An Extension Language for the DNS
draft-levine-dnsextlang-08

Network Working Group                                          J. Levine
Internet-Draft                                      Taughannock Networks
Intended status: Standards Track                                P. Vixie
Expires: March 8, 2017                                 September 4, 2016

                   An Extension Language for the DNS
                       draft-levine-dnsextlang-08

Abstract

   Adding new RRTYPEs to the DNS has required 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
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   This Internet-Draft will expire on March 8, 2017.

Copyright Notice

   Copyright (c) 2016 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
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   publication of this document.  Please review these documents
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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Typical usage . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Extension language syntax . . . . . . . . . . . . . . . . . .   3
     3.1.  Lexical structure . . . . . . . . . . . . . . . . . . . .   3
     3.2.  Storage in the DNS  . . . . . . . . . . . . . . . . . . .   4
     3.3.  Storage in a file . . . . . . . . . . . . . . . . . . . .   5
     3.4.  Stanza structure  . . . . . . . . . . . . . . . . . . . .   5
     3.5.  Field types . . . . . . . . . . . . . . . . . . . . . . .   6
   4.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .   8
   5.  Security considerations . . . . . . . . . . . . . . . . . . .   9
   6.  IANA considerations . . . . . . . . . . . . . . . . . . . . .   9
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     7.1.  References - Normative  . . . . . . . . . . . . . . . . .  10
     7.2.  References - Informative  . . . . . . . . . . . . . . . .  11
   Appendix A.  Change Log . . . . . . . . . . . . . . . . . . . . .  11
     A.1.  Changes from -07 to -08 . . . . . . . . . . . . . . . . .  11
     A.2.  Changes from -06 to -07 . . . . . . . . . . . . . . . . .  11
     A.3.  Changes from -05 to -06 . . . . . . . . . . . . . . . . .  11
     A.4.  Changes from -04 to -05 . . . . . . . . . . . . . . . . .  11
     A.5.  Changes from -03 to -04 . . . . . . . . . . . . . . . . .  12
     A.6.  Changes from -02 to -03 . . . . . . . . . . . . . . . . .  12
     A.7.  Changes from -01 to -02 . . . . . . . . . . . . . . . . .  12
     A.8.  Changes from -00 to -01 . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

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 any RRTYPEs, so that provisioning software can
   parse master file records for the RRTYPEs.  DNS servers can use the

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   extension language to implement RRTYPEs that do not require special
   purpose processing.

2.  Typical usage

   The extension language is written as strings of UTF-8 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.  The extension language includes natural language
   field descriptions intended to be used as prompts in fill-in
   templates, and can handle versions of prompts in multiple languages.

   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.  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.

   The extension language can describe all existing RRTYPEs, which may
   be useful in table driven provisioning software.

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

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   a file, it is stored as a series of lines.  The first line of a
   stanza defines the symbolic RRTYPE name.  Subsequent lines, which
   must start with white space, each define a field in the record.
   Blank lines and comment lines where the first nonblank character is
   "#" are ignored.

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

   ldh = ALPHA 0*(ALPHA | DIGIT | "-")

   dnsextfile = 1*stanza

   stanza = rrtypeline 1*fieldline

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

   fieldline = ftype 0*1qualifiers 0*1(":" ldh ) 0*1(WSP freetext)

   ftype = "I1" | "I2" | "I4" | "A" | "AA" | "AAAA" | "N" | "S" |
     "B32" | "B64" | "X" | "T" | "T6"

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

   qual = ldh "=" 1*DIGIT | "C" | "A" | "L" | "M" | "X"

   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.

   The first two strings in the TXT record are the identification tag
   "RRTYPE=1" to identify the record as an RRTYPE definition, and a
   language tag [RFC5646] that identifies the language in which the
   descriptive text is written.  Each line of the stanza is a string in
   the TXT records.  The leading spaces used in the file format
   (described below) are not used.  For example, if the FOO record type
   were type 999, the two records for an English language description
   would be:

999.RRTYPE.ARPA. TXT "RRTYPE=1" "EN" "FOO:999 Foo record" "I2:count Count" "..."
FOO.RRNAME.ARPA. TXT "RRTYPE=1" "EN" "FOO:999 Foo record" "I2:count Count" "..."

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   If there are descriptions in multiple languages, they are all stored
   at the same name, and applications can choose the most suitable one.

999.RRTYPE.ARPA. TXT "RRTYPE=1" "EN" "FOO:999 Foo record" "I2:count Count" "..."
999.RRTYPE.ARPA. TXT "RRTYPE=1" "FR" "FOO:999 Dossier foo" "I2:count Compte" "..."
FOO.RRNAME.ARPA. TXT "RRTYPE=1" "EN" "FOO:999 Foo record" "I2:count Count" "..."
FOO.RRNAME.ARPA. TXT "RRTYPE=1" "FR" "FOO:999 Dossier foo" "I2:count Compte" "..."

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 where the
   first nonblank character is a # is a comment and is ignored.

   Descriptions in different languages are stored in separate files.

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 a colon and letters, to indicate options
   for the RRTYPE.  The only currently used letter is "X" which means
   that implementing the RRTYPE requires extra processing by DNS
   servers, e.g., the extra processing for DNAME or DNSSEC records.  The
   intention of the option is to allow DNS servers to report an error if
   a zone contains a record defined with "X" for which the server does
   not implement the extra processing.

   That can 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 select the desired RRTYPE.

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

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    FOO:999 Foo record
       field description
       field:tag description
       field[qual,qual] description
       field[qual,qual]:tag 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.  That can be followed by an colon and an
   ldh string.  The string is intended to be used as the name of the
   field in software applications that create data structures for an
   RRTYPE.  Applications will often have to change the punctuation to
   match the syntax of the programming language, such as replacing
   hyphens with underscores.  If two fields in an RRTYPE have the same
   name, the result is undefined.

