Re: [idn] Proposed suggestions from Asia Pacific Top LevelDomain meeting

[Mark.Andrews@nominum.com]

> Mark's comment below about domain name vs. host name character restrictions
> made me wonder.  Please consider the following chain of RFC references,
> which seem to imply otherwise:
> 
> RFC952: Describes host name syntax:
> "1. A "name" (Net, Host, Gateway, or Domain name) is a text string up
> to 24 characters drawn from the alphabet (A-Z), digits (0-9), minus
> sign (-), and period (.).  Note that periods are only allowed when
> they serve to delimit components of "domain style names". (See
> RFC-921, "Domain Name System Implementation Schedule", for
> background).  No blank or space characters are permitted as part of a
> name. No distinction is made between upper and lower case.  The first
> character must be an alpha character.  The last character must not be
> a minus sign or period."
> 
> RFC1035: Section 2.3.1 describes label syntax for domain names:

	Wrong. The title for Section 2.3.1 is "Preferred name
	syntax".  It describes a restricted subset of legal label
	that are unlikely to cause problems.  Any 8 bit values are
	allowed (Section 3) and there is a presentation syntax
	described mainly in Section 5 for how to represent non printing
	ascii characters.

> "<label> ::= <letter> [ [ <ldh-str> ] <let-dig> ]"
> 
> RFC1101: Describes allowances for domain names that begin with a digit:
> "For these reasons, we assume that the syntax of network names will be
> the same as the expanded syntax for host names permitted in [HR].
> The new syntax expands the set of names to allow leading digits, so
> long as the resulting representations do not conflict with IP
> addresses in decimal octet form.  For example, 3Com.COM and 3M.COM
> are now legal, although 26.0.0.73.COM is not.  See [HR] for details."

	RFC1101 describes NETWORK NAMES not DOMAIN NAMES.
	Network names are a *subset* of domain names the same as
	host names are a subset of domain names.

> 
> The [HR] reference is to what eventually became RFC1123.
> 
> RFC1123: Updates host name syntax specifications:
> "The syntax of a legal Internet host name was specified in RFC-952
> [DNS:4].  One aspect of host name syntax is hereby changed: the
> restriction on the first character is relaxed to allow either a
> letter or a digit.  Host software MUST support this more liberal
> syntax."
> 
> My read of the above per RFC1101 is that there are limits on the characters
> that can appear in domain names, even if the DNS specifies only limits on
> length.  Did I miss something that points in another direction?
> 
> Scott Hollenbeck (mailto:shollenb@netsol.com)
> Network Solutions, Inc. Registry
> 
> -----Original Message-----
> From: Mark.Andrews@nominum.com [mailto:Mark.Andrews@nominum.com]
> Sent: Monday, March 06, 2000 6:01 AM
> To: Dan Oscarsson
> Cc: phoffman@imc.org; jseng@pobox.org.sg; dlee@icu.ac.kr;
> idn@ops.ietf.org; iname@aptld.org; bill@mail.nic.nu;
> konishi@jp.apan.net; kwu@yam.com; syhan@cclab.konkuk.ac.kr;
> markk@netsol.com; zwh@cnnic.net.cn; chang@netpia.com;
> tinwee@pobox.org.sg; chon@cosmos.kaist.ac.kr; bmanning@isi.edu;
> kwu@yam.com.tw
> Subject: Re: [idn] Proposed suggestions from Asia Pacific Top
> LevelDomain meeting 
> 
> 
> 
> > >And thanks to Mark, I finally understood the difference between domain
> name
> > >and host name. We havent even reach that defination yet...
> > 
> > So what is the difference?
> > For me a host name is the name of a host while a domain name
> > can be the name of a host or of many other things.
> 
> 	Not bad for a first level answer.  For the second level you
> 	need to remember that host names have a MUCH more restricted
> 	syntax to domain names.
> 
> 	Currently domain names have no restrictions on what is a legal
> 	character (8bit).  The only restrictions are total and label
> 	lengths.  Host names on the other hand are restricted to A-Z, 
> 	0-9, "-" and "." case insensitive.  "." is only allowed between
> 	labels.
> 
> [snip]
--
Mark Andrews, Nominum Inc. / Internet Software Consortium
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: Mark.Andrews@nominum.com