I have a machine that has two interfaces, eth0 and eth1, eth0 facing the INTERNET and eth1 facing DMZ.
I understand OUTPUT and INPUT with regards to eth0 if defined as:
iptables -A INPUT -i eth0 -j eth0_input iptables -A OUTPUT -i eth0 -j eth0_output
But I am a little unsure about the forward chain if defined as
iptables -A FORWARD -i eth0 -j eth0_forward
I never came along the case where I had to think about eth1 with respect to eth0 and the forward chain BUT this morning as in 99.99% (it seems) of the cases it just routes the packets towards the machines that are behind eth1.
Is the eth1 interface part of eth0_input and eth0_output or is it part of eth0_forward?