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Network Working Group                                          J. Levine
Internet-Draft                                      Taughannock Networks
Intended status: Standards Track                                P. Vixie
Expires: June 02, 2013                       Internet Systems Consortium
                                                           December 2012


                   An Extension Language for the DNS
                       draft-levine-dnsextlang-05

Abstract

   Adding new RRTYPEs to the DNS requires that DNS servers and
   provisioning software be upgraded to support each new RRTYPE in
   Master files.  This document defines a DNS extension language
   intended to allow most new RRTYPEs to be supported by adding entries
   to configuration data read by the DNS software, with no software
   changes needed for each RRTYPE.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on June 02, 2013.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

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   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
   2.  Typical usage  . . . . . . . . . . . . . . . . . . . . . . . .  2
   3.  Extension language syntax  . . . . . . . . . . . . . . . . . .  3
     3.1.  Lexical structure  . . . . . . . . . . . . . . . . . . . .  3
     3.2.  Storage in the DNS . . . . . . . . . . . . . . . . . . . .  4
     3.3.  Storage in a file  . . . . . . . . . . . . . . . . . . . .  4
     3.4.  Stanza structure . . . . . . . . . . . . . . . . . . . . .  4
     3.5.  Field types  . . . . . . . . . . . . . . . . . . . . . . .  5
       3.5.1.  Integer fields . . . . . . . . . . . . . . . . . . . .  5
       3.5.2.  IP address fields  . . . . . . . . . . . . . . . . . .  5
       3.5.3.  Domain name fields . . . . . . . . . . . . . . . . . .  6
       3.5.4.  String fields  . . . . . . . . . . . . . . . . . . . .  6
       3.5.5.  Base-64 fields . . . . . . . . . . . . . . . . . . . .  6
       3.5.6.  Hex fields . . . . . . . . . . . . . . . . . . . . . .  6
   4.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
   5.  Security considerations  . . . . . . . . . . . . . . . . . . .  7
   6.  IANA considerations  . . . . . . . . . . . . . . . . . . . . .  7
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     7.1.  References - Normative . . . . . . . . . . . . . . . . . .  8
     7.2.  References - Informative . . . . . . . . . . . . . . . . .  8
   Appendix A.  Change Log  . . . . . . . . . . . . . . . . . . . . .  8
     A.1.  Changes from -04 to -05  . . . . . . . . . . . . . . . . .  9
     A.2.  Changes from -03 to -04  . . . . . . . . . . . . . . . . .  9
     A.3.  Changes from -02 to -03  . . . . . . . . . . . . . . . . .  9
     A.4.  Changes from -01 to -02  . . . . . . . . . . . . . . . . .  9
     A.5.  Changes from -00 to -01  . . . . . . . . . . . . . . . . .  9
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . .  9

1.  Introduction

   The Domain Name System[RFC1034] [RFC1035] is designed to be
   extensible, with new record types, known as RRTYPEs, added as needed.
   While it is straightforward in principle to add a new RRTYPE, in
   practice it can be difficult due to the software changes needed to
   add the new RRTYPE to the master file format read by many
   authoritative DNS servers, and to the provisioning software used to
   create and update the master files or the local equivalent.

   While some new RRTYPEs, notably those for DNSSEC [RFC4033], require
   that DNS servers do new special purpose processing, most new RRTYPEs
   are, from the point of view of the DNS, just static data to return to
   queries, perhaps with some additional section records if the record
   includes another domain name.  This document defines an extension
   language to describe these RRTYPEs, so that server and provisioning
   software can parse master file records for the RRTYPEs.

2.  Typical usage









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   The extension language is written as strings of ASCII text that
   describe new RR types, intended to be stored in the DNS itself.
   (They may also be stored in a local file with a well-known name, for
   debugging and local overrides, but this usage is optional.) All of
   the DNS software that needs to handle master file records fetches
   records from the DNS as needed.  To support a new RRTYPE, one would
   add suitable records to the DNS zone where the descriptions are
   located, or to the local file.

   DNS servers can use the extension language to parse new RRTYPE
   records in master files, and to translate them to the binary
   representation.  Servers that create ASCII master files from zone
   data retrieved via AXFR can use the extension language to create
   master file records for new RRTYPEs.

   Provisioning software can use the extension language to create
   templates for users to fill in, to create new RRTYPE records in
   master files to be passed to DNS servers, and to syntax check records
   entered by users.

   In principle, provisioning software could create TYPEnn master
   records if the local DNS server doesn't implement the extension
   language, although it would be less confusing if both provisioning
   and server software both accept the same master record syntax.

   Some DNS servers store records in ways other than master files, such
   as SQL databases.  In principle, the extension language could be used
   to create new schema entries to handle new RRTYPEs, although the
   details are too specific to particular varieties of DNS server
   software for this document to try to describe the details.

