Combining DNS and NATD

bob prohaska bp at
Tue Dec 14 03:54:34 UTC 2004

Barry Margolin <barmar at> wrote:
> It's solvable, but it requires mechanisms outside the scope of DNS.  For 
> instance, if you have multiple web servers behind a single IP NAT, you 
> can use port-forwarding to map different ports to each server.  To 
> access them, you would include the port numbers in the URLs, e.g.
> http://yourpublicip:81
> http://yourpublicip:82
> ....
> If you want to associate different names with each port, and not require 
> users to type the port number manually, you can make use of HTTP 
> redirects.  All the names would resolve to your public IP address, and 
> the server that port 80 (the default HTTP port) forwards to would look 
> at the hostname in the request, and send back a redirect to a URL with 
> the appropriate port number in it.
> I'll bet there's already an Apache module that supports this, since 
> you're hardly the first person to need this.

The embarrasing fact is that I _don't_ need it, I was simply curious 8-)
The key points to emerge seems to be that tcp/ip packets contain _no_
reference to hostnames and thanks to caching, inferences based on dns
lookups quickly become stale. The notion of port forwarding was raised
by my dsl  router's manual and I wondered if the idea could be extended
if the router and nameserver were cooperative. Evidently it cannot. 

So far it's still beyond my competence to get reverse lookups running
properly on a little /29, much to my disgust 8-(, so it's time to quit
thinking about fun problems and tend to business at hand. 

Thanks to all for patient good counsel!

bob prohaska

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