How can I tell a host name from a subdomain

[John Hascall]

> > > Somebody gave me her web site address.
> > > It's like vi.somename.com .
> > > (somename is an example and vi and com are real).
> > > vi.somename.com could be a host name and a subdomain.
> > > Is there a way to tell one from the other without asking her?

> > Technically every DNS name (except the root name) is a "subdomain" of
> > some other DNS name. It's a purely relative term, like "subdirectory",
> > "subcategory" and so forth.
> Then do you think that a host name is also a subdomain?
> Subdomain can have many hosts in its domain.
> But host is just a computer and can't have lower level nodes.
> And also
> user at subdomain.domain.com is possible but
> user at hostname.domain.com is not.
> Or am I wrong? I am not sure.

   No.  It is perfectly legal to have:

        whatever.example.com                 be a machine, and have
    foo.whatever.example.com                 be another machine.

   and it is possible that any or all of:

               user at example.com
      user at whatever.example.com
  user at foo.whatever.example.com

   be legal and functional email addresses (and all possibly to the
   same mailbox, possibly not).

   And even if whatever.example.com does not exist as a machine,
   it may still be that user at whatever.example.com is a valid email
   address (via what is called an MX record).


John