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

[Kevin Darcy]

David Carmean wrote:

> OK, where exactly do "hostnames" appear in the IN DNS, as opposed
> to "domain names"?
>
> Cricket says: "..in the name fields of A...and MX...records....  also
> in the data fields of SOA and NS records."
>
> So far I haven't been able to figure out from the RFCs whether a
> hostname is just the leftmost label in a domain name, or whether
> the *entire* domain name (fully-qualified or relative) must be
> considered subject to the RFC952/1123 restrictions?
>
> I suppose I could look at gethostby*, but I'd rather get an
> authoritative answer from an RFC.

DNS itself doesn't -- or _shouldn't_ -- care about the character set
used in the names it processes. RFC 952 was a standard for the format of
the HOSTS.TXT file, and RFC 1123 "inherited" the RFC 952 rules mostly,
and applied them to higher-level entities like mail servers, etc. So the
answer to your question is: "it depends". If you want to know what is a
legal connection target for, say, a telnet client or a web browser, then
RFC 952/1123 applies. If you want to know what is legal to exchange
between nameservers, then the rules are much more lax.

> And what happens when I18N/L10N (whichever) rears its head?

We all head for the hills :-)


- Kevin