[TriLUG] Questions on dyndns.org

[Jeremy Portzer]

On Thu, 2002-10-03 at 15:39, Jeremy Portzer wrote:
> 
> You may want to read a refresher on how DNS and TCP connections work in
> general.  Remember, DNS is like a telephone book.  Suppose that you look
> up a phone number in the book, and make a phone call.  You get a
> recording that says to use your fax machine to connect instead.  The
> phone book cannot possibly be "redirecting" you to your fax machine. 
> The phone book is only listing telephone numbers!  The recording at the
> other end of the phone line is doing the redirection.

On further reflection, let me clarify my analogy.  Suppose that you look
up a company in a telephone book, and place a call to the listed
number.  Then, you get a recording that says, "Use your fax machine, and
call this other number."  The recording is giving you two things -- the
new number to call, and the new way to connect (fax instead of voice). 
The recording is providing the "redirection," sending you to a new
number (IP address) and telling you about a new way to connect (new port
number).  

The above analogy could actually happen, if the company changes their
fax number often, so they don't publish it.  But suppose they always a 
1-800 "redirection" number.  Clients just need to call the 1-800 number
(contact the DynDNS web application) every time to get a fax number (IP
address).

Normal dynamic DNS (as opposed to port redirection) would be the
equivalent of a standard 1-800 fax number, for which the "destination"
phone number is unknown (and usually hidden).  When the phone number
changes, the business updates their 1-800 service company with the new
destination number.   But the method of connection (fax) is always the
same.

For port redirection performed by a NAT firewall, you could try using
the analogy of the teletype relay service that's used by the deaf.  See,
analogies are fun. :-)

--Jeremy