3.  Extension language syntax

3.1.  Lexical structure

   The extension language consists of "stanzas", each of which defines
   an RRTYPE.  In the DNS, a stanza is stored as a multi-string TXT
   record, with each string conceptually being a line in the stanza.  In
   a file, it is stored as a series of lines.  The first line of a
   stanza defines the symbolic RRTYPE name.  Subsequent lines each
   define a field in the record.

   The following ABNF imports ALPHA, DIGIT, and WSP from [RFC5234].











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       dnsextfile =  1*stanza

       stanza = rrtypeline 1*fieldline

       rrtypeline = 1*ALPHA ":" 1*DIGIT 0*1(WSP freetext)

       fieldline = WSP ftype 0*1qualifiers 0*1(WSP freetext)

       ftype = "I1" | "I2" | "I4" | "A" | "AAAA" | "N" | "S" | "B" | "X"

       qualifiers = "[" qual 0*(, qual) "]"

       qual = 1*ALPHA "=" 1*DIGIT | "C" | "A" | "L" | "M"

       freetext = 0*(%x20-%xfe)

3.2.  Storage in the DNS

   Each extension language stanza stored in the DNS is stored as two
   identical TXT records, one with a name based on the numeric RR type,
   one with a name based on the text name.  (One record MAY be aliased
   to the other using a CNAME.) The numeric names are located at
   RRTYPE.ARPA, and the text names are located at RRNAME.ARPA.  For
   example, if the FOO record type were type 999, the two records would
   be:

    999.RRTYPE.ARPA TXT "FOO:999 Foo record" "..."
    FOO.RRNAME.ARPA TXT "FOO:999 Foo record" "..."

3.3.  Storage in a file

   All the extension language stanzas stored in a file are stored as
   lines of ASCII text.  The name of the RR type starts in the first
   position of the first line in the stanza.  Subsequent lines in the
   stanza start with white space.  A line that is blank or starts with a
   # character is a comment and is ignored.

3.4.  Stanza structure

   Each stanza starts with a line containing the name of the RRTYPE, a
   colon, and the numeric RRTYPE.  The name of the RRTYPE must start in
   the first position on the line.  When stored in a file, the RRTYPE
   name should not be the same as an existing RRTYPE or DNS class name
   (IN or CH) or bad things will happen.  The RRTYPE may be followed by
   white space and a descriptive comment intended to be displayed to
   human users, but not interpreted by DNS software.  Provisioning
   software might use the comments as prompts or labels to help a user







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   select the desired RRTYPE.

   The rest of the lines in the stanza start with white space and
   describe the fields in the record.  Each field is one or more octets
   long, and fields are stored sequentially in the record:

   FOO:999 Foo record
      field description
      field[qual,qual] description
      field
      ...

   Some fields may be followed by a comma-separated list of qualifiers
   in square brackets.  The qualifiers further define the field, e.g.,
   in a numeric field, the qualifiers may define symbolic names for
   field values or bit masks.  The field and optional qualifiers may be
   followed by white space and a description of the field.  The
   description is intended to be displayed to human users, and is not
   interpreted by DNS software.  Provisioning software might use the
   comments as prompts or labels for templates into which users type RR
   data.

3.5.  Field types

   Each field type is defined by a token name consisting of letters and
   digits, starting with a letter.

3.5.1.  Integer fields

   Integer fields are defined by I1, I2, and I4 tokens, for fields one,
   two, or four octets long.  The corresponding value in a master record
   is an unsigned integer number.  A field may be followed by qualifiers
   defining symbolic field values.

   A symbolic field value is represented as NAME=NN where NAME is the
   symbol and NN is the numeric value to be placed in the field.  The
   corresponding value in a master record is the symbol.  The symbol can
   contain any ASCII printing character other than comma, equal sign,
   vertical bar, angle braces, or backslash.  For example, to define the
   type field in a CERT record [RFC4398]:

   I2[PKIX=1,SPKI=2,PGP=2,IPKIX=4,ISPKI=5,IPGP=6,ACPKIX=7,\
    IACPKIX=8,URI=253,OID=254] Type

3.5.2.  IP address fields

   IP address fields are defined by A or AAAA tokens, for four-octet








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   IPv4 addresses or 16-octet IPv6 addresses.  The corresponding value
   in a master record is an IP address written in the usual way.  There
   are no qualifiers.

3.5.3.  Domain name fields

   Domain name fields are defined by N tokens.  The qualifier C means
   the name is compressed.  The qualifier A means that the DNS server
   should do the usual additional record processing, including related A
   and AAAA records if available.  The qualifier M means the name is
   really an e-mail address, i.e., the first component is the mailbox
   and the rest is the actual domain name.  Multiple qualifiers are
   permitted, e.g.  N[A,C] for a compressed name with additional record
   processing.

   The corresponding value in a master record is a domain name, written
   in the usual way, with \. meaning a literal dot in a record.

