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Re: RFC2396bis, qualified, a nit

From: Scott Seligman <Scott.Seligman@Sun.COM>
Date: Fri, 14 Mar 2003 12:19:10 -0800
Message-Id: <200303142019.h2EKJAh8002747@spin.SFBay.Sun.COM>
To: uri@w3.org

Peter Koch writes:
>
>In the DNS the trailing '.' is never part of the domain name. It is only
>used in zone file format to explicitly declare a domain name as FQDN.
>...
>A trailing '.' should not be allowed.

This view of the distinction between a textual "domain name" and a
"zone file format" is not part of the DNS specification.  Rather, the
DNS spec defines a "domain name" as a list of labels.  Then it describes
how to represent such a list on the wire, and how to represent it in text.
Here's an excerpt from RFC 1034:

    When a user needs to type a domain name, the length of each label is
    omitted and the labels are separated by dots (".").  Since a complete
    domain name ends with the root label, this leads to a printed form which
    ends in a dot.  We use this property to distinguish between:

       - a character string which represents a complete domain name
	 (often called "absolute").  For example, "poneria.ISI.EDU."

       - a character string that represents the starting labels of a
	 domain name which is incomplete, and should be completed by
	 local software using knowledge of the local domain (often
	 called "relative").  For example, "poneria" used in the
	 ISI.EDU domain.

Note that "poneria.ISI.EDU" -- no trailing dot -- is legitimate.  It
can be thought of as a relative domain name, relative to the root domain.
The distinction between that and an absolute name is mostly pedantic,
and rarely made in practice.

Of course a lot of water has flowed under the bridge since RFC 1034,
and we all know that the trailing dot is rarely added when FQDNs are
written in the real world.  Nonetheless, most resolver software can deal
just fine with a properly-added trailing dot.  It would be unwise to
add an incompatible and "artificial" restriction preventing people
from doing so.


Scott Seligman
Java Software Engineering
Sun Microsystems
Received on Friday, 14 March 2003 16:55:47 UTC

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