Just what *is* a hostname (rfc952/1123, etc)

[Jim Reid]

>>>>> "David" == David Carmean <dlc-bu at halibut.com> writes:

    David> It seems to be perfectly legal to create a domain named
    David> "foo_b#r&.com.", if I'm reading RFC2181 correctly; the
    David> question is whether the name of any node in the entire
    David> subtree below that zone cut can be a legal Internet
    David> hostname.

It can't. Valid hostnames can only be built from the characters
[a-zA-Z0-9-]. RFC1123 references RFC952 which could hardly be any
clearer about that:

   1. A "name" (Net, Host, Gateway, or Domain name) is a text string up
   to 24 characters drawn from the alphabet (A-Z), digits (0-9), minus
   sign (-), and period (.).  Note that periods are only allowed when
   they serve to delimit components of "domain style names".

RFC1123 relaxed the above rule to allow longer names (255 char limit)
and to permit a name (label) to start with a digit.

foo_b#r&.com is perfectly valid as a domain name of course. But not as
a hostname. Since foo_b#r&.com is not a valid hostname any names
within that domain can't be valid hostnames either.