[TriLUG] Questions on dyndns.org

Mike Mueller mjm-58 at mindspring.com
Thu Oct 3 11:57:39 EDT 2002


On Thursday 03 October 2002 10:52, Chris Merrill wrote:
> Vestal, Roy L. wrote:
> > All the questions around using dyndns.org's services intrigues me. My
> > question is, with their service, or another like it, can you host from
> > behind a masquerading firewall? Did I miss something when I read their
> > site?
>
> This leads me to another question...I host multiple domains from
> my server.  From my (limited) understanding of Apache, in order
> to use virtual domains, I had to configure the IP address in
> httpd.conf.  This means that anytime the IP address changes, I
> had to change httpd.conf.  I was able to hook into dhcp and get
> a script run when this happens...and wrote a script to change
> the IP address in httpd.conf and restart apache.
>
> So my questions are:
> 1) Is there an easier way to do this?
> 2) Would this be possible if I had a firewall/NAT box in between
>     the server and the cable-modem?

I am researching this right now too.  Port forwarding on the firewall/NAT 
seems to be the thing to do from what I've read so far.  Port 80 (httpd) 
might be blocked on your ISP so you may need to get the dynamic dns to 
translate port 80 to some other port number.  If you want to support multiple 
domains will you need to select a port for each domain?  I know almost 
nothing about Apache.  Can a single instance of Apache serve multiple domains 
that are associated with different ports?

If what I write above is true, then it seems that the Apache config is static 
and that the dynamic dns update client periodically checks the current IP of 
the firewall/NAT and effects a change at the DNS if necessary.  Next 
question: how to automatically update the DNS?

With a firewall there appear to be ready built clients that query the IP and 
effect the change at the DNS.

With a NAT appliance there seems to be three approaches to keeping the DNS 
updated. First, use an appliance that has a built-in client (neatgear has 
one).  Second use a client app that queries the appliance and then feeds the 
IP to the DNS update client.  Third, use a client app that uses an entity 
external to your LAN to reflect the origination IP back and then use the IP 
to feed the DNS update client.  DynDNS offer an external IP reflector for the 
third method.  They ask that it be queried at a rate not to exceed 1/10m.

Information source: http://support.dyndns.org/whitepapers/nat.php

I am currently using a NAT with *no* built-in dynamic dns update client.  
I'll switch to a firewall if I get fail in this effort.  My choice is based 
on keeping power consumption to a minimum.
-- 
mueller, mike

The larger purpose of the economic order, including Wall Street, is to 
support the material conditions for human existence, not to undermine and 
destabilize them.

-Editorial, The Nation, August 19, 2002



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