LinuxQuestions.org - Firewalling a port at gateway

I might be accused of repeating something I asked in a a posting on linux-security but a recent Slackware security advisory makes this pertinent.

Quote:

New cups packages are available for Slackware 12.0, and -current to fix
security issues. The change from CUPS 1.2.x to CUPS 1.3.x was tested here,
but if you're on a completely secured internal network these issues may be
less of a risk than upgrading. If your IPP port is open to the internet,
you'd be advised to upgrade as soon as possible (or firewall the port at
the gateway if you're not in need of printer jobs coming in from the
internet).

Now I have a laptop on my network connecting to the CUPS server on my PC using IPP. I do not know how I would firewall the gateway but enable the laptop to connect. Perhaps this would all be handled by the gateway in the router and there is nothing to worry about. When I tried creating a new local network zone in Guarddog 129.168.1.0/255.255.255.0 I found that my connection to the intenet was blocked.