Domain name pedantry [was Re: [FWP] Recursion, anyone?]

["Keith Calvert Ivey" <kcivey@cpcug.org>]

Abigail <abigail@foad.org> wrote:

> I think the spirit is "use at your own risk". I bet some DNS servers
> out there refuse to resolve non-compliant names.
> 
> But how should www.31338.net ever notice some people can't get to it?
> Mail to hostmaster@www.31338.net isn't likely to arrive when send by
> the same people who can't go to www.31338.net.

It's not quite as chaotic as all that.  There are RFCs after 
1034.  RFC 1101 says:

|   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. 

The "[HR]" refers to what later became RFC 1123, which says:

|   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.
|
|   [...]
|
|   DISCUSSION:
|
|   [...]
|
|       If a dotted-decimal number can be entered without such
|       identifying delimiters, then a full syntactic check
|       must be made, because a segment of a host domain name
|       is now allowed to begin with a digit and could legally
|       be entirely numeric (see Section 6.1.2.4).  However, a
|       valid host name can never have the dotted-decimal form
|       #.#.#.#, since at least the highest-level component
|       label will be alphabetic.

Note that RFC 1123 seems to say that 26.0.0.73.COM is legal, 
despite what RFC 1101 says.

Unfortunately for the cause of clarity, RFC 1123 doesn't say 
that it updates RFC 1034, though RFC 1101 does.

Wasn't that fun?

-- 
Keith C. Ivey <kcivey@cpcug.org>
Washington, DC

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