One document matched: draft-ietf-idn-dnsii-mdnp-00.txt
IDN Working Group Edmon Chung & David Leung
Internet Draft Neteka Inc.
<draft-ietf-idn-dnsii-mdnp-00.txt> August 2000
The DNSII Multilingual Domain Name Protocol
STATUS OF THIS MEMO
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 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 reader is cautioned not to depend on the values that appear in
examples to be current or complete, since their purpose is primarily
educational. Distribution of this memo is unlimited.
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
Historically, the DNS is capable of handling only names within the
basic English alphanumeric character set (plus the hyphen), yet the
standards were so elegantly and openly designed that the extension of
the DNS into a multilingual and symbols based system proves to be
possible with simple adjustments.
These adjustments will be made on both the client side and the server
side. However, DNSII works on the principal that it is preferable to
make the transition to multilingual domain names seamless and
transparent to the end-user. Which means initially the server, or
more specifically, the resolver, SHOULD take the primary
responsibility for the technical implementation of the changes
required for a multilingual Internet.
The DNSII protocol is designed to allow the preservation of
interoperability, consistency and simplicity of the original DNS,
while being expandable and flexible for the handling of any character
or symbol used for the naming of an Internet domain.
This draft forms the introduction of a series of draft including
intended resolution processes and other DNSII documents.
DNSII-MDNP Multilingual Domain Name Protocol August 2000
1. Introduction
This Internet-draft describes details of the DNSII Multilingual
Domain Name protocol. The Internet-Draft assumes that the reader is
familiar with the concepts discussed in the widely distributed RFCs
"Domain Names _ Concepts and Facilities" [RFC 1034] and _Domain Names
_Implementation and Specification" [RFC 1035].
1.1 Terminology
The key words "MUST", "SHALL", "REQUIRED", "SHOULD", "RECOMMENDED",
and "MAY" in this document are to be interpreted as described in RFC
2119 [RFC2119].
A number of multilingual characters are used in this document for
examples. Please select your view encoding type to UTF-8 for it to be
displayed properly.
1.2 DNSII
Many of the current proposals for a multilingual domain name system
involve working around the current ANSI based DNS. So doing either
affects the integrity of the original spirit of the DNS or does not
well address the encoding conflict issues apparent in different
character encoding schemes.
The DNSII specifications takes a radically different approach: it
successfully identifies the difference between original DNS and DNSII
packets within the labels and at the same time allows the use of
multiple charsets to be easily incorporated in a standardized manner.
It causes no harm to the current DNS because it embraces the original
format for DNS laid out in RFC1035, complemented with the ideas
incorporated in EDNS [RFC2671].
2. DNSII Protocol
The DNSII Protocol consists mainly of two parts: the InPacket DNSII
Identifier and the InPacket Label Encoding Type. In addition, there
are several special considerations for specific record types.
2.1 InPacket DNSII Identifier
In the DNSII specifications, an InPacket DNSII Identifier MUST be
inserted before a label to signify that it contains extended
characters that are not supported by the current DNS.
This DNSII flag, which is the first two bits of a label, effectively
distinguishes a DNSII compliant request from the existing format,
without having to conduct a guess from a name check whether the
DNSII-MDNP Multilingual Domain Name Protocol August 2000
incoming packet is multilingual aware. This is a substantial
improvement over character encoding schemes and multilingual
implementations in which it is almost impossible to determine the
language of an incoming request. The DNSII flag makes the process
clear and simple.
Currently:
"00" regular label [RFC1035]
"11" a redirection for DNS compression [RFC1035]
"01" indicates the use of EDNS for multiple UDP packets [RFC2671]
DNSII calls for the use of the bit sequence "10" to identify that the
querying node is DNSII aware. This will mean that all the possible
variations at top two label bits will be used. Therefore, in
consideration, following two bits MUST be reserved for future
flagging use. The 2 bits SHOULD be arbitrarily set to "00". This
effectively opens up 3 more possible implementations for future
enhancements.
The motivation for this approach is the belief there should be no
ambiguity in name resolution. Any name that the client wishes to
resolve, should resolve, regardless of the client side-encoding
scheme.
2.2 InPacket Label Encoding Type (ILET)
Immediately following the 2 assigned DNSII flag and the 2 reserved
bits are 12 bits assigned to determine the InPacket Label Encoding
Type (ILET).
