Subject: Re: I-D ACTION:draft-ietf-dnsind-rfc2052bis-00.txt

From: Bill Woodcock <[email-masked]>
Date: Sun, 6 Sep 1998 20:55:41 -0700 (PDT)

> the underscore is just another character like any other
    
    Okay, so educate me, if you feel it's worth your time.  I assume what
    you're saying is that anything goes in hostnames, and that the leading
    A-Z,a-z,0-9 and hyphen restrictions are on domain names only? How many
    implementations actually differentiate between domains, subdomains,
    and hosts, and apply different validity-checks to them?  How can an
    end-node tell the difference between a subdomain and a host, anyway?
      
                             -Bill

---

From: Robert Elz <[email-masked]>
Date: Tue, 08 Sep 1998 06:32:56 +1000

Date:        Sun, 6 Sep 1998 20:55:41 -0700 (PDT)
    From:        Bill Woodcock <[email-masked]>
    Message-ID:  <[email-masked]>

    I assume what you're saying is that anything goes in hostnames,
    and that the leading A-Z,a-z,0-9 and hyphen restrictions are on
    domain names only?

No, not at all.   The restrictions apply to "hostnames", but the
only meaningful possible definitions of a "hostname" would seem to be
either "something in hosts.txt" (in which case we simply ignore them
completely as 100% irrelevant), or "something which has the syntax of
rfc952 as modified", in which case we have a nice definition of a class
of names, which doesn't seem to be useful for any more than deciding
whether or not something is a member of it.

In the DNS there are almost no restrictions on names at all.   Just lengths,
nothing at all on character sets (except the upper case ascii == lower case
ascii part).

    How many implementations actually differentiate between domains, subdomains,
    and hosts, and apply different validity-checks to them?

There are some implementations that apply validity checks - those are all
broken.

    How can an

That would be difficult - especially as no-one knows what is a host.

There are name restrictions in specific protocols.   E-mail is one of
those - not all DNS names are legal in e-mail headers, or in SMTP
exchanges.    That means that if you want to use a name for e-mail you
need to be aware of its restricted syntax.   A few other protocols have
similar rules.   Most do not.   Eg: if I want to set up a telnet server
(tcp port 23) it can have absolutely any name I like at all - no restrictions
of any kind.   Telnet imposes no rules, and nor need it, as the name isn't
ever transmitted between the systems - you just use it locally to translate
the name into the IP address you use to connect to the server.   Your telnet
client might have some restrictions on what names it can translate, but that's
a purely local problem for you to worry about.

There is certainly no distinction between the various parts of a domain
name for this purpose.   As far as the DNS is concerned, all domain names
are created equal, whatever their parent domain, and whether or not they
have sub-domains.   [Aside: none of this reflects upon the ability of a
domain name registrar to restrict what names they will allow to be registered
in their domain - either based upon length, character set, or almost
anything else you can imagine (only star trek characters in this domain)
and nor is that even slightly relevant - so don't bother quoting internic
rules for registration in .com etc at me).

kre

---

From: Randy Bush <[email-masked]>
Date: Mon, 7 Sep 1998 13:45:17 -0700 (PDT)

> A-Z,a-z,0-9 and hyphen restrictions are on domain names only?

nope.  some documents place restrictions on hostnames.  but, as we are not
even sure what a hostname is in the context of the dns, we tend to ignore
this.

there is no restriction on what characters may be in domain names.  see rfc
2181.  there is a need for case insensitivity, which is a bit of a problem.
but i recently saw a rather nice demonstration of zones full of utf8 names.

randy

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From: "Donald E. Eastlake 3rd" <[email-masked]>
Date: Mon, 07 Sep 1998 23:40:05 -0400

From:  Robert Elz <[email-masked]>
To:  Bill Woodcock <[email-masked]>
Cc:  [email-masked], [email-masked]
In-Reply-To:  Your message of "Sun, 06 Sep 1998 20:55:41 MST."
	                  <[email-masked]> 
Date:  Tue, 08 Sep 1998 06:32:56 +1000
Message-Id:  <[email-masked]>

>...

Since the Internet is about interoperability, it seems entirely
reasonable to me to restrict "host" names in the sense that there is a
restricted set of names that all user interfaces that accept "host"
names are expected to accept.

>...

Thanks,
Donald