draft-ietf-dnsext-insensitive-03.txt

bind-3.2.

INTERNET-DRAFT                                    Donald E. Eastlake 3rd
Clarifies STD0013                                  Motorola Laboratories
Expires September 2003                                        April 2003



       Domain Name System (DNS) Case Insensitivity Clarification
       ------ ---- ------ ----- ---- ------------- -------------
                 <draft-ietf-dnsext-insensitive-03.txt>

                         Donald E. Eastlake 3rd



Status of This Document

   Distribution of this document is unlimited. Comments should be sent
   to the DNSEXT working group at [e-mail].

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC 2026.  Internet-Drafts are
   working documents of the Internet Engineering Task Force (IETF), its
   areas, and its working groups.  Note that other groups may also
   distribute working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet- Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.



Abstract

   Domain Name System (DNS) names are "case insensitive". This document
   explains exactly what that means and provides a clear specification
   of the rules. This clarification should not have any interoperability
   consequences.











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Acknowledgements

   The contributions to this document of Rob Austein, Olafur
   Gudmundsson, Daniel J. Anderson, Alan Barrett, Marc Blanchet, Dana,
   Andreas Gustafsson, Andrew Main, and Scott Seligman are gratefully
   acknowledged.



Table of Contents

      Status of This Document....................................1
      Abstract...................................................1

      Acknowledgements...........................................2
      Table of Contents..........................................2

      1. Introduction............................................3
      2. Case Insensitivity of DNS Labels........................3
      2.1 Escaping Unusual DNS Label Octets......................3
      2.2 Example Labels with Escapes............................4
      2.3 Name Lookup Case Insensitivity.........................4
      2.4 Original DNS Label Types...............................5
      3. Additional DNS Case Insensitivity Considerations........5
      3.1 CLASS Case Insensitivity Considerations................5
      3.2 Extended Label Type Case Insensitivity Considerations..5
      4. Case on Input and Output................................6
      4.1 DNS Output Case Preservation...........................6
      4.2 DNS Input Case Preservation............................6
      4.3 Wildcard Matching......................................7
      5. Internationalized Domain Names..........................7
      6. Security Considerations.................................7

      Normative References.......................................9
      Informative References.....................................9
      -02 to -03 Changes........................................10
      Author's Address..........................................10
      Expiration and File Name..................................10














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1. Introduction

   The Domain Name System (DNS) is the global hierarchical replicated
   distributed database system for Internet addressing, mail proxy, and
   other information. Each node in the DNS tree has a name consisting of
   zero or more labels [STD 13][RFC 1591, 2606] that are treated in a
   case insensitive fashion. This document clarifies the meaning of
   "case insensitive" for the DNS.

   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 [RFC 2119].



2. Case Insensitivity of DNS Labels

   DNS was specified in the era of [ASCII]. DNS names were expected to
   look like most host names or Internet email address right halves (the
   part after the at-sign, "@") or be numeric as in the in-addr.arpa
   part of the DNS name space. For example,

       foo.example.net.
       aol.com.
       www.gnu.ai.mit.edu.
   or  69.2.0.192.in-addr.arpa.

   Case varied alternatives to the above would be DNS names like

       Foo.ExamplE.net.
       AOL.COM.
       WWW.gnu.AI.mit.EDU.
   or  69.2.0.192.in-ADDR.ARPA.

   The individual octets of which DNS names consist are not limited to
   valid ASCII character codes. They are as 8-bit bytes and all values
   are allowed. Many applications, however, interprete them as ASCII
   characters.



2.1 Escaping Unusual DNS Label Octets

   In Master Files [STD 13] and other human readable and writable ASCII
   contexts, an escape is needed for the byte value for period (0x2E,
   ".") and all octet values outside of the inclusive range of 0x21 ("!")
   to 0x7E ("~"). That is to say, 0x2E and all octet values in the two
   inclusive ranges 0x00 to 0x20 and 0x7F to 0xFF.

   One typographic convention for octets that do not correspond to an


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   ASCII printing graphic is to use a back-slash followed by the value of
   the octet as an unsigned integer represented by exactly three decimal
   digits.

   The same convention can be used for printing ASCII characters so that
   they will be treated as a normal label character.  This includes the
   back-slash character used in this convention itself and the special
   label separator period (".") which can be expressed as \092 and \046
   respectively. It is advisable to avoid using a backslash to quote an
   immediately following non-printing ASCII character code to avoid
   implementation difficulties.

   A back-slash followed by only one or two decimal digits is
   undefined. A back-slash followed by four decimal digits produces two
   octets, the first octet having the value of the first three digits
   considered as a decimal number and the second octet being the
   character code for the fourth decimal digit.



2.2 Example Labels with Escapes

   The first example below shows embedded spaces and a period (".")
   within a label. The second one show a 5 octet label where the second
   octet has all bits zero, the third is a backslahs,
   and the fourth octet has all bits one.

         Donald\032E\.\032Eastlake\0323rd.example.
   and   a\000\\\255z.example.



2.3 Name Lookup Case Insensitivity

   The design decision was made that comparisons on name lookup for DNS
   queries should be case insensitive [STD 13]. That is to say, a lookup
   string octet with a value in the inclusive range of 0x41 to 0x5A, the
   upper case ASCII letters, MUST match the identical value and also
   match the corresponding value in the inclusive range 0x61 to 0x7A,
   the lower case ASCII letters. And a lookup string octet with a lower
   case ASCII letter value MUST similarly match the identical value and
   also match the corresponding value in the upper case ASCII letter
   range.

   (Historical Note: the terms "upper case" and "lower case" were
   invented after movable type.  The terms originally referred to the
   two font trays for storing, in partitioned areas, the different
   physical type elements.  Before movable type, the nearest equivalent
   terms were "majuscule" and "minuscule".)



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   One way to implement this rule would be, when comparing octets, to
   subtract 0x20 from all octets in the inclusive range 0x61 to 0x7A
   before the comparison. Such an operation is commonly known as "case
   folding" but implementation via case folding is not required. Note
   that the DNS case insensitivity does NOT correspond to the case
   folding specified in iso-8859-1 or iso-8859-2. For example, the
   octets 0xDD (\221) and 0xFD (\253) do NOT match although in other
   contexts, where they are interpreted as the upper and lower case
   version of "Y" with an acute accent, they might.



2.4 Original DNS Label Types

   DNS labels in wire encoded names have a type associated with them.
   The original DNS standard [RFC 1035] had only two types. ASCII
   labels, with a length of from zero to 63 octets and indirect labels
   which consist of an offset pointer to a name location elsewhere in
   the wire encoding on a DNS message. (The ASCII label of length zero
   is reserved for use as the name of the root node of the name tree.)
   ASCII labels follow the ASCII case conventions described above.
   Indirect labels are, in effect, replaced by the name to which they
   point which is then treated with the case insensitivity rules in this
   document.



3. Additional DNS Case Insensitivity Considerations

   This section clarifies the effect of DNS CLASS and extended Label
   Type on case insensitivity.



3.1 CLASS Case Insensitivity Considerations

   As described in [STD 13] and [RFC 2929], DNS has an additional axis
   for data location called CLASS. The only CLASS in global use at this
   time is the "IN" or Internet CLASS.

   The handling of DNS label case is not CLASS dependent.



3.2 Extended Label Type Case Insensitivity Considerations

   DNS was extended by [RFC 2671] to have additional label type numbers
   available. (The only such type defined so far is the BINARY type [RFC
   2673].)



D. Eastlake 3rd                                                 [Page 5]