INTERNET-DRAFT Donald E. Eastlake, 3rd
IBM
Expires March 2000 September 1999
The Kitchen Sink DNS Resource Record
--- ------- ---- --- -------- ------
Donald E. Eastlake 3rd
Status of This Document
This draft, file name draft-ietf-dnsind-kitchen-sink-02.txt, is
intended to be become an Experimental RFC. Distribution of this
document is unlimited. Comments should be sent to
<namedroppers@internic.net> or to the author.
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. 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. Internet-Drafts may be updated, replaced, or obsoleted by
other documents at any time. It is not appropriate to use Internet-
Drafts as reference material or to cite them other than as a
``working draft'' or ``work in progress.''
The list of current Internet-Drafts can be accessed at
The list of Internet-Draft Shadow Directories can be accessed at
Copyright Notice
Copyright (C) The Internet Society (1999). All Rights Reserved
Abstract
Periodically people desire to put proprietary, complex, and/or
obscure data into the Domain Name System (DNS). This draft defines a
kitchen sink Resource Record that will satisfy this desire for the
storage of miscellaneous structured information.
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Acknowledgements
The suggestions or information provided by the following persons have
improved this document and they are gratefully acknowledged:
Rob Austein
Matt Crawford
Johnny Eriksson
Phillip H. Griffin
Michael A. Patton
David Singer
Table of Contents
Status of This Document....................................1
Copyright Notice...........................................1
Abstract...................................................1
Acknowledgements...........................................2
Table of Contents..........................................2
1. Introduction............................................3
2. Kitchen Sink Resource Record............................3
2.1 The Meaning Octet......................................4
2.2 The Coding and Subcoding Octets........................5
2.2.1 ASN.1 Subcodings.....................................7
2.2.2 MIME Subcodings......................................7
2.2.3 Text Subcodings......................................8
3. Master File Representation..............................8
4. Performance Considerations..............................9
5. Security Considerations.................................9
6. IANA Considerations.....................................9
7. Full Copyright Statement................................9
References................................................11
Author's Address..........................................12
Expiration and File Name..................................12
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1. Introduction
The Domain Name System (DNS) provides a replicated distributed secure
hierarchical database which stores "resource records" (RRs) under
hierarchical domain names. This data is structured into zones which
are independently maintained. [RFC 1034, 1035, 2535]
Numerous types of RRs have been defined. These support such critical
functions as host name to address translation (A, AAAA, etc. RRs),
automatic mail routing (MX etc. RRs), and other functions. In
addition, there are RRs defined related to the zone structure and
administration of the DNS (SOA, NS, and RP RRs), security (SIG, KEY,
and NXT RRs), etc. There is a TXT RR for the inclusion of general
human readable text.
New RRs that are reasonably simple and designed via the open IETF
standards process are periodically added as new needs become
apparent. But there are people who want to put some proprietary,
complex and/or non-standard structured data in the DNS. In the past
they have frequently come up with some way of reinterpreting the TXT
RR, since that is one of the least constrained RRs. This is likely a
bad idea since all previous ways to reinterpreting the TXT RR have
sunk without a trace. (Well, if they actually got an RFC out, it's
still there, but, practically speaking, almost nobody actually uses
it.)
If a new type of data is needed for a global interoperable use in the
DNS, the best course is to design a new RR that meets the need
through the IETF standards process. This draft defines an extremely
general and flexible RR which can be used for other data, such as
proprietary data, where global interoperability is not a
consideration. It includes representations of OSI ASN.1, MIME, XML,
and, recursively, DNS RRs.
2. Kitchen Sink Resource Record
The symbol for the kitchen sink resource record is SINK. Its type
number is 40. This type is defined across all DNS classes.
The RDATA portion of the SINK RR is structured as follows:
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1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| meaning | coding |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| subcoding | /
+--+--+--+--+--+--+--+--+ /
/ data /
/ /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
The "meaning", "coding", and "subcoding" octets are always present.
