Re: [idn] Length limits on a domain name

[Dan <Dan.Oscarsson@trab.se>]

> > Should not the requirement on length of IDNs be:
> > An IDN may have a maximum of 63 CHARACTERS per label and a total
> > length of 255 CHARACTERS?
> > 
> > A CHARACTER can be defined as the number of UCS-4 characters that is
> > used when the name uses when it is in UCS normalised using Unicode
> > normalisation form C. This would give the DNS implementors a maximum
> > limit to adopt their data structures to. (adding that remaining combining
> > characters should not be counted would make it possible to make names taking
> > much more space).
> 
> I would not go as far as making this a requirement. It is definately nice to
> have the ability to have longer domain names (incidently 63 CHAR per label may
> not be long enough for some language either), it means a fumanental change in
> DNS system, comfirm.
> 
> One would wonder with EDNS0 coming in, why not EDNS1 which gives the ability
> to have longer domain names...:-) I am dreaming and talking abt things I dont
> know.

To have more than 63 bytes per label you have to extend the DNS protocol.
Like Patrik Fältström said in his mail, RFC 1035 defines the
CURRENT handling of labels. It restricts a label to 63 bytes.
But leaves the door open to be extended. That is where EDNS comes in.
EDNS can easily be used to add the possibility of long lables.
But old (current) DNS software will not be able to handle those labels,
so during quite some time you will have to use labels that can be
fit into 63 bytes if you want it to work everywhere.
If we want to be able to handle longer labels than 63 bytes, it would
be good if the DNS specification for IDNs included the extention needed
to handle long labels. Then upgraded software would implement that too.

   Dan