Re: [idn] UTF-8 as the long-term IDN solution

["Eric A. Hall" <ehall@ehsco.com>]

"Adam M. Costello" wrote:

> If UTF-8 queries use a new type of request, then they can be used
> only if both the client's resolver and the local DNS server have been
> upgraded to support the new query format.  If you're upgrading the
> resolver, you might as well include an ACE encoder/decoder, because
> ACE queries will always work, even before the local DNS server has
> been upgraded.  And once you have an ACE encoder/decoder, why bother
> implementing the new query format?  Applications will never know or
> care which format the resolver is using.  Even if every other protocol
> and application migrates to UTF-8 and forgets how to encode and decode
> ACE, the resolvers and DNS servers could still be speaking ACE to each
> other and the other protocols/applications would be oblivious.

This is missing a component, which is the resolver-application interface.
Applications store/display names that they are given by DNS, so DNS must
provide them with the data in the appropriate format. Although the
on-the-wire protocol can be ACE as you suggest, the resolver still needs a
way to remember the desired disposition format of the query results.

For example, assume that an ESMTP extension for UTF8 in Received headers
comes to pass, and everybody agrees that displaying the headers in UTF8 is
beneficial to the user community, blah blah blah. When the MTA issues a
reverse lookup for the domain name associated with the IP addr, it doesn't
matter what format DNS uses, but the local resolver still needs to know
that the answer data should be returned in UTF8.

I suppose that it's technically feasible to ask resolvers to maintain
state, but the latest round of proposals have been to use UTF8 as the
default encoding on the wire so that it's preserved end-to-end, with the
expectation that UTF8 will be the preferred default encoding for many
years to come.

> It looks to me like allowing UTF-8 in regular DNS queries may be more
> trouble than it's worth,

Yes

> and creating a new query format just for UTF-8 is certainly more
> trouble than it's worth.

No. The EDNS message is already defined and is required/used for things
like A6 and DNAME already. This would just be another usage of that
message. It also allows us to resolve the sizing problems.

-- 
Eric A. Hall                                        http://www.ehsco.com/
Internet Core Protocols          http://www.oreilly.com/catalog/coreprot/