   The field and optional qualifiers and name 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 enter 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 letters, digits, and hypens.  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 Certificate type

   RRTYPE fields are defined by R tokens, for a two octet field
   containing an RRTYPE.  The corresponding value in a master record is
   a symbolic RRTYPE or TYPEnnn for types without names.

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3.5.2.  IP address and partial address fields

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

   The AA token defines a 64 bit field written like half of an IPv6
   address, with up to four colon separated groups of up to four hex
   digits.

3.5.3.  Domain name fields

   Domain name fields are defined by N tokens.  The qualifier C means
   the name is compressed.  The qualifier M, which can only appear on
   the last field in a record, means there can be an arbitrary number of
   domain names.  The qualifier A means that the domain name represents
   a mailbox, with the first component being the local part of the
   mailbox.  The qualifier L means that the domain name is converted to
   lower case before DNSSEC validation.

   The corresponding value in a master record is a domain name or list
   of domain names, 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 convention for master files.

3.5.4.  String fields

   String fields are defined by S tokens.  The qualifier M means that
   there may be multiple strings, each stored as a string in the record.
   A string field with the M 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.

   A string with the X qualifier is a raw string, stored without any
   length bytes.  It must be the last field in the record.

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3.5.5.  Base-32 and Base-64 fields

   A base32 or base64 field is defined by a B32 or B64 token.  The
   qualifier C means that the field is stored in the record as a string
   with a preceding length byte.  The qualifier S means that the field
   is stored in the record as a string with a preceding two-byte length
   field.  A base32 or base64 field without a C or S 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.  The qualifier C means that the
   field is stored in the record as a string with a preceding length
   byte.  The qualifier S means that the field is stored in the record
   as a string with a preceding two-byte length field.  An unqualified
   hex field must be the last field in the record.

   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.

   EUI48 and EUI64 fields are defined by X6 and X8 tokens, respectively.
   The corresponding fields in master records are six or eight pairs of
   hex digits separated by hyphens.

3.5.7.  Time stamp fields

   A 32-bit timestamp field is defined by a T token.  The corresponding
   value in a master record is a fourteen digit value in the form
   YYYYMMDDHHmmSS indicating a UTC timestamp.  The field is stored in
   the record as a Unix timestamp, the unsigned number of seconds since
   January 1, 1970 00:00:00 UTC.

   A 48-bit timestamp field is defined by a T6 token.  The corresponding
   value in a master record is an integer value representing the number
   of seconds since January 1, 1970 00:00:00 UTC.  The field is stored
   in the record as a six octet binary version of that value.

4.  Examples

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   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.

   When extension language data are imported from the DNS, a hostile
   party might use DNS spoofing techniques to modify the records
   imported.  Methods to defend against DNS spoofing include DNSSEC.

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 ]

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

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

               +------+-----------------+-----------------+
               | TYPE | REFERENCE       | EXTLANG VERSION |
               +------+-----------------+-----------------+
               |  I1  | (this document) | 1               |
               |  I2  | (this document) | 1               |
               |  I4  | (this document) | 1               |
               |  A   | (this document) | 1               |
               |  AA  | (this document) | 1               |
               | AAAA | (this document) | 1               |
               |  N   | (this document) | 1               |
               |  S   | (this document) | 1               |
               | B32  | (this document) | 1               |
               | B64  | (this document) | 1               |
               |  X   | (this document) | 1               |
               |  T   | (this document) | 1               |
               |  T6  | (this document) | 1               |
               +------+-----------------+-----------------+

    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, DOI 10.17487/RFC1034, November 1987,
              <http://www.rfc-editor.org/info/rfc1034>.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
              November 1987, <http://www.rfc-editor.org/info/rfc1035>.

   [RFC3548]  Josefsson, S., Ed., "The Base16, Base32, and Base64 Data
              Encodings", RFC 3548, DOI 10.17487/RFC3548, July 2003,
              <http://www.rfc-editor.org/info/rfc3548>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <http://www.rfc-editor.org/info/rfc5234>.

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   [RFC5646]  Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying
              Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646,
              September 2009, <http://www.rfc-editor.org/info/rfc5646>.

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,
              DOI 10.17487/RFC2782, February 2000,
              <http://www.rfc-editor.org/info/rfc2782>.

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements",
              RFC 4033, DOI 10.17487/RFC4033, March 2005,
              <http://www.rfc-editor.org/info/rfc4033>.

   [RFC4398]  Josefsson, S., "Storing Certificates in the Domain Name
              System (DNS)", RFC 4398, DOI 10.17487/RFC4398, March 2006,
              <http://www.rfc-editor.org/info/rfc4398>.

Appendix A.  Change Log

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

A.1.  Changes from -07 to -08

   Add counted hex and raw strings and other new types.  Added language
   tags.  Added field names.

A.2.  Changes from -06 to -07

   Add RRTYPE=1 tag in TXT records.

   Allow digits and hyphens in qualifier tags, for names like SHA-1.

A.3.  Changes from -05 to -06

   Fix formatting problems.

   Add RRTYPE option "X".

A.4.  Changes from -04 to -05

   DNS publication in RRYPE.ARPA and RRNAME.ARPA.

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A.5.  Changes from -03 to -04

   More use cases.

   Fix up BNF

A.6.  Changes from -02 to -03

   First stab at BNF

   Note $ORIGIN matters

A.7.  Changes from -01 to -02

   Editorial nits

A.8.  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
   950 Charter Street
   Redwood City, CA

   Email: vixie@fsi.io

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