hostA
------------
eth0 172.16.0.10
eth0:0 192.168.1.10
ip_forward = 1

hostB
---------------
eth0 172.16.0.11
default gw = hostA

hostC
-------
etho 192.168.1.12
default gw = hostA


How do you use iptables to stop hostC and hostB from communicating