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INTERNET-DRAFT Donald E. Eastlake, 3rd
IBM
Expires February 2000 August 1999
draft-ietf-dnsind-kitchen-sink-01.txt
The Kitchen Sink DNS Resource Record
--- ------- ---- --- -------- ------
Donald E. Eastlake 3rd
Status of This Document
This draft, file name draft-ietf-dnsind-kitchen-sink-01.txt, is
intended to be become a Proposed Standard 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
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.
To view the entire list of current Internet-Drafts, please check the
"1id-abstracts.txt" listing contained in the Internet-Drafts Shadow
Directories as listed at <http://www.ietf.org/shadow.html>.
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.
D. Eastlake 3rd [Page 1]
INTERNET-DRAFT The Kitchen Sink Resource Record
Acknowledgements
The suggestions or information provided by the following persons have
improved this document and they are gratefully acknowledged:
Rob Austein
Johnny Eriksson
Phillip H. Griffin
Michael A. Patton
David Singer
Table of Contents
Status of This Document....................................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..............................8
5. Security Considerations.................................9
6. IANA Considerations.....................................9
References................................................10
Author's Address..........................................11
Expiration and File Name..................................11
D. Eastlake 3rd [Page 2]
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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 periodically 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 domain name in
the IP DNS class.
Although it is unlikely, it is noted that multiple popular uses of
SINK might 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 RRs which will likely
have 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 or it
would be possible to define an extended query operation that used a
more fine grained selection method than just the RR type.
2.1 The Meaning Octet
The meaning octet indicates whether any semantic labeling appears at
the beginning of the data field and the format of such semantic
labeling. This contrasts with the coding and subcoding octets which
merely indicate format.
The types of labels available are chosen to be globally unique and
under the control of some "owner". The owner designates the meaning
associated with the labels they control. Where the label 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 labels beside an out of
band question to the owner.
D. Eastlake 3rd [Page 4]
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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
labeling 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 label 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 label if indicated by the meaning octet. If
such a semantic label is present, any data prefix required by the
coding or subcoding octet is placed after the semantic label 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
subcoding octet is the number of RRs in the data area as an
D. Eastlake 3rd [Page 5]
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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
use the private formating wishes to make of it.
D. Eastlake 3rd [Page 6]
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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.
3 - binary.
4 - quoted-printable.
D. Eastlake 3rd [Page 7]
INTERNET-DRAFT The Kitchen Sink Resource Record
5 - base64.
6 - 253 - available for assignment, see section 6.
254 - private. The data portion must start with an "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] denoting the private text encoding immediately followed by
one null (zero) octet 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].)
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
D. Eastlake 3rd [Page 8]
INTERNET-DRAFT The Kitchen Sink Resource Record
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.
D. Eastlake 3rd [Page 9]
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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
D. Eastlake 3rd [Page 10]
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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 February 2000.
Its file name is draft-ietf-dnsind-kitchen-sink-01.txt.
D. Eastlake 3rd [Page 11]