[TriLUG] Questions on dyndns.org

[Mike Mueller]

On Thursday 03 October 2002 16:22, Jeremy Portzer wrote:
> 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.

Actually analogies can be flawed.  For instance, 800 service is served by two 
levels of databases along with a GTT database to help find the databases.  
When a switch is translating an 800 number it launches a query to a GTT 
service that actually rewrites the query at the datalink level and redirects 
the query to the database that informs the switch of the service provider 
that has the 800 number. Then a second query is launched using the point code 
of the 800 service provider's 800 database to get the actual phone number.  
This system was implemented to support 800 number portability so an 800 
number can be served by AT&T or Sprint at the 800 number payer's discretion.  
Now the same portability scheme is being applied to land lines.  Soon it will 
applied to wireless numbers.  This is kind of like DNS but there are some 
things that are not like DNS either.
>
> 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. :-)

Port redirection at the NAT/firewall are ineffective if TCP traffic with port 
value 80 is blocked in the ISP network.
>
> --Jeremy
>
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-- 
mueller, mike

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