The ILET is a 12-bit number that is used to determine the encoding
scheme used by the characters of the label. The MIBenum numbers
[RFC1700] SHOULD be used in this field. The allocation of 12 bits
aligns perfectly with the MIBenum specification, of which the value
goes up to over 2200. With 12 bits, the total possible values would
be 4096 (with 11 bits, the largest value that can be represented is
only 2047, slightly short of the specification). The reason for the
adoption of MIBenum is to make use of the existing list of encoding
numbering schemes rather than re-inventing the wheel.
The value in the ILET field SHOULD only be allowed for the valid
encoding schemes defined in the MIBenum list.
DNSII-MDNP Multilingual Domain Name Protocol August 2000
After identifying the encoding type, the regular count-label scheme
of the DNS resumes. The resulting label should look like this:
1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+---+---+-------+---------------+
|1 0| z | ILET |
+---------------+---------------+
| COUNT | characters... |
+---------------+---------------+
To minimize the size of a DNS packet, if the entire label is
constituted in characters only from the ANSI table, the DNS label
will appear identical to current implementations. The first two bits
will remain "00".
For example, using the DNSII format the label for "dns" MAY be
represented as:
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| 1 0| 0 0| 0 0 0 0 0 0 0 0 0 0 1 1| MIBenum 3 = ANSI
+-----------------------------------------------+
| 3 | 6 4 | "d"=64
+-----------------------------------------------+
| 6 E | 7 3 | "n"=6E "s"=73
+-----------------------------------------------+
Or, the same domain label "dns" MAY also be represented as:
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| 3 | d |
+-----------------------------------------------+
| n | s |
+-----------------------------------------------+
With a multilingual domain name ns.
Ιμώ©΄.tld as an example:
1 1 1 1 1 1 1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+---------------------------------------------------------------+
|1 0| z | ANSI=3 | 2 | n |
+---------------------------------------------------------------+
| s |1 0|0 0| UCS-2=1000 | 4 |
+---------------------------------------------------------------+
|
(U+57DF) |
Ιμ (U+540D) |
+---------------------------------------------------------------+
| ώ© (U+7CFB) | ΄ (U+7D71) |
+---------------------------------------------------------------+
|0 0| 3 | t | l | d |
+---------------------------------------------------------------+
| 0 |
+---------------+
DNSII-MDNP Multilingual Domain Name Protocol August 2000
From the above example, we can see that the DNSII format is used for
the first label "ns", as well as for the second label, which is in
Chinese (the MIBenum for UCS-2 or ISO 10646 [Unicode] is 1000). The
third label "tld" however uses the current format.
In any case, the count-label-count-label mechanism is largely
preserved. Especially in the case of extended characters where in
other proposals, the "count" no longer represents the character
count. In the above example, the domain is still represented as
2ns4
Ιμώ©΄3tld0, exactly in line with the original specifications.
Note that the first label in any query SHOULD be represented in DNSII
format to alert the destination server that it is DNSII aware. This
is specifically configured for the considerations with CNAME, A6,
DNAME and PTR records.
This approach is used to ensure that there is no confusion about the
encoding format of the label. ILET allows the capability of
employing all existing encoding schemes (UTF-7, UTF-8, ISO 10646
[UCS-2], ISO 10646 [UCS-4]). ILET also allows the flexibility of
employing future encoding schemes.
2.3 The Rationale for using ILET
Besides being able to preserve the count-label-count-label structure,
which in itself is actually a very important part because of the
problematic non-uniform byte encoding schemes, the use of ILET aligns
perfectly with previous IETF specifications as well as beneficial for
tricky case folding and canonicalization issues.
We know that all protocols MUST identify, for all character data,
which charset is in use [RFC2277], therefore it is necessary to
specify whatever encoding scheme, whether it be UTF-8, UTF-7, 16-bit
UCS-2 or ISO 8859 that is being used. In essence, we understand that
it is paramount that a charset be clearly identified, especially in
situation like the DNS where no direct communication is established.
"At times and in specific cases, language information may be required
to achieve a particular level of quality for the purpose of
displaying a text stream. For example, UTF-8 encoded Han may require
transmission of a language tag to select the specific glyphs to be
displayed at a particular level of quality.
Note that information other than language may be used to achieve the
required level of quality in a display process. In particular, a
font tag is sufficient to produce identical results. However, the
association of a language with a specific block of text has
usefulness far beyond its use in display. In particular, as the
amount of information available in multiple languages on the World
Wide Web grows, it becomes critical to specify which language is in
use in particular documents, to assist automatic indexing and
retrieval of relevant documents." [RFC2130]
DNSII-MDNP Multilingual Domain Name Protocol August 2000
In effect, this means for different languages, it is beneficial to be
able to identify the language in order to perform specific functions
to the characters, including case folding. With ILET, the local
encoding scheme could be used and with them there are well defined
folding methods. Therefore, the use of ILET enables an optimized
folding mechanism brought about by the preservation of local encoding
schemes, which is otherwise very difficult or virtually impossible to
do if only UTF-8 is used.
