RE: [idn] Determining equivalence in Unicode DNS names

["Kenny Huang" <huangk@alum.sinica.edu>]

We have encountered with many equivalence rule discussions.
As you mentioned, if the equivalence rule is simple enough (A=a)
thus the logic can be applied anywhere (service, client, cache, fw..).
If the wg tried to extend rule to a broader domain, that would be difficult
to identify a specific boundary.

Designing a simple equivalence rule in client application is a 
compromise of LDH DNS server.  There is no much technical margin
for designing advanced equivalence rules. Middleware, DNS server 
(UNAME, DNAME) or other naming systems would probably be the remaining 
space for these advanced computations. However, only simple equivalece 
rule got across all demands in application services.


Kenny Huang

> -----Original Message-----
> From: owner-idn@ops.ietf.org [mailto:owner-idn@ops.ietf.org]On 
> Behalf Of Stuart Cheshire
> Sent: Tuesday, January 15, 2002 3:57 AM
> To: idn@ops.ietf.org
> Subject: [idn] Determining equivalence in Unicode DNS names
> 
> 
> I am new to this, so please forgive me if the suggestion I am about to 
> make has been discussed before.
> 
> Some introduction: I work on networking at Apple. Apple cares a lot about 
> international text, and consequently international domain names, and 
> consequently my management looks to me to give them input about what is 
> going on in this area. Hence my need to educate myself about the current 
> state of the world in IDN.
> 
> It seems to me that one of the great problems of IDN is one that is 
> fundamentally unsolvable: an attempt to determine, once and for all time, 
> a single global set of rules for deciding if two strings are "equal" or 
> "equivalent".
> 
> For US ASCII, equivalence is easy: For good or bad, we have decided that 
> upper case and lower case letters are equivalent, and that is the end of 
> the debate. Resolvers know that upper case and lower case are equivalent, 
> servers know it, and caches know it, so they all agree on whether any two 
> given names are equivalent. If a resolver asks for "APPLE.COM" and the 
> server gives an answer for "apple.com", then the client (and any cache) 
> understands that this is an acceptable answer to the question.
> 
> The problem as I see it, right now, is that if a client asks for the 
> address record for "www.pépsi.com." (with an accent), and it gets back a 
> DNS reply with an answer giving the address for "www.pepsi.com." (without 
> an accent), then the client will ignore the answer. Even if the client 
> does know that "pépsi" is equivalent to "pepsi", a caching resolver in 
> between the client and the server may not, and may ignore the answer.
> 
> There are two problems here. The first is that I don't think we ever be 
> able to agree on a single set of equivalence rules for the whole world. 
> The second is that even if we did, we'd have to have a global flag day 
> where every client, server and caching resolver was simultaneously 
> upgraded to know the new rules.
> 
> It seems to me that the solution is to give up on the idea of a single 
> global set of rules, and instead let each name server be authoritative 
> for the equivalence rules for the zones for which it is authoritative. If 
> a client tries to look up "www.pépsi.com.", and the "com" name servers 
> have been configured to treat "pépsi" as equivalent to "pepsi", then they 
> return the answer for "pepsi.com.", and in the reply they also include a 
> (programatically generated) DNAME record which *tells* the client and any 
> intervening caching resolvers that these two names are equivalent:
> 
> pépsi.com.              IN	     DNAME	  pepsi.com.
> pepsi.com.              IN      NS      dnsauth1.sys.gtei.net.
> dnsauth1.sys.gtei.net.  IN      A       4.2.49.2
> 
> This way we don't need to have a global flag day, because as servers are 
> updated to support international domain names, they can "educate" old 
> clients as they go, using DNAME. If we find that text equivalence rules 
> evolve over time to meet changing needs that's fine too, because the 
> servers can be upgraded one at a time as the user's needs demand that. 
> Clients and caches don't need to know any of the equivalence rules at 
> all; they just need to obey the DNAME mappings that they are told.
> 
> Stuart Cheshire <cheshire@apple.com>
>  * Wizard Without Portfolio, Apple Computer
>  * Chairman, IETF ZEROCONF
>  * www.stuartcheshire.org
> 
>