[TriLUG] Understanding Subdomains and Sub-subdomains

[Brian]

Hi,

This is a question for the DNS gurus in the audience.

I have a dynamic DNS service with dynip.  cheetah.dynip.com points at my 
public IP address.

I can go to anything.cheetah.dynip.com and it resolves to the same 
address, and I don't need to go make any settings with dynip.  It just 
works.  I make heavy use of this for setting up name-based virtual hosts 
on my apache server.

On the other hand, I have a 1and1 domain (with 1and1's DNS service), 
undecidedgames.net, which is a CNAME for cheetah.dynip.com.

I cannot go to anything.undecidedgames.net without first registering the 
subdomain with 1and1.

So I can see an obvious difference; the former has four parts 
(a.cheetah.dynip.com) while the latter has only three 
(a.undecidedgames.net).  Is this just a normal way that DNS works?  Is 
there an implied *.cheetah.dynip.com, but not a *.undecidedgames.net? 
Or is it because undecidedgames.net is a CNAME and not an A record?

If I wanted to have *.undecidedgames.com, would that be (a) advisable or 
(b) possible?  1and1 won't let me put in * as a subdomain name.

Thanks y'all!
~Brian