The "data" portion is variable length and could be null in some
cases. The size of the "data" portion can always be determined by
subtracting 3 from the SINK resource record RDLENGTH. The coding
octet gives the general structure of the data. The subcoding octet
provides additional information depending on the value of the coding
nibble.
All references to "domain name" in this document mean a domain name
in the DNS CLASS of the SINK RR.
2.1 The Meaning Octet
The meaning octet indicates whether any semantic tagging appears at
the beginning of the data field and the format of such semantic
tagging. This contrasts with the coding and subcoding octets which
merely indicate format. The inclusion of such semantic tagging is
encouraged and it is expected to be the primary means by which
applications determine if a SINK RR is of the variety in which they
have interest.
It is noted that multiple popular uses of SINK could develop that are
not distinguished by using different parts of the DNS name space or
different DNS classes. If this occurs, retrievals may fetch large
sets of SINK RR to be sorted through at the application level.
Should this occur, such popular uses of SINK should obtain and
migrate to their own RR number using normal RR number allocation
procedures. In addition, it would be possible to define an extended
query operation that selects from among SINK RRs based on the
semantic tag.
The types of tags available are chosen to be globally unique and
under the control of some "owner". The owner designates the meaning
associated with the tags they control. Where the tag is a URI, it is
recommended that a retrieval from the URI fetch material that would
be helpful in determining this meaning. No a priori method is
defined for determining the meaning of other tags beside an out of
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band question to the owner.
INITIAL ASSIGNED MEANING VALUES
0 - reserved.
1 - none.
2 - OID.
3 - domain name.
4 - URI.
5-254 - available for assignment, see section 6.
255 - reserved.
A meaning octet value of 1 indicates that there is no semantic
tagging at the beginning of the data area. The information, whatever
it is, starts at the beginning of the data field and is coded
according to the coding and subcoding octets.
Meaning octet values of 2, 3, or 4, indicate, on the other hand, that
a semantic tag is present. A value of two indicates that a BER
[X.690] encoded OID appears prefixed by a single unsigned octet of
OID length count. A value of three indicates that a DNS domain name
appears in wire format with name compression prohibited. And a value
of four indicates that a null (zero) octet terminated URI appears.
2.2 The Coding and Subcoding Octets
The coding octet gives the major method by which the data in the data
field is encoded. It should always have a meaningful value. The
subcoding octet is intended to give additional coding details.
Although the subcoding octet is always present, it must be
interpreted in the context of the coding octet. For any coding octet
value which does not specify subcoding octet value meanings, the
subcoding octet MUST be ignored and SHOULD be zero.
While not explicitly mentioned below, the data field will actually
start with a semantic tag if indicated by the meaning octet. If such
a semantic tag is present, any data prefix required by the coding or
subcoding octet is placed after the semantic tag and before the data.
CODING OCTET VALUES
0 - reserved.
1 - DNS RRs. The data portion consists of DNS resource records
as they would be transmitted in a DNS response section. The
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subcoding octet is the number of RRs in the data area as an
unsigned integer. Domain names may be compressed via pointers
as in DNS replies. The origin for the pointers is the beginning
of the RDATA section of the SINK RR. Thus the SINK RR is safe
to cache since only code that knows how to parse the data
portion of a SINK RR need know of and can expand these
compressions.
2 - MIME structured data [RFC 2045, 2046]. The data portion is
a MIME structured message. The "MIME-Version:" header line may
be omitted unless the version is other than "1.0". The top
level Content-Transfer-Encoding may be encoded into the
subcoding octet (see section 2.2.2). Note that, to some extent,
the size limitations of DNS RRs may be overcome in the MIME case
by using the "Content-Type: message/external-body" mechanism.
3 - Text tagged data. The data potion consists of text formated
as specified in the TXT RR except that the first and every
subsequent odd numbered text item is considered to be a tag
labeling the immediately following text item. If there are an
odd number of text items overall, then the last is considered to
label a null text item. Syntax of the tags is as specified in
RFC 2396 for the "Authority Component" without the two leading
slashes ("//") or trailing slash using the DNS for authority.
