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Re: domain name definition in RFC2821

2007-03-22 23:44:33

Hi. As it turns out, I'm subscribed after all.  I just
didn't include the folder in my search path for new mail

Let me start by saying I have two quite different points,
not just one.  I think {allowing a tld} and {allowing
the trailing dot} are two separate issues and should not
necessarily be discussed together.  They do have one thing
in common though.

Let's start with the trailing dot:  

On Fri, Mar 23, 2007 at 12:03:26AM +0100, Frank Ellermann wrote:
Ned quoted RFC 1123 5.2.18 in this thread (2006-04-22):

| Some systems over-qualify domain names by adding a
| trailing dot to some or all domain names in addresses
| or message-ids.  This violates RFC-822 syntax.

Something violating RFC-822 doesn't mean 'something' is wrong.
It could also be that RFC-822 is wrong.  At the time, DNS was
a new concept and we've learned since then.

I don't think "overqualifying" is what is really happening:

Let's look at the situation at hand.  A FQDN is built by
starting at a DNS node, writing down its label, and move
to its parent.  RFC 1035 says: "Since every domain name
ends with the null label of the root,...". No doubt, the
empty label is part of the FQDN.  We use dots to separate
labels, thus there is a dot between "com" and "" (root).
This means the FQDN is "" and not "",
and it means the dot isn't even truly trailing.

Look at examples in 1035; they have a "trailing" dot.
By the way: 2821 refers to 1035 but fails to implement it.
(all IMHO ofcourse.)

I also can see the validity of the argumentation to stay
backwards compatible with legacy systems.  This is ofcourse
easily solved: start with "HELLO" (HELO->EHLO->HELLO) and
if both ends speak 2821bis, no problem.

1:  Allow the trailing dot everywhere no matter what 2821
    and 2822 say.  Maybe say "SHOULD have a dot" for TLDs.
2:  Keep it as is in 2821, no trailing dots, and one dot
    required.  This excludes TLDs, unlike (2)822.
3:  Same as (2) with a special rule for TLDs:  TLDs MUST
    have the trailing dot, other domains MUST NOT have the
    trailing dot.

As discussed, the 4th option is to allow a TLD without a
trailing dot. This would probably be rejected by a receiver,
or this receiver would append its own domain to create what
it thinks to be a FQDN (now this really *is* over-qualifying).

Same solution: start a session with a new keyword such as
HELLO. If both ends agree to do it right, they will do so.

Updated servers should always consider domains to be FQDN;
there is no place for local aliases (2821 got that right)
and thus it doesn't really matter if there is or is not a
trailing dot in the domain.  The alias "" should
be seen as FQDN "" and similarly "ws" should be
seen as "ws.".  This said, using the trailing dot does
cater for those that wish to use local aliases in their own,
internally used, SMTP systems.  See my previous message which
Frank forwarded (thanks Frank).


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