[LINK] Domain names: something I thought I understood

[George Michaelson]

  So: www.blah.com.au is a 'domain name'? (ie, the whole thing is a domain
  name?)

This is called a 'Fully Qualified Domain Name or FQDN'
  
  .au is the 'top level domain'?

Yes. a so-called CCtld for C(ountry) C(ode) t(op) l(evel) d(omain)
as opposed to .com which is a gtld for G(eneric) 'tld'
  
  .com is the 'second level domain'?

well .com from .com.au, yes. :-) Also called a 2LD.
  
  blah is the 'third level domain' (i have seen american sites (based upon
  www.blah.com for example) say that blah is the 'second level domain' for an
  obvious reason)
  
  and 'www' is a sub-domain or simply a server name?

It can be either. these things can nest. Nobody would do it, but you could
define foo.www.company.com.au if you want to. And don't be fooled, not all
objects with . in the name have a matching domain 'element' because once
the .something.com.au has been delegated, you can make foo.bar. a sub-name
under .something.com.au and it just works (tm) fine. There doesn't have to
'be' a delegation under something.com.au or something.com, you can add dots
without delegating. Again, its not always useful to do this, but it can be 
done. Typically, its what happens in transitional domain spaces like conf.au
where Robert Elz has been known to keep the delegation and just make one or
two specific bindings for you.
  
When something is 'delegated' there is a specific kind of DNS record called
an SOA or start-of-authority record created. This lists who is responsible
for the sub-delegation, and has tied to it, what machines act as nameservers
for that delegation (called NS) and the act of delegating is basically about
making there be an SOA, and making specific NS point at something.

  So when you go to melbourne IT (for example) to 'register a domain name',
  you're basically registering a third level domain in the .com.au 'domain
  space'....?

Yes. You are showing M-IT or their agents you have a justification to be
given a registration, and if you have one, nominating a specific delegation
into the global DNS system, so that you can sub-delegate, and make further
delegations and bindings of other useful information.
  
  Is all this correct?

Yes. With Caveats. :-)

cheers
	-George

--
George Michaelson         |  DSTC Pty Ltd
Email: ggm@dstc.edu.au    |  University of Qld 4072
Phone: +61 7 3365 4310    |  Australia
  Fax: +61 7 3365 4311    |  http://www.dstc.edu.au