Ingress filtering

[Pedro Corte-Real <typo@netcabo.pt>]

I wanted to do ingress filtering. I was going to use the command:

ipchains -I input -s <net_to_block> -i eth0 -j REJECT

Which networks should I block?

I know they are:

10.0.0.0        -   10.255.255.255
172.16.0.0      -   172.31.255.255
192.168.0.0     -   192.168.255.255

But how do I translate this to net/num format?

Greetings,

Pedro.