simple network question please

[Carl]

On Saturday 25 June 2005 7:19 am, Bobby Singh wrote:
> Hello,
>
> Can anyone answer just this simple question.
>
> SETUP:
> I have a modem/router on my computer (host). And in
> another room a wireless enabled computer.  Everything
> works, both computers or just 1 computer can access
> the internet.
>
> QUESTION:
> I have a firewall/anti-virues on my computer and all
> OS.  Now does the other computer need its own firewall
> or does my computer being the host with its firewall
> protects it (when its on of course).
> The router has option for a firewall.  If i enabled it
> i assume it will protect the other computer.  However
> will there be conflict with the firewall i have on my
> computer (guarddog and zonealarm).
>
> Cheers
>
> Bob

Bob,

If your computer with the wireless connection is connecting wirelessly to the 
router (i.e. the router is its gateway), then the other computer's firewall 
does *not* protect it.  This is the most likely scenario.

The firewall on your router will not interfere with your Ubuntu firewall, 
other than to act as a first filter.  I will attempt a little ASCII art to 
make my point.

 Internet      router        guarddog
                   firewall
                             |             |
                        port 22    port 22    ----> Goes through
                             |             |
                             |          port 80   ----> Blocked at router
                             |             | 
                        port 25        |           ----> Blocked at guarddog


In this diagram, the router lets inbound traffic for ports 22 (ssh) and 25 
(smtp) pass.  Guarddog is configured to let port 22 (ssh) and port 80 (http) 
traffic pass.  In this configuration, the only traffic that can actually get 
to your Kubuntu computer is port 22 traffic.

In the same configuration, port 22 traffic and port 25 traffic could reach the 
wireless computer on your home network, because it doesn't have its own 
firewall.

Carl Waldbieser