Thus any organization with a domain name can assign tags without
fear of conflict. The subcodings octet specifies the encoding
of the labeled text items as specified in section 2.2.3.
4 - HTML. The subcoding octet indicates the version of HTML
with the major version number in the upper nibble and the minor
version number in the lower nibble. Thus, for example, HTML 3.2
would be indicated by a 0x32 octet.
5 - XML. The subcoding octet is the version of XML, currently
1.
6 - ASN.1 [X.680, etc.]. See section 2.2.1.
7-251 - Available for assignment, see section 6.
252 - Private coding format indicated by an OID. The format of
the data portion is indicated by an initial BER encoded OID
which is prefixed by a one octet unsigned length count for the
OID. The subcoding octet is available for whatever use the
private formating wishes to make of it.
253 - Private coding format indicated by a domain name. The
format of the data portion is indicated by an initial wire
format domain name with compression prohibited. (Such names are
self delimiting.) The subcoding octet is available for whatever
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use the private formating wishes to make of it.
254 - Private coding format indicated by a URI. The format of
the data portion is indicated by an initial URI [RFC 2396] which
is terminated by a zero (null) valued octet followed by the data
with that format. The subcoding octet is available for whatever
use the private formating wishes to make of it. The manner in
which the URI specifies the format is not defined but presumably
the retriever will recognize the URI by some pattern match.
255 - reserved.
NOTE: the existence of a DNS RR coding and the infinite possibilities
of ASN.1, XML, and MIME permit one to SINK to even greater depths by
nesting.
2.2.1 ASN.1 Subcodings
For ASN.1 [X.680, etc.] data, a specific concrete encoding must be
chosen as indicated by the subcoding octet.
ASN.* SUBCODINGS
0 - reserved.
1 - BER ( Basic Encoding Rules [X.690] ).
2 - DER ( Distinguished Encoding Rules [X.690] ).
3 - PER ( Packed Encoding Rules ) Aligned [X.691].
4 - PER Unaligned [X.691].
5 - CER ( Canonical Encoding Rules [X.690] ).
6-253 - available for assignment, see section 6.
254 - private. This subcoding will never be assigned to a standard
set of encoding rules. An OID preceded by a one octet unsigned
length of OID appears at the beginning of the data area after
the ASN coding OID.
255 - reserved.
2.2.2 MIME Subcodings
If the coding octet indicates the data is MIME structured, the
precise encoding is given by the subcoding octets as listed below.
MIME SUBCODINGS
0 - reserved, see section 6.
1 - 7bit.
2 - 8bit.
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3 - binary.
4 - quoted-printable.
5 - base64.
6 - 253 - available for assignment, see section 6.
254 - private. The data portion must start with an "x-" or "X-"
token denoting the private content-transfer-encoding immediately
followed by one null (zero) octet followed by the remainder of
the MIME object.
255 - reserved, see section 6.
2.2.3 Text Subcodings
If the coding octet indicates the data is text, the exact encoding of
the text items is indicated by the subcoding octet as follows:
TEXT SUBCODINGS
0 - reserved, see section 6.
1 - ASCII.
2 - UTF-7 [RFC 1642].
3 - UTF-8 [RFC 2044].
4 - ASCII with MIME header escapes [RFC 2047].
5 - 253 - available for assignment, see section 6.
254 - private. Each text item must start with a domain name [RFC
1034] in wire format without compression denoting the private
text encoding immediately followed by the remainder of the text
item.
255 - reserved, see section 6.
3. Master File Representation
SINK resource records may appear as lines in zone master files. The
meaning, coding, and subcoding appear as unsigned decimal integers.
The data portion can be quite long. It is represented in base 64
[RFC 2045] and may be divided up into any number of white space
separated substrings, down to single base 64 digits, which are
concatenated to obtain the full data. These substrings can span
lines using the standard parenthesis notation. (This type of base64
master file data is also required to support the DNS KEY and SIG
security RRs [RFC 2535].)
