Re: DNS and subdomains

[Stephane Bortzmeyer via NANOG <nanog () nanog org>]

On Tue, Feb 25, 2025 at 07:36:16AM -0500,
 Harry Hoffman via NANOG <nanog () nanog org> wrote 
 a message of 168 lines which said:

> I had a thought similar to what Bill describes, that everywhere there's a
> dot (.) there's a subdomain.

This is true. But a sub-domain is not always delegated (not every
domain is a zone).

> to use the publicsuffix.org site to divine suffix and domain and
> then consider everything to the left of that as a subdomain. I've
> now updated my understanding.

Sorry, but not yet. Every domain name is a subdomain, except the root
(which has no parent). And not every domain name is a host name
(saying that the DNS is "to translate names into IP addresses" is a
gross simplification).