[PLUG] CIDR in ipv4 addressing questions...

[Paul Heinlein]

On Mon, 14 Apr 2003, Michael Robinson wrote:

> If I use this 192.168.0.0/16 or 172.16.0.0/12 in a firewall for
> class A and class B can I use them to block all private class B and
> private class C nets?

I think the answer is 'yes.' Here's what I did back when I was using 
Linux/iptables for my home firewall:

# ------ snip -------

iptables=/sbin/iptables
if_ext=eth1
any=0/0
unassigned="0.0.0.0/8 10.0.0.0/8 127.0.0.0/8 169.254.0.0/16 172.16.0.0/12"
unassigned="${unassigned} 192.0.2.0/24 192.168.0.0/16"

for net in ${unassigned}; do
  $iptables -t nat -A PREROUTING -i $if_ext -s $net -d $any -j DROP
done

# ------ snip -------

Is that what you're asking?

--Paul Heinlein <heinlein at attbi.com>