Re: [idn] length restrictions on IDN label

["James Seng" <jseng@pobox.org.sg>]

Let me repeat again,

the restriction is octet(ToASCII(X)) <= 63 (sorry, forget the =).

The length restriction of a domain name (incidently, UTF-8 encoded string
which looks like domain name is not a domain name) in a DNS UDP packet is
something beyond this working group. Please bring it to the DNSEXT working
group.

-James Seng

> What I request is confirmation and clarification about that restriction.
>
> If UTF8-encoded, that valid 8bit label will exceed 63 octets limits (up
> to 168 octets or more)
>  which is imposed by RFC1035 even upon non-ASCII 8bit labels .
>  IDNA section 6.3 does not rule out that  utf8 encoded labels may be used
>  in DNS wire protocols in the future. And that will affect UDP based
>  DNS protocols
>  which suffers from lack of space in the UDP packet length limits (512).
>  Packet truncation or protcol errors are inevitable.
>
> That is why i suggest that some separate length restriction on utf8
> (other encoding) IDN labels
>  be needed. Or clarifications about those problems, at least.
>
> Soobok Lee
>
> >
> >-James Seng
> >
> >
> >
> >>That is true only in  protocols predating IDNA draft.
> >>IDN labels can be typed in/ displayed/ copy&pasted/ or exchanged in
> >> UTF8 (or other) encoding
> >>in now and future applications or protocols slots as described in IDNA
> >>draft itself.
> >>See enclosed excerpts from IDNA draft  ( "SEE HERE").
> >>
> >>I think some length restriction in code points is needed, rather than in
> >>octets ....
> >>IDNA is the right place to put such things..
> >>
> >>Soobok Lee
> >>
> >>6.3 DNS servers
> >>
> >>Domain names stored in zones follow the rules for "stored strings" from
> >>[STRINGPREP].
> >>
> >>For internationalized labels that cannot be represented directly in
> >>ASCII, DNS servers MUST use the ACE form produced by the ToASCII
> >>operation. All IDNs served by DNS servers MUST contain only ASCII
> >>characters.
> >>
> >>If a signaling system which makes negotiation possible between old and
> >>new DNS clients and servers is standardized in the future, the encoding
> >>of the query in the DNS protocol itself can be changed from ACE to
> >>something else, such as UTF-8. The question whether or not this should
> >>
> >>
> >(SEE HERE)
> >
> >
> >>be used is, however, a separate problem and is not discussed in this
> >>memo.
> >>
> >>
> >>
> >>6.1 Entry and display in applications
> >>
> >>(snip)
> >>
> >>In protocols and document formats that define how to handle
> >>specification or negotiation of charsets, labels can be encoded in any
> >>charset allowed by the protocol or document format. If a protocol or
> >>document format only allows one charset, the labels MUST be given in
> >>that charset.
> >>
> >>In any place where a protocol or document format allows transmission of
> >>the characters in internationalized labels, internationalized labels
> >>SHOULD be transmitted using whatever character encoding and escape   (
SEE
> >>
> >>
> >HERE )
> >
> >
> >>mechanism that the protocol or document format uses at that place.
> >>
> >>All protocols that use domain name slots already have the capacity for
> >>handling domain names in the ASCII charset. Thus, ACE labels
> >>(internationalized labels that have been processed with the ToASCII
> >>operation) can inherently be handled by those protocols.
> >>
> >>
> >>6. Implications for typical applications using DNS
> >>
> >>In IDNA, applications perform the processing needed to input
> >>internationalized domain names from users, display internationalized
> >>domain names to users, and process the inputs and outputs from DNS and
> >>other protocols that carry domain names.
> >>
> >>The components and interfaces between them can be represented
> >>pictorially as:
> >>
> >>                     +------+
> >>                     | User |
> >>                     +------+
> >>                        ^
> >>                        | Input and display: local interface methods
> >>                        | (pen, keyboard, glowing phosphorus, ...)
> >>    +-------------------|-------------------------------+
> >>    |                   v                               |
> >>    |          +-----------------------------+          |
> >>    |          |        Application          |          |
> >>    |          |   (ToASCII and ToUnicode    |          |
> >>    |          |      operations may be      |          |
> >>    |          |        called here)         |          |
> >>    |          +-----------------------------+          |
> >>    |                   ^        ^                      | End system
> >>    |                   |        |                      |
> >>    | Call to resolver: |        | Application-specific |
> >>    |              ACE  |        | protocol:            |
> >>    |                   v        | ACE unless the       |
> >>    |           +----------+     | protocol is updated  |
> >>    |           | Resolver |     | to handle other      |
> >>    |           +----------+     | encodings            |   (SEE HERE)
> >>    |                 ^          |                      |
> >>    +-----------------|----------|----------------------+
> >>        DNS protocol: |          |
> >>                  ACE |          |
> >>                      v          v
> >>           +-------------+    +---------------------+
> >>           | DNS servers |    | Application servers |
> >>           +-------------+    +---------------------+
> >>
> >>
> >>
> >>
> >>
> >>
> >>
>
>
>
>