For the DNS however, a language tag is less feasible because if a
name is consisted of multiple languages, it would be very difficult
for tagging to be performed. The possibility of having multiple
languages is very sound, and is used frequently as trademarks around
the world. For example the famous Toys"Ο―"Us name, uses a character
from the Cyrillic language set.
2.4 Considerations for Specific Requests
For certain requests, an ANSI only name could result in a
multilingual domain as an answer. These include PTR, CNAME, A6 and
DNAME requests. Special considerations are made within the DNSII
protocol to make sure that non-DNSII aware servers will not be fed
with a DNSII format packet.
2.4.1 PTR Records
For all PTR requests, the first label of the query MUST use DNSII
format to alert the destination server. Upon which, a DNSII packet
will be replied should the name contain extended characters.
If the DNSII format is not used, and the PTR record stumbles upon a
multilingual domain name, one of the following responses SHOULD be
given:
a. The implementer of DNSII MAY chose to reject the request;
or
b. An ACE format domain with a "for.ref.only" suffix MAY be returned;
or
c. A DNSII compliant server MAY return an 8-bit format of the
requested domain.
Since the PTR record is usually used for display purposes only, the
rejection (the IP address will then be used) or ACE format is
acceptable. If the response is however used for further resolution,
an ACE format MUST not be used.
DNSII-MDNP Multilingual Domain Name Protocol August 2000
2.4.2 CNAME, A6 & DNAME
For queries concerning the record types CNAME, A6 or DNAME, a DNSII
aware server should first check to see if the incoming request is
DNSII compliant (flagged by the "10" bits in the first label):
If so, and the domain to be returned includes extended characters,
the response SHOULD be in DNSII format.
If not, any multilingual domains returned should be in an 8 bit form.
For the above record types it is strongly RECOMMENDED not to
associate an alphanumeric label to a multilingual label as the
RDATA. However, it is permissible to associate a multilingual label
with an alphanumeric label as the RDATA.
3. Alternate Implementations
The DNSII-MDNP is intended to be a framework for the implementation
of multilingual domain names. While the core concepts and the design
principles remain consistent, it is possible to contemplate
alternative implementations, which for some people may feel easier to
implement.
3.1 Restricted ILET Values
One possible implementation guideline is for the ILET to be
restricted to values only representing ISO 10646 transformations
including UCS-2, UCS-4, UTF-7, UTF-8, UTF-16 and other as they become
available and included as a standard MIBenum.
Although this takes away some of the benefits of keeping the local
encoding scheme which includes the issues of case folding,
canonicalization and other related concerns, it creates a system that
on one hand contains only encoding schemes from ISO 10646, but on the
other hand still provides the flexibility of deploying new encoding
schemes that stem from ISO 10646, such as the 32-bit format that is
due to be used soon.
We understand it is specified that in protocols, which up to now have
used US-ASCII only, UTF-8 forms a simple upgrade path; however, its
use should be negotiated either by negotiating a protocol version or
by negotiating charset usage, and a fallback to UTF-7 MUST be
available. [RFC2130] With DNSII, the required fallback to UTF-7
could easily be done by setting the ILET value to reflect UTF-7.
DNSII-MDNP Multilingual Domain Name Protocol August 2000
3.2 Reduced ILET Bit Allocation
Furthering the restriction of the ILET to ISO 10646 transformations
only, the ILET bit allocations could also be reduced from 12 bit to 5
bit. This successfully creates a total of 32 possible values. The
reserved bits are also reduced to one.
1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+---+-+---------+---------------+
|1 0|z| ILET | COUNT |
+---------------+---------------+
| characters... |
+---------------+
For example, the label "
Ιμώ©΄" will now be reflected in DNS packets
in the following form:
1 1 1 1 1 1 1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+---------------------------------------------------------------+
|1 0|z| ILET=1 | 4 |
(U+57DF) |
+---------------------------------------------------------------+
|
Ιμ (U+540D) | ώ© (U+7CFB) |
+---------------------------------------------------------------+
| ΄ (U+7D71) |
+--------------------------------+
To start off with, the ILET values MAY be determined as follows:
0 = reserved for ANSI only
1 = 16 bit UCS-2
2 = UTF-8
3 = UTF-7
4 = 32 bit UCS-4
4. Implementation & Deployment Strategies
The first step in any multilingual domain name implementation should
be to encourage an 8-bit clean approach to DNS. However, even when
the system is 8-bit clean the problem with conflicting characters
still exists. This is where the DNSII protocol becomes most
valuable.
