Internet DRAFT - draft-yoneya-dns-variant-label-rr
draft-yoneya-dns-variant-label-rr
Network Working Group Y. Yoneya
Internet-Draft JPRS
Intended status: Standards Track February 25, 2013
Expires: August 29, 2013
Variant Label Resource Record
draft-yoneya-dns-variant-label-rr-01
Abstract
Definition and operation of variant domain names are differ from zone
administrators, and there is no generic rules, therefore, in general,
it is hard to guess variant labels for end users and / or
applications. Meanwhile, zone administrators are understanding all
variant labels list because they generate variant labels and activate
them according to rules they defined. Thus, if there is a mechanism
that end users and / or applications can obtain variant labels list
from zone administrators, then it would be useful. The Variant
Labels Resource Record (VL RR) provides such variant labels list for
that purpose.
Status of this Memo
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1. Introduction
Some of the zone administrators such as TLD registries that accepting
IDNs are bundling variants as a package. Also, in conjunction with
the deployment of IDN TLDs, consideration of Variant IDN TLD is in
progress. It is hard to guess variant labels list from short string
that does not have context like domain name, because definition of
variants are differ from languages even though using the same script.
The zone administrators such as registries have complete list of
variant labels for a label, so if they have mechanism to provide the
list, end users and / or applications can obtain variant labels list
without guessing. The Variant Labels Resource Record (VL RR) is a
new DNS RR that provides variant labels for a label.
2. Definition of VL RR
VL RR format is as follows:
variant1 TTL IN VL priority1 variant1.
priority2 variant2.
priority3 variant3.
Here, the variant1 is a left most label in a query name, the
variant1, variant2 and the variant3 are the list of activated
(delegated) variant labels for the variant1. Variant label which is
not activated must not be listed. The values of right hand side can
be listed multiple times as RRset like other RRs. Period at the end
can't be omitted. If the variant label is IDN, then it must be
written in A-label [RFC5890]. The priority1, priority2 and priority3
are the integer numbers which indicate priorities for the variant1,
variant2 and variant3 respectively. The smallest number means that
the variant label is the canonical label.
All variant labels must be defined inside of one zone, and they can't
refer labels outside of the zone. See Appendix A for examples.
The VL RR can't set to the zone apex in child zone. This means that
VL RR for zone apex must be set in parent zone.
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3. Behaviour of full resolvers
The full resolvers send VL RR query to the authoritative DNS
server(s) for the FQDN which is generated from the query name
omitting left most label (parent zone authoritative DNS server(s))
and get response. The full resolvers may cache the response during
the TTL time.
4. Behaviour of authoritative DNS servers
The authoritative DNS servers must ignore VL RR which is set to the
zone apex in child zone. The authoritative DNS servers respond
NXDOMAIN for queries to non-existent label. The authoritative DNS
servers respond VL RRset for queries to existing label if it has VL
RRs, or respond NOERROR for queries to existing label if it does not
have VL RRs.
The full resolvers which is not VL RR capable can't send queries to
the parent zone's authoritative DNS server(s), therefore, it can't
obtain VL RR for the zone apex actively. Thus, parent zone's
authoritative DNS server(s) should respond VL RRset in additional
section when it respond NS RRset.
5. Behaviour of applications
The applications treat a label with most small number priority as a
canonical label from list of variant labels obtained by the query.
Other labels may be displayed to the users as list of variant labels.
6. Issues of VL RR
The VL RR increases volume of large zone such as TLD registries have.
This will impact zone generation and / or zone transfer time.
Deployment of VL RR capable applications will increases queries to
Root zone or TLD zones. This will impact Root / TLD authoritative
servers in performance and / or bandwidth.
The zone administrators who will introduce VL RR are recommended to
have enough assessment previously with recognition above.
7. IANA Considerations
IANA is required to assign VL RR type and number.
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8. Security Considerations
Because the VL RR can set many variant labels, it can be a source of
DNS amplifier attack. The zone administrators can avoid this issue
by suppressing number of activating variant labels appropriately.
9. Normative references
[RFC5890] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document Framework",
RFC 5890, August 2010.
Appendix A. Examples
A word "International Academy" in Simplified Chinese consists from 4
Hanji characters and each character has a few variants. Following
codepoint (U+XXXX means Unicode codepoint XXXX) list shows canonical
Simplified Chinese Hanji character and its variants.
U+56FD
U+570B U+56EF U+5700
U+9645
U+969B
U+5B66
U+5B78 U+6588
U+4F1A
U+6703
In this example, the word "International Academy" produces 48 variant
labels, but mixture of Simplified and Traditional Hanji in a label is
unrealistic, so the zone administrator will reduce activated variant
labels into two (all Simplified and all Traditional).
Thus, VL RR definition for this example becomes as follows:
xn--6oq05q1ydn21f IN VL 0 xn--6oq05q1ydn21f.
IN VL 10 xn--9csw6hk7lo31c.
xn--9csw6hk7lo31c IN VL 0 xn--6oq05q1ydn21f.
IN VL 10 xn--9csw6hk7lo31c.
Note that no other (not activated) variant labels appear in the zone.
Appendix B. Change Log
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B.1. Changes since -00
o Some editorial collections.
o Explicitly described that VL RR must be set to activated labels.
o Add Appendix A for examples.
Author's Address
Yoshiro Yoneya
JPRS
Chiyoda First Bldg. East 13F
3-8-1 Nishi-Kanda
Chiyoda-ku, Tokyo 101-0065
Japan
Phone: +81 3 5215 8451
Email: yoshiro.yoneya@jprs.co.jp
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