   Names are absolute if they end with a dot, otherwise relative to
   $ORIGIN, the existing convention for master files.

3.5.4.  String fields

   String fields are defined by S tokens.  The qualifier L means that
   the string may be long, more than 255 bytes, in which case it is
   stored in the record as multiple strings, with the location of the
   boundary between the strings undefined.  The qualifier M means that
   there may be multiple strings, each stored as a string in the record.
   A string field with either qualifier must be the last field in the
   record.

   The corresponding value in a master record is a string enclosed in
   single or double quotes, or multiple strings if the M qualifier is
   present.  Embedded quotes may be escaped with a backslash, and a
   double backslash represents a backslash.  If a non-null string
   contains no white space, quote characters, or backslashes, the quotes
   may be omitted.

3.5.5.  Base-64 fields

   A base64 field is defined by a B token.  The qualifier C means that
   the field is stored in the record as a string with a preceding length
   byte.  A base64 field without a C qualifier must be the last field in
   the record.

   The corresponding value in a master record is a string represented as
   base64 [RFC3548].  The value of a base64 field without a C qualifier
   may include embedded spaces for readability, which are ignored.

3.5.6.  Hex fields

   A hex field is defined by an X token.  There are no qualifiers.  A
   hex field must be the last field in the record.


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   The corresponding value in a master record is a string represented as
   an even number of hexadecimal digits.  The value may include embedded
   spaces for readability, which are ignored.

4.  Examples

   If a DNS server didn't already have support for MX records, they
   could be defined as:

   MX:15 Mail exchanger
     I2 Priority (lower values are higher priority)
     N[A,C] Host name

   The name is MX, the RRTYPE is 15, and the data includes a two-octet
   number and a compressed domain name, with additional section records
   for the domain name.

   The SRV record [RFC2782] could be defined as:

   SRV:33 Service location
     I2 Priority
     I2 Weight
     I2 Port
     N[A] Target host name

   The name is SRV, the RRTYPE is 33.  The record contains three two-
   octet fields for the priority, weight, and port, and a domain name.
   The domain name is not compressed, but the DNS server should include
   additional section records for it.

5.  Security considerations

   The extension language makes it possible to create master files that
   represent arbitrary DNS records.  Since most DNS servers already
   provide ways to represent arbitrary data, this doesn't introduce any
   new security issues to the DNS and DNS servers, although it may
   create security issues in provisioning software if the provisioning
   system is intended to limit the kinds of records its users can
   define.

   Extension language files with accidentally or deliberately invalid
   field definitions could provoke odd bugs in server or provisioning
   software that doesn't check the syntax before using it.

6.  IANA considerations

   This document requests that IANA create the RRTYPE.ARPA and
   RRNAME.ARPA zones.  Their initial contents are as follows: [ list of
   description of existing RRs here ]

   When new RR types are defined, the defining documents SHOULD request
   IANA to add appropriate records to RRTYPE.ARPA and RRNAME.ARPA.


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   This document requests that IANA create a registry of DNS Extension
   Language Field Types.  Its initial contents are as follows

                      +------+------------------+
                      | TYPE | REFERENCE        |
                      +------+------------------+
                      |  I1  | (this document)  |
                      |  I2  | (this document)  |
                      |  I4  | (this document)  |
                      |  A   | (this document)  |
                      | AAAA | (this document)  |
                      |  N   | (this document)  |
                      |  S   | (this document)  |
                      |  B   | (this document)  |
                      |  X   | (this document)  |
                      +------+------------------+

  Table 1: DNS Extension Language Field Types Registry Initial Values

7.  References

7.1.  References - Normative

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, November 1987.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

   [RFC3548]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 3548, July 2003.

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

7.2.  References - Informative

   [RFC2782]  Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
              specifying the location of services (DNS SRV)", RFC 2782,
              February 2000.

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements", RFC
              4033, March 2005.

   [RFC4398]  Josefsson, S., "Storing Certificates in the Domain Name
              System (DNS)", RFC 4398, March 2006.

Appendix A.  Change Log

   *NOTE TO RFC EDITOR: This section may be removed upon publication of
   this document as an RFC.*


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A.1.  Changes from -04 to -05

   DNS publication in RRYPE.ARPA and RRNAME.ARPA.

A.2.  Changes from -03 to -04

   More use cases.

   Fix up BNF

A.3.  Changes from -02 to -03

   First stab at BNF

   Note $ORIGIN matters

A.4.  Changes from -01 to -02

   Editorial nits

A.5.  Changes from -00 to -01

   Switch to multi-line format.  Add comments for provisioning.

Authors' Addresses

   John Levine
   Taughannock Networks
   PO Box 727
   Trumansburg, NY  14886

   Phone: +1 831 480 2300
   Email: standards@taugh.com
   URI:   http://jl.ly


   Paul Vixie
   Internet Systems Consortium
   950 Charter Street
   Redwood City, CA>

   Email: vixie@isc.org











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