Re: getaddrinfo(3) on numerical addresses

[Robert Elz <kre%munnari.OZ.AU@localhost>]

    Date:        Tue, 24 Oct 2017 17:17:19 +0200
    From:        Edgar =?iso-8859-1?B?RnXf?= <ef%math.uni-bonn.de@localhost>
    Message-ID:  <20171024151719.GO73396%trav.math.uni-bonn.de@localhost>

  | What's wrong with the following argument?
  | 1a. domain name componentss consist of letters, digits and hyphens

That's not true, they can be almost anything (specifically including
dots and \0's) though many of the possibilities are not really practical.

  | 1b. purely numeric components may be allowed, but are crazy

Have you never seen 1.2.3.4.in-addr.arpa ??

They certainly are allowed, and are not at all crazy.   Not even in
other domains.

What's more, the resolver has no idea why a name is being looked up,
just that it is.

  | 2. syntactically correct numerical IPv6 addresses contain at least one colon

That's correct.  At least 2 really I think.

  | 3. syntactically correct numerical IPv4 addresses contain digits and dots

Which is exactly what a domain name can contain.   The only reason that
IP addresses (in textual format) are not currently valid domain names, is
that there are currently no top level domains with all numeric labels.
But who knows what ICANN will create next week?

  | 4. So a numeric IPv4 address can't be a a numeric IPv6 address,

That's obvious, they're different lengths aside from anything else.

  | and vice versa, and neither of them can be a FQDN.

v4 addresses exactly meet the criteria for a FQDN.

kre