2.  We are now talking about what it means for a name server to
   synthesize a zone for a response.  To date, no implementation has
   done this.  Thinking ahead though, anyone choosing to pursue this
   would have to be aware that a server would have to be able to
   distinguish between queries for data it will have to synthesize and
   queries that ought to be treated as if they were prompted by a lame
   delegation.

   It is not a protocol error to have an SOA RR owned by a wild card
   domain name, just as it is not an error to have zone name be
   syntactically equivalent to a domain name.  However, this situation
   requires careful consideration of how a server chooses the
   appropriate zone for an answer.  And an SOA RR is not able to be
   synthesized as in step 3c.

6.2. NS RR's at a Wild Card Domain Name

   Complimentary to the issue of an SOA RR owned by a wild card domain
   name is the issue of NS RR's owned by a wild card domain name.  In
   this instance, each machine being referred to in the RDATA of the NS
   RR has to be able to understand the impact of this on step 2, the
   choosing of the authoritative zone.

   Referring to the same machine in such a NS RR will probably not work
   well.  This is because the server may become confused as to whether
   the query name ought to be answered by the zone owning the NS RR in
   question or a synthesized zone.  (It isn't known in advance that the
   query name will invoke the wild card synthesis.)



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