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4. Performance Considerations
Currently DNS is optimized for small data transfers, generally not
exceeding 512 octets including overhead. Larger transfers are less
efficient but do work correctly and efforts are underway to make them
more efficient.
It is easy to create very large RRs or RR sets using SINK. DNS
administrators should think about this and may wish to discourage
large RRs or RR sets. Consideration should also be given to putting
zones from which large RRs or RR sets will be commonly retrieved on
separate hosts which can be tuned for the load this will represent.
5. Security Considerations
Since the SINK resource record can be used to store arbitrary data in
the DNS, this data could have security consequences, particularly if
it is control, executable, macro, or interpretable information or
very large and might cause buffer overflow. Due care should be
taken.
[RFC 2535] covers data original authentication of the data in the
domain name system including SINK RRs.
6. IANA Considerations
Assignment of specific meaning to the values listed herein as
"reserved" requires an IETF standards action.
All other assignments of available meaning, coding, or subcoding
octet values are by IETF consensus.
The many provisions for private indicita specified by separately
allocated OIDs, domain names, or URIs should cover most requirements
for private or proprietary values.
7. Full Copyright Statement
Copyright (C) The Internet Society (1999). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
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kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
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References
[RFC 1034] - P. Mockapetris, "Domain names - concepts and
facilities", 11/01/1987.
[RFC 1035] - P. Mockapetris, "Domain names - implementation and
specification", 11/01/1987.
[RFC 1642] - D. Goldsmith, M. Davis, "UTF-7 - A Mail-Safe
Transformation Format of Unicode", 07/13/1994.
[RFC 2044] - F. Yergeau, "UTF-8, a transformation format of Unicode
and ISO 10646", 10/30/1996.
[RFC 2045] - N. Freed, N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Bodies",
12/02/1996.
[RFC 2046] - N. Freed, N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", 12/02/1996.
[RFC 2047] - K. Moore, "MIME (Multipurpose Internet Mail Extensions)
Part Three: Message Header Extensions for Non-ASCII Text",
12/02/1996.
[RFC 2396] - T. Berners-Lee, R. Fielding, L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", August 1998.
[RFC 2535] - D. Eastlake, "Domain Name System Security Extensions",
March 1999.
[X.680] - ITU-T Recommendation X.680 (1997) | ISO/IEC 8824-1:1998,
Information Technology - Abstract Syntax Notation One (ASN.1):
Specification of Basic Notation
[X.681] - ITU-T Recommendation X.681 (1997) | ISO/IEC 8824-2:1998,
Information Technology - Abstract Syntax Notation One (ASN.1):
Information Object Specification
[X.682] - ITU-T Recommendation X.682 (1997) | ISO/IEC 8824-3:1998,
Information Technology - Abstract Syntax Notation One (ASN.1):
Constraint Specification
[X.683] - ITU-T Recommendation X.683 (1997) | ISO/IEC 8824-4:1998,
Information Technology - Abstract Syntax Notation One (ASN.1):
Parameterization of ASN.1 Specifications
[X.690] - ITU-T Recommendation X.690 (1997) | ISO/IEC 8825-1:1998,
Information Technology - ASN.1 Encoding Rules: Specification of Basic
Encoding Rules (BER), Canonical Encoding Rules (CER) and
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Distinguished Encoding Rules (DER)
[X.691] - ITU-T Recommendation X.691 (1997) | ISO/IEC 8825-2:1998,
Information Technology - ASN.1 Encoding Rules: Specification of
Packed Encoding Rules (PER)
Author's Address
Donald E. Eastlake 3rd
IBM
65 Shindegan Hill Road
Carmel, 10512 USA
Telephone: +1 914-276-2668 (h)
+1 914-784-7913 (w)
FAX: +1 914-784-3833 (w)
EMail: dee3@us.ibm.com
Expiration and File Name
This draft expires March 2000.
Its file name is draft-ietf-dnsind-kitchen-sink-02.txt.
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