Although the DNSII protocol could be implemented at any level of the
DNS, the following phased rollout is contemplated.
(1) Registry Level - The most meaningful starting point for
deployment would be at the registry level since this creates the
demand from the end users to use multilingual and extended character
domain names for Second Level Domains.
DNSII-MDNP Multilingual Domain Name Protocol August 2000
(2) Host Level - At the same time, registrants of the new extended
domain names could start to implement DNSII to host these special
kinds of domain names. All other hosts that do not wish to use
extended characters do not have to migrate to the DNSII.
(3) Client Level - Once the multilingual aspect and the DNSII
specifications become mainstream, the user level resolvers will begin
to migrate. This will include both the client resolver as well as
the ISP's DNS.
(4) Root Level - Eventually, as the DNSII is proven to be stable and
beneficial for the Internet at large, it could be used in the Root
Level so that new multilingual TLDs could be created.
5. IDN Requirements Considerations
The DNSII protocol specification is in line with most if not all of
the requirements identified by the IDN work group.
6. DNSSEC, EDNS and IPv6 Considerations
The use of DNSII should not require any adjustments with the
implementation of DNSSEC, EDNS or IPv6. EDNS as well as compression
in fact will be done exactly the same as the existing system.
For example, the domain host.dns.
Ιμώ©΄.tld running with EDNS as
well as compression after host will look as follows:
1 1 1 1 1 1 1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+---------------------------------------------------------------+
20|0 1| ELT |0 0| 3 | d | n |
+---------------------------------------------------------------+
| s |1 0|0 0| UCS-2=1000 | 4 |
+---------------------------------------------------------------+
|
(U+57DF) |
Ιμ (U+540D) |
+---------------------------------------------------------------+
| ώ© (U+7CFB) | ΄ (U+7D71) |
+---------------------------------------------------------------+
|0 0| 3 | t | l | d |
+---------------------------------------------------------------+
| 0 |
+---------------+
+---------------------------------------------------------------+
|0 0| 4 | h | o | s |
+---------------------------------------------------------------+
| t |1 1| 21 |
+-----------------------------------------------+
DNSII-MDNP Multilingual Domain Name Protocol August 2000
7. Intellectual Property Considerations
It is the intention of Neteka to submit the DNSII protocol and other
elements of the multilingual domain name server software to IETF for
review, comment or standardization.
Neteka Inc. has applied for one or more patents on the technology
related to multilingual domain name server software and multilingual
email server software suite. If a standard is adopted by IETF and
any patents are issued to Neteka with claims that are necessary for
practicing the standard, any party will be able to obtain the right
to implement, use and distribute the technology or works when
implementing, using or distributing technology based upon the
specific specifications under fair, reasonable and non-discriminatory
terms.
8. References
[RFC1700] J. Reynolds, J. Postel, "ASSIGNED NUMBERS", RFC
1700, October 1994.
[ISO10646] ISO/IEC 10646-1:2000. International Standard --
Information technology -- Universal Multiple-Octet Coded
Character Set (UCS)
[RFC1034] Mockapetris, P., "Domain Names - Concepts and
Facilities," STD 13, RFC 1034, USC/ISI, November 1987
[RFC1035] Mockapetris, P., "Domain Names - Implementation and
Specification," STD 13, RFC 1035, USC/ISI, November
1987
[RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels," RFC 2119, March 1997
[RFC2130] C. Weider, et al. _The Report of the IAB Character Set
Workshop held 29 February - 1 March, 1996_ RFC 2130, April
1997
[RFC2277] H. Alvestrand, _IETF Policy on Character Sets and Languages_
RFC 2277, January 1998
[RFC2671] Paul Vixie, "Extension Mechanisms for DNS (EDNS0)", August
1999, RFC 2671.
Authors:
Edmon Chung
Neteka Inc.
DNSII-MDNP Multilingual Domain Name Protocol August 2000
2462 Yonge St. Toronto,
Ontario, Canada M4P 2H5
edmon@neteka.com
David Leung
Neteka Inc.
2462 Yonge St. Toronto,
Ontario, Canada M4P 2H5
david@neteka.com
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