--On Friday, 28 September, 2007 09:48 +1000 Mark Andrews
<Mark_Andrews(_at_)isc(_dot_)org> wrote:
...
It's not. Even without IPv6, having search domains means you
can get unexpected results. If that's not acceptable, don't
complain, but put a period behind your FQDNs.
Please state were in RFC 952 a final period is legal in
a hostname.
Remember applications take HOSTNAMES not DOMAIN NAMES.
There are HOSTNAMES that you cannot store in the DNS.
There are DOMAIN NAMES that are not legal HOSTNAMES.
Mark, your recollection and understanding of history and
vocabulary may be different from mine (and probably is), but I
think you are getting confused by some informal terminology and
risking confusing others even further.
RFC 952 in fact prohibits trailing periods in domain names used
as host names, but 952 is a very early document, superceded by
all sorts of things both formally and informally. I note, for
example, that it has been a rather long time since every
boundary router on the network (a "gateway") had a name ending
in "-GW" or "-GATEWAY". Please don't read sentences of 952 out
of context and consider them binding.
You will not find the "hostname" versus "domain" distinction
made in RFC 1034. 1034 and its conceptual predecessors
discusses the domain name system as a replacement for the
hostname one and even notes (correctly) that different
applications have different syntax rules for names for hosts.
To make the ambiguity worse, when the term "host" or "hostname"
is used in applications in conjunction with the DNS, that term
often refers to the leaf-note label and not to the FQDN. See,
for example, section 3.7 of RFC 821, which describes
"Fred.Cambridge.UK" as a possible "host-and-domain identifier".
However, the familiar "mailbox" is defined as
<mailbox> ::= <local-part> "@" <domain>
Note that it is not
<local-part> "@" <hostname>
or
<local-part> "@" <host-and-domain>
RFC 1034 also seems to believe that all fully-qualified (aka
"absolute") domains names, including those used to refer to
hosts, end in a period, even if that period is typographically
omitted for convenience. Of course, it also contains a
masterwork of apparently-circular definition: "A domain is
identified by a domain name, and consists of that part of the
domain name space that is at or below the domain name which
specifies the domain."
While 1034 suggests that the trailing period is always
permitted, even if it is implied, Section 2.3.1 of 1035 gives a
syntax that doesn't permit them. But it does so without trying
to distinguish between a "host" and a "domain". In particular,
it says that [all of] "The labels must follow the rules for
ARPANET host names", which is ultimately a reference to 952
although 1035 repeats the rule. That rule is applied to all
labels, not just the leaf one or ones identifying hosts.
As an indirect illustration of this, note that 1035 Section 3.5
describes IN-ADDR.ARPA as supporting "host address to host name
mapping". That mapping is to an FQDN, not a label or "hostname"
as you use the term above.
RFC 1123 makes explicit provision for trailing dots in
application interfaces to domain names ("hosts") while noting
that RFC 822 (and 821) do not permit that syntax in the
protocols. Nothing has ever permitted a UI designer, even for a
mail-related program, from accepting the trailing dot as long as
it is removed (and any searching or aliases resolved) before the
name goes out on the wire.
So I believe the distinction you are trying to make is not
historically supported, not particularly helpful, ambiguous, and
probably just plain wrong.
regards,
john
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